Japanese encephalitis virus in pigs and vectors in the Mekong Delta : with special reference to urban farming

• Japanese encephalitis Virus (JEV) is a mosquito-borne flavivirus in East and South Asia, estimated to cause 60 000 human cases of Japanese encephalitis each year. The main transmission cycle for JEV is via mosquito vectors, mainly Culex species, between pigs and wading birds, the reservoir hosts. Incidental infection in humans can result in encephalitis with 30% case fatalities, and half of the survivors may have neurological sequelae. Some of the most important vectors, such as Culex tritaeniorhynchus, commonly breed in rice fields, and the disease is therefore mainly considered to be a risk in rural areas. However, increasing urbanisation creates needs and opportunities for urban agriculture, and since pork is popular in Southeast Asia, it is common to keep pigs in cities. With this in mind, this thesis focuses on three important aspects of JEV circulation; the pig, the vectors and the virus itself. Pigs are usually only clinically affected by JEV during pregnancy. Sows in the area around Can Tho city in the Mekong delta region of South Vietnam, where JEV occurs endemically, were investigated for the association between JEV seropositivity and reproduction. In total 315 sows were included, with 60% seropositive. In sows less than 1.5 years of age, seropositivity was associated with the occurrence of more stillborn piglets, but this association could not be observed when all sows were included in the analysis. Mosquitoes were collected in households within and surrounding Can Tho city. The numbers of the zoophilic vectors Cx. tritaeniorhynchus and Culex gelidus were positively associated with pigs, whereas Culex quinquefasciatus, an anthropophilic vector, was positively associated with the number of people in the household. Of the 7885 mosquitoes collected, seven mosquito pools, collected close to pigs, were positive for JEV using nested RT-PCR. Four PCR fragments were similar to JEV genotype III and three to genotype I, indicating that both genotypes circulate in Can Tho city at the same time. Within Can Tho city all pigs sampled (43/43) were seropositive for JEV. These findings demonstrate that JEV can be a public health issue in urban as well as in rural areas and that it is associated with few reproductive problems in sows in an endemic area.

Ämnesord

LANTBRUKSVETENSKAPER  -- Veterinärmedicin -- Klinisk vetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Veterinary Science -- Clinical Science (hsv//eng)

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