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Human African trypanosomiasis

Human African trypanosomiasis (HAT) is the only vector-borne parasitic disease with a  geographical distribution limited to the African continent. People in the age range 15-45 years  living in remote rural areas are the most affected, leading to economic loss and social misery.  In the early 1960s, the prevalence of HAT had been reduced to very low levels. Unfortunately,  due to lack of regular surveillance activities and reduced resource allocation the disease has  undergone resurgence with an estimated 300 000 to 500 000 individuals infected.   

Geographical risk:

Commonly known as “sleeping sickness”, HAT is endemic in 36 of the world’s poorest  countries where reporting difficulties make estimation of the numbers of infected individuals  very difficult.  Within this area, sleeping sickness threatens over 60 million people. Fewer than  10% of the at-risk population are currently under surveillance. In recent years, an annual  average of about 10 000 new cases has been reported, although the actual incidence of  unreported cases is thought to be much higher. 

Transmission

The T. brucei parasite is transmitted by the bite of the tsetse fly (Glossina species) which is  native to rural Africa. Two subspecies that are morphologically indistinguishable cause distinct  disease patterns in humans: T. b. gambiense causes West African sleeping sickness and T. b. rhodesiense causes East African sleeping sickness. During a blood meal, an infected tsetse  fly injects metacyclic trypomastigotes into the skin tissue. The parasites enter the lymphatic  system and pass into the bloodstream. Inside the host, they transform into bloodstream  trypomastigotes and are carried to fluids in other sites throughout the body (e.g., lymph,  spinal fluid). Here they continue replication by binary fission. The entire life cycle of African  Trypanosomes is represented by extracellular stages. The proportion of tsetse flies that are  infected with these parasites is low. Tsetse flies are found in woodland and savannah areas  and they bite during daylight hours therefore placing, the local active, rural population at the  greatest risk. Occasional cases of in utero infection have been reported and in theory  infection could pass through a blood transfusion, but such cases have been rarely  documented.  

Pathology

The disease progresses through two stages following an asymptomatic period of several  weeks or months. The early stage is usually characterised by “malaria-like” symptoms,  including fatigue, headache, recurrent fever and swollen lymph nodes. In advanced stages  the disease affects the central nervous system, causing severe neurological and mental  disorders and making the individual dependent on others. Infected individuals are weakened,  often for many years, causing economic loss, poverty and social misery. HAT is fatal within  several months if untreated. T. b. gambiense infection (West African sleeping sickness)  progresses more slowly than East African sleeping sickness.

Future trends

HAT constitutes a major public health problem in the African Region. Given the resurgence of  both human and animal trypanosomiasis, the epidemic potential, high fatality rate and  significant impact on socioeconomic development, many countries have requested more  active WHO support to control the disease. The aims of this proposed strategy are to control  the intensity of transmission in endemic and epidemic countries in the medium term and to  eliminate the disease in the long term. 

References

Control of Human African Trypanosomiasis: a Strategy for the African Region. WHO REGIONAL OFFICE FOR AFRICA. June 2005  http://www.cdc.gov/parasites/sleepingsickness/ last accessed 15th March 2013 Simarro et al. The Human African Trypanosomiasis Control and Surveillance Programme of the World Health Organization 2000–2009: The Way Forward http://www.plosntds.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjour nal.pntd.0001007&representation=PDF Further information  CDC_Centers for Disease Control and Prevention  http://www.cdc.gov/dpdx/trypanosomiasisAfrican/index.html  Infection landscapes  http://www.infectionlandscapes.org/2011/04/trypanosomiasis-part-1-sleeping.html  World Health Organisation  http://www.who.int/trypanosomiasis_african/en/ 

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Human African Trypanosomiasis