By Chua Kim Beng, with information by Dr Thien Siew Yee, Consultant, Department of Infectious Diseases, Singapore General Hospital
In their quest for unusual travel experiences, adventurous Singaporeans are exposing themselves to so-called Neglected Tropical Diseases (NTDs). Most NTDs have been wiped out in more developed places, but persist, especially in poorer and isolated communities in warmer countries. Caused by viruses, bacteria, protozoa or single-cell organisms, and helminths or parasitic worms, NTDs are often linked to environmental conditions, have animal reservoirs, and are related to complex life cycles, making public health control challenging.
Food-borne flatworms
A class of flatworms or flukes known as trematodes can cause infections that result in severe liver and lung disease, disabilities and death worldwide every year. Examples are:
Clonorchis sinensis (Chinese or Oriental liver fluke): endemic in Korea, China, Taiwan, Northern Vietnam, Japan; >35 million people infected
Opisthorchis viverrine (Southeast Asian liver fluke): endemic in Cambodia, China, Laos, Thailand, Vietnam; >23 million people infected
Opisthorchis felineus (cat liver fluke): endemic in Southeast Asia, Central and Eastern Europe; >16 million people infected
Fasciola hepatica/gigantica (common liver fluke): endemic in China, Korea, Taiwan, Thailand, Vietnam, Central and South America, France, Portugal, Spain , Turkey; >17 million people infected
Paragonimus westermani (Oriental lung fluke): endemic in China, Japan, Korea, India, Philippines, Taiwan; >20 million people infected
TRANSMISSION
Eating contaminated raw or undercooked fish, crustaceans or vegetables like watercress and other water plants.
SYMPTOMS
Depending on the organism, patients can have fever, lethargy, vomiting, abdominal pain, liver abscess, pancreatitis, or no symptom.
HOW TO AVOID
Ensure seafood and vegetables are well cooked before eating.
Parasitic worms
Parasitic worms can cause schistosomiasis, one of the most devastating of parasitic diseases, with an estimated 240 million people worldwide infected.
Examples are:
Schistosoma mansoni: endemic in Sub-Saharan Africa, South America, South Caribbean islands
Schistosoma japonicum: endemic in China, Philippines, Sulawesi (Indonesia)
Schistosoma haematobium: endemic in Sub-Saharan African, Middle East, Arabian peninsula Schistosoma mekongi: endemic in Cambodia, Laos
Schistosoma malayensis: endemic in Malaysia
Schistosoma intercalatum: endemic in Democratic Republic of Congo
Schistosoma guineensis: endemic in West Africa
TRANSMISSION
Contact with fresh water contaminated with the parasites — swimming, wading, rafting, paddling, bathing and laundry. The parasite infects people by penetrating the skin.
SYMPTOMS
Depending on the organism, patients can have skin reaction, fever, cough, diarrhoea, abdominal pain, cough, blood in urine and stools, breathlessness, lesion in brain, spinal cord, liver, spleen, or no symptom.
HOW TO AVOID
Ensure safe drinking water and avoid contact with fresh water in endemic areas.
Rabies
An estimated 59,000 people die of rabies each year. The disease is caused by the rabies virus, which is present in many animals. Animals that host and spread the infection include dogs (99 per cent), bats, raccoons, skunks, foxes and coyotes. These animal reservoirs are found worldwide, most commonly in Africa and Asia.
Rabies has no known effective treatment once infected, and fatality is high once symptoms appear. Post-exposure options
are prophylaxis treatment with vaccine and rabies immunoglobulin.
TRANSMISSION
Exposure to saliva of infected animal, usually via bite.
SYMPTOMS
Fever, malaise, nausea, vomiting, headache, numbness, weakness, pain at site of bite, hydrophobia (fear of water), aerophobia (fear of flying), paralysis, coma and death. Fatality is high once symptoms appear.
HOW TO AVOID
Rabies vaccine for high-risk adventure travellers, cave explorers.
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