LB 13-124 - Humans, Dogs, and Rats: Does Leptospira vaccination in one species influence infection in other species?

Leptospirosis is a globally distributed disease, which disproportionately affects impoverished communities such as subsistence farmers. Humans are most commonly exposed to the Leptospira bacterium through contact with the urine of an infected animal, such as a dog or rat, either directly, or indirectly through contaminated water. During Leptospira outbreaks, a commonly recommended public health measure to prevent human infections is to vaccinate domestic animals such as dogs, however, the efficacy of this measure has never been tested. Does vaccinating dogs against Leptospira lower infection prevalence in humans and rats? To answer this question, we vaccinated >75% of dogs living in a rural village in northeastern Madagascar against Leptospira, then monitored dogs, humans, and small mammals living in that village over the next year. We found that despite the vaccination providing strong protection to the vaccinated dogs, we observed no carryover protective effects on unvaccinated dogs, people, or rats. Leptospira prevalence varied seasonally in all 3 groups, ranging from 0-6% in rats, 3-27% in dogs, and 3-10% in humans. At one-year post-vaccination, the expected protective period of the vaccine, the proportion of infected people (2%, 2/89) was not significantly different from the baseline pre-vaccination measurement (5%, 8/162), however, the proportion of infected dogs increased by 12%.Our findings demonstrate that a one-off vaccination effort in dogs against the zoonotic Leptospira bacteria does not have strong protective effects for humans and rats. However, the development of a more effective vaccine or the development of a more robust public health response against this neglected disease may decrease rates of Leptospira infections in humans and rats.