Field and Experimental Investigations of an Outbreak of African Swine Fever in Nigeria

ABSTRACT

An outbreak of African Swine Fever (ASF), characterized by a mortality of 50 to

100% in various herds, was diagnosed among free-ranging domesticated pigs

in Delta State, Nigeria, in August 1998. The etiological confirmation of ASF

was made by virus isolation, PCR and sequencing of a 280 base pair fragment

of the major capsid protein (VP72) gene. Experimental infection of pigs with

infected blood resulted in pyrexia, which peaked two to four days postinfection,

followed by death in five to six days postinfection. Postmortem examination

revealed widespread hemorrhage, congestion and edema of tissues. The

lymph nodes, spleen, liver and kidneys showed marked focal random necrosis

and loss of lymphocytes from the splenic and lymphoid follicles. There was

an acute orchitis with massive neutrophilic and macrophage infiltrates into the

intertubular connective tissue. Meningitis and focal hemorrhages were observed

in the brain and spinal cord. The outbreak was believed to be a continuation of

an eastward spread of ASF from neighboring Benin, which began the previous

year (1997

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