Role of small mammals in the persistence of Louping‐ill virus: field survey and tick co‐feeding studies

Abstract

Louping-ill (LI) is a tick-borne viral disease of red grouse, Lagopus lagopus scoticus Lath. (Tetraonidae: Galliformes), and sheep, Ovis aries L. (Bovidae: Artiodactyla), that causes economic loss to upland farms and sporting estates. Unvaccinated sheep, grouse and mountain hares, Lepus timidus L. (Leporidae: Lagomorpha), are known to transmit LI virus, whereas red deer, Cenrus elaphus L. (Cervidae: Artiodactyla), and rabbits, Oryctolagus cuniculus L. (Leporidae: Lagomorpha), do not. However, the role of small mammals is unknown. Here, we determine the role of small mammals, in particular field voles, Microtus agrestis L. (Muridae: Rodentia), in the persistence of LI virus on upland farms and sporting estates in Scotland, using field sampling and non-viraemic transmission trials. Small mammals were not abundant on the upland sites studied, few ticks were found per animal and none of the caught animals tested seropositive to LI virus. Laboratory trials provided no evidence that small mammals (field voles, bank voles, Clethrionomys glareolus L. (Muridae: Rodentia), and wood mice, Apodemus sylvaticus L. (Muridae: Rodentia), can transmit LI virus between cofeeding ticks and, in the field, LI virus was prevalent only in areas with known LI virus competent hosts (grouse, mountain hares or unvaccinated sheep) and absent elsewhere. In contrast to the case of tick-borne encephalitis (TBE) virus in Europe, it is concluded that small mammals seem to be relatively unimportant in LI virus persistence.

The extent of homologous recombination in members of the genus Flavivirus

“…Similarly, co-infection in the vertebrate host would require transmission to an already viraemic host by a tick infected with a different strain. This is a relatively unlikely prospect as in those vertebrate hosts that develop a systemic viraemia, its duration is short and mortality is high (Gilbert et al, 2000;Randolph et al, 1996).…”

Investigating the loss of recruitment potential in red grouse (Lagopus lagopus scoticus): the relative importance of hen mortality, food supply, tick infestation and louping-ill

“…Prevalence in sheep with grouse present can vary between 16 and 45.6 % (Gilbert et al 2000) and on grouse chicks in Scotland between 0 and 36 % (Reid et al 1978). The effect of acaricide treatment on LIV is difficult to determine in this study because LIV prevalence in grouse chicks was only 3 % (2/67) on moor 1 and zero on moor 2 (Moseley et al 2007).…”

The wild life of tick-borne pathogens

“…Small mammals are considered the most important hosts for larval I. ricinus 190 (Chapter 2), however, when small mammals are absent, deer are able to feed a substantial number of larvae. This might be the explanation for a linear correlation of I. ricinus density and estimates of deer density in several studies in Scotland 38,[206][207][208] where small mammals occur in low abundance and carry few ticks in some habitats 209 . Therefore, deer are important hosts for I. ricinus, but the other hosts in the vertebrate assemblage need to be considered as well when studying relationships between host abundance and I. ricinus density.…”

“…Although deer abundance was not directly correlated to nymphal density (Chapter 4), the indirect correlation might explain the increase of I. ricinus densities with deer abundance found in previous studies 38,55,208 . Especially in locations or habitats where small mammals are scarce, the abundance of deer or thrushes might be an important determinant of nymphal density 141,209 . In my sites, questing adult density increased with questing nymphal density (GLMM with negative binomial distribution and log link function and a random intercept per year: β = 1.2, p < 0.001), but not with the density of any of the vertebrate hosts (Chapter 4).…”