A new viral disease in grey squirrels?

Last November a cluster of mortalities of grey squirrels (Sciurus carolinensis) was reported in the City of Montreal. A concerned citizen, who suspected malicious poisoning, submitted one of the squirrels’ bodies found in her backyard to the CWHC – Quebec regional centre.

The squirrel submitted was an adult female with an average body condition (reduced body fat reserves). The only significant finding was the presence of congested areas covering more than 50% of the lung volume. These areas, which appeared to be somewhat consolidated, were suggestive of pneumonia. The first thing a pathologist will do in order to confirm a suspected disease is to sample tissue for histological analysis. The microscopic examination of the lung confirmed the lesions of pneumonia. These were characterized by a thickening of the walls of the alveoli due to an infiltration of these walls by inflammatory cells and an increase in number of a cell call type II pneumocytes. These type II pneumocytes are cells that are lining the walls of the pulmonary alveoli and are known to proliferate in case of infection. Very unusual syncytial cells (cells that are fused together) were also regularly observed in the lung.

This is a microscopic image of the lung of the affected squirrel showing a marked thickening of the alveolar walls associated with an infiltration by inflammatory cells (the black dots). Multinucleated cells (arrow) are commonly observed. AL: Alveolar lumens.

Because these lesions (interstitial pneumonia with syncytial cells and type II pneumocytes hyperplasia) are suggestive of a viral infection, a frozen sample of lung tissue was sent to the virology lab to be screened for the presence of viruses. Interestingly, a previously undescribed coronavirus was detected in the lung of this animal. Even if this remains speculative at this time, the presence of this virus associated with pulmonary lesions characteristic of viral infection make us believe that this squirrel died of a fatal infection by a coronavirus.

Different species of coronavirus are known to cause pneumonia in different species of hosts such as rats and pigs and people. To our knowledge pulmonary infection of grey squirrels by coronaviruses has never been reported. We are currently trying to better characterise this virus. This case shows that even if we have been studying wildlife diseases for several decades we still have a lot to discover. If there is any wildlife pathologists that have seen similar cases, please contact me.

Stéphane Lair, CWHC – Quebec

You may also like...

4 Responses

  1. Jk says:


    Is this the same virus which is now spreed all over the world. Just for curiosity.

    • CWHC says:

      Hi Jk, thanks for the query.

      Our Regional Director in Québec has provided this answer: “Not, this is not the same virus. Numerous different coronavirus have been described to infect different species of animals. The one found in this squirrel is a new one, but it is different than COVID-19.”

  2. Andrea says:

    My daughter and I recently noticed two dead grey squirrels. We saw the first one on Saturday lying at the bottom of a tree in Laurier Park, near Christophe-Colomb. It was removed as of yesterday. We saw the second this morning. It is lying at the foot of a tree at 5071 Christophe-Colomb. I mention it because it seems unusual to me, and I wondered if they were sick. People do try to play with them and feed them.

    • CWHC says:

      Good Morning,
      I would suggest contacting the Quebec regional centre at 450.773.8521 ext. 8346 or quebec@cwhc-rcsf.ca. They would be happy to answer any questions regarding dead wildlife. Thanks!

Leave a Reply

Your email address will not be published. Required fields are marked *