In the "Story of Dr. Wassell" Cecil B. De Mille (1944), Gary Cooper plays Dr. Corydon M. Wassell, estimated health care professional, invaghitosi an American nurse named Madeline, he enlisted as a medical missionary in China, where a passion for research on Schistosoma and discovers that the intermediate host of the parasite is a clam d 'fresh water. Then he learns that a colleague, in turn fan of Madeline, preceded him in this discovery. In his disappointment, he decided to enlist in U.S. Navy, becoming a war hero. I do not know the extent to which the film reflects the true story of Dr. Wassel, but in my mind is inextricably linked to the Schistosoma fumettone this romantic science-production holliwoodiana.
What is currently the risk of schistosomiasis in travelers? What are the areas and groups most at risk? What are the clinical features
in travelers and in immigration? How is it diagnosed? What preventive and therapeutic measures are currently available? All these aspects of the problem are treated in a valuable review just published in Travel Medicine and Infectious Disease : Jan Clerinx, Alfons Van Gompel. Schistosomiasis in travelers and migrants. Travel Medicine and Infectious Disease - January 2011 (Vol. 9, Issue 1, Pages 6-24, DOI: 10.1016/j.tmaid.2010.11.002).
This is a very thorough review and you can not summarize the content in these few lines. However, I want to emphasize certain aspects that I think are very interesting for those who practice the Travel Medicine.
start with a ome signs of etiopathogenesis.
schistosomiasis or bilharzia is a parasitic disease caused by tropical worms of the genus Schistosoma Platyhelminthes. E 'widespread in Africa, in parts of South America and in many parts of Asia.
man become infected by coming into contact with fresh water contaminated by human feces or urine. In human adult schistosomes of both sexes living in the mesenteric veins and / or bladder. Their eggs are released into the urine or stool, and in fresh water is their transformation into larvae (miracidia) and then - through the passage in a freshwater clam (guest intermediate) - in the cercaria, the weed form for humans. The cercaria infects humans by penetrating the skin healthy, then migrates to the perivesical or mesenteric vessels.
Various stages of the life cycle are illustrated in the following figure (Source: CDC, Centers for Disease Control and Prevention, Atlanta, USA http://www.cdc.gov/).
Where most of the travelers become infected?
In Africa, and only very rarely in South America. As for Asia, were occasionally reported in travelers who had traveled in the rapids of the Mekong River, straddling the border between Laos and Cambodia. Based on this premise, we turn our attention to Africa: what are the streams most at risk?
Based on the data contained in the article, I constructed the following table of African rivers at highest risk. For a precise location, clicking on the name of each lake or river, you can access the Google map.
| Rivers and lakes at high risk | Location |
| Malawi-Mozambique-Tanzania | |
| DR Congo-Tanzania | |
| Rwanda - DR Congo | |
| Tanzania-Kenya-Uganda | |
| Zambia-Zimbabwe | |
| Ghana | |
| Nzilo Lake, located in Katanga along the River Lualaba | RD Congo |
| Rwanda | |
| Senegal | |
| West Africa | |
| West Africa | |
| Zambia-Angola | |
| Mali | |
| Ethiopia | |
| Uganda |
E 'worth recalling that the intermediate host develops only in freshwater environments where the temperature is equal to or above 18 ° C . Consequently, Normally in Africa there is no risk of schistosomiasis in streams at altitudes above 2000 meters altitude.
The disease has different clinical and epidemiological characteristics among travelers and immigrants who come to our attention: I tried to make a summary in the table below.
| | travelers in areas at risk | Immigrants from areas at risk |
| mode of infection | Recreation and Sports in fresh water (eg swimming, rafting) | E 'expression of the environmental community of origin |
| frequency of infection | 1.5% according to a Canadian study . Observed frequencies large cluster of cases: 32% after swimming in Lake Malawi,> 90% after a shower under a waterfall in the Dogon region | Detected frequencies vary widely (2% in Somali refugees in the U.S., 44 Sudanese refugees in%) |
| Clinical | pruritic papular rash (10-36% of cases) in the early hours of the penetration of cercariae. Later (from 3 weeks to 3 months later) in> 50% of cases the acute hypersensitivity reaction (Katayama fever): fever, sometimes preceded by a rash, sometimes nonproductive cough with dyspnea, abdominal pain and diarrhea | Two possibilities: a) absence of symptoms; b) manifestations of chronic schistosomiasis, urinary (granulomatous inflammation, changes in fibrosis and calcification of the bladder) and intestinal (granulomatous inflammation of the colon) |
What can a traveler do to prevent schistosomiasis?
Obviously the most effective precaution is to avoid contact with water from rivers, lakes and other freshwater collected in areas considered at risk. If for any reason such contact occurs, two measures are of proven effectiveness in preventing the penetration of cercariae, which happens very quickly:
a) as soon as you exit the water, you must scrub the skin with a towel;
b) immediately after it is useful applied to the skin repellent DEET (N, N-diethyl-m-toluamide), possibly with a high concentration (50%).
There is a post-exposure prophylaxis medication? were reported experiences with praziquantel and artemisinin, but uncertainty persists on the dosage and duration of treatment required for an effective post-exposure prophylaxis. This therefore requires further research.
Conclusions
The advice given to travelers in tropical areas should include information on the risk of schistosomiasis. Especially for travelers to Africa, you should always carefully consider your route to check if it includes rivers at high risk. The traveler should know the precautions to avoid infection and measures to be taken in case of exposure.
