Cases of West Nile virus infections in common loons in Quebec
During the months of July and August, five adult common loons (Gavia immer) were found dead in the same area in the Outaouais region, Quebec. Three of these birds were submitted for analysis to the CWHC Quebec regional center (CQSAS).
The pathological examination performed in these birds revealed the presence of lesions in the spleen and intestines: a fibrinonecrotic splenitis (inflammation of the spleen) and an enteritis (inflammation of the intestine) characterized by multifocal necrosis of the intestinal crypts (Figure 1). It should be noted that all three birds were in very good body condition, indicating death from an acute process. The lesions observed were suggestive of a bacterial or viral infection. Two viruses, of exotic origin, which are present in Quebec in wild birds, can potentially cause these types of lesions: highly pathogenic avian influenza (H5N1) and West Nile virus (WNV). The H5N1 virus first appeared in North America last winter. This virus, which has so far caused a large number of mortalities in different species of wild and domestic birds, is known to induce lesions in different organs, including the intestines and the spleen. The WNV, which was introduced to Canada in the early 2000s, can also cause enteritis and splenitis in some species of birds.
Molecular analyzes carried out on the spleen of the loons examined revealed infections by WNV in the three loons tested. Analyzes were negative for H5N1. These results allowed us to conclude that the death of these three loons was caused by an acute WNV infection.
West Nile virus is a flavivirus that is transmitted from bird to bird by mosquito bites. This virus can affect several species of wild birds; corvids and birds of prey being particularly sensitive to it. It should be mentioned that certain species of mammals, including horses, squirrels and humans can also be affected by this virus. In the majority of cases, WNV causes clinical signs of neurological natures. As in the cases presented here, this virus can also be associated with acute mortalities, without neurological damage. The acute nature of the lesions seen in the three loons examined indicates rapid disease progression in this species, suggesting a high species susceptibility to this viral infection.
Although cases of WNV have already been reported in common loons in Minnesota (see Wünschmann, A. 2021. Pathology in Practice. 1410–1412), to our knowledge, the cases presented here are the first cases reported in this species in Canada. In fact, no case of a common loon infected with WNV was found in the CWHC database (WHIP), which contains the results of analyzes carried out on more than 500 common loons since the beginning of the 2000s. In Quebec, cases of WNV are mainly observed in the southern part of the province. The documentation of these three cases may suggest that the WNV is expanding its range to more northern regions of the province. It can be hypothesized that the increase in temperatures associated with climate changes will promote the reproduction of mosquito species vectors of this virus in the more northern regions of Canada. This virus will therefore be able to infect bird species, such as common loons, which spend the summer in these areas.
It should be noted that so far in 2022, 58 cases of WNV infections have been documented in wild birds in 2022 in Quebec, which indicates a fairly significant viral activity for WNV in Quebec. This suggests that the spring and summer environmental conditions were favorable to the transmission of this virus in 2022 in Quebec, at least among wild birds. This case report demonstrates that WNV infection should be considered as a potential cause of acute mortality in common loons during the summer season, especially in the presence of inflammatory lesions of the spleen and intestines. The rapid nature of the infections observed suggests that this species relatively susceptible to this virus and could therefore be significantly affected in the event that this exotic virus becomes increasingly widespread in its summer breeding area.
CWHC – Quebec