Epizootiology and pathologic findings associated with a newly described adenovirus in the red squirrel, Sciurus vulgaris.

An infectious disease caused by Squirrelpox virus has contributed to the decline of red squirrels, Sciurus vulgaris, in the British Isles. Because of the heightened disease surveillance activity in red squirrels, adenovirus infection with associated mortality has been detected. Adenoviral disease is described in other rodent species usually associated with stressors. Here we 1) describe the pathologic findings in red squirrels found dead with adenoviral infection and gastrointestinal disease, and 2) investigate the epizootiology of the disease through pathologic investigation, scanning surveillance, and virologic studies. Ten red squirrels involved in conservation studies were diagnosed with adenoviral infection by electron microscopy or PCR. All squirrels exhibited diarrhea and small intestinal inflammation or hemorrhage was evident in seven cases. Lesions indicative of splenic lymphocytolysis were observed in one squirrel and leukocytic hepatitis in another. No adenovirus was detected in grey squirrels, Sciurus carolinensis, inhabiting the same forest area, but previous serologic studies showed that grey squirrels cannot be discounted as a reservoir of the virus. Scanning surveillance showed that 12% of 493 red squirrels had diarrheal disease and two of 13 free-living red squirrels with diarrheal disease had adenovirus infection. Adenoviral disease in declining free-living wild red squirrel populations in the British Isles occurs at a detectable frequency and its impact on the conservation of this species deserves further attention.

Poxviral disease in red squirrels Sciurus vulgaris in the UK: spatial and temporal trends of an emerging threat.

The squirrel poxvirus (SQPV) is the probable mediator of apparent competition between the introduced invading gray squirrel (Sciurus carolinensis) and the red squirrel (Sciurus vulgaris) in the UK, and modeling studies have shown that this viral disease has had a significant impact on the decline of the red squirrel in the UK. However, given our limited understanding of the epidemiology of the disease, and more generally the effects of invasive species on parasite ecology, there is a need to investigate the transmission dynamics and the relative pathogenicity of the virus between species. We aimed to increase our knowledge of these processes through an empirical study in which we: (i) used pathological signs and transmission electron microscopy (TEM) to diagnose SQPV disease in red squirrels found dead during scanning surveillance between 1993 and 2005; (ii) detected antibody to SQPV using an enzyme-linked immunosorbent assay (ELISA) in the same animals; and (iii) mapped cases of the disease, and the gray squirrel distribution, using a geographical information system. We analyzed the distribution of cases of SQPV disease according to woodland type, a measure of squirrel density. SQPV disease occurred only in areas of England also inhabited by seropositive gray squirrels, and as the geographical range of gray squirrels expanded, SQPV disease occurred in these new gray squirrel habitats, supporting a role for the gray squirrel as a reservoir host of the virus. There was a delay between the establishment of invading gray squirrels and cases of the disease in red squirrels which implies gray squirrels must reach a threshold number or density before the virus is transmitted to red squirrels. The spatial and temporal trend in SQPV disease outbreaks suggested that SQPV disease will have a significant effect on Scottish populations of red squirrels within 25 years. The even spread of cases of disease across months suggested a direct rather than vector-borne transmission route is more likely. Eight juvenile and sub-adult free-living red squirrels apparently survived exposure to SQPV by mounting an immune response, the first evidence of immunity to SQPV in free-living red squirrels, which possibly suggests a changing host-parasite relationship and that the use of a vaccine may be an effective management tool to protect remnant red squirrel populations.

Genomic characterization of a novel poxvirus contributing to the decline of the red squirrel (Sciurus vulgaris) in the UK.

The genome of a virulent squirrelpox virus (SQPV) isolate was characterized in order to determine its relationship with other poxviruses. Restriction enzyme analysis suggested a genome length of approximately 158 kb, whilst sequence analysis of the two ends of the genome indicated a G + C composition of approximately 66 %. Two contiguous stretches of 23 and 37 kb at the left-hand and right-hand ends of the genome, respectively, were sequenced allowing the identification of at least 59 genes contained therein. The partial sequence of a further 15 genes was determined by spot sequencing of restriction fragments located across the genome. Phylogenetic analysis of 15 genes conserved in all the recognized genera of the subfamily Chordopoxvirinae confirmed that the SQPV does not group within the family Parapoxvirinae, but instead partitions on its own in a separate clade of the poxviruses. Analysis of serum from British woodland rodents failed to find any evidence of SQPV infection in wood mice or bank voles, but for the first time serum samples from grey squirrels in the USA were found to contain antibody against SQPV.