Parasites susceptible to be acquired by travellers are different depending upon the region of the world they visited. Actually, some parasites can be endemic in one region and totally absent from another. This is linked to the conditions required for the parasite to fulfill its life cycle, for example the presence of an insect vector or of an intermediate host. Consequently, it is important to know which parasitic diseases (as well as other infectious diseases) are present in the country that you want to visit before to travel. Usually, health professional in traveller’s clinics can inform you about which specific parasites’ species are present in a specific country or world area and about specific prevention means available. It is important to note that, even if parasitic diseases are more frequent in underdeveloped countries, it is also possible to acquire a parasite when travelling in developed countries.
Travellers are more susceptible to acquire parasitic diseases by ingestion of contaminated food or water, or by the bite of an insect vector. The foodborne parasitic diseases can remain asymptomatic or cause a mild to severe gastrointestinal illness. According to the Centers for Disease Control and Prevention, the protozoan parasites Giardia, Cryptosporidium and Cyclospora are the main parasites susceptible to be acquired by ingesting cysts present in contaminated food or water while traveling. Giardia and Cryptosporidium are more or less present worldwide. Cyclospora is more common in tropical and subtropical regions. It is noteworthy that this last parasite had also been linked to foodborne epidemic caused by fresh imported food, such as raspberries, basil, snow peas and lettuce. These three parasitic diseases can also be acquired by contact with recreational waters, such as unfiltered swimming pool or lakes. Furthermore, it is interesting to note that some Cryptosporidium and Cyclospora species can be resistant to chlorine and though persist in not sufficiently sanitized pools.
Other less common parasites are also linked to foodborne parasitic diseases in travellers according to the Centers for Disease Control and Prevention. The protozoan parasite Entamoeba histolytica is endemic in certain parts of the world, such as developing countries with old sanitation system containing contaminated water. The nematode Ascaris lumbricoides is distributed worldwide but is more common in Africa and Southeast Asia where sanitation is insufficient. The nematode Trichinella is also present everywhere, but is now rare in developed countries because of the pork industry regulation and surveillance. The cestode Taenia is present worldwide in countries where people eat pork and beef, but is found primarily in Asia, Africa, Latin America, Middle East and some parts of Eastern Europe. Finally, the trematode Fasciola, which is mainly transmitted by the ingestion of aquatic plants, like watercress, is distributed worldwide but is more prevalent in Latin America, Asia and Europe.
Among the vector-borne parasitic diseases affecting travellers, the Centers for Disease Control and Prevention estimates that the protozoan parasites Plasmodium and Leishmania are the most common. Plasmodium, which is responsible for the malaria disease, is endemic in a large area around the equator including Latin America, Asia and Africa. Leishmania infections, which cause cutaneous, mucocutaneous or visceral diseases according to the species involved, occur in some distinct parts of Central and South America, Southern Europe, Middle East, Africa and Asia.
According to the Centers for Disease Control and Prevention, other less frequent parasites are also linked to vector-borne parasitic infections in travellers. This is the case of two distinct species of the protozoan parasite (link to two types of parasites) Trypanosoma causing the Chagas disease and the African sleeping sickness. The former one is exclusively present in rural areas of Latin America, while the latter one is only found in rural Africa. Different nematodes of the superfamily Filarioidea are also problematic in different tropical and subtropical regions, such as Africa, Asia, Latin America and the Pacific region. Finally, the nematode Onchocerca volvulus, causing a disease known as «river blindness», is primarily found in Africa, but also exist in some distinct places in Latin America and Yemen.
Prevention of many infectious diseases for travellers includes usually vaccination. However, as there is no vaccine available yet for parasitic diseases, it is very important to use other means of prevention appropriate for the visited country.
Sources: Centers for Disease Control and Prevention, World Health Organization