Study reveals evidence of hepatitis E virus circulating in Brazil’s horses

Serological evidence from a study suggests that significant numbers of horses in Brazil have been exposed to the hepatitis E virus (HEV).

The serological results suggest prior exposure to the virus because of the presence of antibodies against the virus, but no viral DNA was detected among the horses in the study.

Caroline Roberta Soares Salgado and her fellow researchers, writing in the journal Microorganisms, said HEV infection has been demonstrated in various animal species.

Because of its potential to cross species barriers and infect humans, HEV has become a public health concern worldwide, they said.

Of the eight genotypes (HEV-1 to HEV-8) identified so far, HEV-1 and HEV-2, which are transmitted through the oral-fecal route, infect humans exclusively and are often associated with waterborne outbreaks of acute hepatitis in developing countries.

HEV-3, HEV-4 and HEV-7 are zoonotic – that is, capable of being transmitted between animals and humans. They are mainly transmitted through the consumption of raw or undercooked animal products.

HEV-3 is associated with hepatitis cases in high-income and developing countries. Other potentially zoonotic hosts have been reported, such as horses, cattle, goats, sheep, dogs, rodents, rabbits and camelids. HEV-5 and HEV-6 have been described in wild boars from Japan. HEV-7 was described in dromedary camels from the Middle East, and its zoonotic transmission was confirmed in an immunocompromised transplant patient. HEV-8 has been described in farmed camels from China.

In Brazil, HEV-3 is the only genotype identified in humans and swine nationwide. It has also been identified in a colony-breeding cynomolgus monkey and, recently, in bovines and capybara rodents.

“The epidemiology of HEV in Brazil is considered similar to that of high-income countries, where HEV-3 circulates as a silent (mainly asymptomatic) infection among swine and human populations,” the researchers said.

The expanding host range and the recent increase in human infections associated with zoonotic HEV-3 in some countries (e.g., in the European Union and Brazil) have highlighted the possible contribution of other susceptible animals to HEV transmission, variously via the consumption of raw or undercooked meat, direct contact, or occupational means.”

Horses, they said, have been shown in overseas studies to be susceptible to HEV infection since 2007, and their contribution as natural reservoirs has been evaluated in recent years.

Their role in zoonotic transmission cannot be ruled out since contact with horses was significantly associated with a higher risk of exposure to HEV in Denmark, and anti-HEV antibodies and RNA detection rates ranging from 11% to 16.3% and 0% to 4% have been reported in horses from Africa, Asia and Europe, respectively.

Brazil holds one of the largest horse populations in the world, with about six million animals used for work, sports, reproduction, pets and meat production.

The study team sought to investigate the exposure of Brazilian horses to HEV infection, given the lack of information regarding the circulation of HEV in horses in the country.

The study population comprised 257 horses from three Brazilian states, Bahia, Goiás and Rio de Janeiro. In all, 132 had been bred for slaughter and 125 for sport/reproduction purposes.

Serum samples were grouped according to the horses’ breeding purposes.

The researchers, from a range of Brazilian institutions, tested the samples for antibodies against the virus, as well as for viral RNA.

The overall seroprevalence of antibodies against the virus was 26.5% (68 of the 257 samples). There was no detection of HEV RNA. Most municipalities (53.3%) and farms (58.8%) had positive horses.

Animals slaughtered for human consumption had a higher risk of HEV exposure (45.5%) than those bred for sports or reproduction (6.4%).

Males, it was found, presented an approximately 1.9-fold greater chance of exposure to HEV than females.

Among the positive animals, 45.6% (31 of the 68 horses) were raised in contact with pigs and other animals, such as cattle.

“In Brazil, the co-grazing of horses with other animals is practiced nationwide, with benefits for the ecosystem and improvements in vegetation and animal health (e.g., decreasing parasitism).

“In this study, a large proportion of the investigated animals were bred together with mules, donkeys, cattle, hogs and/or other animals (45.6%), further supporting the possible contribution of the breeding environment to HEV exposure.”

The authors said their findings – the first serological evidence of HEV circulation in Brazilian equines – reinforce the need for the surveillance of HEV host expansion in a One Health approach.

“Although the viral genome was not detected, an important proportion of horses slaughtered for human consumption had contact with the virus, which poses a challenge to researchers and authorities to further investigate the potential of horses as HEV reservoirs and possible routes of the transmission of HEV to humans and other animals.

“Further studies are needed to assess other potential risk factors and to confirm the prevalence of HEV infection in Brazilian horses.”

The study team comprised Salgado, Aldaleia do Nascimento e Silva, Igor Falco Arruda, Patrícia Riddell Millar, Maria Regina Reis Amendoeira, Luciane Almeida Amado Leon, Raffaella Bertoni Cavalcanti Teixeira, Jorge Tiburcio Barbosa de Lima, Flávia Löwen Levy Chalhoub, Ana Maria Bispo de Filippis, Ana Beatriz Monteiro Fonseca, Jaqueline Mendes de Oliveira, Marcelo Alves Pinto and Andreza Soriano Figueiredo.

Salgado, C.R.S.; Silva, A.d.N.e.; Arruda, I.F.; Millar, P.R.; Amendoeira, M.R.R.; Leon, L.A.A.; Teixeira, R.B.C.; de Lima, J.T.B.; Chalhoub, F.L.L.; Bispo de Filippis, A.M.; et al. Serological Evidence of Hepatitis E Virus Infection in Brazilian Equines. Microorganisms 2023, 11, 2743. https://doi.org/10.3390/microorganisms11112743

The study, published under a Creative Commons License, can be read here.