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.