Which animal is Covid’s ‘intermediary host’? Hunt on for likely spreader species

The virus is thought to have originated in bats – but where did it go next?

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Sars-Cov-2, the virus that causes Covid-19, most likely emerged in pangolins or bats and jumped to another animal before it was transmitted to human hosts, a World Health Organisation investigation into the origins of the pandemic has concluded.

No one is sure what animal the "intermediary host" could have been but experts have identified some possible species.

Dr Peter Ben Embarek, the investigation’s leader, said that as animals such as mink had tested positive for Sars-Cov-2, several species, including dogs, could have passed the virus on to humans.

How the Covid-19 virus could have emerged in China

Here are other possible culprits:

Rabbit

A study by scientists in the Netherlands last August found that Sars-Cov-2 can infect rabbits, which means the virus could circulate in rabbit farms and is a possible source of animal-to-human transmission.

Rabbits are one of the most commonly farmed animals in the world.

Ferret-badgers

In 2007, scientists wrote the first description of a previously unidentified coronavirus lineage detected from Chinese ferret badgers in southern China. 

The research was carried out on ferret-badgers found in China’s live-animal markets.

Ferret-badgers can have close relationships with humans, even in the wild. They are known to live in agricultural areas such as rice paddies or grass fields, where they can feed on insects, small animals and worms.

Bamboo rats

Scientists in Vietnam found in 2014 that bamboo rats could carry coronaviruses. The animals are raised on wildlife farms in Asia for human consumption as food.

After Covid-19 erupted in China, Beijing banned the breeding of large rats. It is thought that farmers were breeding tens of millions of bamboo rats in China before the ban.

Bamboo rats can grow up to about 16 inches long and are only found in southern and eastern Asia.

Civet cats

The civet cat is a luxury food in China. When Sars, the coronavirus most closely linked to Covid-19, first emerged in China in 2003, civet cats were thought to be the intermediary host, leading to a nationwide cull. Thousands of captive civet cats were slaughtered. 

Civet cats were thought to be the intermediary host of Sars

Credit: AP

Scientists from the Universities of Minnesota and South Carolina argued in a 2020 paper that there are several differences in the civet cat’s ACE2 chemical receptors that made it less able to bind Sars-Cov-2.

Bats

According to Nature, in 2020 researchers found a coronavirus that is closely related to Sars-Cov-2 in horseshoe bats kept in a freezer in Cambodia and a team in Japan found another closely related coronavirus in frozen bat droppings.

The Sars-Cov-2 may have passed from bats directly to humans, without an intermediary animal.

Bat meat consumption is common in parts of Asia and, due to increased urbanisation and trade, more bats interact with livestock or people.

Coronaviruses in bats

Pangolins

In 2020, scientists found Sars-Cov-2-related coronaviruses in Malayan pangolins which were seized in anti-smuggling operations in southern China.

Pangolins are the only mammals with tough keratin scales for skin. These scales are popular in traditional Chinese medicine and the animals are widely trafficked.

Scientists in China discovered last year that some genetic sequences of viruses in pangolins were a 99 per cent match with Sars-Cov-2. It is not known whether the virus could have jumped from pangolins into humans.