All of the lions and tigers living in the Smithsonian's National Zoo in Washington, D.C. have tested presumptive positive for Covid-19, it was announced in a statement.

In the statement on Friday, the zoo, which is one the oldest in the US, fecal samples for all the big cats, including six African lions, a Sumatran tiger and two Amur tigers, were collected and tested presumptive positive, Xinhua news agency reported.

Final results are expected in the next few days.

No other animals at the zoo are showing any signs of infection, the statement added.

According to the zoo, animal keepers observed decreased appetites, coughing, sneezing and lethargy in several lions and tigers last weekend.

All lions and tigers were being treated with anti-inflammatories and anti-nausea medication to address discomfort and decreased appetite, as well as antibiotics for presumptive secondary bacterial pneumonia, it said

They remain under close observation, the zoo added.

Zoo staff still managed the cats' access to their outdoor habitats since their condition does not require they remain inside. However, given the substantial distance between the animals and visitors, the public is not at risk, the statement said.

So far there is no evidence to pinpoint the source of the infection, it said, adding the zoo has conducted a thorough investigation of all staff that were in close proximity to the lions and tigers.

The US Department of Agriculture has authorised the use of a SARS-COV-2 vaccine made specifically for zoo animals by Zoetis.

The first round of vaccine disbursement will be administered to select animals identified as susceptible species at both the zoo and Conservation Biology Institute in Virginia when it becomes available in the coming months, said the zoo.

It has been standard practice for all animal care staff and essential staff working in the zoo to wear masks indoors at all public and non-public areas.