No net effect of host density on tick-borne disease hazard due to opposing roles of vector amplification and pathogen dilution.

To better understand vector-borne disease dynamics, knowledge of the ecological interactions between animal hosts, vectors, and pathogens is needed. The effects of hosts on disease hazard depends on their role in driving vector abundance and their ability to transmit pathogens. Theoretically, a host that cannot transmit a pathogen could dilute pathogen prevalence but increase disease hazard if it increases vector population size. In the case of Lyme disease, caused by Borrelia burgdorferi s.l. and vectored by Ixodid ticks, deer may have dual opposing effects on vectors and pathogen: deer drive tick population densities but do not transmit B. burgdorferi s.l. and could thus decrease or increase disease hazard. We aimed to test for the role of deer in shaping Lyme disease hazard by using a wide range of deer densities while taking transmission host abundance into account. We predicted that deer increase nymphal tick abundance while reducing pathogen prevalence. The resulting impact of deer on disease hazard will depend on the relative strengths of these opposing effects. We conducted a cross-sectional survey across 24 woodlands in Scotland between 2017 and 2019, estimating host (deer, rodents) abundance, questing Ixodes ricinus nymph density, and B. burgdorferi s.l. prevalence at each site. As predicted, deer density was positively associated with nymph density and negatively with nymphal infection prevalence. Overall, these two opposite effects canceled each other out: Lyme disease hazard did not vary with increasing deer density. This demonstrates that, across a wide range of deer and rodent densities, the role of deer in amplifying tick densities cancels their effect of reducing pathogen prevalence. We demonstrate how noncompetent host density has little effect on disease hazard even though they reduce pathogen prevalence, because of their role in increasing vector populations. These results have implications for informing disease mitigation strategies, especially through host management.

Prospective cohort study reveals unexpected aetiologies of livestock abortion in northern Tanzania.

Livestock abortion is an important cause of productivity losses worldwide and many infectious causes of abortion are zoonotic pathogens that impact on human health. Little is known about the relative importance of infectious causes of livestock abortion in Africa, including in subsistence farming communities that are critically dependent on livestock for food, income, and wellbeing. We conducted a prospective cohort study of livestock abortion, supported by cross-sectional serosurveillance, to determine aetiologies of livestock abortions in livestock in Tanzania. This approach generated several important findings including detection of a Rift Valley fever virus outbreak in cattle; high prevalence of C. burnetii infection in livestock; and the first report of Neospora caninum, Toxoplasma gondii, and pestiviruses associated with livestock abortion in Tanzania. Our approach provides a model for abortion surveillance in resource-limited settings. Our findings add substantially to current knowledge in sub-Saharan Africa, providing important evidence from which to prioritise disease interventions.

Experimental evidence for opposing effects of high deer density on tick-borne pathogen prevalence and hazard.

BACKGROUND: Identifying the mechanisms driving disease risk is challenging for multi-host pathogens, such as Borrelia burgdorferi sensu lato (s.l.), the tick-borne bacteria causing Lyme disease. Deer are tick reproduction hosts but do not transmit B. burgdorferi s.l., whereas rodents and birds are competent transmission hosts. Here, we use a long-term deer exclosure experiment to test three mechanisms for how high deer density might shape B. burgdorferi s.l. prevalence in ticks: increased prevalence due to higher larval tick densities facilitating high transmission on rodents (M1); alternatively, reduced B. burgdorferi s.l. prevalence because more larval ticks feed on deer rather than transmission-competent rodents (dilution effect) (M2), potentially due to ecological cascades, whereby higher deer grazing pressure shortens vegetation which decreases rodent abundance thus reducing transmission (M3). METHODS: In a large enclosure where red deer stags were kept at high density (35.5 deer km-2), we used an experimental design consisting of eight plots of 0.23 ha, four of which were fenced to simulate the absence of deer and four that were accessible to deer. In each plot we measured the density of questing nymphs and nymphal infection prevalence in spring, summer and autumn, and quantified vegetation height and density, and small mammal abundance. RESULTS: Prevalence tended to be lower, though not conclusively so, in high deer density plots compared to exclosures (predicted prevalence of 1.0% vs 2.2%), suggesting that the dilution and cascade mechanisms might outweigh the increased opportunities for transmission mechanism. Presence of deer at high density led to shorter vegetation and fewer rodents, consistent with an ecological cascade. However, Lyme disease hazard (density of infected I. ricinus nymphs) was five times higher in high deer density plots due to tick density being 18 times higher. CONCLUSIONS: High densities of tick reproduction hosts such as deer can drive up vector-borne disease hazard, despite the potential to simultaneously reduce pathogen prevalence. This has implications for environmental pathogen management and for deer management, although the impact of intermediate deer densities now needs testing.

The duration of antibiotic treatment is associated with carriage of toxigenic and non-toxigenic strains of Clostridioides difficile in dogs.

Clostridioides difficile is a leading cause of human antibiotic-associated diarrhoeal disease globally. Zoonotic reservoirs of infection are increasingly suspected to play a role in the emergence of this disease in the community and dogs are considered as one potential source. Here we use a canine case-control study at a referral veterinary hospital in Scotland to assess: i) the risk factors associated with carriage of C. difficile by dogs, ii) whether carriage of C. difficile is associated with clinical disease in dogs and iii) the similarity of strains isolated from dogs with local human clinical surveillance. The overall prevalence of C. difficile carriage in dogs was 18.7% (95% CI 14.8-23.2%, n = 61/327) of which 34% (n = 21/61) were toxigenic strains. We found risk factors related to prior antibiotic treatment were significantly associated with C. difficile carriage by dogs. However, the presence of toxigenic strains of C. difficile in a canine faecal sample was not associated with diarrhoeal disease in dogs. Active toxin was infrequently detected in canine faecal samples carrying toxigenic strains (2/11 samples). Both dogs in which active toxin was detected had no clinical evidence of gastrointestinal disease. Among the ten toxigenic ribotypes of C. difficile detected in dogs in this study, six of these (012, 014, 020, 026, 078, 106) were ribotypes commonly associated with human clinical disease in Scotland, while nontoxigenic isolates largely belonged to 010 and 039 ribotypes. Whilst C. difficile does not appear commonly associated with diarrhoeal disease in dogs, antibiotic treatment increases carriage of this bacteria including toxigenic strains commonly found in human clinical disease.

Emergence of Lyme Disease on Treeless Islands, Scotland, United Kingdom.

Lyme disease is usually associated with forested habitats but has recently emerged on treeless islands in the Western Isles of Scotland. The environmental and human components of Lyme disease risk in open habitats remain unknown. We quantified the environmental hazard and risk factors for human tick bite exposure among treeless islands with low and high Lyme disease incidence in the Western Isles. We found a higher prevalence of Borrelia burgdorferi sensu lato-infected ticks on high-incidence than on low-incidence islands (6.4% vs. 0.7%); we also found that residents of high-incidence islands reported increased tick bite exposure. Most tick bites (72.7%) occurred <1 km from the home, including many in home gardens. Residents of high Lyme disease incidence islands reported increasing problems with ticks; many suggested changing deer distribution as a potential driver. We highlight the benefits of an integrated approach in understanding the factors that contribute to Lyme disease emergence.

Sampling scale and season influence the observed relationship between the density of deer and questing Ixodes ricinus nymphs.

BACKGROUND: The relationship between environmentally transmitted tick parasites, Ixodes spp., and their main reproductive host, deer, is generally thought to be positive. However, measuring host abundance and density directly can be challenging and indirect methods are often used. The observed relationship between the parasite and host may be affected by sampling scale and season, which could lead to different inferences being made. Here, we aimed to test the effect of sampling scale and season on the relationship between density of deer and the density of questing Ixodes ricinus nymphs. METHODS: The density of deer (primarily Dama dama) was estimated using line transect distance sampling of deer dung quantified in different seasons (winter and summer) and measured at three different nested scales (site, transect and observation level). Questing nymph density was measured using blanket drag methods and estimates were calculated at the same scales as deer density estimates. General linear models were used to evaluate the relationship between questing nymphs, deer density and other environmental variables at each sampling scale and each season deer density was measured at. RESULTS: While a positive relationship between deer density and questing nymph density was detected at the site and transect scale, no relationship was apparent at the observation level. This was likely due to increased variation and reduced precision of deer dung counts at the finest sampling scale. Seasonal changes in deer populations were observed likely reflecting seasonal shifts in habitat usage. The summer estimates of deer density explained questing nymph density whereas winter estimates did not. CONCLUSIONS: Our results show that the scale of sampling can affect the detectability of the positive association between host and vector species. Furthermore, such associations can be obscured if hosts exhibit seasonal changes in habitat use. Thus, both sampling scale and season are important to consider when investigating the relationship between host and vector species.

Clinical and magnetic resonance imaging findings of a cerebellar medulloblastoma in a heifer.

Reports of medulloblastoma in cattle are scarce; however, this neoplasm should be included as a differential diagnosis in cases of cerebellar or central vestibular signs in young cattle. The MRI appearance of the medulloblastoma reported here, previously unreported in cattle, consisted of a T1-weighted hypointense and T2-weighted heterogeneously hyperintense intra-axial mass.

Landscape structure affects the prevalence and distribution of a tick-borne zoonotic pathogen.

BACKGROUND: Landscape structure can affect pathogen prevalence and persistence with consequences for human and animal health. Few studies have examined how reservoir host species traits may interact with landscape structure to alter pathogen communities and dynamics. Using a landscape of islands and mainland sites we investigated how natural landscape fragmentation affects the prevalence and persistence of the zoonotic tick-borne pathogen complex Borrelia burgdorferi (sensu lato), which causes Lyme borreliosis. We hypothesized that the prevalence of B. burgdorferi (s.l.) would be lower on islands compared to the mainland and B. afzelii, a small mammal specialist genospecies, would be more affected by isolation than bird-associated B. garinii and B. valaisiana and the generalist B. burgdorferi (sensu stricto). METHODS: Questing (host-seeking) nymphal I. ricinus ticks (n = 6567) were collected from 12 island and 6 mainland sites in 2011, 2013 and 2015 and tested for B. burgdorferi (s.l.). Deer abundance was estimated using dung transects. RESULTS: The prevalence of B. burgdorferi (s.l.) was significantly higher on the mainland (2.5%, 47/1891) compared to island sites (0.9%, 44/4673) (P < 0.01). While all four genospecies of B. burgdorferi (s.l.) were detected on the mainland, bird-associated species B. garinii and B. valaisiana and the generalist genospecies B. burgdorferi (s.s.) predominated on islands. CONCLUSION: We found that landscape structure influenced the prevalence of a zoonotic pathogen, with a lower prevalence detected among island sites compared to the mainland. This was mainly due to the significantly lower prevalence of small mammal-associated B. afzelii. Deer abundance was not related to pathogen prevalence, suggesting that the structure and dynamics of the reservoir host community underpins the observed prevalence patterns, with the higher mobility of bird hosts compared to small mammal hosts leading to a relative predominance of the bird-associated genospecies B. garinii and generalist genospecies B. burgdorferi (s.s.) on islands. In contrast, the lower prevalence of B. afzelii on islands may be due to small mammal populations there exhibiting lower densities, less immigration and stronger population fluctuations. This study suggests that landscape fragmentation can influence the prevalence of a zoonotic pathogen, dependent on the biology of the reservoir host.

Spinal extradural T-cell lymphoma with paraneoplastic hypereosinophilia in a dog: clinicopathological features, treatment, and outcome.

Spinal lymphoma is a rare manifestation of a common canine hematopoietic neoplasia. Description of treatment, outcome, and MRI features are scarce. The latter can be heterogeneous, stressing the importance of lesion excision and analysis. Clinicians should also be aware of hypereosinophilia as accompanying paraneoplastic syndrome and its potential prognostic implications.

Effects of conservation management of landscapes and vertebrate communities on Lyme borreliosis risk in the United Kingdom.

Landscape change and altered host abundance are major drivers of zoonotic pathogen emergence. Conservation and biodiversity management of landscapes and vertebrate communities can have secondary effects on vector-borne pathogen transmission that are important to assess. Here we review the potential implications of these activities on the risk of Lyme borreliosis in the United Kingdom. Conservation management activities include woodland expansion, management and restoration, deer management, urban greening and the release and culling of non-native species. Available evidence suggests that increasing woodland extent, implementing biodiversity policies that encourage ecotonal habitat and urban greening can increase the risk of Lyme borreliosis by increasing suitable habitat for hosts and the tick vectors. However, this can depend on whether deer population management is carried out as part of these conservation activities. Exclusion fencing or culling deer to low densities can decrease tick abundance and Lyme borreliosis risk. As management actions often constitute large-scale perturbation experiments, these hold great potential to understand underlying drivers of tick and pathogen dynamics. We recommend integrating monitoring of ticks and the risk of tick-borne pathogens with conservation management activities. This would help fill knowledge gaps and the production of best practice guidelines to reduce risks.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

Heterogeneity in the abundance and distribution of Ixodes ricinus and Borrelia burgdorferi (sensu lato) in Scotland: implications for risk prediction.

BACKGROUND: Cases of Lyme borreliosis, a vector-borne zoonosis caused by bacteria in the Borrelia burgdorferi (sensu lato) species group, have increased in recent years in Europe. Knowledge of environmental factors associated with abundance of the tick vector Ixodes ricinus and the pathogen B. burgdorferi (s.l.) is of interest to understand responses to environmental changes, predict variation in risk and to inform management interventions. METHODS: Nineteen woodland sites across Scotland were surveyed in 2012 for B. burgdorferi (s.l.) infection in questing I. ricinus nymphs (n = 200 per site), deer abundance and vegetation. Climatic factors were extracted for each site. Six additional sites were surveyed for questing nymphs in both 2012 and 2013 (n = 200 per site and year) to test for variation in B. burgdorferi (s.l.) prevalence between years. RESULTS: The mean prevalence of B. burgdorferi (s.l.) across 19 sites was 1.7% (95% CI: 1.4-2.2%; range 0-6%), all four genospecies known to be present in the UK were detected: B. garinii, B. afzelii, B. burgdorferi (sensu stricto) and B. valaisiana. A higher prevalence of B. burgdorferi (s.l.), higher densities of nymphs and higher densities of infected nymphs were found at sites with warmer climates, estimated with growing degree-days. No association between infection prevalence in nymphs and woodland type (semi-natural mixed vs coniferous) or deer density was found. At six sites sampled in 2012 and 2013, there was a significant increase in B. afzelli prevalence at two sites and a decrease in B. garinii prevalence at one site. CONCLUSIONS: This study highlights challenges for the prediction of risk of Lyme borreliosis, reflecting the sensitivity of both pathogen and vector ecology to habitat, host and climatic factors. Significant changes in the prevalence of individual genospecies at sites monitored across time are likely to be due to variability in the host community composition between years. Our results indicate the importance of monitoring dynamic variables such as reservoir host populations as well as climate and habitat factors over multiple years, to identify environmental factors associated with Lyme borreliosis risk.

Biogeography of Parasitic Nematode Communities in the Galápagos Giant Tortoise: Implications for Conservation Management.

The Galápagos giant tortoise is an icon of the unique, endemic biodiversity of Galápagos, but little is known of its parasitic fauna. We assessed the diversity of parasitic nematode communities and their spatial distributions within four wild tortoise populations comprising three species across three Galápagos islands, and consider their implication for Galápagos tortoise conservation programmes. Coprological examinations revealed nematode eggs to be common, with more than 80% of tortoises infected within each wild population. Faecal samples from tortoises within captive breeding centres on Santa Cruz, Isabela and San Cristobal islands also were examined. Five different nematode egg types were identified: oxyuroid, ascarid, trichurid and two types of strongyle. Sequencing of the 18S small-subunit ribosomal RNA gene from adult nematodes passed with faeces identified novel sequences indicative of rhabditid and ascaridid species. In the wild, the composition of nematode communities varied according to tortoise species, which co-varied with island, but nematode diversity and abundance were reduced or altered in captive-reared animals. Evolutionary and ecological factors are likely responsible for the variation in nematode distributions in the wild. This possible species/island-parasite co-evolution has not been considered previously for Galápagos tortoises. We recommend that conservation efforts, such as the current Galápagos tortoise captive breeding/rearing and release programme, be managed with respect to parasite biogeography and host-parasite co-evolutionary processes in addition to the biogeography of the host.

An Invasive Mammal (the Gray Squirrel, Sciurus carolinensis) Commonly Hosts Diverse and Atypical Genotypes of the Zoonotic Pathogen Borrelia burgdorferi Sensu Lato.

Invasive vertebrate species can act as hosts for endemic pathogens and may alter pathogen community composition and dynamics. For the zoonotic pathogen Borrelia burgdorferi sensu lato, the agent of Lyme borreliosis, recent work shows invasive rodent species can be of high epidemiological importance and may support host-specific strains. This study examined the role of gray squirrels (Sciurus carolinensis) (n = 679), an invasive species in the United Kingdom, as B. burgdorferi sensu lato hosts. We found that gray squirrels were frequently infested with Ixodes ricinus, the main vector of B. burgdorferi sensu lato in the United Kingdom, and 11.9% were infected with B. burgdorferi sensu lato. All four genospecies that occur in the United Kingdom were detected in gray squirrels, and unexpectedly, the bird-associated genospecies Borrelia garinii was most common. The second most frequent infection was with Borrelia afzelii. Genotyping of B. garinii and B. afzelii produced no evidence for strains associated with gray squirrels. Generalized linear mixed models (GLMM) identified tick infestation and date of capture as significant factors associated with B. burgdorferi sensu lato infection in gray squirrels, with infection elevated in early summer in squirrels infested with ticks. Invasive gray squirrels appear to become infected with locally circulating strains of B. burgdorferi sensu lato, and further studies are required to determine their role in community disease dynamics. Our findings highlight the fact that the role of introduced host species in B. burgdorferi sensu lato epidemiology can be highly variable and thus difficult to predict.

Analysis of suspected wildlife crimes submitted for forensic examinations in Scotland.

This study describes the occurrence of suspected wildlife crimes submitted for forensic examination in Scotland in 2010. The study aims were to determine which types of crimes were committed, which species were targeted, and the outcome of investigations, in order to assess the contribution of forensic examinations in the prosecution of wildlife crimes. Information on suspected wildlife crimes submitted between January 1 and December 31, 2010 to the SAC Consulting: Veterinary Services Disease Surveillance Centers, Science and Advice for Scottish Agriculture, and to the University of Glasgow, was used. The location of suspected crimes, the species targeted, cause of death, and types of the 188 submitted wildlife crimes were summarized. More information regarding cases involving birds were submitted than cases involving mammals, and included 114 raptors, 14 waterfowl, and 22 "other bird species." Mammal cases (n = 38) included 12 badgers, 8 foxes, 7 deer, 4 hares, and 7 "other mammals." The cause of death was determined in 124 suspected crimes; malicious or accidental trauma was the most likely cause of death in 72, and 33 were poisoned. Forensic evidence supporting criminal activity was found in 53 cases, and poisoning was the most frequent crime recorded. At least five individuals were successfully prosecuted, representing 2.7 % of submissions. It was challenging to track cases from submission through to prosecution and laboratories conducting forensic investigations were often not informed of the outcome of prosecutions or court decisions.

Evaluating the use of house sparrow nestlings as sentinels for West Nile virus in Saskatchewan.

This study evaluated the use of house sparrow (Passer domesticus) nestlings as sentinels of West Nile virus (WNV) in the prairie grasslands of Saskatchewan. In the summer of 2006, 600 house sparrow nestlings were collected and pooled tissues tested by reverse transcriptase-polymerase chain reaction. All tested negative for WNV. During the same period, no WNV was detected by mosquito surveillance in the study area and 15 WNV-infected pools were collected from the nearby city of Estevan. Six percent of avian carcasses collected from Regina, a city 100 km from the study area in the same ecozone, were infected with WNV. In 2007, 200 house sparrow nestlings were collected and 4 tested positive for WNV, a prevalence of 2%. Ninety-seven house sparrow eggs were also collected and WNV antibodies were measured in the yolk. Seven eggs had measurable titers, a prevalence of 7.2%. Combined WNV surveillance showed high levels of WNV transmission in 2007; 112 WNV-infected mosquito pools were collected from nearby cities of Estevan and Weyburn, and the proportion of WNV infected avian carcasses from Regina was 78%. There were 1456 human cases of WNV in Saskatchewan in 2007, compared to 19 cases in 2006. The study concluded that house sparrow nestlings are not useful as an early warning of WNV circulation, or as a measure of the intensity of WNV activity in the prairie grasslands. Also, the study determined that maternally derived antibody did not have a significant limiting effect on WNV transmission to house sparrow nestlings in 2007, a year of epidemic WNV activity in the study area.

Avian pox infection with secondary Candida albicans encephalitis in a juvenile golden eagle (Aquila chrysaetos).

Abstract: A juvenile golden eagle (Aquila chrysaetos) was presented with proliferative epithelial lesions, consistent with avian poxvirus infection, around the eyes, on commissures of the beak, and on both feet. Despite treatment, the eagle declined clinically, and, 15 days after presentation, the eagle began seizuring and was euthanatized because of a poor prognosis. On postmortem examination, avian poxvirus infection was confirmed in the nodular skin lesions, and Candida albicans was cultured from the skin, lungs, and brain. Breaks in the skin barrier from poxvirus infection likely led to secondary infection with C albicans. Systemic vascular dissemination of C albicans to the brain resulted in thrombosis, hemorrhage, local hypoxia, and the clinically observed seizures. The combination of the breach in the primary immune system, immunosuppression, and a prolonged course of antibiotics were contributory factors to the opportunistic fungal infection in this eagle. Candida albicans should be considered as a differential diagnosis for encephalitis in an immunocompromised avian patient.

Intracellular yeasts in endothelial cells of a great blue heron (Ardea herodias).

Intracellular organisms in the endothelial cells of several organs of an adult great blue heron (Ardea herodias) were identified as a yeast in the family Saccharomycetales based on ultrastructural morphology and sequence data from the ribosomal RNA operon. Morphologically similar organisms of unknown identity have been described previously in Muscovy (Cairina moschata) and domestic (Anas platyrhynchos domestica) ducks.

Evaluation and delivery of domestic animal health services in remote communities in the Northwest Territories: A case study of status and needs.

Domestic animal health services are supplied to communities in Canada's Northwest Territories (NT) in diverse ways, including private veterinary practices in 2 of 33 communities, and by mail-order, fly-in, free clinics, and a government-coordinated lay vaccinator program in some of the other 31 communities. We evaluated delivery, needs, and potential uptake of domestic animal health services in the Sahtu Settlement Area, NT by offering free clinics for 225 dogs in 2008 and 2009; and administered questionnaires to 42 dog owners and 67 students in 2008. Owners indicated that 20% of dogs were neutered, 37% had had rabies vaccinations, and 29% had been dewormed. Physical examination of dogs demonstrated that 54% were "thin" and 4% were "emaciated." Owners and youth showed a range of attitudes toward dogs and supported improved domestic animal health services. Future services need to build on existing programs and collaborate with communities to ensure relevance, ownership, and sustainability.