RC NTDs – an introduction

Definition

NTD is a relatively new identity. The term NTD was first used in 2003. It was coined by Peter Hotez and colleagues to counterbalance the attention given to HIV/AIDS, tuberculosis and malaria.

The list

There are 20 NTDs on the list, even though different sources give different numbers of NTDs. This is relevant because it is very difficult for diseases not on the list to find money for research and therapy. The 3 most recent diseases listed by the WHO are mycetoma, scabies and snakebites. Snakebites is the only non-infectious disease on the list.

Several NTDs are not restricted to the tropics, such as:

• Snakebites
• Scabies
• Rabies
• Echinococcosis
• Leprosy

NTDs which are restricted to the tropics because of climate are:

• African Sleeping Sickness
• Chagas
• Onchocerciasis
• Schistosomiasis
• Dengue
• Buruli ulcer
• Leishmaniasis
• Soil-transmitted helminthiases
• Mycetoma
• Yaws
• Lymphatic filariasis

These diseases all need a vector, which can only survive in tropical areas.

Causes

NTDs occur in the most poor communities of the world:

• Common, poverty related, risk factors
• Occur in 149 endemic countries
• People are infected with at least one NTD

Often, if one has 1 NTD, they have many NTDs because the risk factors are the same. The advantage of this is that multiple diseases can be controlled at the same time.

Microorganisms

NTDs can be caused by:

• Bacteria
  • Buruli ulcer
  • Leprosy
  • Trachoma
  • Yaws
• Viruses: the rarest
  • Rabies
  • Dengue and chikungunya
• Parasites
  • Protozoa
    • Chagas disease
    • Leishmaniasis
    • Human African Trypanosomiasis
  • Helminths: occur the most often
    • Cysticercosis
    • Guinea-worm disease
    • Echinococcosis
    • Foodborne trematodiases
    • Lymphatic filariasis
    • Soil-transmitted helminthiases
    • Schistosomiasis
    • River blindness

There is no existing vaccine against helminths.

Epidemiology

Most NTDs have a high morbidity and disability, while the mortality is low → many NTDs are chronic and don’t immediately cause death. This is why the diseases are so often neglected. NTDs promote poverty and interfere with economic development.

Prevalence

The most prevalent NTDs are the soil-transmitted helminths (STH):

• Roundworms
• Whipworms
• Hookworms

1,5 billion people have a STH. The NTD intestinal nematodes (STH) costs the highest burden of disease around the world, because so many people are infected with them.

Fatality

3 NTDs with the highest case fatality rate are:

• Rabies
  • 99% fatality
• African trypanosomiasis
  • 100% fatality
• Visceral leishmania

In case of these diseases, as soon as there are symptoms and there is no treatment, the patient dies.

Blindness

2 NTDs which cause blindness are:

• Onchocerciasis
• Trachoma
  • Causes infections of the eye

Stigma

3 NTDs which are a stigma, causing high social-economic impact, are:

• Lymphatic filariasis
• Buruli ulcer
• Yaws

Treatment and intervention

Multiple NTDs have a common treatment and share a similar way of intervention:

• MDA
• Vector control
• Safe water, sanitation and hygiene

For example, by deworming communities and schools, the burden of helminthic diseases can be reduced effectively and with a low cost. Deworming doesn’t prevent infection, but keeps the number of worms low in the body. This concept is called mass-drug administration (MDA) or preventive chemotherapy.

Clinical aspects of NTDs

Leishmania

Classification

Leishmania infections are spread by sandflies. These sandflies mainly are active at night and remain close to the ground → sleeping high up protects you from being infected. Leishmania parasite species all look alike. Classically the leishmania found in humans are divided into large groups:

• Worlds
  • Old world: Africa and Europe
  • New world: the Americas
• Subtypes
  • Leishmania
  • Leishmania viannia

A distinction for species occurring in the old world can easily be made, as they’re separated per region. In the new world, this is more difficult because they all occur in the same regions.

Leishmania can give 3 different clinical presentations:

• Viscerotropic: the organs
  • Is lethal as soon as people get symptoms and aren’t treated
• Dermotropic: the skin
• Mucotropic: the mucosa

One of the major differences between the old and new world, is that in the Americas, the dermotropic version may develop into the mucotropic version. The mucotropic version can develop into an ulcerative disease which can be lethal in the end.

Viral response

Leishmania often are colonized by viral RNA → metastasizing parasites have a high Leishmania RNA virus-1 burden. This induces a strong proinflammatory cytokines and chemokines response. This deviates the immune response away from the leishmania and to the virus, which promotes parasite persistence.

Leishmania types:

• Leishmania major
  • Occurs in rural Northern Africa, but is expanding into the Mediterranean area
  • Transmitted to humans via zoonosis
  • The incubation period is <4 months
  • Causes a painless ulcer, which spontaneously heals after 2-8 months, although a scar will remain
  • Very inflamed
  • Occurs in the extremities
• Leishmania tropica
  • Disease of the old world
  • Transmitted between humans in densely populated urban areas
  • The incubation period is 2-8 months
  • It causes painless dry scaling ulcers which remain for 12 months, leaving disfiguring scars
  • Sometimes it can infect the internal organs and leave a visceral disease
  • Very scaly
  • Occurs in the face
• Leishmania infantum
  • Classically occurs in the Mediterranean, although it has transferred to the Americans via slave trade
  • The dog is the main reservoir → the sandfly bites the dog
  • Leishmania infantum causes nodular lesions, which are sometimes ulcerative and heal spontaneously in 12 months
  • Visceral infections occur frequently in children or patients with HIV
  • Dry, volcano-like appearance with central scaling

Eosinophilia

Eosinophilia is a condition of having an increased number of eosinophils in the peripheral blood. The most common cause of eosinophilia are helminthic infections. The more intense the contact between the helminth and the tissue is, the higher the eosinophil count will be. The highest levels of eosinophilia occur when the parasite is migrating through the tissues. When the parasite moves to the intestines, the distance between the parasite and tissue becomes larger and the eosinophil count lowers.

Eosinophilia is often accompanied with fever and tissue damage → fibrosis. Strongyloidiasis, schistosomiasis (in freshwater) and hookworms can be transmitted via skin contact and can cause eosinophilia.

Hypereosinofilia

One speaks of hypereosinofilia when the count becomes >1000/L. Potential causes of hypereosinofilia are:

• Ascariasis
• Mijnworminfectie

• Strongyloidiasis
• Toxocariasis
• Tropical pulmonary eosinophilia
• Loiasis
• Schistosomiasis
• Fascioliasis
• Clonorchiasis
• Trinchinellosis

Strongyloidiasis stercoralis

Strongyloidiasis stercoralis can lead to a very high eosinophilia.It is the most dangerous soil-transmitted helminth, especially for the immune-compromised. It is usually diagnosed using PCR of the stool, although serology (antibody-detection) is the most sensitive way to find it.

The primary mode of infection is through contact with soil that is contaminated with free-living larvae. When the larvae come in contact with skin, they are able to penetrate it and migrate through the body, eventually finding their way to the small intestine where they burrow and lay their eggs. Unlike other soil-transmitted helminths such as hookworm and whipworm, whose eggs do not hatch until they are in the environment, the eggs hatch into larvae in the intestine. Most of these larvae will be excreted in the stool, but some of the larvae may mature and immediately re-infect the host either by burrowing into the intestinal wall, or by penetrating the skin around the anus. This characteristic of strongyloidiasis stercoralis is termed auto-infection. The significance of auto-infection is that unless treated, persons may remain infected throughout their lifetime.

Wolbachia and filariasis

Wolbachia is an intracellular bacteria which has specialized in infecting arthropods. 40-60% of all insects are infected with Wolbachia. Wolbachia has either a parasitic or mutualistic relationship with insects. In parasitic relationships, Wolbachia is very male-unfriendly → either kills males or forces them to develop into a female. A Wolbachia infected male cannot reproduce with a Wolbachia uninfected female due to cytoplasmic incompatibility, although this cannot be applied in 100% of cases. This causes the insect population to become more and more Wolbachia infected.

Antibiotic treatment for parasitic infections

Wolbachia has a mutualistic, thus symbiotic, relationship with filarial parasites → the parasites need Wolbachia to survive and produce offspring. This creates another treatment option for filariasis → antibiotics. Currently, Wolbachia bacteria are targets of antibiotic therapy with doxycycline, which have profound effects on the development, viability and fertility of filarial parasites. Thus, doxycycline became the standard treatment for many filarial diseases. However, this is difficult in endemic areas because the treatment has to last for 6 weeks.

This mechanism can be used for any disease caused by potentially Wolbachia-infected insects, even malaria.

Mass-drug administration

The London Declaration

MDA is very effective because it is very cheap and communities can be treated without having a diagnosis. MAD is made possible thanks to the London Declaration, where big donors and pharmaceutical industries decided to give drugs for free. The London Declaration was initiated by the WHO in 2012. The goal of Uniting to Combat NTDs is to support the WHO Roadmap in its aim to reach control, elimination and eradication targets for 10 specific NTDs by 2020:

1. Chagas disease
2. Guinea worm disease
3. Human African Trypanosomiasis
4. Leprosy
5. Lymphatic filariasis/elephantiasis
6. Onchocerciasis/river blindness
7. Schistosomiasis
8. Soil-transmitted helminths
9. Trachoma
10. Visceral leishmaniasis

Commitments of all partners of the London Declaration are:

• Supply of drugs for free for MDA/preventive chemotherapy
• Advance research and development to find next-generation treatments and intervention
• Support collaboration and coordination on NTDs at national and international levels through public and private multilateral organisations

Targets were to by 2020:

• Eradicate Guinea worm disease
• Eliminate lymphatic filariasis, leprosy, sleeping sickness and blinding trachoma
• Control schistosomiasis, soil-transmitted helminths, Chagas disease, visceral leishmaniasis and tonchocerciasis

The goals weren’t reached entirely. Approximately, the treatment of these diseases cost $0,50/person/year. MAD only works if communities are involved in the campaigns and distribution of drugs.

New targets of Uniting to Combat NTDs are:

• Increase the visibility of NTDs on the global stage
• Improve collaboration and consistency of messaging for advocacy and resource mobilization
• Monitor progress of stakeholder commitments towards the London Declaration through a scorecard and report on progress
• Promote NTD community collaboration
• Identify funding gaps and challenges to meeting the WHO goals for NTDs targeted by the London Declaration
• Advocate to bridge the identified gaps

Medication

The NTDs mainly controlled by MDA are:

• Lymphatic filariasis
  • Single dose of ivermectin or DEC + albendazaole for at least 6 years
• Onchocerciasis/river blindness
  • Single dose of ivermectin 1-2x/year for 15 years
• Schistosomiasis
  • Single dose of praziquantel
• Soil-transmitted helminths
  • Single dose of albendazole or mebendazole
• Trachoma
  • Single dose of azithromycin
• Yaws
  • Single dose of azithromycin

Disadvantages of MDA

Specific reasons not to use MDA are when drugs needed for treatment are highly toxic, such as in case of Chagas, or when there is no drug available, such as in case of Guinea worm disease. In these cases, MDA is not the solution → the more costly Innovative and intensified disease management (IDM) is necessary:

• Individual diagnosis and treatment
• Surgery where needed
• Care and rehabilitation of infected individuals

Preventive measures such as supplying safe drinking water, improving hygiene with the WASH-initiative, and vector control also are helpful.

Remaining challenges

One of the issues of Uniting to Combat NTDs are diagnostics. The standard diagnosis is microscopy of stool samples. However, the sensitivity is rather low → eggs excreted in stool are easily missed. This leads to underestimation of the prevalence. Other problems are asymptomatic carriers, new zoonotic sources and confusing terminology such as eradication/elimination.

Because the 2020 targets weren’t reached, new 2021 developments were established by the WHO. Here, the focus is more on collaboration, ownership and community involvement instead of on MDA.

Soil-transmitted helminths

Soil-transmitted helminths

Helminths are transmitted through soil that contains feces with eggs in tropical and subtropical countries. The helminths make their way to the intestines, where they live and grow. Approximately 1,5 billion people are infected by a STH. Strongyloides stercoralis can also be considered an STH.

Main helminths species:

• Roundworms/ascaris: mature into an infective form → are not directly infectious
  • Make their way to the large intestine through the heart and lungs
  • Oral transmission
• Whipworms/trichuris: mature into an infective form → are not directly infectious
  • Make their way to the large intestine directly
  • Oral transmission
• Hookworms: mature and hatch into larvae that can penetrate skin
  • Make their way to the large intestine through the heart and lungs
  • 2 species: ancylostoma and necator
    • Ancylostoma may be more dangerous

The helminths can live in the wall of the large intestine for many years and feed on tissues, blood or nutrients. They produce thousands of eggs per day, which again are spread through the feces.

Symptoms:

• Asymptomatic
• In case of hookworm infections
  • Anemia → the worms hook to the intestinal wall and suck up blood
  • Skin irritation
• Loss of protein
• Reduced nutrient absorption
• Malnutrition
• Diarrhea
• Abdominal pain
• Malaise and weakness
• Loss of appetite
• Bowel obstruction
• Prolapse

Consequences are impaired physical and mental development. Eosinophilia also often occurs.

Prevention:

• Control programs
• Clean uncontaminated water
• Improving sanitation and hygiene
• Not walking barefoot
• Periodic mass drug administration (deworming)

There is no effective vaccine yet. Ivermectin is often used as treatment for STHs.

MDA

Mass-drug administration is often given to treat STHs. This usually is given in a single-dose regimen with Albendazole. The custom is to do a pilot of school-aged children. If the prevalence of STHs is >50%, MDA is to be applied.

Benefits of STHs

Because STHs are able to survive for so long in the body and suppress the immune system, they may prevent auto-immune diseases and may be a potential treatment of these diseases.

Schistosomiasis

Schistosomiasis is tropical disease caused by a group of parasitic worms called schistosomes/blood flukes. 85% of all schistosomiasis cases occur in Sub-Saharan Africa, where it causes over 200.000 deaths per year. Globally, there are 200-240 million cases per year and 800 million people are at risk. After malaria, it is considered the most important parasitic infection in travel medicine.

Types

There are 5 main types of schistosomiasis:

• S. haematobium
  • Causes urinary and genital disease → urogenital schistosomiasis
  • Mostly in Africa and the Middle East
• S. mansoni
  • Affects the bowel and liver
  • Mostly in Africa and South America
• S. japonicum
• S. mekongi
• S. guineensis

However, the distribution of schistosomiasis is extremely focal. S. haemotobium causes urogenital schistosomiasis, while all other types manifestate in the bowel and liver.

Life cycle

The life cycle consists of humans, infected water and snails:

1. Infected humans produce urine and feces with eggs
2. The eggs reach water and produce larvae
3. The larvae infect freshwater snails
4. Larvae are released into the water as cercae
5. Cercae penetrate human skins
6. Cercae become adult worms and migrate into blood vessels and surrounding organs
   • This takes 6-8 weeks
   • Schistosoma is a blood parasite, not an intestinal parasite
7. Cercae produce eggs which migrate through the vessel wall and leave the body via human stool

The freshwater snails can only survive in the tropics → limits schistosomiasis to certain areas.

Symptoms:

• Swimmer’s itch or fisherman’s itch
• Self-limiting acute schistosomiasis/Katayama syndrome
  • General malaise
  • Fever/night sweating
  • Eosinophilia
  • Respiratory complaints
• Serious long-term effects caused by eggs trapped in organs → granuloma formation and collagen deposits
  • Hardening, obstruction or cancer in the bladder
  • Abdominal pain, diarrhea or blood in the stool
  • Scarring of tissue or enlargement of the liver
  • Anemia in children
  • In case of S. haemotobium, genital presentation → bloody sperm or contact bleeding
    • Facilitates HIV-transmission

Prevention:

• Elimination in humans with medication
• Reduce the contamination of water
• Eliminating snails with chemicals
• Reducing contact with contaminated water

Diagnostics

Schistosomiasis is bestly diagnosed with microscopy. Not only the prevalence, but also the severity of the infection needs to be known → the eggs are counted by measuring the number of eggs in a fixed volume. This form of diagnosis gives many issues:

• Overestimation of cases
• Limitations

 Thus, alternatives to traditional microscopy are PCR, serology and antigen detection.

Controlled Human Schistosoma Infection (CoHSI) consists of several studies in Leiden where volunteers get infected with schistosoma and get followed for 12 weeks and are treated. A lot of new information was acquired thanks to this model.

Treatment

The recommended treatment for schistosomiasis is 40 mg/kg praziquantel. This is quite a large dose, but still doesn’t kill all the worms. However, giving a higher dose would give more side effects. There also are national control programs and population based treatment with:

• Preventive chemotherapy
• MDA

MDA only is not enough → a multidisciplinary approach is essential.

RC Emerging Infectious Diseases

Infections as a cause of disease

Infections represent an encounter between two organisms, each living in its own niche. The chances for such an encounter to occur are highly variable. Any change in any niche may have effect on the chance of an infection. Biological changes such as adaptation, selection and evolution in the organisms will also determine the likelihood of an infection.

Infections as a cause of disease are unstable → they may emerge and re-emerge. The majority of emerging and re-emerging infectious diseases are RNA viruses.

Zoonotic pathogens

Zoonotic transmission occurs when an infection that naturally occurs in an animal vertebrate host also can subsequently infect humans, without initial human to human transmission.

A vector-borne disease is transmitted by means of an intermediate species, often an arthropod, carrying the disease pathogen. Thus, zoonoses can be direct (avian influenza or rabies) or vector-borne (West-Nilevirus or Zikavirus).

Africa as a source of emerging infections

Africa is the cradle for many emerging viral diseases. Besides the general determinants of emerging viral disease, there are some more “Africa-specific” aspects:

• Close contact to non-human primates and other reservoir animals like bats
• Globally the most poor and remote communities
• Poor health systems or little access to health systems
• Cultural aspects related to health
• Africa is extremely large and densely populated in many parts

In 1968, the virological professor Frits Dekking suggested that virological surprises should be expected in the future, in particular from the African continent. This was surprising, because in those times much was unknown about Africa. However, indeed soon remarkable viral diseases came from Africa:

• Filoviridae
  • Marburgvirus
  • Ebolavirus
• Arenaviridae
  • Lassavirus
• Retroviridae
  • HIV

Many other viruses also started emerging, with roots in Africa. All of these viruses are RNA viruses.

Zika virus

Zika virus is a typical recent example of an emerging infection. It is transmitted by mosquitoes. It became prominent when microcephaly cases started to occur in Brazil in 2015. Around that time, an epidemic of Zika virus was occurring.

Zika was first found in Africa, were the mosquito-borne virus was found in a monkey in Uganda. Before 2007, very few cases of human infection occurred. The symptoms didn’t seem severe, and epidemics weren’t considered a serious problem. However, the virus started spreading around the world in an Eastern direction. Cases of microcephaly were first described in 2013 in Polynesia. The epidemic only started being taken seriously in 2015, when it reached Brazil.

Zika virus is a congenital infection:

• Microcephaly, craniofacial malformations, calcifications and ventriculomegaly
• 1-13% risk among Zika-positive mothers
• Sometimes ocular abnormalities occur

Transmission

Zika virus can be transmitted as follows:

• Mosquito bite
• Maternal-fetal
• Sexual contact (oral and penetrative)
• Blood transfusion
• Organ transplantation
• Laboratory exposure

Diagnostics

Zika virus can be diagnosed in serum and urine:

• PCR: positive after 0-14 days after the onset of symptoms
• Serology: positive after >4 days after onset of symptoms

Vectors

The primary vector of Zika virus is the aegypti and albopictus mosquito. Zika virus is a type of Flavivirus.

Immunity

Rapid spread of mosquito-borne viruses often lead to population immunity. The Zika epidemic in the Americas didn’t last very long. Cases were highest in 2016, but soon population immunity was achieved → in July 2017, most cases had disappeared.

Factors

Factors contributing to Zika virus emergence

• Increasing migration/globalization
• Increased presence of the vector (aedes aegypt) due to climate changes, urbanization and inappropriate vector control
• Asymptomatic carriers of the virus
• Sexual transmission
• Underestimation of the problem
• No vaccine of appropriate diagnostic tests at early stage

Coronaviruses

Coronaviruses are widespread among most animals. Thus, coronaviruses often cross species barriers. Sometimes this has occurred long ago, sometimes recently. There are 4 categories of coronaviruses:

• Alphacoronavirus
• Betacoronavirus
• Deltacoronavirus
• Gammacoronavirus

Some of these coronaviruses can affect humans, causing respiratory infections. In total, there are 7 known human coronaviruses, of which 6 are circulating:

• Low pathogenic coronaviruses
  • Human coronavirus 229E
  • Human coronavirus NL63
  • Human coronavirus OC43
  • Human coronavirus HKU1
• Highly pathogenic coronaviruses
  • Severe acute respiratory syndrome CoV (SARS-CoV1)
  • Middle East respiratory syndrome CoV (MERS-CoV)
  • Severe acute respiratory syndrome CoV-2 (SARS-CoV2)

SARS-CoV1

SARS-CoV1 was a problem in 2003 in China. There were thousands of cases, with a mortality of 10%. Fortunately, the disease only lasted for one winter and disappeared the next summer.

MERS-CoV

MERS-CoV was a severe virus that was first reported in 2012 in Saudi Arabia. Although this infection solely occurred zoonotic, it caused fatal pneumonia and acute kidney injury. The mortality of MERS-CoV is very high → 30%.

Transmission of MERS-CoV occurred through contact with nasal secrete of dromedary camels. There is no evidence for sustainable human-to-human transmission, although there were a few cases and short-chain clusters where this did occur. This mainly happened in close contact situations → health care workers and airplane passengers were typically at risk. There is no treatment and no available vaccine.

SARS-CoV2

SARS-CoV2 turned into a real pandemic. On September 13 2021, 225 million cases of SARS-CoV2 had been reported, with 4,6 million deaths worldwide.

SARS-CoV2 became a problem because viral transmission properties were particularly unfavorable:

• Early peak in viral load → often, even before symptoms develop
• Relatively long incubation period
• Usually mild or absent symptoms
• Considerable mortality with underlying conditions
  • The case fatality rate otherwise is low
• Broad susceptibility and transmission
  • There is no pre-existing immunity
• Incomplete seasonal reduction
• No lifelong immunity
  • Like most respiratory infections
• Tendency to develop variants with increased replication

Earlier pandemics by coronaviruses

In 1889, there was a widespread pandemic around the world called the “Russian Flu”. It is still unknown what was the cause of this pandemic. Possibly, it is a human CoV-OC43 of bovine origin. This is another example of a coronavirus settling in mankind from an animal source. However, this suspicion hasn’t been confirmed yet.

Prediction key factors that underlie emergence and re-emergence of infectious diseases

Some major factors underlie disease emergence and re-emergence:

• The microbial agent
  • Genetic adaptation and change
  • Polymicrobial disease
• The human host
  • Human susceptibility to infection
  • Human demographics and behavior
  • International trade and travel
  • Intent to harm
  • Occupational exposures
  • Inappropriate use of antibiotics
• The human environment
  • Climate and weather
  • Changing ecosystems
  • Economic development and land use
  • Technology and industry
  • Poverty and social inequality

Examples of viral emerging infectious diseases are:

• Ebolavirus outbreaks
• Avian H5N1 influenza
• SARS Coronavirus outbreak
• HIV-1 pandemic
• Hantavirus Pulmonary Syndrome (Sin Nombre Virus)
• Chikungunya virus
• West-Nile virus
• Dengue virus 1-4

These all are re-emerging vector-borne infections.

Why viruses occur so often as emerging diseases

Viruses are so widely spread because all organisms are surrounded by viruses:

• 40% of all bacteria and protozoa in seawater are killed every day by viruses
• Viruses are highly specific for cells they can infect → an insect virus cannot infect a human
• Viruses do not compete with cells, they are a product of those same cells
• Increasing density of any cellular population will increase the susceptibility for viruses that are produced by these same cells → viruses can stop the growth of any population
• Dominant populations in marine environments are always suppressed by their own viruses
• The system of life is very stable → viruses have existed for 35 million centuries

RNA and DNA viruses

Newly emerging infections are mainly RNA viruses due to the nature of the nucleic acid itself:

• RNA viruses
  • RNA is labile and intended to be transient in the cell
  • High frequency of mutation
  • Often cross-species transmission
  • Causes emerging infections and epidemics
  • Persisting infections are very unusual → RNA is often destroyed within the cell
• DNA viruses
  • DNA is stable and cherished within the cell
  • Low frequency of mutation
  • Highly adapted to species → no cross-species transmission
  • Causes widespread stable and endemic diseases
  • Often causes persisting infections → the virus forms a balance within the host

Due to these differences, DNA and RNA viruses require different types of virologists to study the infections.

RC Malaria

Introduction

Malaria is transmitted by mosquitoes infected with a protozoa. When the mosquito bites the host, large numbers of parasites enter the host. These parasites replicate inside the liver, leave the liver and enter red blood cells. Inside the red blood cells, the protozoa replicate in large numbers.

Malaria causes 409.000 deaths every year. Many of these deaths are of children <5 years old in Sub-Saharan Africa.

Species

The official names of the 5 species known to cause malaria in humans are:

• P. falciparum
• P. malariae
• P. vivax
• P. ovale
• P. knowlesi

The 2 most common species are p. falciparum and p. vivax. P. falciparum is a potentially fatal malaria specie. The distribution of malaria species varies around the world. This has to do with the type of mosquito. In most cases, malaria is transmitted by the female anopheles mosquito.

Transmission

The malaria parasite life cycle involves two hosts:

1. During a blood meal, a malaria-infected female anopheles mosquito inoculates sporozoites into the human host
2. Sporozoites infect liver cells and mature into schizonts, which rupture and release merozoites
   • In p. vivax and p. ovale a dormant stage (hypnozoites) can persist in the liver and cause relapses by invading the bloodstream weeks or even years later
3. After this initial replication in the liver, the parasites undergo asexual multiplication in the erythrocytes
4. Merozoites infect red blood cells
5. The ring stage trophozoites mature into schizonts, which rupture releasing merozoites
6. Some parasites differentiate into sexual erythrocytic stages → gametocytes
   • Blood stage parasites are responsible for the clinical manifestations of the disease
7. The gametocytes (male (microgametocytes) or female (macrogametocytes)) are ingested by an anopheles mosquito during a blood meal
8. While in the mosquito’s stomach, the microgametes penetrate the macrogametes generating zygotes
9. The zygotes in turn become motile and elongated (ookinetes) which invade the midgut wall of the mosquito where they develop into oocysts
10. The oocysts grow, rupture, and release sporozoites, which make their way to the mosquito’s salivary glands
11. Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle

The transmission of malaria is highly focal. Malaria mosquitoes breed in water → in the dry season only a couple of individuals will carry malaria, which will increase in the wet season.

Infection

In endemic areas, people can get re-infected with malaria. Eventually, they develop some kind of immunity. This immunity keeps the density of the parasites low and doesn’t give any symptoms. However, these people can still transmit malaria.

Preventing transmission

Malaria transmission can be prevented by preventing mosquito transmission and human transmission. There are 3 main ways to prevent malaria transmission:

• Bed rest
• Residual spraying
• Diagnostics

Indoor residual spraying

Indoor residual spraying: spraying the inside and outside of the house with insecticides. Because mosquitoes rest on the wall, they die before or after they bite. Issues are toxicity for people and the environment and resistance.

IPTI

In case of intermittive preventive treatment in infants (IPTI), whole groups of infants are preventively treated for malaria.

Antimalarial medication

There are different kinds of antimalarial medication:

• Chloroquine
  • Not used anymore due to resistance in South-East Asia
• ACT (artemisinin combination therapy)

Some old malaria drugs gave psychological side effects, such as hallucinations.

Diagnostics

There are various ways to test for malaria:

• Rapid diagnostic tests
• PCR
  • Only tests for genetic material of the parasite → doesn’t differentiate for the severity of the infection
  • Expensive
  • It takes long to get results

Vaccination

There aren’t any vaccines for any parasitic diseases, so there still is no available fully-working malaria vaccine. The main issue for the development of a malaria vaccination is that the parasite goes through different stages and changes continuously. However, there is a vaccine for malaria that is highly (but not fully) effective → the RTS,S/AS02 vaccine. This vaccine has a 30% efficacy. The R21/MM vaccine developed in 2021 is basically the same vaccine as the RTS,S one.

Ebola

Outbreak

The 2014-2016 Ebola-outbreak started in Milandou in Guinea. When the outbreak was reported in March 2014, the epidemic was already widely spread. In June, the epidemic was totally out of control. There were failures at every level → not enough treatment facilities, war-torn countries, insufficient health care systems. Cleaning and decontamination of the areas was extremely difficult. Population growth, increased urbanization and connectivity resulted in an even more rapid spread.

Spain accepted Ebola-patients, but in reality was in no condition to do this. This was also the case in the USA, where a nurse caught Ebola from an infected patient:

• Suits weren’t the correct size
• Too small changing areas, making safe doffing impossible
• No training on the job
• Failure to recognize and isolate a suspected case
• Initially no shoe covers in a patient with diarrhea
• Uncovered skin neck was taped
• Difficulties handling waste and patient remains

This caused people to feel personally threatened.

The virus

Ebolaviruses are pathogenic agents associated with a severe, potentially fatal, systemic disease in man and great apes. Four species of ebolaviruses have been identified in 22 countries in West and Central Africa. Once the more virulent forms enter the human population, transmission occurs primarily through contact with infected body fluids and can result in major epidemics in under-resourced settings. These viruses cause a disease characterized by systemic viral replication, immune suppression, abnormal inflammatory responses, major fluid and electrolyte losses, and high mortality.

The Ebola virus is an enveloped negative-stranded RNA virus, with a characteristic filamentous shape. Moist, tropical regions are suitable for transmission of the Ebola virus. Deforestation attracted bats → Ebola is a zoonotic bat virus. It is transmitted via person-to-person contact or direct contact with blood or excreta. It also possibly can be sexually transmitted. The virus envelope can be disrupted by water and soap or alcohol-based hand-sanitizers.

Pathophysiology

The Ebola virus infects dendritic cells → release of cytokines and tissue factor. The virus induces lymphocytic apoptosis, resulting in:

• High viraemia
• Endothelial dysfunction
• Disturbance of the gastro-intestinal function, liver cells and adrenal cortex

Clinical characteristics

The Ebola virus leads to shock and multi-organ failure. It soon became clear that haemorrage is a late, uncommon but unfavourable sign. The most common clinical characteristics are:

• Fever
• Chills
• Malaise
• Myalgia
• Vomiting
• Diarrhea
• Cough
• Conjunctival injection
• Confusion
• Rash
• Haemorrage and sepsis in the second week

Mistakes

There are many things that can be learned from the Ebola-outbreak:

• Failures of leadership
• Fragile national health systems
• Highly mobile population
• Delays in international response
• Deficient resource mobilization
• Ill-defined responsibilities
• Cases with unknown source of infection
• Failure to recognize and isolate suspected cases
• Continuing unsafe burials

End of the epidemic

At the end of the epidemic, a new rVSV-vectored vaccine preventing Ebola virus disease was introduced. By December 2015, the epidemic was declared to have ended. Survivors suffered from trauma, stigma and social disruption.

According to a systematic survey, 76% of the survivors suffered from arthralgia. Other symptoms also occurred, such as:

• Tinnitus and hearing loss
• Eye complaints and uveitis
• Encephalitis

2021 DRC outbreak

In February 2021, the 12^th Ebola outbreak of DRC was declared. This outbreak oriented in Guinee → genomic sequencing proved that this outbreak was very similar to the 2014 outbreak in that area.

RC HIV

Definition

HIV (human immunodeficiency virus) is a virus that attacks the body’s immune system. If HIV is not treated, it can lead to AIDS (acquired immunodeficiency syndrome).

Current global HIV/AIDS situation

Currently:

• 37,7 million people are estimated to be living with HIV globally
• This number has declined with 31% over the 10 last years → 2,1 million new HIV infections in 2010 and 1,5 million new HIV infections in 2020
• In Africa 23,8 million people have HIV, while in the Netherlands 28.593 people have HIV
• 690 thousand people died of AIDS-related illnesses

The incidence of HIV is highest in Sub-Saharan Africa. South-Africa is the country with the highest HIV incidence. In LMIC, HIV mostly occurs in younger women, while in high income countries it mostly occurs among men.

Globally, there is a positive trend in HIV infections. In 2019, of all people living with HIV:

• 81% knew their status
• 67% were accessing treatment
• 59% were virally suppressed

HIV infections have reduced with 80% since 1990.

Modes of transmission

• Unprotected sexual intercourse with an infected partner
• Vertical transmission
  • In utero
  • During delivery
  • Through breastmilk
• Injection drug use

In the Netherlands, all pregnant women are tested for HIV.

Origin of the HIV-virus

HIV in humans came from a type of chimpanzee in Central Africa. The chimpanzee version of the virus, called simian immunodeficiency virus (SIV) was probably passed to humans when humans hunted these animals for meat, and came in contact with their infected blood. This most likely happened in the late 1800s. Over the decades, HIV slowly spread across Africa and later into other parts of the world.

Diagnosis

HIV can be diagnosed with:

• HIV-combotest: positive 3 weeks after transmission
• HIV-antibody test: positive 5 weeks after transmission

The average time between transmission and diagnosis is 2,5 years.

Natural course of HIV-infection

HIV infections typically progress through 3 stages:

1. Stage 1: Acute HIV infection
   • People have a large amount of HIV in their blood → very contagious
   • Some people have flu-like symptoms → natural response to the infection
     • Fever, muscle ache, skin rash, etc.
   • Can only be diagnosed with antigen/antibody tests or nucleic acid tests
2. Stage 2: Chronic HIV infection
   • Is also called asymptomatic HIV infection or clinical latency
   • HIV is still active but reproduces at very low levels
   • People may not have symptoms or get sick
   • HIV is still transmittable in this phase
   • Can last for years
   • At the end of this phase, the viral load goes up and the CD4-cells go down
     • The CD4 cells are infected by HIV and go down
3. Stage 3: Acquired Immunodeficiency Syndrome (AIDS)
   • Most severe phase of the infection
   • People get an increasing amount of severe illnesses → opportunistic infections
   • Is diagnosed when the CD4 cell count is <200 cells/mm or when certain opportunistic infections occur
   • Without treatment, people with AIDS typically survive about 3 years

The viral load is the highest during stage 1 (acute HIV infection) and stage 3 (AIDS). The consequences of this are that patients are highly contagious and experience more symptoms.

Opportunistic infections

Opportunistic infections that often occur with HIV/AIDS are:

1. At the start
   • Herpes zoster virus
   • Candidiasis (thrush)
     • A fungal infection
   • Seborrhoic eczema
   • Kaposi’s sarcoma
   • NHL
2. More severe
   • PCP
   • Toxoplasmosis
   • Herpes simplex virus 1 (HSV-1) infection
     • Viral infection that causes sores on the lips and mouth
   • Cryptosporidium
3. End stage infections
   • Central nervous system disease
   • Cytomegalovirus
   • Mycobacterium avium-intracellular infection
   • Microsporidosis
   • Non-Hodgkin lymphoma
   • Kaposi’s sarcoma

These infections typically occur when the CD4-cell count is low (<200 cells/mm).

Treatment

Up to now, HIV/AIDS isn’t curable. However, patients can receive combination anti-retroviral therapy (ART).

There are various types of HIV medication, which can interfere in various stages of the process:

1. RNA HIV virus enters the CD4-cell → can be inhibited by entry-inhibitors
2. Virus enters the cells and viral RNA has to be transcribed into viral DNA → can be inhibited by reverse transcriptase inhibitors
3. Viral DNA is integrated into the DNA of the CD4-cell → can be inhibited by integrase inhibitors, the newest HIV medication
4. Viral RNA has to be assembles again with proteases → can be inhibited by protease inhibitors

Triple therapy

The most common anti-retroviral drug combination against HIV used in the Netherlands is a pill consisting of an integrase-inhibitor (INSTI) with 2 nucleoside reverse-transcriptase inhibitors (NRTI’s) → triple therapy. Such combination therapy reduces HIV to a chronic condition, without many complications and a normal life expectancy. Also, by lowering the viral load, the virus cannot be transmitted to another person. Earlier, treatment was only started when the CD4-cell count had gone down, but now it is immediately started after the diagnosis.

In developing countries, combination therapy with new anti-retroviral drugs is practically unattainable. Even basic treatments for opportunistic infections, such as aspirin and morphine, are hard to find.

Prevention

Ways to prevent transmission of HIV are:

• Abstinence
• Never sharing needles
• Safe sex
• Condoms
• HIV prevention medication
  • Pre-exposure prophylaxis (PrEP)
  • Post-exposure prophylaxis (PEP)
• Preventing mother-to-child transmission
  • Getting tested for HIV
  • PrEP if you have a partner with HIV
  • Taking HIV medicine during pregnancy and giving HIV medicine to the infant 4-6 weeks after birth
  • Avoiding breastfeeding

PEP and PrEP

• PrEP: medicine people at risk for HIV take to prevent getting HIV from sex or injection drug use → Truvada
  • 1 pill/per day
  • Continuously or intermittently, dependent on the frequency of possible exposure
  • 30 euros/months
  • 100% HIV protection
    • Does not protect against other STDs
• PEP: medicine people take to prevent HIV after a possible exposure
  • Should only be used in emergency situations
  • Must be started within 72 hours after a recent possible exposure to HIV

RC TB

Key facts

TB results in 4000 daily deaths and 1,4 million yearly deaths globally → it is one of the top 10 causes of death worldwide and the leading cause of death from a single infectious agent (ranking above HIV/AIDS). In 2019, 10 million people fell ill with TB. It still is a global pandemic, which is mostly a problem in LMIC → incidence rates are highest in Sub-Saharan Africa and the Sub-Indian regions.

TB forms a problem because it isn’t easy to treat. Also, resistance to the 1^st line drug rifampicin is increasing.

Trends:

• Ending the TB epidemic by 2030 is among the health targets of the Sustainable Development Goals
• An estimated 63 million lives were saved through TB diagnosis and treatment between 2000 and 2019
• There is a large gap between the number of new cases reported and the estimated 10 million incident cases in 2019
• Globally, the TB incidence rate fell by 9% between 2015 to 2019, including a reduction of 2,3% between 2018 and 2019

KNCV

KNCV is a NGO which cooperates in many countries throughout the world. KNCV aims to improve the TB control and treatment in high burden countries.

Risk factors and drivers

• Direct risk factors
  • Exposure
    • Prevalence
    • Poor ventilation and crowding
  • Host defense
    • Age, gender, genetical factors
      • Men are more susceptible to TB than women
    • HIV, malnutrition, substance abuse, co-morbidity
      • HIV is the most relevant risk to develop TB → 20-35% chance of developing TB, 11% of TB cases are caused by HIV
      • Malnutrition causes 27% of TB cases
    • Tobacco smoking and air pollution
• Indirect risk factors
  • General
    • Weak social and economic context
    • Globalization, urbanization, migration
    • Weak health care infrastructure
  • Individual
    • Poverty, SES, education
    • (Un)healthy behavior
    • Inadequate health seeking behavior

Infection

TB is an infectious disease caused by mycobacterium tuberculosis. It is communicable from human to human through air, which contains infectious droplets. TB can cause extensive granulomatous reactions and necrolysis of body tissues. If untreated, the 10-year case fatality is reported to be between 53% and 86%. Most deaths occur within 3 years.

Infection pathway of TB:

1. A human contact inhales droplets into the lungs
2. A (latent) TB infection can occur, but exposure doesn’t always result into an infection
3. After infection, 10% of cases leads to disease → 5% within 2-5 years and 5% within >5 years

Symptoms

The most recognizable symptoms of TB disease are:

• Specific symptoms
  • Persistent cough that lasts 2-3 weeks
  • Cough blood
  • Chest pain
• Aspecific symptoms
  • Weight loss
  • Night sweats
  • Loss of appetite
  • Fever

Types of TB

• Pulmonary TB: 60-80% of cases
• Extrapulmonary TB
  • Pleura
  • Lymph nodes
  • Abdomen
  • Urogenital system
  • Skin
  • Joints and bones
  • Meningitis
  • Miliary: disseminated throughout the body

Symptoms that occur in extrapulmonary TB are related to the organ in which they occur. Extrapulmonary TB is more common in low burden TB areas.

Diagnosis

TB can be detected in the body as follows:

• TB skin test (TST)/Mantoux tuberculin test: antigenic fluid is injected, which causes a cellular reaction → skin reaction can be measured after 2-3 days
  • Low specificity
    • Cross-reacts with other infections and the BCG vaccine
  • Needs to have a different cut-off for HIV patients
    • Sputum samples or cultures are preferred for patients with immune-deficiencies
  • Preferred for children <5 years
  • 2 visits are necessary
• TB blood tests/Interferon-gamma release assays (IGRA): measure the intracellular response of the blood
  • High specificity
    • Although negative tests may be unreliable
  • 2 tests: quantiferon TB Gold and T-spot TB test
    • Quantiferon TB Gold is done with a blood sample
    • T-spot TB test is done with cell isolation
  • Doesn’t test positive for the BCG vaccine

These tests can only detect the immune response towards TB → cannot differentiate between latent TB or TB disease. Other tests, such as a chest X-ray and a sample of sputum are needed to see whether the infection is latent or not.

Guideline

If a patient has a cough for more than 3 weeks, the following should be done:

• Physical examination
• Chest X-ray
  • Detects pulmonary TB
  • Sensitivity: 87-89%
  • Specificity: 75-89%
  • High intra- and interobserver variability
  • CAD4TB: software that gives diagnostic-aid
  • Expensive in LMIC
  • High-tech
• Sputum examination
  • Xpert if available → fast PCR-based test
    • Automized PCR
    • Identifies DNA and genotypic drug resistance against rifampicin
    • Higher sensitivity than sputum smears
    • Very high specificity (99%)
    • Improved diagnosis of TB and rifampicin resistance in children and patients with broad range of extrapulmonary TB
  • Otherwise direct smear microscopy or culture
    • Laboratory diagnosis (direct smear microscopy)
      • Usually infectious if positive, usually non-infectious if negative
      • Moderate specificity and low sensitivity
      • Cheap and “low technology”
      • Can be performed in 30 minutes
    • Culture
      • High specificity and sensitivity
      • Time consuming → diagnosis can take weeks to months
      • Expensive and “high technology”

Diagnostic algorithm pulmonary TB:

• At least 2x sputum examination (including 1 morning sputum) and culture
• Chest X-ray if available

Criteria for bacteriological confirmation are a positive Xpert, smear microscopy and culture. If all tests are negative or tests are not available the following should be done:

• Chest X-ray
• Clinical diagnosis after no improvement after treatment

In reality, in high burden countries, diagnosis is still often based on symptom screening + sputum microscopy or clinical diagnosis.

Treatment

Active TB treatment

The treatment of TB consists of 2 phases:

1. Intensive phase: 2 months 4 drugs → isoniazid, rifampicin, pyrazinamide, ethambutol
2. Continuation phase: 4 months 2 drugs → isoniazid, rifampicin

Standard multidrug therapy is highly effective when compliance is ensured → 1-2% relapse rate.

Latent TB treatment

Preventive treatment in case of latent TB infections can consist of:

• Daily isoniazid for 6-9 months
• Daily rifampicin for 4 months
  • 4 months of rifampicin is as effective as 9 months of isoniazid
• Daily isoniazid and rifampicin for 3 months
• Weekly isoniazid and rifapentine for 12 weeks
  • Rifapentine is not registered in Western countries

These all are oral medications. While treating latent TB, the incidence of active pulmonary TB in later stages is lower.

Side effects

Adverse side events of (preventive) TB treatment are:

• Depression
• Numbness
• Nausea
• Pain
• Abdominal complaints
• Fatigue
• Etc.

1 per 6-7 persons can experience side events.

Multi-drug treatment

TB treatment requires so many different drugs because this way, each drug can be given in a lower dosage, reducing the change of resistance and lessening side effects. Multi drug-resistant TB can be treated with multiple drugs based largely on fluoroquinolone.

Challenges

The biggest challenge in TB treatment is antimicrobial resistance → drug-resistant forms of TB are currently on course to be the world’s deadliest pathogens. Isoniazid-resistant forms of TB are the most common forms of drug-resistant TB in the world. However, each year more than half a million people become sick with rifampicin-resistant forms of TB. The incidence of this form of TB will continue to increase. Whole-genome sequencing is likely to become the preferred method for TB drug-resistance testing in the next decade.

Another challenge in TB treatment is compliance → latent TB doesn’t give any symptoms, making it hard for patients to take their treatment seriously. Nowadays, there are digital tools to ensure adherence to treatment. Also, TB is a slow growing bacteria → replicates 1x/day. This makes it difficult to interfere and makes the chance of resistance higher.

Drug resistant TB

Types of drug resistant TB are:

• Monoresistance against 1^st line drugs: isoniazid or rifampicin
• Multi-drug resistant (MDR) TB: combined resistance against rifampicin and isoniazid
• Pre-extensively drug resistant (pre-XDR) TB: MDR tuberculosis also resistant to any fluoroquinolone
• Extensively drug resistant TB: TB resistant to (almost) all drugs

Multi-resistant TB is especially a problem in Russia and China. Dangers of MDR TB are:

• Long diagnostic delay: long infectious period → risk of nosocomial infection of other patients and health care workers
• High mortality, especially in combination with HIV (60-70%)
• Amplification of resistance against 2^ndline anti-TB drugs
• Expensive, often clinical treatment with hepatotoxic drugs
• Limited possibility for preventive treatment of infected contacts

MDR and XDR TB developed as a global problem due to:

• Treatment with only 1 effective drug
• Inadequate dosage or irregular drug administration
• Poor adherence to treatment
• Poor quality of the drugs
• Reduced absorption
  • HIV co-infection
• Transmission of MDR resistance

The WHO provides guidelines for how to use specific drugs to treat MDR and XDR TB. The treatment should always be given by specialists in specialized hospitals.

Vaccination

Up to date, there is no effective vaccine against TB. Novel vaccines would contribute strongly to reduce the burden of TB because they prevent the progression of infection of the disease.

Challenges

The design of TB vaccines is so cumbersome compared to the rapid design of vaccines against SARS-CoV2 because the immune response necessary to combat a TB infection is reliant on cellular processes with T-cells, which is different from the immune response that is generated in case of viral infections. Thus, several things make it difficult to develop a TB vaccine:

• T-cell response
• MT manipulates the host immune system
• The protective immune response against TB is unknown → different

Current vaccines

BCG is the most used global vaccine. It protects against severe TB during childhood, but otherwise is insufficiently effective. Revaccination with BCG during teenage years may give additional protection.

M72 is a new vaccine candidate that also can give protection against pulmonary TB development.

Practicalities

TB vaccine trials are expensive → $3 million dollars are needed for a phase I trial of a TB vaccine. Also, acquiring trial participants is difficult, while 12.000 participants per arm are necessary. Summarized, trials are complex, require large populations and have long follow-ups.

Evaluation week 2

Declaration of Helsinki

The declaration of Helsinki deals with:

• Wellbeing of subjects goes above science and society
• Greater access to benefit
• Written informed consent
• Caution if a participant is in a dependent relationship with the researcher
• Limited use of placebo