Quantitative evaluation of dogs as sentinels for Rift Valley fever virus circulation in Madagascar

Sentinel animals may play a key role in surveillance of zoonotic arbovirus circulation, particularly in developing countries with low levels of investment in health. This study aimed to assess the relevance of using dogs as sentinel animals for Rift Valley fever virus (RVFV) surveillance in Madagascar.

Serological surveys were conducted on 513 dogs and 135 cattle in the Ifanadiana district. In addition, 486 human dry blood samples available from the same area were used. Serostatus against RVFV was determined using a competitive Enzyme-Linked Immunosorbent Assay (cELISA) for dog and cattle samples, and a Multiplex Bead Assay (MBA) for human samples. Serocatalytic models fitted to age-stratified serological data were developed to estimate the RVF force of infection (FOI) under several hypotheses, ranging from no relationship to proportional FOIs between humans, cattle, and dogs.

Antibodies to RVFV were detected in 23 of 513 dogs (4.5%; 95% confidence interval (95% CI): [2.9 - 6.7]), in 86 of 486 humans (17.7%; 95% CI: [14.4 – 21.4]), and in 33 of 135 cattle (24.4%; 95% CI: [17.5 - 32.6]). Based on the deviance information criterion, the best supported model indicated that FOI in humans and cattle was proportional to FOI in dogs. Proportionality parameters were estimated at 2.6 (95% credible interval (95% CrI): [1.4 - 5.1]) for humans and 3.5 (95% CrI: [1.3 - 6.4]) for cattle.

Our findings suggest that sampling dogs could be used to identify RVFV circulation in endemic areas, and infer the exposure of humans and cattle in these areas in Madagascar. This original result paves the way for an innovative surveillance method for RVFV in Madagascar and other endemic countries, but also for other arboviruses such as West Nile virus.

Author Summary

Rift Valley fever (RVF) is a viral zoonosis transmitted by mosquitoes and through contact with the blood, tissues or body fluids of infected animal. The disease has caused at least three major epidemics in Madagascar to date. RVF mainly affects ruminants through abortion and high mortality rate in young animals, and a range of influenza-like to more severe syndromes that can lead to death in some cases in humans. Dogs that interact with humans and are exposed to mosquito bites in the same environment may not develop clinical signs or sufficient viremia to infect vectors, but they could still develop an immune response when exposed to RVF virus (RVFV). This study aimed to assess the relevance of using dogs as sentinel animals for RVFV circulation on the island. Serocatalytic models were developed using serological data to represent and quantify the relationships between the force of infection (FOI) of RVFV exerted on dogs, humans and cattle. We found a proportional relationship between the FOI exerted on dogs and that exerted on humans and cattle. These findings support the relevance of using dogs as sentinel animals for monitoring the circulation of RVFV and arboviruses in general.