An investigation of 11 outbreaks of foot-and-mouth disease in villages in northern Thailand

The results of investigations of 11 outbreaks of foot-and-mouth disease in villages in northern Thailand are described. The causative virus was Asia in one in seven outbreaks, Type O in two outbreaks and unknown in two outbreaks. The most probable sources of the outbreaks were co-mingling of cattle and/or buffalo with livestock from an infected neighbouring village (four) and recent introductions of infected cattle from a public livestock market (two) while the probable source could not be determined in five outbreaks. Attack rates in cattle and buffalo ranged from 0.28% to 50.9% but no pigs became sick during any of the outbreaks. Most outbreaks lasted 4 weeks or less. Adult cattle and buffalo were at higher risk of becoming a case when compared with work cattle. Beef cattle were at higher risk than buffalo and adult cattle and buffalo were at higher risk than calves less than 1 year of age. There was significant clustering of cases within households. Serological investigations indicated that many unaffected animals were probably not exposed to virus during the outbreaks. We concluded that close contact between animals was the main method of spread and that differences in attack rates between animal classes reflected differences in animal management. We further concluded that simple quarantine of early cases during outbreaks is likely to be effective in reducing spread within and between villages.