Epidemiology and control of Menangle virus in pigs

Objective To describe the epidemiology and eradication of Menangle virus in fection in pigs. Design Field observations and interventions, structured and unstructured se rological surveys, prospective and cross-sectional serological studies and laboratory investigations. Procedure Serum samples were collected from pigs at a 2600-sow intensive pi ggery in New South Wales that experienced an outbreak of reproductive disea se in 1997. Serum samples were also collected from piggeries that received pigs from or supplied pigs to the affected piggery and from other piggeries in Australia. Serum and tissue samples were collected from pigs at piggeri es experiencing reproductive disease in New South Wales. Sera and faeces we re collected from grey-headed flying foxes (Pteropus poliocephalus) in the region of the affected piggery. Serum samples were tested for neutralising antibodies against Menangle virus. Virus isolation was attempted from faece s. Results Following the outbreak of reproductive disease, sera from 96% of ad ult pigs at the affected piggery, including sows that produced affected lit ters, contained neutralising antibodies against Menangle virus. Neutralisin g antibodies were also detected in sera from 88% of finisher pigs at two pi ggeries receiving weaned pigs from the affected piggery. No evidence of Men angle virus infection was found in other piggeries in Australia. In cross-s ectional studies at the affected piggery, colostral antibodies were undetec table in most pigs by 14 to 15 weeks of age. By slaughter age or entry to t he breeding herd, 95% of pigs developed high antibody titres (greater than or equal to 128) against Menangle virus in the virus neutralisation test. M enangle virus was eradicated from the affected piggery following a program of serological testing and segregation. Neutralising antibodies against Men angle virus were also detected in P poliocephalus from two colonies in the vicinity of the affected piggery. Two piggery workers were infected with Me nangle virus. There was no evidence of infection in cattle, sheep, birds, r odents, feral cats and a dog at the affected piggery. Conclusions Serological evidence of infection with Menangle virus was detec ted in pigs at a piggery that had experienced reproductive disease, in pigs at two associated piggeries and in fruit bats in the region of the piggery . Two humans were infected. The mode of transmission between pigs is unknow n, but spread by faecal or urinary excretion is postulated. This virus can be eradicated by the segregation of pigs into discrete age groups.