Neglected Tropical Diseases

More than 1 billion people are affected by diseases such as malaria, tuberculosis, and sleeping sickness each year. Ten million people die from these diseases annually. Millions more are so incapacitated by disease that they are unable to work, care for themselves, or care for their children. For more information, please visit the World Health Organization website. Each disease or condition listed below links directly to the WHO website content.

 

Buruli Ulcer

Buruli ulcer (BU) is an infectious disease caused by bacteria from the same family of bacteria that cause tuberculosis and leprosy. The bacteria produce a destructive toxin which causes tissue damage and inhibits immune response to the infected area. Human-to-human transmission has rarely been reported.

BU affects mainly poor rural communities located near still bodies of water; cases have also occurred following floods. Instances have been reported in 30 countries, mainly those with tropical and subtropical climates. Although BU has a low mortality rate, it is estimated that 7,000 people are infected with the disease annually.

It is one of the most common, and perhaps least understood major mycobacterial infections. Currently, there are six main research priorities that will lead to better understanding and prevention of BU. These research areas include mode of transmission, development of simple diagnostic tests, drug treatments and new treatment modalities, development of vaccines, social and economic studies, and studies to determine the incidence and prevalence.

Infection of BU leads to extensive destruction of the skin and soft tissue with the formation of large ulcers usually on the legs or arms. Ulcerations are generally painless unless complicated by a secondary infection. BU can destroy nerves, appendages, and blood vessels and can also invade bone tissue. The disease progresses without pain or fever, which may partially explain why infected persons often do not seek prompt treatment. Infected persons not treated early often suffer long-term functional disability, such as restriction of joint movements as well as the obvious cosmetic problems.

Chagas disease (American trypanosomiasis)

Chagas disease, also known as American trypanosomiasis, is a potentially life-threatening illness caused by the protozoan parasite, Trypanosoma cruzi (T. cruzi). It is found mainly in Latin America, where it is mostly transmitted to humans by the faeces of triatomine bugs, known as 'kissing bugs’, among other names, depending on the geographical area. An estimated 10 million people are infected worldwide, mostly in Latin America where Chagas disease is endemic. More than 25 million people are at risk of the disease. It is estimated that in 2008 Chagas disease killed more than 10'000 people.

Chagas disease presents itself in two phases. The initial, acute phase lasts for about two months after infection. During the acute phase, a high number of parasites circulate in the blood. In most cases, symptoms are absent or mild, but can include fever, headache, enlarged lymph glands, pallor, muscle pain, difficulty in breathing, swelling and abdominal or chest pain. In less than 50% of people bitten by a triatomine bug, characteristic first visible signs can be a skin lesion or a purplish swelling of the lids of one eye. During the chronic phase, the parasites are hidden mainly in the heart and digestive muscle. Up to 30% of patients suffer from cardiac disorders and up to 10% suffer from digestive (typically enlargement of the oesophagus or colon), neurological or mixed alterations. In later years the infection can lead to sudden death or heart failure caused by progressive destruction of the heart muscle.
The two available drugs are benznidazole and nifurtimox. Contra-indications are pregnancy, renal or hepatic failure; for nifurtimox, additional contra-indications include psychiatric or neuronal disorders (such as seizures). There is no vaccine for Chagas disease. Vector control is the most effective method of preventing Chagas disease in Latin America. Blood screening is necessary to prevent infection through transfusion and organ transplantation.

Cysticercosis

Human cysticercosis is caused by the development of tissue infection after exposure to eggs of Taenia solium cysticerci in human tissues. Cysticerci that develop in the central nervous system cause neurocysticercosis.

Neurocysticercosis is considered to be a common infection of the human nervous system and is the most frequent preventable cause of epilepsy in the developing world. More than 80% of the world’s 50 million people who are affected by epilepsy live in developing countries, many of which are endemic for T. solium infections in people and pigs.

Cysticercosis mainly affects the health and livelihoods of subsistence farmers in developing countries of Africa, Asia and Latin America as it can lead to epilepsy and death in humans, reduces the market value of pigs and makes pork unsafe to eat.

Although theoretically amenable to control and declared eradicable by the International Task Force for Disease Eradication in 1993, cysticercosis remains a neglected disease.

This is mainly because of a lack of information about its burden and transmission, the lack of diagnostic tools available for use in the field, and the lack of validation of simple intervention packages used as part of integrated helminth control strategies.

Dengue/dengue haemorrhagic fever (DHF)

Dengue is the most common mosquito-borne viral disease, prominently transmitted by the female Aedes mosquito. Once a mosquito acquires the virus from an infected human, it is capable of transmitting the virus for the rest of its life-span.

Although dengue is rarely fatal, the deadly complication of dengue, dengue hemorrhagic fever (DHF), has a 6% to 30% death rate, with the most deaths occurring in children and young adults. It is estimated that DHF causes 22,000 deaths per year.

Dengue occurs in tropical and sub-tropical parts of the world. There are no specific antiviral medicines for dengue, but currently those infected are prescribed pain relievers to treat fever and pain.

Symptoms of dengue include severe flu-like symptoms ranging from a mild fever, to an incapacitating high fever with a severe headache, pain behind the eyes, muscles and joint pain, and rash.

DHF causes fever, abdominal pain, vomiting, bleeding, enlargement of the liver, and circulatory failure. During DHF, hemorrhagic manifestations occur after two to seven days. Complications include the tendency to bruise easily and other types of skin hemorrhages, bleeding nose or gums, and possible internal bleeding. Capillaries can become extremely permeable, allowing for fluid to escape from the blood vessels. This may lead to failure of the circulatory system, followed by death if the circulatory system is not corrected.

Dracunculiasis (guinea-worm disease)

Dracunculiasis is a crippling infectious disease caused by a parasitic worm, Dracunculus medinesus. The disease is transmitted exclusively by drinking contaminated water.

Although dracunculiasis is rarely fatal, death can occur through a secondary infection to the wound. To prevent a secondary infection, wounds are treated with tropical antibiotics.

Dracunculiasis affects people in rural, deprived, and isolated areas who depend on open water sources, like ponds, for drinking water. There is currently no vaccine or drugs available to prevent or heal the disease.

Drinking water becomes contaminated with the parasite when infected persons try to relieve the burning sensation by sticking the parasite infected part of the body in water. Once the female worm is submerged in water it releases hundreds of thousands of first-stage larvae into the body of water. The larvae are then ingested by tiny water fleas, which are then ingested by those who drink the contaminated water. The water fleas are digested by the stomach acids, leaving the parasite larvae to migrate through the intestinal wall. After 100 days, the male and female parasites mate. The male parasite dies and the female migrates down the muscle planes, and after nearly a year the female worm emerges, usually from the feet, with a uterus filled with larvae, repeating the cycle.

In dracunculiasis, as the parasite migrates through the infected person's subcutaneous tissues, it causes severe pain, especially in the joints. When the parasite emerges, from the feet in 90% of cases, it causes an intensely painful oedema, a blister and an ulcer accompanied by fever, nausea, and vomiting. A few days or even hours before the worm emerges the person may develop a fever, swelling, and pain in the area.

Echinococcosis

Cystic echinococcosis (hydatid disease) is a parasitic disease that affects both humans and mammals, more commonly dogs, horses, sheep and rodents. Both cystic and alveolar echinococcosis develop when humans ingest eggs of Echinococcus granulosus or E. multilocularis which are shed in the faeces of dogs harbouring adult stages of these tapeworms.

Echinococcosis has a global distribution and causes serious morbidity and death if left untreated. Cystic echinococcosis is principally maintained in a dog–sheep–dog cycle. Human cystic echinococcosis (or hydatidosis) is a disease caused by the larval stages of the dog tapeworm E. granulosus (Cestoda). The infection is transmitted to dogs when they are fed infected viscera of sheep or other ruminants during the home-slaughter of animals. Dogs also become infected through scavenging. Direct contact with dogs and consuming vegetables and water contaminated with infected dog faeces are important modes of transmission to humans.

Cystic echinococcosis, a chronic disease with an asymptomatic period of several years. It is difficult to diagnose without imaging tools (such as computed tomography or ultrasound) and laboratory confirmation of the disease relies on good serological tests.

Treatment comprises mainly surgical intervention or percutaneous treatment and/or high dose, long-term therapy with albendazole alone or in combination with praziquantel.

Endemic treponematoses (Yaws)

Endemic treponematoses are a group of chronic bacterial infections caused by treponeme, a bacterium called Treponema pertenue, which include yaws (also known as framboesia, pian), endemic syphilis (bejel) and pinta. All these infections often present as skin lesions and the most common of these is yaws.

Yaws is a chronic infection that affects mainly the skin, bone, and cartilage. It is transmitted primarily through direct skin contact with an infected person. Overcrowding, poor personal hygiene, and poor sanitation facilitate the spread of the disease.

The disease occurs mainly in poor communities in warm, humid, tropical areas of Africa, Asia and Latin America. Currently there is no global coordination to fight the disease.

Yaws can be completely eradicated from an area by giving penicillin or another appropriate antibiotic to everyone in the population, yet this may cost more than an impoverished country can afford. In the 1990's it was estimated that the global prevalence of yaws stood at 2.5 million, with 460,000 new cases each year. Almost 75% of people affected are children under 15 years, although peak incidence occurs in children between the ages 6-10.

Yaws is transmitted primarily through skin contact with an infected person. A single skin lesion develops at the point of entry of the bacterium after 2-4 weeks. If left untreated, multiple lesions appear all over the body. Although rarely fatal, yaws can lead to chronic disfigurement and disability. Overcrowding, poor personal hygiene and poor sanitation facilitate the spread of the disease.

Foodborne trematode infections

  • Clonorchiasis
  • Opistorchiasis
  • Fascioliasis
  • Paragonimiasis

The foodborne trematode (FBT) infections are among the most neglected tropical diseases due to helminths. While major progress has been made in recent years in reaching populations in need of treatment for lymphatic filariasis, onchocerciasis, schistosomiasis and soil transmitted helminthiasis, those affected by FBT infections and taeniasis/cysticercosis frequently have no access to adequate assistance.

Over 100 species of foodborne trematodes are known to cause infections – trematodiasis – in humans. Clonorchiasis, opisthorchiasis, fascioliasis and paragonimiasis are the infections that pose the most significant public health and economic burden. Clonorchiasis and opisthorchiasis are confined to Asia, while paragonimiasis can be found in Africa, Asia and Latin America. Fascioliasis is a global disease, affecting a significant number of countries throughout the world.

Transmission of paragonimiasis is usually limited to a group of districts and the disease can still be described as focal. Clonorchiasis, opisthorchiasis and fascioliasis, on the other hand, tend to be more diffuse and to affect larger geographical areas. Core interventions against FBT infections include preventive chemotherapy and a series of complementary measures.

Fascioliasis is caused by trematodes belonging to the genus Fasciola (F. hepatica and F. gigantica). Fascioliasis can cause blockage of the bile ducts in the liver. Fascioliasis is a zoonosis, or a disease of animals that can be transmitted to humans. Susceptible hosts include main domestic animals like cattle, sheep, pigs, horses, donkeys, and others, and sylvatic animals such as hares, rabbits, and rodents. It is now also believed that human-to-human transmission can occur.

Fascioliasis cases are widespread throughout the world. It is estimated that between 2.4 and 17 million people are infected worldwide, and 180 million more are at risk.

The disease is transmitted through a fecal-oral route. Parasitic eggs are passed in feces of infected animals or humans and contaminate the water where they develop within snails. Snails then release mature larvae onto aquatic or semi-aquatic vegetation. Humans typically become infected by drinking contaminated water or using utensils or eating food washed with contaminated water. Fascioliasis can also be transmitted through the consumption of raw liver from infected sheep, goats, or cows.

The most common symptoms include fever, enlarged liver, malaise and weight loss, hives, cough, shortness of breath and/or chest pain, change in bowel habits, nausea, anorexia, vomiting, diarrhea, and/or jaundice, and abdominal pain. Human fascioliasis can be distinguished by four phases. The incubation phase is from the time of the ingestion of parasites to the visibility of the first symptoms, and may last from days to months. During the acute phase immature worms migrate through the liver. Symptoms include hemorrhage and inflammation and are usually severe, including fever, abdominal pain, respiratory disturbances, and skin rashes. The latent phase can last from months to years and most cases are asymptomatic. The chronic phase starts when the worms reach the bile duct. Symptoms during this phase are non-specific and usually mild; however, progressive inflammation can lead to more serious health problems.

Human African trypanosomiasis (HAT)

African trypanosomiasis is an infectious parasitic disease caused by protozoa parasites. The disease is transmitted to humans by infected tsetse flies, which acquire the infection through other infected humans or animals.
African trypanosomiasis currently affects more than 500,000 people, with more than 12,000 new cases developing every year. If left untreated, African trypanosomiasis is fatal, but the cure rate approaches 95 percent when those infected are treated with drugs that work inside the CNS.

There is no vaccine available for African trypanosomiasis. Most patients fully recover from African trypanosomiasis if treated during the first stage of the disease. However, the disease occurs mostly in remote rural areas where the health system is weak or nonexistent, making detection in the first stage difficult. Diagnosis is usually not made until the second, ultimately fatal stage when CNS manifestations develop.

There are two types of African trypanosomiasis. Trypanosomabruceigambiense (TPG) is found in West and Central Africa, and represents 90% of African trypanosomiasis cases. This form of the disease is represented by chronic infection. Persons can be infected for months or years with no symptoms, but when symptoms do emerge the infected person is already in an advanced stage of the disease and the central nervous system (CNS) is already affected.

Trypanosomabruceirhodesiense (TBR) is found in Eastern and Southern Africa and is represented by an acute infection. The first signs and symptoms of TBR appear after a few weeks or months. This form of the disease typically progresses rapidly and invades the CNS quickly.

There are also two phases of African trypanosomiasis. During the initial phase of the disease, the haemolymphatic phase, symptoms can include bouts of fever, headache, joint pain, and itching. Infected persons may also experience symptoms of extreme fatigue that can last for several years before the second phase of the disease, called the neurological phase, sets in. This longtime fatigue is why the disease is known as the "sleeping sickness".

The Neurological phase begins when the parasite crosses the blood/brain barrier and invades the CNS. This is generally when symptoms of the disease appear, including confusion, sensory disturbances, and poor coordination. Sleep cycle disturbance is also an important feature of African trypanosomiasis.

Leishmaniasis

Leishmaniasis is an infectious parasitic disease with a wide range of clinical symptoms. The disease is transmitted by the bite of a sand fly. Some types of these parasites can be transmitted through blood transfusions or contaminated needles. Congenital transmission, spread from pregnant woman to baby, has also been reported.

There are no vaccines or drugs to prevent infection. The best ways to prevent the disease are to wear protective clothing, insect repellant, bed nets, and place screens on doors and windows. With early treatment, the disease cure-rate is higher than 90%. If left untreated, death can occur in as quickly as three to 20 months. Approximately 80,000 people die from leishmaniasis each year.

Leishmaniasis occurs within the world's inter-tropical temperature regions, wherever the sand fly is found.

In leishmaniasis, a sand fly becomes infected with the parasite through biting an infected human. Then there is an incubation period of four to 25 days during which the parasite develops inside the sand fly. Once the sand fly feeds again, its painful sting infects the new victim with the parasite.

There are three forms of leishmaniasis. The cutaneous form of the disease normally produces skin ulcers on exposed parts of the body, such as the face, arms, and legs. The disease can produce a large number of lesions, sometimes up to 200, causing serious disability and leaving the patient permanently scarred. In the mucocutaneous form, lesions can lead to partial or full destruction of the mucous membranes of the nose, mouth, and throat cavities and surrounding tissues. The visceral form, also known as kalaazar, is characterized by irregular bouts of fever, substantial weight loss, swelling of the spleen and liver, and anemia.

Leprosy

Leprosy is a chronic infection caused by bacteria. It affects the skin, nerves of the hands and feet, and can also cause problems in the eyes and nose. Leprosy is spread through long-term contact with an untreated person who has the disease, usually through coughing and sneezing. However, within two weeks of starting treatment an infected person is no longer contagious.

Currently, there is no vaccine for leprosy. The BCG (BacilleCalmette-Guerin) vaccine, used to prevent tuberculosis, provides some protection against leprosy, but is not often used to prevent the disease. Leprosy is a curable disease and treatment in early stages helps to avoid permanent disability. If left untreated, leprosy can cause progressive and permanent damage to skin, nerves, eyes, and limbs. People with long-term leprosy may lose use of hands and feet due to repeated traumatic injury because of lack of sensation due to nerve damage.

Multidrug therapy is recommended to treat leprosy; however medication cannot reverse any nerve damage that has already occurred. Leprosy is rarely fatal, but people with leprosy often suffer psychological and social problems due to the disfigurement and significant disability the disease can cause. It is estimated that 2.4 million people suffer from disabilities from leprosy and need ongoing care, with 300,000 new cases developing each year.

There are two variations of the disease, tuberculoid leprosy and lepromatous leprosy. Tuberculoid is milder than lepromatous and is characterized by skin discoloration. In this variation, fewer skin areas are affected and the disease is less contagious. A rash can develop that can eventually cause bacterial nerve damage.

The lepromatous variation is more common than the tuberculoid form. It is characterized by symmetric skin lesions, nodules, plagues, a thickened dermis, and nasal mucosa complications resulting in congestion and nose bleeds. In the lepromatous variation more skin areas are affected and the disease is more severe and contagious. People can also develop borderline leprosy, when they have features from both the Tuberculoid and Lepromatous variations.

Lymphatic filariasis

Lymphatic filariasis, or Elephantiasis, is a parasitic and infectious tropical disease caused by one of three types of thread-like parasitic worms. The disease is transmitted through mosquito bites.

Lymphatic filariasis affects an estimated 120 million people in 80 countries throughout the tropics and subtropics, and approximately another 1.3 billion, 20% of the world's population, are at risk of acquiring the disease.

There is no vaccine for lymphatic filariasis. The best treatment for the disease is a combination of drugs to kill the parasite, skin care to prevent secondary infections, and elevation, exercises, and in some cases pressure bandages to reduce swelling.

Most people infected with lymphatic filariasis are asymptomatic and will never develop clinical symptoms. A small percentage of people will develop lymphedema, which is caused by irregular functioning of the lymph system.

Lymphedema leads to fluid collection and swelling of the legs, arms, breast, and genitalia. Lymphedema can then lead to elephantiasis. Elephantiasis occurs in about 5% of cases and is characterized by the hardening and thickening of the skin caused by bacterial infections within the skin and lymph system. It leads to severe disfigurement, decreased mobility, and long-term disability.

In addition to these symptoms, there can also be internal damage to the kidneys and lymphatic system caused by the parasite. Although rarely fatal, the disease can also cause recurring infections, fever, severe inflammation of the lymph system, and a lung condition called tropical pulmonary eosinophilia.

Onchocerciasis

Onchocerciasis, or River Blindness, is a parasitic disease that is transmitted through the bites of black flies.

There is no vaccine or recommended drug to help prevent onchocerciasis. It is estimated that 17.7 million people are infected with the disease worldwide, and 99% of all cases are found in Africa. Approximately 270,000 of those infected suffer from blindness and another 500,000 have visual impairment.

In onchocerciasis, the parasites are transferred from an infected human to the female black fly through a bite. Over the course of one to three weeks the transferred parasite develops inside the black fly to form infective larvae. The larvae are then passed to another human through another bite. Once in a human, the larvae migrate to the subcutaneous tissue and slowly form into adult worms, completing the disease cycle.

An adult worm can live for 15 years in the human body. After mating, the female worm releases around 100 parasitic larvae a day in the surrounding subcutaneous skin tissue. The parasites can live in the human body for one to two years, and when they die they cause an inflammatory response that leads to skin rashes, lesions, intense itching, and skin depigmentation.

Over several years, severe dermatitis can occur. The skin can waste away and lose elasticity, giving the appearance of early aging. The parasites can also migrate to the eye where they cause inflammation and other complications. Over time the area becomes opaque, leading to impaired vision and eventually blindness. This is what gives the disease its common name, "River Blindness".

Rabies

Rabies is a zoonotic disease (a disease that is transmitted from animals to humans) that is caused by a virus. It is known to be present on all continents except Antarctica and infects domestic and wild animals.

Rabies is spread to people through close contact with infected saliva via bites or scratches. The main route of rabies transmission to humans is the bite of rabid dogs. Most of the deaths occur in the absence of post-exposure prophylaxis. Rabies is nearly always fatal when left untreated.

Although it is a vaccine-preventable disease, rabies still poses a significant public health problem in many countries in Asia and Africa where 95% of human deaths occur even though safe, effective vaccines for both human and veterinary use exist.

Nearly half of those bitten by suspect rabid animals are children under 15 years of age. Although the efficacy and safety of modern cell culture vaccines have been recognized, some countries still produce and use nervous tissue vaccines, which are less effective.

Schistosomiasis

Schistosomiasis, or Bilharzias, is a parasitic infectious disease caused by parasitic worms. The disease is transmitted through contaminated freshwater where snails that carry the parasites live. Schistosomiasis can also be transmitted when the parasites penetrate the skin of persons who are wading, swimming, or bathing in the contaminated water. The freshwater becomes contaminated when infected people urinate or defecate in the water source.

There is no vaccine available for schistosomiasis. Next to malaria, schistosomiasis is considered humanity's most serious parasitic infection. Although schistosomiasis is rarely fatal, it can become a chronic illness that damages internal organs and causes cognitive deficiencies in children. The disease is most prevalent in rural areas in which standards of hygiene are low. More than 200 million people are infected worldwide.

Once the parasite penetrates human skin it matures in the lungs or liver and then migrates to the bladder, rectum, intestines, liver, portal venous system, spleen, or lungs causing inflammation or scarring. Parasitic eggs can become embedded in the tissues of the body, leading to the formation of granuloma. Once the disease progresses to the granuloma stage the damage is irreversible; it is possible to kill the parasite but not to repair the damage already done. Rarely, eggs are found in the brain or spinal cord and can cause seizures, paralysis, or spinal cord inflammation.

There are several variations of schistosomiasis, eastern, intestinal, and urinary. The type the infected has depends on the specific parasite that infects the individual and where it migrates to.

Within one to two months symptoms can include fever, chills, cough, and muscle aches, but most people have no symptoms at the early phase of the infection. Children who are repeatedly infected can develop anemia, malnutrition, and learning difficulties.

Complications of this disease can include bladder cancer, chronic kidney failure, chronic liver damage, an enlarged spleen, colon inflammation with bloody diarrhea, kidney and bladder obstruction, pulmonary hypertension, repeated blood infections can occur, right-sided heart failure, and seizures.

Soil transmitted helminthiasis

Soil-transmitted helminths commonly known as intestinal worms, are the most common infections worldwide affecting the most deprived communities.

The causal agent of soil-transmitted helminthiasis is any of the following worms: Ascarislumbricoides, Trichuristrichiura and the hookworms. Recent estimates suggest that A. lumbricoides infects over 1 billion people, T. trichiura 795 million, and hookworms (Ancylostomaduodenale and Necatoramericanus) 740 million. The greatest numbers of soil-transmitted helminth infections occur in sub-Saharan Africa, the Americas, China and east Asia. Infection is caused by ingestion of eggs from contaminated soil (A. lumbricoides and T. trichiura) or by active penetration of the skin by larvae in the soil (hookworms).

Soil-transmitted helminths produce a wide range of symptoms including intestinal manifestations (diarrhoea, abdominal pain), general malaise and weakness, that may affect working and learning capacities and impair physical growth. Hookworms cause chronic intestinal blood loss that results in anaemia.

Trachoma

Trachoma is an infectious disease caused by Chlamydia trachomasis an organism and usually occurs when the discharge from an infected person's eye is passed to another by way of hands, clothing, or flies. Children are the most susceptible to this disease because of their tendency to play and get dirty.

Trachoma is the leading cause of preventable blindness. It is estimated that 6 million people worldwide are blind due to trachoma and more than 150 million more are in need of treatment. Trachoma accounts for 15.5% of the global burden of blindness.

Trachoma occurs worldwide, most often in poor, rural communities within developing countries. The disease is easily preventable with the practice of good facial hygiene and environmental changes to produce cleaner living conditions. Although there is no vaccine, Trachoma is treatable with surgery to reverse the inward growth of the eyelashes and antibiotics.

Symptoms of trachoma include cloudy cornea, discharge from the eye, swelling of the lymph nodes just in front of the ears, swollen eyelids, and turned-in eyelashes.

Infection typically occurs during childhood and repeats over lifetime, eventually causing damage to the interior of the eyelid that forces the eyelashes to grow inward. The inward growth of the eyelashes results in rubbing on the front of the eye, damaging the cornea. The damage done to the cornea leads to severe vision loss and eventual blindness.

Podoconiosis

Podoconiosis is a type of tropical lymphoedema clinically distinguished from lymphatic filariasis (LF) through being ascending and commonly bilateral but asymmetric. Evidence suggests that podoconiosis is the result of a genetically determined abnormal inflammatory reaction to mineral particles in irritant red clay soils derived from volcanic deposits.

Podoconiosis is found in highland areas of tropical Africa, Central America and north-west India. Podoconiosis occurs in populations living at high altitudes (more than 1'000 meters above sea level).

Disease starts in the foot and progresses up the leg to the knee but rarely involves the groin; conversely, LF is found at lower altitudes and changes often are noticed first in the groin.

Snakebite

Envenoming resulting from snake bites is a particularly important public health problem in rural areas of tropical and subtropical countries situated in Africa, Asia, Oceania and Latin America. A recent study estimates that at least 421,000 envenomings and 20,000 deaths occur worldwide from snakebite each year, but warns that these figures may be as high as 1,841,000 envenomings and 94,000 deaths. The highest burden of snakebites is in South Asia, Southeast Asia, and sub-Saharan Africa.

Snake bite is primarily a problem of the poorer rural populations in these regions and affects mainly those involved in subsistence farming activities. Poor access to health services in these settings and, in some instances, a scarcity of antivenom, often leads to poor outcomes and considerable morbidity and mortality. Many victims fail to reach hospital in time or seek medical care after a considerable delay because they first seek treatment from traditional healers. Some even die before reaching hospital. Hospital statistics on snakebites therefore underestimate the true burden. In addition to mortality, some snakebite victims survive with permanent physical sequelae due to local tissue necrosis and, sometimes psychological sequelae. Because most victims are young, the economic impact of snakebite can be considerable.

Snake venom is a complex mixture of many different compounds. The composition and effects of venom varies considerably between species to species, but can broadly be divided into categories which include i) cytotoxins causing local swelling and tissue damage, ii) haemorrhagins which disturb the integrity of blood vessels, iii) compounds which lead to incoagulable blood, iv) neurotoxins causing in neurotoxicity and iv) myotoxins which cause muscle breakdown.

The mainstay of treatment of snakebite is the infusion of an appropriate antivenom. Snake venoms are diverse, and therefore the efficacy of antivenoms is geographically and biologically restricted, meaning that a large number of antivenoms have been developed for use in different settings.

Malaria

Malaria is a parasitic infectious disease, caused by eukaryotic protists of the genus Plasmodium, usually P. falciparum or P. vivax that is transmitted to people through the bites of infected Anopheles gambiae mosquitoes. Malaria can also be transmitted through blood transfusions, organ transplants, or the shared use of contaminated needles or syringes. It can also be transmitted from mother to unborn baby before or during delivery. Malaria is not contagious and cannot be sexually transmitted.

Malaria is considered one of humanity's most serious parasitic infections. Each year, 350-500 million cases of malaria occur worldwide. If malaria is not treated promptly with effective medicines it can cause severe illness and is often fatal. Each year, more than 1 million people die of malaria, and a child dies of malaria every 30 seconds.

Malaria is found in tropical and subtropical regions. Approximately half the world's population is at risk for malaria, particularly those living in lower income areas.

There is no vaccine for malaria. Prevention measures focus on controlling the disease-carrying mosquito with the use of mosquito nets treated with long-term insecticides and indoor residual spraying of insecticides.

Initial symptoms of Malaria usually appear 10 to 15 days after the infected bite, and include fever, headache, chills, and vomiting. Other symptoms can include flu-like symptoms, muscle aches, lethargy, anemia, and jaundice. If not promptly treated, the falciparum variation can potentially cause kidney failure, seizures, mental confusion, coma, and death. In certain types pf malaria some parasites can lay dormant in the liver for months to four years, causing the disease to eventually recur (recurring malaria).

Tuberculosis

Tuberculosis (TB) is a contagious disease caused by various strains of mycobacterium, usually Mycobacterium tuberculosis that spreads through the air. When people cough, sneeze, talk, or spit they release TB germs, known as bacilli, into the air. A person only needs to inhale a small amount of bacilli to become infected. Left untreated, each person with active TB disease will infect on average between 10-15 people per year.

Approximately one-third of the world's population is currently infected with TB bacillus. Each year there are more than 8 million new cases of TB reported and almost 2 million TB related deaths. TB is a leading killer of people who are HIV infected due to their weakened immune defenses.

Bacille Calmette Guerin (BCG) is a vaccine for TB given throughout many parts of the world. BCG is especially effective in infants and children, but when administered the vaccine as a child people can still contract TB as an adult. There are currently several drugs to treat TB infections; however there are multiple strands of the disease that are drug-resistant.

TB most commonly affects the lungs, but can also involve almost any organ of the body. People infected with TB bacilli may not immediately become sick with the disease because the immune system blocks the TB bacilli, leaving the disease to lie dormant for years. When the immune system is weakened a person's chance of becoming sick increased.

When TB bacteria are inhaled they can multiply and cause a local lung infection, pneumonia, and then can spread to other parts of the body. The body's immune system stops the infection from spreading by forming scar tissue around the TB bacteria and isolating it from the rest of the body. Once the infection is contained, the disease is in an inactive state, latent TB, unless the body's immune system weakens and the bacteria can break through the scar tissue and become active again.

Symptoms of active TB are generally tiredness or weakness, weight loss, fever, and night sweats. If the infection in the lung worsens, further symptoms can include coughing, chest pain, coughing up of material from the lung, sputum and/or blood, and shortness of breath. If the infection spreads beyond the lungs the symptoms will depend on the organs involved.

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