New disease threat for Red squirrels

Red squirrels (Sciurus vulgaris) in the UK are facing a new threat to their survival with adenovirus-related mortalities identified in both free-living and captive populations. This is unwelcome news for a species that has already suffered significant regional declines as a result of squirrel pox virus (SQPV) spread by the non-native Grey squirrel (Sciurus carolinensis).

Researchers have found an increase in the number of cases of adenovirus in wild populations of red squirrels and in captive collections used for breeding and wild re-enforcement programmes. The virus, which affects the intestinal mucosa, can present as a clinically significant infection resulting in the death of the animal, or as a sub-clinical infection with no obvious signs of disease or ill health. Of note is the finding that Grey squirrels and Wood mice (Apodemus sylvaticus) are sub-clinical carriers of the infection, which has particular implications for disease transmission at point food sources where all three species are present.

With histological identification of the virus in the intestine of dead individuals confounded by rapid autolysis at death, and some individuals presenting only sub-clinically, the researchers investigated optimal methods for detecting the presence of the virus in living and dead individuals. Polymerase chain reaction (PCR) analysis of spleen tissue was found to be best for detecting sub-clinical infections, while transmission electron microscopy (TEM) was suitable for detecting viral particles in faecal material of individuals with a clinically significant infection. For live animals, the only method for identifying the presence of the disease was found to be an enzyme-linked immunosorbent assay (ELISA) of the blood.

Much of what is known about this virus in squirrels has come from captive populations and further work is needed to investigate the situation in wild populations. However, the authors of the paper, published in Mammal Review, regard adenovirus as a serious disease threat to red squirrel re-introduction and captive breeding programmes, and to red squirrel populations in places where grey squirrels, red squirrels and wood mice can interact at point food sources.

Mammal Review doi:10.1111/mam.12025

Photo: Karen Arnold






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