Detection of African swine fever virus and phylogenetic characterization of Ornithodoros ticks collected from Lake Mburo - and Murchison Falls National Parks in Uganda

University essay from SLU/Dept. of Biomedical Sciences and Veterinary Public Health

Abstract: This master thesis was performed as a Minor Field Study (MFS), funded by the Swedish International Development Cooperation Agency (Sida), Gulli Strålfeldts fond and the Swedish University of Agricultural Sciences (SLU). The study was performed in collaboration between SLU, the National Veterinary Institute (SVA) in Uppsala and the Makerere University in Kampala, Uganda. The study was part of an on-going project on African swine fever in Uganda called ASFUganda. African swine fever (ASF) is a devastating haemorrhagic viral disease with a mortality approaching 100% among naïve domestic pigs and currently there is no vaccine available. African swine fever virus (ASFV) is characterized by high stability and effective spread. The virus is transmitted through direct and indirect contact. Pork products stored frozen, salted or smoked may remain infective for months. ASF is endemic in many countries in Africa south of the Sahara where it is circulating in tree different cycles; an ancient sylvatic cycle that involves soft ticks of the genus Ornithodoros and wild warthogs, a cycle between Ornithodoros ticks and domestic pigs, and a domestic pig cycle that occurs in absence of ticks. Warthogs and soft ticks are considered natural reservoirs of the virus and do not show clinical illness. The epidemiological role of this sylvatic cycle is not fully understood. The aim within this study was to increase the knowledge about the soft ticks role in the epidemiology of ASF. Therefore, in order to clarify how the disease was spread the geographic distribution of different Ornithodoros genetic lineage and the prevalence of ASFV in soft ticks collected in two of Uganda’s national parks, Lake Mburo and Murchison Falls was investigated and determined. The phylogenetic characterization revealed that the ticks belong to O. porcinus porcinus with a small genetic diversity between the two parks. All specimens revealed a close genetic relationship to specimens derived from Tanzania. Virus- DNA was detected in two ticks from two burrows in Murchison Falls NP using a commercial realtime PCR when performed in Uganda. These results were not possible to repeat in Sweden and therefore we were not able to get any sequences for further studies. It is not clear if these two positive samples was a result from contamination or a methodological problem in Sweden.

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