Horses can be infected by the Zika and Dengue viruses, researchers who conducted a study in the South Pacific relationship.
A significant proportion of horses in New Caledonia and French Polynesia tested in the research was found to have mounted an immune response against viruses.
The immune response to the Zika virus was found in 4.3% of the horses tested in New Caledonia and 15.4% of those tested in French Polynesia.
163 horses blood was tested in New Caledonia. Seven of these had activated an immune response to Zika and 130 had been tested by French Polynesia, 20 of which had a positive result.
The study provided similar results for the dengue virus, with 6.1% of horses in New Caledonia showing evidence of increased immune response and 7.7% in French Polynesia.
"This seroprevalence study in the horse population shows that horses can be infected with Dengue and Zika viruses and that these infections lead to seroconversion in horses," said Cécile Beck and his colleagues, writing in the open access journal PLOS pathogens.
The consequences of these infections in horses and their role in the incidence, distribution and control of these diseases deserve further investigation, they wrote.
New Caledonia and French Polynesia are areas in which viruses transmitted by insects circulate widely.
The study group, composed of 13 people, conducted their serological investigation into the two groups of islands to investigate the seroprevalence among the flavivirus horses – the family of viruses that includes West Nile virus, dengue virus, tick-borne encephalitis, yellow fever virus, Zika virus and many others.
The researchers used three methods to test sera. Samples were analyzed for flavivirus using a competitive enzyme-linked enzyme assay (cELISA).
The positive samples were then confirmed using a flavivirus-specific microsphere (MIA) and serum neutralization assay.
In total, 16.6% of New Caledonian horses and 30.8% of French Polynesia were positive for flaviviruses using the CELISA test. However, the MIA technique, which targets only the flaviviruses that cause neurological problems in humans and horses – that is, West Nile virus, Japanese encephalitis virus and encephalitis virus transmitted by ticks [TBEV]) – showed negative results for more than 85% of cELISA-positive animals.
The seroprevalence between Japanese encephalitis and West Nile flaviviruses among the 293 samples of both insular groups was relatively lower (less than 2%).
The authors stated that a series of epidemics caused by the four serotypes of the Dengue virus have been documented in the Pacific island over the last 50 years.
The Zika virus occurred for the first time in the Yap Islands (the Federated States of Micronesia) in 2007. It was not present in French Polynesia until October 2013, when the virus emerged in French Polynesia and caused a large outbreak among people. It was first seen in New Caledonia in 2014 and has spread widely.
Zika generally causes few or only mild symptoms, similar to a mild case of dengue fever. Symptoms may include fever, red eye, joint pain, headache and a rash. The greatest danger is that Zika may spread from a pregnant woman to her child, causing severe brain malformations and other birth defects.
Discussing their findings, the researchers said that the presence of specific antibodies against Dengue and Zika viruses in equine populations suggests that the Aedes the mosquitoes responsible for its diffusion feed on a series of mammals.
"In conclusion, our study clearly shows that horses can be infected by Aedes viruses transmitted by mosquitoes such as Dengue or Zika, which are known to have a primate reservoir. "
They said that while the Dengue virus and the rate of seropositivity of the Zika virus are much higher among men than horses in the region at the center of the study, the results show the need to learn more about the role of pets in the pathological cycle of both viruses.
The entire study group included Cécile Beck, Isabelle Leparc-Goffart, Denise Desoutter, Estelle Debergé, Hervé Bichet, Steeve Lowenski, Marine Dumarest, Gaelle Gonzalez, Camille Migné, Jessica Vanhomwegen, Stéphan Zientara, Benoit Durand and Sylvie Lecollinet, from a range of institutions in France and the South Pacific.
Beck C, Leparc-Goffart I, Desoutter D, Debergé E, Bichet H, Lowenski S, et al. (2019) Serological evidence of dengue and Zika virus infection in horses in the French Pacific islands. PLoS Negl Trop Dis 13 (2): e0007162. https://doi.org/10.1371/journal.pntd.0007162
The study, published under a Creative Commons license, can be read here. https://doi.org/10.1371/journal.pntd.0007162