The potential of oral vaccines for disease control in wildlife species

Numerous infectious diseases caused by bacteria or viruses persist in developed and developing countries due to ongoing transmission among wildlife reservoir species. Such diseases become the target of control and management programmes in cases where they represent a threat to public health (for example rabies, sylvatic plague, Lyme disease), or livestock production (for example bovine tuberculosis, brucellosis, pseudorabies), or where they threaten the survival of endangered animal populations. In the majority of cases, lethal control operations are neither economically feasible nor publicly supported as a practical means for disease management. Prophylactic vaccination has emerged over the last 15 years as an alternative control strategy for wildlife diseases, mainly driven by the success of widescale oral rabies vaccination programmes for meso-carnivores in North America and Northern Europe. Different methods have been trialled for the effective delivery of wildlife vaccines in the field, however oral vaccination remains the most widely used approach. Successful implementation of an oral wildlife vaccine is dependent on a combination of three components: an efficacious immunogen, a suitable delivery vehicle, and a species-specific bait. This review outlines the major wildlife disease problems for which oral vaccination is currently under consideration as a disease management tool, and also focuses on the technological challenges that face wildlife vaccine development. The major conclusion is that attenuated or recombinant live microbes represent the most widely-used vaccines that can be delivered by the oral route; this in turn places major emphasis on effective delivery systems (to maintain vaccine viability), and on selective baiting systems, as the keys to wildlife vaccine success. Oral vaccination is a valuable adjunct or alternative strategy to culling for the control of diseases which persist in wildlife reservoirs.     

Prevalence of Coxiella burnetii in ticks after a large outbreak of Q fever

Q fever has emerged as an important human and veterinary public health problem in the Netherlands with major outbreaks in three consecutive years. Goat farms are probably the prime source from which Coxiella burnetii have spread throughout the environment, infecting people living in the vicinity. Coxiella burnetii infection not only spilled over from animal husbandry to humans but could also have spread to neighbouring wildlife and pets forming novel reservoirs and consequently posing another and lingering threat to humans, companion animals and livestock. In these cases, transmission routes other than airborne spread of contaminated aerosols may become significant. Therefore, the role of ticks in the transmission of Coxiella burnetii in the current situation was investigated. A total of 1891 questing Ixodes ricinus ticks and 1086 ticks feeding on pets, wildlife and livestock were tested by a recently developed multiplex Q-PCR. All ticks were negative, except for a few ticks feeding on a herd of recently vaccinated sheep. Coxiella-positive ticks were not detected after resampling this particular herd three months later. Based on these data we conclude that the current risk of acquiring Q fever from questing ticks in the Netherlands is negligible. However, for future risk assessments, it might be relevant to sample more ticks in the vicinity of previously C. burnetii infected goat farms and to assess whether C. burnetii can be transmitted transovarially and transstadially in I. ricinus ticks.     

Effects of supplemental feeding on gastrointestinal parasite infection in elk (Cervus elaphus): preliminary observations

The effects of management practices on the spread and impact of parasites and infectious diseases in wildlife and domestic animals are of increasing concern worldwide, particularly in cases where management of wild species can influence disease spill-over into domestic animals. In the Greater Yellowstone Ecosystem, USA, winter supplemental feeding of Rocky Mountain elk (Cervus elaphus) may enhance parasite and disease transmission by aggregating elk on feedgrounds. In this study, we tested the effect of supplemental feeding on gastrointestinal parasite infection in elk by comparing fecal egg/oocyst counts of fed and unfed elk. We collected fecal samples from fed and unfed elk at feedground and control sites from January to April 2006, and screened all samples for parasites. Six different parasite types were identified, and 48.7% of samples were infected with at least one parasite. Gastrointestinal (GI) nematodes (Nematoda: Strongylida), Trichuris spp., and coccidia were the most common parasites observed. For all three of these parasites, fecal egg/oocyst counts increased from January to April. Supplementally fed elk had significantly higher GI nematode egg counts than unfed elk in January and February, but significantly lower counts in April. These patterns suggest that supplemental feeding may both increase exposure and decrease susceptibility of elk to GI nematodes, resulting in differences in temporal patterns of egg shedding between fed and unfed elk.     

Wildlife–livestock interactions in a western rangeland setting: Quantifying disease-relevant contacts

Disease transmission between wild ungulates and domestic livestock is an important and challenging animal health issue. The potential for disease transmission between wildlife and livestock is notoriously difficult to estimate. The first step for estimating the potential for between-species disease transmission is to quantify proximity between individuals of different species in space and time. This study estimates second-order statistics of spatio-temporal location data from radio-collared free-ranging deer, elk and cattle in northeast Oregon. Our results indicate, that when observed simultaneously, elk and cattle occur in closer proximity to each other than what would be expected based on general space use of these species. The same is true for deer and elk but not for deer and cattle. Our analysis also demonstrates that average distances between cattle and elk are largely driven by rare events of close co-mingling between the species, which extend over several hours. Behavioral causes for these co-mingling events are currently unknown. Understanding the causes for such events will be important for designing grazing practices that minimize wildlife–livestock contacts.     

Contacts between domestic livestock and wildlife at the Kruger National Park Interface of the Republic of South Africa

One of the most important transboundary animal diseases (TADs) in the southern African region is foot-and-mouth disease (FMD). In this region, a pathway for spread of FMD virus is contacts between cattle and certain species of wildlife. The objective of this study was to evaluate contacts between cattle and wildlife in the Kruger National Park (KNP) and the adjacent Limpopo province for the time periods October 2006 to March 2007 and April to September 2007. In this study, 87 livestock owners and 57 KNP field rangers were interviewed. Fifteen (17%) livestock owners reported contacts between wildlife and cattle. More livestock owners reported observing contacts between cattle and all wildlife species during October-March than April-September (p = 0.012). However, no difference was found between these periods for contacts between cattle and individual wildlife species. A total of 18 (32%) field rangers reported contacts between cattle and wildlife. The most common species-specific contacts were between cattle and buffalo (63/year), cattle and impala (17/year) and cattle and lion (10/year). There were no significant differences in rangers reporting observed contacts between cattle and wildlife during October-March versus April-September or between rangers reporting observed contacts outside versus within the KNP. Overall, there was no evidence of higher contact rates between cattle and wildlife in the study area during October-March compared to April-September. Contact data collected in this study can be used to better understand the transmission of FMD virus in this region.     

The transmission of Cowdria ruminantium by Amblyomma sparsum

Transmission of Cowdria ruminantium (heartwater) by nymphs of Amblyomma sparsum has been demonstrated. Adults of the same tick species failed to transmit the disease after feeding on infected sheep in either the larval or the nymphal stage, and there was no transovarian transmission. A. sparsum seldom parasitizes domestic livestock but could be of importance in maintaining reservoirs of heartwater infection in wildlife populations.     

The sero‐epidemiology of Coxiella burnetii (Q fever) across livestock species and herding contexts in Laikipia County,Kenya

Coxiella burnetii, the causative agent of Query fever (Q fever), is among the most highly infectious zoonotic pathogens transmitted among livestock, with chronic effects challenging to veterinary and medical detection and care systems. Transmission among domestic livestock species can vary regionally due to herd management practices that determine which livestock species are raised, whether or not livestock are in contact with wildlife, and the susceptibility of these livestock to infection. To explore how different livestock management practices are associated with the risk of infection in multispecies environments, we carried out a comparative study of three types of herd management systems in the central Kenyan county of Laikipia: agro‐commercial, mixed conservancy/commercial, and smallholder ranches. We tested C. burnetii antibody seroprevalence in four common livestock species. Across all management types, the highest seroprevalence was in camels (20%), followed by goats (18%), sheep (13%), and cattle (6%). We observed a lower odds of testing seropositive for young compared to adult animals (adjusted OR = 0.44 [95% CI 0.24, 0.76]), and for males compared to females (adjusted OR = 0.52 [95% CI 0.33, 0.80]). Animals from mixed conservancy/commercial and smallholder operations had a higher odds of testing seropositive compared to animals from agro‐commercial ranches (adjusted OR = 5.17 [95% CI 2.71, 10.44] and adjusted OR = 2.21 [95% CI 1.17, 4.43] respectively). These data suggest that herd management practices might affect the transmission dynamics of C. burnetiiin arid African ecosystems like those seen in Kenya where several transmission modes are possible, risk of drought has promoted new livestock species such as camels, and multiple wildlife species may co‐occur with livestock on the landscape. Further longitudinal studies are needed to disentangle the mechanisms underlying these patterns, and further explore transmission patterns between wildlife, domestic animal, and human populations.     

The role of wildlife in transboundary animal diseases

This paper identifies some of the more important diseases at the wildlife-livestock interface and the role wildlife plays in disease transmission. Domestic livestock, wildlife and humans share many similar pathogens. Pathogens of wild or domestic animal origin that can cause infections in humans are known as zoonotic organisms and the converse are termed as anthroponotic organisms. Seventy-seven percent of livestock pathogens and 91% of domestic carnivore pathogens are known to infect multiple hosts, including wildlife. Understanding this group of pathogens is critical to public health safety, because they infect a wide range of hosts and are most likely to emerge as novel causes of infection in humans and domestic animals. Diseases at the wildlife-livestock interface, particularly those that are zoonotic, must be an area of focus for public health programs and surveillance for emerging infectious diseases. Additionally, understanding wildlife and their role is a vital part of understanding the epidemiology and ecology of diseases. To do this, a multi-faceted approach combining capacity building and training, wildlife disease surveillance, wildlife-livestock interface and disease ecology studies, data and information sharing and outbreak investigation are needed.     

Wild deer as a source of infection for livestock and humans in the UK

Wild deer can feature in the epidemiology of a wide range of livestock and human diseases in the United Kingdom by representing a source of disease via various transmission routes. This review highlights current and possible future infections of deer in the UK which may have an impact on livestock and/or human health. Increases in deer abundance as well as range expansion are likely to exacerbate the potential for disease persistence due to the formation of multi-species deer assemblages, which may act as disease reservoirs. Climatic changes are likely to have a direct impact on the presence and abundance of various pathogens and their vectors, so that with a warming climate exotic diseases may play a role in future UK livestock and wildlife disease management. This paper highlights the need for a monitoring strategy for wildlife diseases, in particular infections in wild deer, in the UK.     

Zoonotic aspects of Mycobacterium bovis and Mycobacterium avium-intracellulare complex (MAC)

Pathogens that are transmitted between the environment, wildlife, livestock and humans represent major challenges for the protection of human and domestic animal health, the economic sustainability of agriculture, and the conservation of wildlife. Among such pathogens, the genus Mycobacterium is well represented by M. bovis, the etiological agent of bovine tuberculosis, M. avium ssp. paratuberculosis (Map) the etiological agent of Johne disease, M. avium ssp. avium (Maa) and in a few common cases by other emergent environmental mycobacteria. Epidemiologic surveys performed in Europe, North America and New Zealand have demonstrated the existence and importance of environmental and wildlife reservoirs of mycobacterial infections that limit the attempts of disease control programmes. The aim of this review is to examine the zoonotic aspects of mycobacteria transmitted from the environment and wildlife. This work is focused on the species of two main groups of mycobacteria classified as important pathogens for humans and animals: first, M. bovis, the causative agent of bovine tuberculosis, which belongs to the M. tuberculosis complex and has a broad host range including wildlife, captive wildlife, domestic livestock, non-human primates and humans; the second group examined, is the M. avium-intracellulare complex (MAC) which includes M. avium ssp. avium causing major health problems in AIDS patients and M. avium ssp. paratuberculosis the etiological agent of Johne disease in cattle and identified in patients with Crohn disease. MAC agents, in addition to a broad host range, are environmental mycobacteria found in numerous biotopes including the soil, water, aerosols, protozoa, deep litter and fresh tropical vegetation. This review examines the possible reservoirs of these pathogens in the environment and in wildlife, their role as sources of infection in humans and animals and their health impact on humans. The possibilities of control and management programmes for these mycobacterial infections are examined with regards to the importance of their natural reservoirs.