Featured paper: Domestic pigs are acting as potential sources of sleeping sickness in sub-Saharan Africa

Many of the domestic pigs kept by subsistance farmers across sub-Saharan Africa are carrying the cause of fatal human diesease human African Trypanosomiasis, or sleeping sickness.

Louise Hamill and her colleagues in the Division of Pathway Medicine at the University of Edinburgh, and their collaborator from the Tanzania Wildlife Research Institute, have found that almost 5% of the pigs they sampled in an area of northern Tanzania were infected with Trypanosoma brucei rhodesiense.  This finding has significant implications for WHO efforts to irradicate sleeping sickness.

Across Sub-Saharan Africa, millions of people rely on subsistence farming to survive. Pig keeping is becoming more popular, as they can be maintained in a free-roaming, zero input system requiring little investment of time or money.  However the increase in pig farming is also increasing the risk of human infection with a number of pathogens, including the causative agent of acute human African trypanosomiasis (HAT); Trypanosoma brucei rhodesienseT. rhodesiense is a vector borne disease that occurs in discrete foci across East Africa and is transmitted by the tsetse fly.

L:  Woman with piglet like those sampled in study, image (c) K. Picozzi; R:  laboratory tsetse fly, image (c) L. Hamill

T. b. rhodesiense infection in pigs is usually asymptomatic.  As a result they can often tolerate infection for most of their lives, and without clinical signs, the animals will not be treated.  In contrast the course of infection in humans is very different; T. b. rhodesiense is a rapidly fatal infection, with death ensuing in as little as six months after becoming infected.

Previous studies have shown domestic and wild animals harbour T. b. rhodesiense, but their significance in disease epidemiology remains unclear.  In particular, very few studies have applied molecular diagnostic techniques to detect trypanosome infections in pigs, meaning their potential role harbouring species of trypanosome pathogenic to humans and other animals is unknown.  Hamill et al  analysed 168 pig blood samples from northern Tanzania using sensitive molecular means, to discover if infection with T. b. rhodesiense or other trypanosomes was present.

These new results showed that 4.8% of pigs sampled were infected with T. b. rhodesiense, indicating they could act as a significant HAT reservoir in Northern Tanzania.  This poses a serious threat to human health in the area, and also has wider implications considering the World Health Organization’s aim to eliminate HAT as a public health problem by 2020.  In areas of East Africa where HAT is endemic the role of pigs in the epidemiology of human disease should be thoroughly investigated.  Quantifying the reservoir potential of pigs and other animals offers the potential to improve the health and livelihoods of vulnerable human populations using a “One Health” approach.

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