Wildlife Vectors Research Articles

Mink (Neovison vison) as a natural vector in the dispersal of the diatom Didymosphenia geminata

Considerable resources have been invested worldwide in response to the spread of the diatom Didymosphenia geminata in rivers and streams. Considering the very low possibility of elimination of an invasive microbe, management has focused on biosecurity protocols, addressed exclusively toward the human role in dispersal (e.g. ‘check, clean dry’ campaigns and gear-washing stations for recreational users). Natural dispersal by wildlife vectors may also play an important role in the spread of D. geminata and other algal species, potentially limiting or negating the efficacy of biosecurity measures. We investigated the possibility that introduced mink (Neovison vison) may be a potential dispersal agent for D. geminata and other stream diatoms in Chilean Patagonia. Neovison were trapped near a zone of strong and persistent D. geminata blooms in the fifth order Río Simpson, and also in a fourth order upstream tributary, Río Huemules, the latter with smaller, more incipient blooms. Epibiotic D. geminata cells were identified from Neovison at Río Simpson (44% positive, average 791 cells per animal, n=18 animals), and Río Huemules (20% positive, average 40 cells per animal, n=5 animals). Many other species were also observed: 20 genera, 5683 cells per mink in Río Simpson, and 18 genera, 3605 cells per mink in Río Huemules. Navicula, Epithemia, Fragilaria and Placoneis were among the genera most frequently encountered. Neovison are known to prefer the riparian ecotone of streams of all sizes, have the capacity to travel several kilometers upstream and downstream, and possibly as far as 10 km overland to colonize new catchments. Together with an estimated survival time of 60 or more days for D. geminata in a humid environment (e.g. mink fur), Neovison represent a potentially significant factor in the colonization of upstream reaches and adjacent catchments. We comment on the potential for other wildlife vectors in Patagonia, and respective alternative patterns of short- to long-distance dispersal of diatoms in continental waters. Our results suggest that wildlife vectors should be considered in the management of D. geminata, and in the case of Neovison, integrative management of multiple invasive species, and a reassessment of conservation priorities may be necessary.

Host-seeking mosquito distribution in habitat mosaics of southern Great Plains cross-timbers.

Landscape fragmentation often increases contact between humans, wildlife, and potential disease vectors. We examined how adult host-seeking mosquitoes respond to small-scale habitat differences within southern Great Plains cross-timber habitat mosaics in northern Oklahoma consisting of eastern red cedar (Juniperus virginianus L.) woodlands, mixed-deciduous woodlands, and adjacent grasslands. Mosquitoes responded most markedly to an overall grassland-woodland habitat gradient, with species separating by habitat based largely on tree density. Differences in abundance of host-seeking females occurred at fine spatial scales, sometimes varying dramatically over distances as little as 200 m when tree density changed abruptly. Tree type was not as important as tree density, although the West Nile virus vector Culex tarsalis Coquillett showed a greater affinity for areas containing eastern red cedar than for deciduous woodlands. The invasive Aedes albopictus Skuse showed equal affinity for both tree types. Conversion of grassland habitats in the Great Plains to more vegetated environments associated with humans (towns and homesteads) and the invasion of grasslands by eastern red cedar may change the species composition of mosquito, bird, and mammal assemblages and potentially alter arbovirus exposure for humans.

IS Q fever a significant cause of reproductive failure in cattle?

Q FEVER is a zoonotic disease considered as emerging or re-emerging in many countries around the world. The aetiological agent is Coxiella burnetii , a pleomorphic Gram-negative bacterium able to...

Epidemiology of human rabies in South Africa, 1983–2007

Rabies remains a global public health problem but increasingly so in the developing world. Given a lack of awareness, priority and diagnostic capability, very few developing countries, especially in Africa, report on laboratory confirmed human rabies cases. Here we present a retrospective study on the epidemiology of human rabies in Republic of South Africa for a 25-year period, 1983–2007, based on laboratory confirmed cases. The study highlights the role of the domestic dog as a reservoir and vector of rabies and contrasts this to the almost negligible contribution of wildlife vectors to the overall burden of human rabies in dog rabies endemic areas. From the collective data set, epidemiological aspects that include various features of these human rabies cases as well as failures in or towards the treatment of exposures are reported. Molecular analysis of virus isolates did not identify any additional cases of rabies attributed to infection with the Duvenhage, Lagos bat or Mokola or any other rabies-related viruses.

Potential influence of climate change on vector-borne and zoonotic diseases: a review and proposed research plan.

BackgroundBecause of complex interactions of climate variables at the levels of the pathogen, vector, and host, the potential influence of climate change on vector-borne and zoonotic diseases (VBZDs) is poorly understood and difficult to predict. Climate effects on the nonvector-borne zoonotic diseases are especially obscure and have received scant treatment.ObjectiveWe described known and potential effects of climate change on VBZDs and proposed specific studies to increase our understanding of these effects. The nonvector-borne zoonotic diseases have received scant treatment and are emphasized in this paper.Data sources and synthesisWe used a review of the existing literature and extrapolations from observations of short-term climate variation to suggest potential impacts of climate change on VBZDs. Using public health priorities on climate change, published by the Centers for Disease Control and Prevention, we developed six specific goals for increasing understanding of the interaction between climate and VBZDs and for improving capacity for predicting climate change effects on incidence and distribution of VBZDs.ConclusionsClimate change may affect the incidence of VBZDs through its effect on four principal characteristics of host and vector populations that relate to pathogen transmission to humans: geographic distribution, population density, prevalence of infection by zoonotic pathogens, and the pathogen load in individual hosts and vectors. These mechanisms may interact with each other and with other factors such as anthropogenic disturbance to produce varying effects on pathogen transmission within host and vector populations and to humans. Because climate change effects on most VBZDs act through wildlife hosts and vectors, understanding these effects will require multidisciplinary teams to conduct and interpret ecosystem-based studies of VBZD pathogens in host and vector populations and to identify the hosts, vectors, and pathogens with the greatest potential to affect human populations under climate change scenarios.

Safety studies on an adenovirus recombinant vaccine for rabies (AdRG1.3-ONRAB ®) in target and non-target species

A replication-competent human adenovirus vector in which the rabies virus glycoprotein gene was inserted (AdRG1.3-ONRAB ®) was given by direct instillation into the oral cavity to representatives of three wildlife vector species of concern in Ontario (red fox, raccoon and striped skunk) and to a variety of non-target wildlife species, domestic and laboratory species. Despite use of a relatively high dose of vaccine, no untoward clinical signs were observed. Subsequent to vaccine exposure, detection of vaccine virus in lung, spleen, intestine, liver, kidney and brain of each animal was attempted using an ONRAB ®-specific assay combining PCR with Southern blotting (PCR–SB). Of the 1280 tissue samples obtained from vaccinates or contact animals, 18 (1.4%) were found to be PCR–SB positive. Virus isolation attempts were performed utilizing cell culture for all PCR–SB positive tissues and a selection of PCR–SB negative tissues. Histological examination performed on all PCR–SB positive tissues failed to identify lesions attributed to the vaccine. A quantitative real-time PCR was used to determine the excretion of the vaccine in feces and in the oral cavity with 0.8% of oral swabs and 6.8% of fecal specimens found to be positive. The low rates of recovery of vaccine virus from tissues, feces and the oral cavity suggest that the likelihood of ONRAB ® causing a negative impact on wildlife species is unlikely.

A longitudinal study of environmental salmonella contamination in caged and free-range layer flocks

The environmental contamination by salmonella was examined over a 12-month period in 74 commercial layer flocks from eight farms in the UK, which previously had been identified as being contaminated with salmonella. Samples of faeces, dust, litter, egg belt spillage and wildlife vectors were taken, plus swabs of cages, feeders, drinkers, floors, egg belts and boots. Some sampling was performed in each month of the year. Numerous serovars were detected but Salmonella enterica serotype Enteritidis was the only persistent serotype found among single-age flocks. There was a significant correlation between qualitative environmental samples and semi-quantitative faeces samples. The level of environmental contamination increased significantly over time. There were significant temperature and seasonal effects upon contamination. Wildlife vectors proved to be sensitive samples for the detection of salmonella. The efficacy of cleaning and disinfection upon residual salmonella contamination, and upon subsequent flock contamination, was highly variable between and within premises. The variability between detected prevalences over time and between flocks indicates a need for regular, sensitive monitoring of flocks for salmonella to permit targeting of control measures aimed at eliminating contamination of the layer environment by salmonella. There is substantial scope for improvement of cleaning and disinfection procedures.

Assessment of cleaning and disinfection in S almonella-contaminated poultry layer houses using qualitative and semi-quantitative culture techniques

Salmonella infection of laying flocks in the UK is predominantly a problem of the persistent contamination of layer houses and associated wildlife vectors by Salmonella Enteritidis. Methods for its control and elimination include effective cleaning and disinfection of layer houses between flocks, and it is important to be able to measure the success of such decontamination. A method for the environmental detection and semi-quantitative enumeration of salmonellae was used and compared with a standard qualitative method, in 12 Salmonella-contaminated caged layer houses before and after cleaning and disinfection. The quantitative technique proved to have comparable sensitivity to the standard method, and additionally provided insights into the numerical Salmonella challenge that replacement flocks would encounter. Elimination of S. Enteritidis was not achieved in any of the premises examined although substantial reductions in the prevalence and numbers of salmonellae were demonstrated, whilst in others an increase in contamination was observed after cleaning and disinfection. Particular problems with feeders and wildlife vectors were highlighted. The use of a quantitative method assisted the identification of problem areas, such as those with a high initial bacterial load or those experiencing only a modest reduction in bacterial count following decontamination.

Canine parvoviral myocarditis

A 5-week-old crossbred pigdog pup was presented in respiratory distress. It appeared to dry retch, and then died suddenly before a clinical examination was performed; a littermate had died suddenly the week before. Histopathological examination revealed an ongoing lymphocytic myocarditis, characterised by myofibril degeneration and lymphocytic inflammatory infiltrates. In scattered degenerate myofibres, there were large amphophilic intranuclear inclusion bodies distending their nuclei. There was also marked pulmonary oedema. Canine parvoviral myocarditis, due to canine parvovirus type 2, was diagnosed. Further questioning regarding the history of this pup revealed that it had been born to an unvac-cinated dam that had been moved late in her pregnancy from an isolated farm on to another property. It seems likely that the dam was naïve and only became exposed to the virus immediately prior to whelping. The lack of wildlife vectors and a well-controlled population of dogs in rural New Zealand means that there may be isolated areas of the country where dogs can reach maturity without becoming exposed to parvovirus, creating the potential for development of this now uncommon syndrome. When parvovirus first arose in New Zealand, between 1979–;1981, parvoviral myocarditis was relatively common, occurring in neonates when the virus was introduced to breeding kennels that previously had been unexposed.

Recovery from Rabies

Worldwide, some 55,000 people die every year from rabies, mostly in Asian and African countries where canine rabies is endemic. Children are frequently the victims of rabies. In the United States, indigenous cases of rabies in humans usually occur through transmission of rabies virus from wildlife vectors, and molecular characterization of the variants indicates that the majority of these cases originate from insect-eating bats.In this issue of the Journal, Willoughby et al.1 report the case of a young patient in whom rabies developed after a clear history of having been bitten by a bat. Most of the cases of . . .

Improving protective efficacy of BCG vaccination for wildlife against bovine tuberculosis

Possums are a wildlife vector of bovine tuberculosis in New Zealand. Vaccination of possums with BCG is being considered as a measure to control the spread of bovine tuberculosis to cattle and deer. Delivery via oral bait is feasible but BCG is degraded in the stomach. The aim was to determine whether ranitidine (Zantac) would reduce gastric acidity and enhance the efficacy of intragastrically administered BCG. A dose of 75 mg reduced gastric acidity for at least 4 h. Thus, possums were vaccinated intragastrically with BCG after receiving 75 mg ranitidine or ranitidine or BCG alone, as controls, before challenge with virulent Mycobacterium bovis. Proliferative responses of blood lymphocytes to M. bovis antigens after vaccination were significantly higher in possums given ranitidine/BCG compared to controls and seven weeks after challenge they had significantly lower lung weights and spleen bacterial counts than ranitidine alone controls. Vaccination with BCG alone only gave a reduction in loss in body weight. Agents that reduce gastric acidity may be useful in formulating BCG for oral bait delivery to wildlife for vaccination against bovine tuberculosis.

Impact of bovine tuberculosis on a population of brushtail possums (Trichosurus vulpecula Kerr) in the Orongorongo Valley, New Zealand

Brushtail possums are the main wildlife vectors of bovine tuberculosis (Tb) in New Zealand. Possum–Tb models form the basis of possum control aimed at eradicating the disease, and yet competing models show different behaviour, and are highly sensitive to parameters about which there is considerable uncertainty. One area of great uncertainty is the impact of the disease on possum populations. We investigated the impact of Tb on a local population of brushtail possums in the Orongorongo Valley, Wellington. Bovine Tb was first detected in 1997 at one site within an intensively studied population, but has not been detected in another intensively studied population 3 km away since the early 1980s. Using a Before-After-Control-Impact (BACI) analysis, detection of Tb coincided with a 42% (95% CI = 23–56%) reduction in the odds of apparent yearly survival of a possum >17 months of age, i.e. a decrease in yearly survival from 0.85 to 0.77 in 'good' years, and a decrease from 0.71 to 0.60 in 'bad' years. This suggests that Tb had a significant impact on overall survival. However, there was no impact on local population density in September each year due to compensatory recruitment.

An enzootic transmission cycle of Lyme borreliosis spirochetes in the southeastern United States.

Lyme borreliosis, or Lyme disease (LD), is a tick-borne zoonotic infection of biomedical significance, caused by Borrelia burgdorferi sensu lato (s.l.) spirochetes and transmitted by Ixodes species ticks. It usually circulates among wildlife vertebrate reservoirs and vector ticks but may infect humans, causing multisystem problems. In far western and northern North America, the host reservoirs, tick vectors, and genospecies of Borrelia are well known but not so in the southern U.S., where there is controversy as to the presence of "true" LD. Here we report the presence of the LD spirochete B. burgdorferi sensu stricto (s.s.) and Borrelia bissettii, three main reservoir hosts, and two enzootic tick vectors in the southeastern U.S. The two enzootic tick vectors, Ixodes affinis and Ixodes minor, rarely bite humans but are more important than the human biting "bridge" vector, Ixodes scapularis, in maintaining the enzootic spirochete cycle in nature. We also report extraordinary longevities and infections in the reservoir rodents Peromyscus gossypinus, Sigmodon hispidus, and Neotoma floridana.

Molecular fingerprinting evidence of the contribution of wildlife vectors in the maintenance of Salmonella Enteritidis infection in layer farms.

To provide molecular fingerprinting evidence of the contribution of wildlife vectors in the on-farm epidemiology of Salmonella Enteritidis infections. Salmonella Enteritidis strains were isolated from wildlife and from farm environment samples collected in 10 egg layer farms. Isolates were typed using plasmid profiling, XbaI-pulsed field gel electrophoresis and PstI-SphI ribotyping. In all 10 farms we were able to identify the same S. Enteritidis clones in wildlife vectors and farm environment. On several occasions the same clones were found before and after cleansing and disinfecting the farm premises. Also in some instances the same clones were present in mice samples, egg contents and spent hens. Definitive molecular evidence for the involvement of several wildlife species (mice, rats, flies, litter beetles and foxes) in the maintenance of S. Enteritidis infection on farms has been presented. Failures in biosecurity seriously compromise the control of this pathogen on laying farms. This paper reports on the use of molecular tools for the study of the epidemiology of S. Enteritidis. It gives useful information to be considered in control programmes for this organism on poultry farms.

Vaccination of the brushtail possum ( Trichosurus vulpecula) against Mycobacterium bovis infection with bacille Calmette-Guérin: the response to multiple doses

In New Zealand, the brushtail possum ( Trichosurus vulpecula) is the principal wildlife vector of bovine tuberculosis. Control of infected possum populations contributes to the control of tuberculosis in domestic livestock. Vaccination is potentially a complementary strategy to population control, but to be cost-effective, administration of the vaccine to possums would need to be from an appropriately designed automatic vaccinator. Possums themselves would activate the vaccinator so that it would deliver an aerosol spray of vaccine. There would be no direct way to prevent possums receiving multiple doses of vaccine. This study examined the effect on protective immunity of repeated vaccination. Captive possums were vaccinated with BCG strain pasteur 1173P2 either 12 times at weekly intervals, twice at 6-weekly intervals, or once. Vaccination was by a combination of intranasal aerosol and conjunctival instillation. Eight weeks after the last dose of vaccine, all possums were challenged intratracheally with Mycobacterium bovis strain 83/6235. Vaccination induced a significant immune response as measured by the lymphocyte proliferation assay (LPA). A significant level of protection, as measured by the response to challenge, developed in all the vaccinated possum groups, but protection was greatest in the group vaccinated 12 times. It was concluded that protection would be enhanced if vaccinations were repeated at short intervals (weekly), but no benefit or detriment resulted from revaccination after longer intervals (1–2 months).

Mycobacterium bovis infection in wildlife in New Zealand

Bovine tuberculosis (Tb) is the most important disease of livestock in New Zealand, and it puts at risk the nation's trade in dairy, beef and venison products. Elimination of the disease from livestock is based on a herd test and slaughter programme and carcass inspection at abbatoirs. However, this programme has not been as successful as expected, because the disease also occurs in wild or feral animals acting as vectors of the disease to livestock. Brushtail possums are the major wildlife vector and self-sustaining maintenance host of Tb, and play a role analogous to that of the badger in Great Britain. In contrast, some deer species and ferrets may act as vectors of the disease, but their role in transmitting Tb to livestock is unclear. Hedgehogs, pigs, cats, sheep and goats are now considered to be amplifier hosts, and spread the disease to other species only when inspected or their carcasses scavenged. In the absence of infected possum populations, these species do not appear to be capable of maintaining the infection in their own populations and are not thought to be involved in the maintenance of Tb in livestock. Tuberculosis has also been recorded from stoats, hares, and a rabbit, but the level of infection recorded in their populations indicates these species are unlikely to spread the disease to other animals and hence are not involved in the transmission of Tb to livestock.

Models of Mycobacterium bovis in wildlife and cattle

Following the first model of wildlife tuberculosis (in European badgers) there has been a spate of papers modelling wildlife TB. These have looked at population parameters and disease dynamics in the badger and possum. Recent papers in particular have looked at various methods of controlling the wildlife vector to reduce the incidence of TB in cattle. The author examines the role of modelling to show what insights it has given us, which issues have not been addressed, and where the shortfalls lie. Particular attention will be paid to a comparison between models of badgers and possums, and between simple and more complex models, and possible areas of future research will be revealed.

Bat lyssavirus infections.

Bats, which represent approximately 24% of all known mammalian species, frequently act as vectors of lyssaviruses. In particular, insectivorous bats play an important role in the epidemiology of rabies and some rabies-like viruses, while the haematophagous vampire bats are the major wildlife vector for rabies in Latin America. In contrast, the role of fruit bats (flying foxes) in the epidemiology of the recently discovered Australian bat lyssavirus is only just emerging. Information on the pathogenesis of lyssaviruses in bats is scarce. However, in general, mortality in bats infected via a natural route appears to be low, and seroconversion occurs in many of those that survive. While transmission of rabies from an infected bat may be via a bite, other routes are apparently also possible. Methods for the diagnosis of bat lyssavirus infections in bats and terrestrial mammals (including humans) are similar to the classical procedures for rabies. Measures for the prevention and control of these diseases are also similar to those for rabies, although additional innovative methods have been tested, specifically to control vampire bat rabies.

Genetic, geographical and temporal variation of porcine reproductive and respiratory syndrome virus in Illinois.

Porcine reproductive and respiratory syndrome virus (PRRSV) ORF5 gene sequences were generated by RT-PCR from 55 field isolates collected in Illinois and eastern Iowa. Spatial and temporal patterns of genetic variation in the virus were examined on a local geographical scale in order to test the hypothesis that the genetic similarity of PRRSV isolates (measured as their percentage pairwise ORF5 nucleotide similarity) was positively correlated with their geographical proximity. Levels of genetic variability in the Illinois/eastern Iowa PRRSV sample were similar to levels of variability seen across broader geographical regions within North America. The genetic similarity of isolates did not correlate with their geographical distance. These results imply that the movement of PRRSV onto farms does not generally occur via distance-limited processes such as wind or wildlife vectors, but more typically occurs via the long-distance transport of animals or semen. Genetic distances between PRRSV isolates collected from the same farms at different times increased as the time separating the collection events increased. This result implies rapid movement of new genetic types of PRRSV into and out of farms. PRRSV ORF5 displayed a pattern of third-codon-position diversity bias that was not evident in a geographically comparable sample of pseudorabies virus (a swine alphaherpesvirus) gC gene sequences. This result provides evidence that PRRSV ORF5 is experiencing stabilizing selection against structural novelty. Despite high genetic variability at all geographical levels, PRRSV ORF5 nevertheless contained potentially antigenic regions that were invariant at the amino acid level. These regions should make effective vaccine targets if they prove to be immunogenic.

Intracellular survival of virulent Mycobacterium bovis and M. bovis BCG in ferret macrophages

The intracellular survival of virulent Mycobacterium bovis and avirulent M. bovis BCG in ferret alveolar macrophages was investigated. In addition, the effects of endogenous and exogenous modulators of macrophage oxidative function on bacterial survival and growth in vitro were determined. Ferret macrophages limited the initial growth of BCG, while virulent M. bovis replicated within macrophages. Intracellular bacterial survival was unaffected by the addition of specific inhibitors of macrophage oxidative function. A T-cell supernatant (TCS), derived from mitogen-stimulated lymphocyte cultures, activated ferret macrophages for heightened oxidative burst performance. However, macrophages activated by TCS, bacterial LPS or a combination of both, failed to control infection, and actually enhanced the intracellular survival of M. bovis. These results are discussed in relation to the role of macrophages in mediating tuberculosis-related pathogenesis, with respect to the fact that ferrets are important wildlife vectors of bovine tuberculosis in New Zealand.