Abstract

Leptospirosis is a bacterial disease that in pigs primarily causes reproductive disturbances. The disease is a zoonosis, i.e. it can be transmitted between animals and humans. Leptospirosis is spread worldwide, although it is of most importance in tropical regions where animal management and climate favour transmission and survival of the bacteria in the environment, such as the tropical Mekong delta (MD) in southern Vietnam. In the MD, reproduction disturbances in pigs due to infectious agents are of concern. This thesis investigates Leptospira infection among pigs in the MD with aspects on epidemiology, clinical affection and bacteriology. Such information is of importance if preventive measures are to be implemented. This study showed that leptospiral seroprevalences among sows were high and that a larger proportion of sows on small-scale farms compared with large-scale farms were seropositive. Few risk factors were found that could explain seropositivity in the sows. It was also found that the seroprevalences for some serovars were higher during the dry period compared with the wet period. Furthermore, some serovars were associated with impaired reproductive performance of the sows, such as an increased number of piglets born dead per litter and a longer weaning to service interval. Also, seroprevalences among fattening pigs at slaughter were high, and in these animals leptospires were demonstrated in a large number of kidneys with macro- and microscopic kidney lesions. One leptospiral serovar was isolated from a kidney. Taken together, Leptospira infection, indicated by seropositivity, is common among pigs in the MD, which may be explained by a favourable environment rather than certain risk factors. Small-scale farms are in closer contact with the surrounding environment than large-scale farms, which may explain the differences between the farming systems. Even in regions with high leptospiral seroprevalences, infection, as indicated by seropositivity, has a negative impact on the reproductive performance of sows. Furthermore, a large proportion of fatteners with macroscopic renal lesions carry the bacteria, which constitutes a health hazard for personnel at abattoirs and persons exposed elsewhere.