Molecular and Epidemiological characterization of the African swine fever virus in Cameroon

THE STATE OF THE ART Cameroon being a lower income country with a population of 23.4million inhabitants in 2016 of which 43.5% live below the national poverty line (income less than 3.1 US dollars/day/capita). An estimated 24% of its population lives below the international poverty line (income of 1.9 dollars/day/capita). The agricultural sector contributes 20% of the Gross domestic product (GDP) of Cameroon with the livestock sector contributing 13% and employs 30% of the rural population. In Cameroon, one third of the households are involved in livestock production. 23.3% of these livestock rearing households farm pigs. Livestock provides these families with an income and nutrition. The current pig production is estimated to be 2.02kg/person and is substantially lower compared to the expected 5kg/person . Although Cameroon is the fourth largest pork producer in Africa, it does not reach its maximum capacity for reasons being that the sector is facing numerous livestock diseases of which African swine Fever (ASF) is of utmost important. The first ASF outbreak occurred in 1982 and affected over 80% of the 1.6 million pigs in Cameroon. Since 1982, there were numerous outbreaks, with the most recent one in 2017 in which the southwest and north part of the country were affected. The ASF virus (ASFV) is a double stranded DNA virus of the family Asfaviridae, genus Asfivirus. It causes lethal hemorrhagic fever in domestic pigs; while warthogs and bush pigs remain asymptomatic. ASFV is transmitted by arthropod vectors of the soft tick genus Ornithodoros amongst other modes of transmission. The virion has an icosahedral symmetry with an average diameter of 200nm. The virion consists of a nucleoprotin core surrounded by an inner envelope, an outer capsid layer and an outer envelope. The linear viral genomes encodes ~160 genes that are translated in more than 50 proteins. ASFV mainly targets immune cells of the myeloid lineage, especially monocytes and macrophages, which are thought to be crucial for viral persistence and dissemination. Bush pigs and warthogs are natural reservoir hosts of African swine fever virus, showing no clinical signs of disease when infected with the same highly virulent isolates of ASFV that induce rapid, hemorrhagic death in domestic pigs.  To date there are no commercially available vaccines or antivirals for African swine fever (ASF). Although a number of experimental, live attenuated vaccines are promising, e.g. BA71ΔCD2. The current prospects for the development of a vaccine are good as pigs that survived from the disease can resist challenge by related virulent viruses. Unfortunately, inactivated ASF virions are not sufficient to induce a protective immune response, neither do they induce neutralizing antibodies. It is not surprising that with so many ASF outbreaks experienced in Cameroon since 1982, the genetic and serologic difference of ASF virus isolated is substantial. Hence, they are named per the year of isolation as CAM82, CAM 85, CAM 87, CAM87 and CAM88. The current circulating strain still remains to be characterized. Genetic heterogeneity and diversification are major challenges for disease prevention by vaccination because of the selection of mutants that are not significantly affected by the vaccine-induced immune response. An interesting approach for the treatment/prevention of ASFV could involve host-directed immunomodulatory therapies. This strategy aims to exploit natural mechanisms in the host to initiate or enhance protective antimicrobial immunity while limiting inflammation-induced tissue injury. With numerous outbreaks of ASFV in Africa and many other countries such as Poland, Russia Ukraine Moldova, and Czech republic in 2017, Cameroon might be at the verge of a new outbreak if nothing is done. Thus ASF remains a continuous threat to both Cameroon and the world at large. The epidemiological situation of ASF in the country is highly underestimated because of the multitude of factors that impact here-on. For example: (i) limited education and lack of training for livestock farmers, (ii) weak advisory services that hinders access to innovative techniques by farmers, (iii) low capacity for laboratories for diagnosis. Very limited research is being done at the level of Cameroon for the eradication of the ASF virus and the creation of prophylactic strategies in spite of the government’s utmost effort to control the disease.

GENERAL OBJECTIVES

The aim of this project is to explore the epidemiology and molecular characterization of ASFV isolates and SLA class I diversity from ASFV susceptible and tolerant breeds of pigs in Cameroon. Generally, three main cycles for the spread of the ASFV in Africa are known, but in Cameroon, so far, it is proven that only a single cycle exists based on research conducted in 1985. Similarly, the indigenous pigs in Cameroon are tolerant to the ASFV but the exotic breeds are not. In this project, we aim to determine the main routes for the spread of the ASFV in Cameroon based on which appropriate control measures will be enacted by the authorities to help fight the disease. We will also molecularly characterize the isolates from Cameroon, which will help in the future in determining the origin of future outbreak strains if they are different from those already present in the country. Finally, we will compare the swine MHC within the tolerant (local and crosses between local and exotic) and susceptible (local and exotic) breeds with the aim of investigating for evidence of positive selection and heterogeneity. The results from this study will greatly help policy makers in the country and the ministry of livestock to develop and follow up with all stakeholders in the pig industry, aiming to reduce and eradicate the ASFV from Cameroon.