The epidemiology of louping-ill, a tick borne infection of red grouse (Lagopus lagopus scoticus)

The epidemiology of louping-ill in red grouse was studied in northern Britain concentrating on the possible role of other species and mechanisms of disease persistence. This tick borne viral disease caused heavy mortality in red grouse, particularly chicks. Louping-ill induced mortality reduced the strength of the density dependence that generates the tendency of grouse populations to cycle and in some populations may cause population sinks. Four routes of transmission were examined and non-viraemic transmission of virus between ticks cofeeding on hares was considered significant. Field data supported the hypothesis that disease dynamics is influenced greatly by mountain hares, both as passive amplifiers and as hosts for the tick vector. Genetic variation in louping-ill within Britain was small.

Seroepidemiological survey of sympatric domestic and wild dogs (Lycaon pictus) in Tsumkwe District, north-eastern Namibia

Disease is a potential threat to many endangered populations and may originate from sympatric domestic species. This paper describes a cross-sectional serological survey of canine pathogens carried out in domestic (n = 70) and wild dogs (Lycoan pictus) (n = 6), in Tsumkwe District, northeastern Namibia. Evidence of past exposure to canine distemper virus, canine adenovirus and parainfluenza virus was evident in both wild and domestic dogs with this, the first, documented exposure of free-living wild dogs to canine distemper. Domestic dogs were also exposed to rabies virus, canine parvovirus and coronavirus. There was no pathogen to which wild dogs, but not domestic dogs, were exposed. With wild dogs known to be susceptible to rabies and canine distemper, these may be the greatest threat to this population of wild dogs, although some wild dogs can clearly survive infection with canine distemper.

Transmission of louping ill virus between infected and uninfected ticks co-feeding on mountain hares

Most of the data on oral infection of ticks by louping ill virus have been obtained from experiments in which animals were infected by syringe inoculation with infectious material. Using infected ticks to mimic the natural situation, we have demonstrated that louping ill (LI) virus transmission can occur from infected to uninfected Ixodes ricinus feeding in close proximity on mountain hares (Lepus timidus). Under these conditions the hares developed either low or undetectable viraemias. Highest prevalence of LI virus infection was observed in recipient nymphs which had fed to repletion between days 3 and 7 post-attachment of virus-infected adults; following engorgement, 56% of nymphs acquired virus. These results demonstrate the efficient transmission of LI virus between co-feeding ticks on naive mountain hares. However, when ticks were allowed to co-feed on virus-immune hares a significant reduction in the frequency of infection was observed. Neither red deer (Cervus elaphus) nor New Zealand White rabbits supported transmission of LI virus. The significance of virus transmission between cofeeding ticks on LI virus epidemiology is discussed.

Aspects of rabies epidemiology in Tsumkwe District, Namibia

Aspects of rabies epidemiology were investigated in the Tsumkwe District, Namibia, during December 1993 and January 1994. A cross-sectional seroepidemiological survey for rabies antibodies was carried out in domestic (n = 70) and wild dogs [Lycaon pictus (n = 6)]. An overall seroprevalence rate of 30% was found in domestic dogs, but it must be borne in mind that seroconversion can result from infections from either rabies or rabies-related viruses. Older dogs were more likely to be seropositive and there was spatial and temporal clustering of seropositivity. No wild dogs were found seropositive. A demographic survey of the domestic-dog population in the area showed that the total dog-population size was 132, or 0.027 dogs per km2. The dog population consisted mainly of young dogs with a median age of 1.5 years, and had a female bias of 0.63 males per female. Questionnaire surveys suggested that spotted hyaenas (Crocuta crocuta) and black-backed jackals (Canis mesomelas) were the most common larger carnivores found in and around villages, and that dogs were kept mainly for guarding.

Definitive identification of louping ill virus by RT-PCR and sequencing in field populations of Ixodes ricinus on the Lochindorb estate

Rapid and precise virus detection procedures are an important component of any epizootiological study. An automated one tube reverse transcriptase and nested primer polymerase chain reaction (RT-PCR) followed by nucleotide sequencing of the cDNA product, was used for the rapid detection and identification of louping ill (LI) virus in field caught Ixodes ricinus and compared with a classical isolation method i.e. infectivity in cell culture. The results establish the genetic identity of LI virus on the Lochindorb Estate. There was a high correlation between the results obtained by RT-PCR and infectivity assays. RT-PCR and sequencing proved to be a rapid and accurate system for identifying LI virus in field specimens. Development of this system should improve the capacity to undertake detailed epizootiological studies of LI virus.