A guard stands at the entrance to the Bronx Zoo on April 6, 2020 in New York City. A tiger at the zoo tested positive for covid-19, the Wildlife Conservation Society said. Photo : Spencer Platt ( Getty Images )

New research and surprising developments are teaching us more about covid-19 and the coronavirus that causes it.




Cats and covid-19

Over the weekend, the Bronx Zoo announced that one of its big cats, a 4-year-old female Malayan tiger named Nadia, tested positive for the coronavirus. The tiger and at least five other big cats at the zoo, including three lions, are also reported to have mild symptoms associated with covid-19 in people, particularly a dry cough, but all seem to be doing well otherwise.


Nadia and her feline friends are believed to be the first documented cases of covid-19 in animals living in the U.S., and this outbreak is suspected to have started from an asymptotic zookeeper who interacted with them. There have been reports of both pet cats and dogs testing positive for the virus elsewhere in the world, b ut it’s still unclear just how dangerous it really is to non-human animals.

Hong Kong officials reported in February and March that several dogs in the country had tested weakly positive for the virus, for instance, but also that none had shown any signs of respiratory illness or an immune response to the virus (a 17-year-old Pomeranian did die two days after testing virus-free and leaving quarantine, but its owner declined an autopsy to determine the cause of death, authorities said).

A preliminary study released last week tested a variety of different animals, including cats, ferrets, and dogs, to see if they could get infected with the coronavirus, known as SARS-CoV-2, and if they could pass it on further. They found that the virus grew poorly in dogs, pigs, chickens, and ducks but could take root in cats and ferrets. Infected cats even seemed capable of infecting other cats through exhaled droplets, much as the virus spreads among people. None of these infected cats, however, became physically sick.


At this point, it’s fair to say that while cats may be more susceptible to covid-19 than other animals, the overall threat to our pets seems to be minimal at this time.

Not just “flu like”

While covid-19 is perhaps best known for attacking the respiratory system and causing flu-like symptoms, most prominently a long-lasting dry cough and fever, evidence is mounting that it can manifest in many other distur b ing ways.


Doctors and researchers have reported that many severe cases end up developing heart damage during the course of their infection, sometimes culminating in a fatal cardiac arrest in which the heart stops beating. More rarely, suspected or confirmed patients have also shown symptoms and signs of neurological illness, such as brain swelling, seizures, and strokes (loss of smell or taste, commonly reported by sufferers, can also be linked to neurological damage). E ven early on in the outbreak, a sizable percentage of patients also reported gastrointestinal symptoms like diarrhea.


These less standard sym ptoms may, at least in some cases, reflect the immune system’s own counterproductive response to the infection. Younger covid-19 patients in particular can develop a condition known as a cytokine storm, where the immune system starts to fire en masse against the body’s own organs, causing systemic damage everywhere. But some researchers also suspect that the virus itself can infect heart tissue or the brain directly.

A still-muddled picture for hydroxychloroquine

On Sunday at a news briefing, President Donald Trump once again trumpeted two antimalarial drugs as a likely treatment for covid-19: chloroquine and a modified version known as hydroxychloroquine.


When a reporter asked Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, if he agreed with the president, Trump interrupted and refused to let Fauci answer. Fauci has repeatedly said that more research is needed to know anything definitive about how useful they could be in treating covid-19.


Right now, that research still paints a mixed picture. A trial of patients in China in late March, for instance, found no evidence that hydroxychloroquine alone had any effect on the recovery time of patients. Another trial in China released a few days later, however, did find a small effect on the length of fever and other symptoms among patients with mild covid-19. But yet another small study released last week found that hydroxychloroquine in combination with the antibiotic azithromycin did nothing to help patients with severe symptoms and underlying health conditions.

These studies all have their own limitations, particularly their small sample sizes. Larger, randomized, controlled trials of hydroxychloroquine and other potential treatments are on the way, including those being conducted with the help of the World Health Organization. For now, hydroxychloroquine shouldn’t be seen (or praised) as a sure thing.


As I’ve written previously , what we think we know about the coronavirus is going to keep changing. Conclusions drawn from small and preliminary research may turn out to be incorrect, and we will likely learn much more as time goes on about who is most at risk of serious complications from this virus.