Dozens of people in China have become ill with a new virus that is also found in shrews, according to a report, but there is so far no evidence of human-to-human transmission.

The infections were found in China's eastern Shandong and central Henan provinces, affecting 35 people, according to a report in the New England Journal of Medicine this month.

The virus is called Langya henipavirus or LayV, and patients reported symptoms that include fever, fatigue, cough, nausea and headaches.

Some people also developed blood cell abnormalities and impaired liver and kidney functions, the report said.

Research findings suggested shrews may be a natural reservoir for the pathogen.

"There was no close contact or common exposure history among the patients, which suggests that the infection in the human population may be sporadic," according to the report.

But it also cautioned that its sample size "was too small to determine the status of human-to-human transmission for LayV."

Patients were mostly farmers and cases were found with help from a detection system for people with acute fever and a history of animal exposure, it added.

Further investigation is needed to better understand illnesses associated with the virus, according to the researchers in China, Singapore and Australia who were involved in the paper.

Cases of Langya henipavirus have so far not been fatal or very serious, Linfa Wang of the Duke-NUS Medical School in Singapore, told Chinese state outlet Global Times.

Wang was one of the researchers involved in writing the paper.

Zoonoses are animal diseases that transmit to humans, and comprise a large percentage of new and existing diseases in people, according to the World Health Organization.

Some are preventable through vaccination, while others mutate into human-only strains or cause recurring outbreaks.

What is this new virus?

A new virus, Langya henipavirus, is suspected to have caused infections in 35 people in China’s Shandong and Henan provinces.

It’s related to Hendra and Nipah viruses, which cause disease in humans. However, we don’t know much about the new virus – known as LayV for short – including whether it spreads from human to human.

Here’s what we know so far:

Researchers in China first detected this new virus as part of routine surveillance in people with a fever who had reported recent contact with animals. Once the virus was identified, the researchers looked for the virus in other people.

Symptoms reported appeared to be mostly mild – fever, fatigue, cough, loss of appetite, muscle aches, nausea and headache – although we don’t know how long the patients were unwell.

A smaller proportion had potentially more serious complications, including pneumonia and abnormalities in liver and kidney function. However, the severity of these abnormalities, the need for hospitalization, and whether any cases were fatal were not reported.

The authors also investigated whether domestic or wild animals may have been the source of the virus. Although they found a small number of goats and dogs that may have been infected with the virus in the past, there was more direct evidence that a significant proportion of wild shrews harbored the virus.

This suggests humans may have caught the virus from wild shrews.

The researchers used a modern technique known as metagenomic analysis to find this new virus. Researchers sequence all genetic material and then discard the "known" sequences (for example, human DNA) to look for "unknown" sequences that might represent a new virus.

This raises the question of how scientists can tell whether a particular virus causes the disease.

We have traditionally used "Koch’s postulates" to determine whether a particular micro-organism causes disease:

1. It must be found in people with the disease and not in well people.
2. It must be able to be isolated from people with the disease.
3. The isolation from people with the disease must cause the disease if given to a healthy person (or animal).
4. It must be able to be re-isolated from the healthy person after they become ill.

The authors acknowledge this new virus doesn’t yet meet these criteria, and the relevance of these criteria in the modern era has been questioned.

However, the authors say they didn’t find any other cause of the illness in 26 people, there was evidence that 14 people’s immune systems had responded to the virus, and more unwell people had more virus.

This new virus appears to be a close cousin of two other viruses that are significant in humans: the Nipah virus and Hendra virus. This family of viruses was the inspiration for the fictional MEV-1 virus in the film Contagion.

Hendra virus was first reported in Queensland in 1994 when it caused the deaths of 14 horses and the trainer, Vic Rail.

Many outbreaks in horses have been reported in Queensland and northern New South Wales since and are generally thought to be due to "spillover" infections from flying foxes.

In total, seven human cases of Hendra virus have been reported in Australia (mostly veterinarians working with sick horses), including four deaths.

Nipah virus is more significant globally, with outbreaks frequently reported in Bangladesh.

The severity of infection can range from very mild to fatal encephalitis (inflammation of the brain).

The first outbreak in Malaysia and Singapore was reported in people who had close contact with pigs. However, it is thought more recent outbreaks have been due to food contaminated with the urine or saliva of infected bats.

Significantly, the Nipah virus appears to be transmitted from person to person, mostly among household contacts.

Little is known about this new virus, and the currently reported cases are likely to be the tip of the iceberg.

At this stage, there is no indication the virus can spread from human to human.

Further work is required to determine how severe the infection can be, how it spreads, and how widespread it might be in China and the region.