Rat hepatitis. Preparing to attack
For the first time, researchers in Spain identified dozens of human cases of rat hepatitis E infection. Patients appeared in several regions, including Andalusia, Galicia, Navarre and Catalonia. The discovery came from analyzing samples from more than 250 patients across 10 hospitals, indicating the virus is present in a wide portion of the country.
The causative agent is Rocahepevirus ratti (RHEV). It was first described in Germany in 2010, though initial studies suggested humans could not be infected. Subsequent research showed that roughly 18% of gray rats carried a hepatitis E virus primarily found in the liver and spleen. These rodents may carry the virus closer to farms and could potentially transmit it to humans through poorly cooked meat from infected animals, especially when animals share spaces with domestic livestock.
In 2018, the first human case of rat hepatitis E was confirmed, and another instance involved a liver transplant recipient who contracted the virus. The patient experienced ongoing liver issues, yet standard hepatitis virus panels returned negative results, while tests for the rat-associated hepatitis E virus were positive. The patient recovered after a course of antiviral therapy used for chronic hepatitis E in humans. The reasons why this particular patient contracted a rat-derived strain remain unclear.
Research published in 2023 indicated that rat hepatitis E virus (RHEV) can spread to humans through contaminated food or water and was most prevalent in Asia, where about 60% of RHEV infections occur in animals and 16 human cases have been reported. Experts note that the number of infections appears to be rising in this region (citation: regional health institutes).
Should we expect an epidemic?
The exact mechanism by which rodents transmit the virus to humans has not been fully determined. A leading hypothesis is that people may become infected after contact with surfaces or items tainted by rodent feces or urine, such as grain products.
Researchers concluded that Spain’s outbreak likely involved grain contaminated with the virus that was distributed within the country. Rodents commonly inhabit grain storage and transfer points, and droppings could contaminate products during transport and storage. The broader question remains whether this situation is isolated or part of a wider pattern (citation: independent health researchers).
Experts say the transmission of the hepatitis E pathogen from mice to humans reflects an ongoing effort by the virus to cross the interspecies barrier. This does not guarantee a global pandemic, but it raises concerns that the virus could spread further if conditions allow high viral concentrations in places where humans and rodents intersect. Because the virus is primarily transmitted via a fecal-oral route rather than through respiratory droplets, hygiene and sanitation play a critical role in prevention (citation: virology specialists).
One senior expert cautions that a pandemic is unlikely, but the Spain outbreak serves as a warning sign. With each transmission cycle from rodent to human and back, the interspecies barrier may become easier to cross, increasing the prospects for human-to-human transmission under suitable circumstances (citation: virology experts).
Is it fatal?
Hepatitis describes liver inflammation caused by various agents, with five viruses commonly recognized as hepatitis viruses A, B, C, D and E. Human hepatitis E virus is often shed through contaminated drinking water and is widespread in parts of Africa and Southeast Asia. The disease typically presents as mild jaundice and appetite loss, and it rarely becomes chronic or requires hospitalization. However, pregnant women face a markedly higher risk, with mortality rates that can reach about 30 percent in the third trimester (citation: gastroenterology professionals).
Hepatitis E virus belongs to the Hepeviridae family, with human-infecting strains in the Orthohepevirus genus, and four main genotypes. The first two genotypes tend to affect humans and spread via the fecal-oral route; genotypes three and four mainly affect animals but can cross to humans (citation: medical educators).
Scientific observers note that many animals—pigs, deer, camels, shellfish and rats—can carry hepatitis E virus. The same strains have been found to infect humans on rare occasions, but such cases remain uncommon. Ongoing surveillance and research are underway, but it is premature to draw firm conclusions about a new, sustained animal-to-human source of hepatitis E. Prevention and treatment options are expected to align with established methods for hepatitis E, based on observed patterns thus far (citation: research teams).
Prevention strategies emphasize simple measures to curb the fecal-oral transmission route. Boiling water or choosing bottled water from trusted sources is advised, and raw or undercooked meat products should be avoided. In some cases, travelers may be advised to avoid using tap water for brushing teeth in regions with uncertain water safety. These recommendations reflect general safety practices to reduce exposure (citation: public health guidelines).
For those who become infected, many individuals recover without needing hospitalization, particularly if immune function is robust. Immunocompromised individuals may develop acute or chronic hepatitis E requiring medical management. There is no universally specific treatment for acute hepatitis E, but most patients recover spontaneously. Hospital care is reserved for severe cases, pregnancy-related complications, or fulminant illness. In chronic hepatitis E among immunocompromised patients, antiviral therapy such as ribavirin may be considered (citation: clinical guidelines).
Virologists emphasize that while rat hepatitis E is not typically lethal, outcomes can be worse in regions with poor hygiene, crowded living conditions, and high HIV prevalence, where case fatality may be higher. These areas may also represent hotspots for initial human exposure and potential viral adaptation. Ongoing monitoring remains essential as researchers consider the risk of broader transmission (citation: virology researchers).