Tropical diseases for beginners

Chris Simoens
01 December 2014
Tropical diseases cover all diseases that occur exclusively or primarily in the (sub)tropics. In practice, the term usually refers to infectious diseases that thrive in a warm and humid climate. Developing countries are particularly susceptible to them. Glo.be presents the 15 most common tropical diseases below.

MALARIA

 

What

Life-threatening disease caused by single-cell parasites (Plasmodium – 5 species), transmitted by biting mosquitoes (Anopheles – 20 species).

 

Symptoms

Early: high fever, chills, headaches, vomiting. Later: anaemia and respiratory problems (children), organ damage (adults).

 

Where

Primarily Sub-Saharan Africa, also in Asia and Latin America. Less so in the Middle East and parts of Europe.

 

Impact

Roughly estimated at 207 million new cases and 627,000 deaths (2012). Risk groups: young children and pregnant women. A child dies of malaria every minute. Around half of the world's population lives in high-risk areas.

 

Treatment

Artemisinin-based combination therapy in the early stages.

 

Prevention

Covering beds with mosquito nets impregnated with insecticides (pyrethroids) & spraying indoors with insecticides. A promising vaccine (RTS,S) is currently being tested in Africa. For short stays in a region where the disease is prevalent, medication such as malarone can prevent the disease.

 

Challenges

In certain areas, mosquitoes are resistant to pyrethroids. There is resistance to artemisinin in the Mekong region as a result of 'monotherapy' (treatment exclusively with artemisinin).

 Poster against malaria
© IRD-C. Duos

DENGUE FEVER and SEVERE DENGUE

 

What

Viral infection transmitted by biting mosquitoes (predominantly Aedes aegypti). There are 4 related types of the virus.

 

Symptoms

Flu-like state with high fever (40°C), severe headaches, painful muscles and joints, swollen lymph nodes, etc.

Severe dengue fever is a potentially fatal complication of dengue fever, after several infections, with pain in the lower abdomen, continuous vomiting (with blood) etc.

 

Where

In tropical and subtropical climates, especially in (semi) urban areas. Mosquitoes breed in any stagnant water-containing recipient.

 

Impact

50-100 million infections a year. 500,000 people (mainly children) are admitted to hospital with severe dengue fever every year; 2.5% of them die. 2.5 billion people live in high-risk areas.

 

Treatment

No specific medication. In the case of severe dengue fever, it is particularly important to maintain body fluids.

 

Prevention

Among other things, avoid breeding sites, prevent mosquitoes from entering the house, insecticides. Research is being conducted into vaccines.

 

Challenges

Dengue fever can also break out in Europe. First outbreak in 2010 in France and Croatia, in 2012 in Madeira and Portugal, among other places. In 2013 in the US and China. Aedes albopictus, a less important but cold-tolerant carrier from Asia, has spread to Europe and North America via international transport (tyres, bamboo, etc.).

An Aedes aegypti mosquito
© IRD-N. Rahola

CHOLERA

 

What

Diarrhoea infection caused by ingestion of food or water contaminated with the bacteria Vibrio cholerae. Can be fatal within hours if left untreated.

 

Symptoms

Watery diarrhoea. 75% of infected people show little (mild diarrhoea) or no symptoms. People with weak resistance (malnourished children, AIDS patients, etc.) are particularly vulnerable.

 

Where

From the Ganges Delta in India, the disease spread throughout the world in the 19th century. Endemic (stable presence) in various developing countries. Common in places with poor hygienic conditions: slums, refugee camps.

 

Impact

3-5 million cases every year and 100,000-120,000 deaths.

 

Treatment

More than 80% of patients can easily be treated with 'oral rehydration salts'. For sick people who have lost a lot of water: they must be put on a liquid drip. Antibiotics may be prescribed.

 

Prevention

Adequate hygiene (sanitation) and clean water. Reacting quickly to avoid epidemics. There are two effective oral vaccines, especially for vulnerable people in high-risk areas.

 

Challenges

Recent new strains of bacteria which cause more severe cholera. Global warming can create favourable environments for the bacteria.

 Banks of the Ganges lined with dumps and slums
© Stanley Greene

CHAGAS DISEASE (AMERICAN TRYPANOSOMIASIS)

 

What

Life-threatening disease caused by the single-cell parasite Trypanosoma cruzi, transmitted by bloodsucking predatory bugs. The deposit infected faeces near the puncture wound, so the victim can infect themselves when scratching.

 

Symptoms

First (acute) phase (2 months) with at most mild symptoms such as skin lesions, headaches and muscle pain. Second (chronic) phase in which 30% of victims have heart problems, and 10% digestive and/or nervous problems. Sudden death or heart failure is possible years later.

 

Where

Primarily in Latin America. Due to mobility, recently also in US, Canada and Europe, among other places.

 

Impact

7-8 million people are infected. In 2008, the medical cost in Colombia amounted to €207 million. Spraying insecticides costs around €3.9 million annually.

 

Treatment

Highly effective medication is available (benznidazole, nifurtinox) if administered early. Requires accessible health care.

 

Prevention

Containment of carrier: spraying insecticides, bed nets, good hygiene in food preparation and transport and such like. Eradication is impossible due to large reservoir of T. cruzi in wild animals.

 

Challenges

Disease is prevalent in areas that were previously free of Chagas (Amazon region, etc.). There have been new outbreaks in areas where control has been successful (Chaco in Bolivia, etc.). It has spread to the rest of the world.

Insect blood sucker (predatory midge)
© IRD-N. Rahola

LEISHMANIASIS

 

What

3 types of diseases caused by single-cell parasites (Leishmania - more than 20 species), transmitted by the bite of sandflies.

 

Symptoms

Visceral leishmaniasis (VL): irregular fever, weight loss, enlarged liver, anaemia, etc. Fatal if left untreated.

Cutaneous leishmaniasis (CL): large skin ulcers at the site of the fly bite. Permanent scars. This is the most common variant.

Muco-cutaneous leishmaniasis (ML): partial to total degradation of mucous membranes in the nose, mouth and throat.

 

Where

VL: India and East Africa. CL: Especially North and South America, the Mediterranean Basin, Middle East, Central Asia. ML: Primarily in Bolivia, Peru and Brazil.

The poorest people in particular are victims (relating to malnutrition, poor housing, etc.). It is also linked to deforestation, irrigation, construction of dams, etc.

 

Impact

20,000-30,000 deaths every year. VL: 200,000-400,000 new cases every year. CL: 0.7-1.3 million new cases every year.

 

Treatment

Treatable and curable. Victims of VL in particular must be treated quickly.

 

Prevention

Early diagnosis, containment of carriers (insecticides, insecticide-impregnated bed nets, etc.), awareness-raising, etc.

 

Challenges

Climate change may make the situation worse.

Child with leishmaniasis infection on the cheek
© Damiaanactie

SCHISTOSOMIASIS (BILHARZIA)

 

What

Disease caused by parasitic worms that bore through the skin (Schistosoma - 5 species). Infection occurs through swimming in or drinking contaminated water (faeces from contaminated freshwater snails). Two variants: intestinal and urogenital.

 

Symptoms

Intestinal: pain in the lower abdomen, diarrhoea, blood in stools, etc. Urogenital: blood in urine, etc.

 

Where

In (sub)tropical areas, especially in poor, rural communities without proper sanitation and access to clean drinking water (farmers, fishermen, playing children, etc.). 90% of victims live in Africa.

 

Impact

In Sub-Saharan Africa, it is estimated that more than 200,000 people die each year. In 2012, at least 249 million people received preventive treatment; 42.1 million patients were treated.

 

Treatment

Effective, safe and affordable medication is available (praziquantel).

 

Prevention

Large-scale treatment of at-risk groups, access to clean water, better sanitation, awareness raising of hygiene, snail control.

 

Challenges

Shortages of praziquantel. In 2012, only 14.4% of people who needed preventive treatment received it. More and more tourists are getting infected (eco-tourism, travelling off the beaten track).

 Insect blood sucker (predatory midge)
© Reynaers-Greenpeace

 

LEPROSY

 

What

Disease caused by the slow-multiplying bacterium Mycobacterium leprae. Infection from close and frequent contact, via droplets from the nose and mouth of an infected person.

 

Symptoms

Skin lesions, but also peripheral nerves, eyes and mucous membranes of the upper respiratory tract are affected. Over time, the affected skin can become insensitive or deformed. The victim can also become blind or lame.

 

Where

Remnants in various countries including Angola, Bangladesh, Brazil, China, DR Congo, Ethiopia, India, Indonesia, Madagascar, Mozambique, Myanmar, Nepal, Nigeria, Philippines, South Sudan, Sudan and Tanzania.

 

Impact

At the end of 2012, there were 189,018 victims worldwide, and 232,857 new cases. In the last 20 years, nearly 16 million people infected with leprosy have been cured.

 

Treatment

A combination of dapsone, rifampicin and clofazimine is highly effective.

 

Challenges

Focusing on people not yet reached, including in remote areas. Incorporating leprosy treatment into general healthcare. Eliminating the stigma that prevents victims from asking for help.

Child with leishmaniasis infection on the cheek
© Damiaanactie

EBOLA VIRUS DISEASE

 

What

Severe viral disease caused by the Ebola virus (5 species). Virus originated in infected animals such as gorillas and chimpanzees. Fruit bats are presumed to be the natural host.

 

Symptoms

These include sudden fever, extreme weakness, headaches and muscle pain, followed by vomiting, diarrhoea, kidney and liver problems and sometimes bleeding. 40-90% of patients die.

 

Where

Primarily in remote villages in Central and West Africa, close to tropical rainforest. A strain of Ebola has also been recorded in China and the Philippines, so far with no effect on humans.

 

Impact

The first outbreaks in 1976 had a death toll of 280 (DR Congo) and 151 (Sudan). Since then, there have been regular outbreaks, with the most severe in the DR Congo, Congo and Uganda. The current outbreak in West Africa is the most serious, with 4,808 deaths as of 2 November 2014 (37% of the victims) in the 3 most affected countries (Guinea, Liberia and Sierra Leone).

 

Treatment

Vaccines and treatments are in the test phase. Seriously ill victims need general intensive care. Drinking a lot (including rehydration fluid = water with dissolved salts and sugars) increases the chance of survival.

 

Prevention

Awareness raising of careful contact with (wild) animals, avoiding close contact with infected people (body fluids) and safe funeral rituals.

 

Challenges

Finding an effective treatment.

Young boys playing in a forest pond in Congo
© UNICEF-NYHQ2014-1027-Jallanzo

(HUMAN AFRICAN) TRYPANOSOMIASIS (SLEEPING SICKNESS)

 

What

Disease caused by single-cell parasite Trypanosoma brucei, transmitted by the bite of infected tsetse flies (Gambus). There are 2 sub-types: T. brucei gambiense (around 98% of cases) and T. brucei rhodosiense.

 

Symptoms

First phase: fever, headache, joint pain, itching. Second phase: impairment of the central nervous system with confusion, changes in behaviour, disturbance of sleep etc. Fatal if left untreated. Gambiense: slow development of symptoms.

Rhodesiense: rapid development of symptoms.

 

Where

Gambiense: West and Central Africa. Rhodesiense: East and Southern Africa. Primarily rural populations (farmers, fishermen, hunters, pastoralists). Over the last 10 years, 70% of cases have been recorded in the DR Congo.

 

Impact

3 major epidemics during the 20th century. 70 million people are threatened by the disease. 40,000 official cases in 1998, although the actual number was possibly 300,000. 9,878 official cases in 2012, the actual number was 20,000.

 

Treatment

Medication is available. First phase: pentamidine and suramine; second phase: melarsoprol, eflornithine, nifurtimox.

 

Challenges

The World Health Organization (WHO) is making sustained efforts to eradicate the disease through public-private partnerships. Belgium is one of the main donors in the fight against sleeping sickness in the DR Congo.

Jeune garçon atteint de la lèpre
© IRD-M. Dukhan

 

BURULI ULCER

 

What

Debilitating infection of the skin and connective tissue caused by the bacteria Mycobacterium ulcerans.

 

Symptoms

Starts as a painless lump, primarily on the arms and legs. Later, large ulcers can destroy the skin and connective tissue. Can lead to deformities and disability.

 

Where

33 countries in Africa, South America, East Asia and Oceania. Primarily (sub)tropical except for China, Australia and Japan. Most cases are in West and Central Africa (Benin, Cameroon, Ivory Coast, DR Congo, Ghana).

 

Impact

5,000-6,000 cases every year, in Africa 48% of cases are people younger than 15.

 

Treatment

A cocktail of antibiotics such as rifampicin with streptomycin, possibly in combination with skin ulcer treatment.

 

Prevention

No prevention possible as the carrier is not known. There are also no effective vaccines.

 

Challenges

Early detection, rapid diagnostic test, identifying the carrier.

 Person infected with a Buruli ulcer on the lower leg
© IRD-S. Meyinaebong

DRACUNCULIASIS (GUINEAWORM DISEASE)

 

What

Disease caused by the parasitic roundworm Dracunculus medinensis. Contamination occurs by drinking water containing infected water fleas.

 

Symptoms

When digested in the stomach, the larvae break out of the water fleas and bore their way through the intestinal wall, after which they migrate through the body. After about 1 year, one or more fertilized female worms migrate subcutaneously to the lower legs and form a blister. The painful burning sensation can be alleviated by keeping the blisters under water. At that point, the worms leave the body and can infect water fleas. Other symptoms include nausea, fever and allergic reactions.

 

Where

Primarily in South Sudan, in addition to Chad, Ethiopia, Mali and Sudan. In poor rural populations who use surface water as drinking water.

 

Impact

In the 1980s, there were 3.5 million cases in 20 countries; in 2013, only 148 cases in 5 countries.

 

Treatment

None

 

Prevention

Prevention measures have almost eradicated the disease: breaking the cycle by preventing the worm from getting into water (removing the worm manually from the blister), better drinking water, awareness-raising, killing the larvae of water fleas with temephos. There is no vaccine.

 

Challenges

Detecting the remaining cases is the biggest challenge. Quasi-extermination can result in less funding and interest.

Leg of a person with Guinea worm disease
© AJC1

INTESTINAL WORM INFECTIONS TRANSMITTED BY SOIL

 

What

Infections caused by various types of parasitic worms: roundworm (Ascaris lumbricoides), hookworm (Ancylostoma duodenale, Necator americanus), whipworm (Trichuris trichiura)... Their eggs are transmitted by soil contaminated with faeces from infected people (via vegetables and water, children playing, etc.).

 

Symptoms

Clearer symptoms as more worms are present in the body. Diarrhoea, abdominal pain, general weakness, impaired physical and mental development, anaemia (due to blood loss in the intestines in the case of hookworms). Possible shortage of essential nutrients (vitamin A, etc.) as the worms also eat them.

 

Where

Sub-Saharan Africa, North and South America, East Asia, China. In areas with inadequate sanitation.

 

Impact

More than 1.5 billion people (almost 1 in every 4 humans) have intestinal worms. More than 270 million very young children and more than 600 million school-age children live in areas with a high incidence of intestinal worms. Other risk groups: pregnant women, miners, tea pickers, etc.

 

Treatment

Medication which is effective, cheap and easy to administer is available (albendazole, mebendazole).

 

Prevention

Adequate sanitation, awareness-raising (hygiene), regular worming of risk groups.

 

Challenges

Eradicating intestinal worm infections in children by 2020.

A nematode
© IRD-L. Penchenier

CHIKUNGUNYA

 

What

Viral disease transmitted by infected mosquitoes: primarily Aedes aegypti ((sub)tropics) and Aedes albopictus (also in temperate regions). They also transmit dengue fever.

 

Symptoms

Sudden fever and severe joint pain, along with headache, muscle pain, fatigue, skin rash, etc. Most patients fully recover, although joint pain can last from months to years. Sometimes fatal in old people. Can be confused with dengue fever.

 

Where

Occurs naturally in Africa and Asia, including India. Recently also in Europe and the Caribbean.

 

Impact

Severe outbreaks: DR Congo (1999-2000), islands in the Indian Ocean (2005), India (2006-2007), Gabon (2007). In 2007 in North-East Italy (197 cases), at the end of 2013 in the Caribbean. Since 2005, 1.9 million cases in India, Indonesia, Thailand, the Maldives and Myanmar.

 

Treatment

None - only alleviation of symptoms.

 

Prevention

Avoiding breeding sites for mosquitoes (stagnant water in tyres, bowls under plant pots, tree cavities, coconut husks, puddles, etc.). During an outbreak, using insecticides, insect repellents and mosquito nets impregnated with insecticides, etc.

 

Challenges

Better notification, training of care providers, drafting guidelines, limiting the carriers.

 Green vases containing water
© IRD-J.-P. Gonzales

LYMPHATIC FILARIASIS

 

What

Disease caused by parasitic roundworms: mainly Wuchereria bancrofti (90% of cases) and Brugia malayi. Biting mosquitoes such as Culex (urban areas) and Anopheles (rural areas) absorb larvae from blood and spread them when they bite again.

 

Symptoms

Adult worms live in the lymphatic system and undermine the immune system. There are often no symptoms, but the lymphatic system and kidneys are damaged. Inflammation of skin and lymph nodes. Unsightly, painful deformity of limbs, genitals and breasts caused by lymphoedema (swelling of tissues) and elephantiasis (thickening of skin and tissues). Social stigma, permanent disability.

 

Where

80% of cases in Bangladesh, DR Congo, Ethiopia, India, Indonesia, Myanmar, Nigeria, Nepal, Philippines and Tanzania.

 

Impact

More than 120 million people are infected, 40 million people suffer from deformities. 1.4 billion people live in high-risk areas.

 

Treatment

Albendazole along with, e.g. ivermectin, kill larvae in blood. No treatment if the disease is advanced.

 

Prevention

Annual preventive treatment for 4-6 years can break the cycle (no more larvae in blood). Controlling mosquitoes and preventing mosquito bites.

 

Challenges

Continuous efforts are necessary. Between 2000 and 2012, 4.4 billion treatments were administered to 984 million people.

A mosquito on human skin
© IRD-N. Rahola

ONCHOCERCIASIS (RIVER BLINDNESS)

 

What

Disease caused by the parasitic worm Onchocerca volvulus, transmitted by repeated bites from black flies (Simulium).

 

Symptoms

Inflammation reactions, severe itching, skin lesions and deformities, sometimes eye lesions and permanent blindness.

 

Where

Primarily in the tropics. More than 99% of the cases are in Sub-Saharan Africa. Some disease hot spots in Latin America (Brazil, Ecuador, Guatemala, Mexico, Venezuela) and Yemen. Often in remote villages with fertile land near fast-flowing rivers (breeding ground for black flies).

 

Impact

Prior to the monitoring programme (see below), half of the men over 40 in certain West African communities were blinded by the disease. Major economic losses due to abandonment of fertile land.

 

Treatment

Medication is available (ivermectin - every year for 10-15 years).

 

Prevention

In West Africa, the disease was brought under control between 1974 and 2002 by eradicating the larvae of black flies with insecticides, and thanks to intensive treatment: 40 million people were saved from infection, 600,000 people from blindness. 25 million hectares of fertile land could be cultivated again.

 

Challenges

Completely eradicating the disease. In 2010, 76 million ivermectin treatments were distributed in 16 African countries. At least 15 million people still need to be treated.

 

Parasitic worm Onchocerca volvulus
© IRD-M. Boussinesq
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