Feline SARS-CoV-2 Experimental Infection Study

By Scott Weese on June 2, 2020

A new experimental study in cats (Bosco-Lauth et al) re-inforces information from earlier studies and provides some important new insights.

The standard disclaimer that the information is from a pre-print (non-peer-reviewed) paper applies, but the science seems pretty sound.

For this study, seven adult cats and three adult dogs were studied.

Cats…group 1

One group of 3 cats infected intra-nasally and then tested on days 1-5, 7, 10 and 14 after infection, looking for the virus. Blood was collected on days 7, 14, 21, 28, 35 and 42, looking for an antibody response.

This group was then re-exposed to the virus on day 28, with samples for virus detection collected 1, 3, 5, 7 and 10 days after 2nd exposure.

None of the cats got sick.

Cats shed the virus for up to 5 days after exposure, with peak shedding at day 3.

Nasal viral levels (from nasal flush samples) were higher than oral viral levels. That’s important information for surveillance studies.

Fecal samples don’t seem to have been collected. That’s unfortunate since fecal shedding of virus seems to be a potential issue worth exploring more.

Infected cats developed detectable antibodies as early as day 7, with all cats reaching a threshold titres by day 14. Antibody titres stayed stable or increased between days 28 and 42.

After re-exposure, a moderate increase in antibody titres was noted in the 14d after exposure. No viral shedding was noted after re-exposure.

Cats ….group 2

Two cats were infected, then mixed with two unexposed cats 48h after infection. Exposed cats shed virus like Group 1 cats.

Interestingly, the other cats started shedding virus within 24h of being housed with infected cats, but had a more prolonged shedding period, with peak shedding occurring at 7 days post-exposure.

Experimentally infected cats and those infected via contact all developed an antibody response.

Dogs

Three dogs were exposed and tested as per the cats in group 1. None developed any signs of disease and viral shedding was not detected. Antibody response wasn’t evaluated.

CONCLUSIONS:

The short duration of shedding by infected cats is encouraging (although a bit different from some natural infections that have been followed).

However, the longer duration in the in-contact (vs directly infected) cats may be more relevant to a natural exposure situation. 

Shorter duration reduces the risk of passing the virus onto another animal or person.

 The relatively short period of shedding also shows how active surveillance studies like we’re doing, where we sample pets of infected people, can underestimate transmission because of the narrow window of time that infected animals may shed the virus. This show again why antibody testing will be useful to characterize how much human-pet transmission has occurred.

Resistance to repeated viral shedding after second exposure is also encouraging, as it suggests that previous infection provides protection.

There are many caveats, such as the very small sample size, experimental nature of infection and short interval between first infection and re-exposure, but it’s a start and provides more hope that people are resistant (to at least some degree, and for at least a while) after infection.

The consistent production of antibodies and their presence over at least 42 days is good for future antibody surveillance studies that can look back at previous infection. It’s also encouraging from an immunity standpoint since rapidly disappearing titres would suggest less of a protective effect from subsequent infection.

The lack of disease in this small group of cats is a bit different than other studies and we can’t say much about disease based on a small experimental study, since it seems like disease can occur in naturally exposed cats.

This study shows that not all exposed cats get sick, as expected.

Experimental studies can provide useful information but we have to be careful extrapolating too much to the real world situation, where animal health status, other risk factors and different types of exposure can occur.