17 February 2013

Tanzania: Schistosomiasis - Lake Tanganyika - Disease in Humans and Baboons

Photo: King James Yiye/RNW
People get infected with schistosomiasis from contact with water containing parasites, which are released by infected snails.

In terms of the two types of schistosomiasis (kichocho) in Tanzania, urinary schistosomiasis (S. haematobium) appears to be much more prevalent than intestinal schistosomiasis (S. mansoni).

The atlas of human helminth infections in East Africa has recently been updated by Brooker and colleagues (2009). To construct these maps, scientific data collected between 1980 and 2008 were used. Details of survey population, diagnostic methods, sample size and numbers infected with schistosomes (as well as hook worms, Ascaris and whipworms) were recorded.

The authors attempted to identify the geographical location of each record and then assembled the data into a geographical information system. There were big gaps in the data set as no studies had been conducted in nine regions including: Arusha, Dodoma, Iringa, Kigoma, Lindi, Mara, Rukwa, Ruvuma, and Singida. According to this updated atlas, S. haematobium was found in 14 of the 17 regions that were tested in Tanzania - with a national median prevalence of over 30%.

Urinary schistosomiasis is distributed along the Indian Ocean coast and Lake Victoria. The highest mean prevalence was in Mwanza (58.3%). A common symptom was blood in the urine. S. mansoni was found in nine regions. The prevalence generally appears to be comparatively low. In three regions none was found. The highest rates were found in Kilimanjaro and North Unguja.

Jared Bakuza of the Dar es Salaam University College of Education, addressed a gap in the atlas with data from his PhD dissertation. Bakuza and colleagues from Glasgow University, in the UK, mapped the epidemiology of intestinal schistosomias along the shores of Lake Tanganyika. Between January and September 2010, stool samples were collected from 235 children and 171 adults at Gombe National Park and four neighboring villages.

The stools were examined for parasite ova using the usual method (Kato-Katz technique). Baboon and vervet monkey stools were also examined. High rates of S. masoni in Kigoma region were found. The results showed that S.mansoni infection was recorded at an overall prevalence of 45% across study sites, ranging from 19% at Mtanga to 68% at Mwamgongo.

About half the adults in each village were infected with S. mansoni. Amongst the children however there were marked differences between neighboring villages. The biggest differences were seen in the prevalence of schistosomiasis in children; differences ranged from two villages - Gombe and Mtanga - with childhood prevalences of about 10%, to Mwamgogo with a childhood prevalence of almost 90%.

The important questions of what are the differences between villages is not yet explained. Child care practices, hygiene practices, latrine siting, water usage, and previous exposure to Praziquantel could all be partial answers and need to be urgently sorted out.

Snails known to harbour the schistosome, were also analyzed for infection. The rate of snail infection paralleled that of human infection so that the lowest was at Gombe (zero) and the highest percentage of infected snails were at Mwamgogo, where 57% were infected. While none of the 16 vervet monkeys appeared to be infected with S. haematobium, the stools of 13% of 136 baboons harbored S. mansoni.

Moreover the DNA tests imply that the baboons were probably becoming infected with schistosomiasis through closer interaction with humans and their waste. Baboons spend more time than vervets on the ground. Baboons are also more willing to be play and swim in the water so the cercariae have time to burrow into their skin.

The researchers, as part of their ethical obligations to their human research subjects, gave those who had been infected, Praziquantel, which is the standard and recommended drug of choice. The Praziquantel cleared only about 75% of the infections and reduced egg intensity by 96%.

On the surface you feel that such results are acceptable. But it needs to be noted that treatment is not 100% effective and a significant minority of people were left harboring schistosomes. In summary, the people living around Gombe National Park are highly infected with a disease which is not very curable and according to World Health Organization, is 100% attributed to the environment - e.g. lack of or faulty sewage practices.

Moreover these people are infecting the baboons. It is a case of protecting the wildlife - one of the goals of Gombe National Park - by helping to increase the standard of living for the nearby human beings by improving toileting practices. This can be fairly easily done - the areas involved are small - the benefits are great.

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