The role of wildlife and livestock in the emergence and persistence of zoonosis in Scotland, and novel interventions

Challenges

Changes to climate and trade patterns potentially bring several disease and public health threats to Scotland. Babesiosis are tick-transmitted zoonotic diseases currently underdiagnosed in Scotland and in the UK. Different pathogen species (B. venatorum, B. divergens and B. odocoilei) have been linked to different host ranges, pathogenicity, zoonotic capability, and clinical presentations. Despite cases of human Babesia spp. infection increasing in the UK, there is still a lack of robust and reliable diagnostic tools to effectively monitor the disease in livestock and humans.

Anaplasma phagocytophilum (AP) is another tick-transmitted zoonotic pathogen identified in wildlife and livestock in the UK. AP is currently regarded as a single species and can cause infection in humans, dogs, horses, birds, and wild rodents. Different AP isolates (also called ecotypes/haplotypes) have been associated with changes in host susceptibility and clinical presentation. The role of wildlife species in the circulation of AP is still to be determined, with at least two different main lineages recognised to date. One is linked to zoonosis and disease in livestock and maintained in deer species other than roe deer. The other is thought to be non-zoonotic and maintained by roe deer.

A substantial increase in cases of human AP infections have recently been recorded in the United States, linked to an increase in tick activity and geographical spread. AP can induce immune suppression and exacerbate other diseases, as commonly seen in livestock. AP has also been implicated in co-infections in people with symptomatic Lyme disease. No evaluation has been carried out of the different Scottish/UK isolates and their pathogenic potential. Therefore, a genetic analysis could help to clarify the pathogenicity and zoonotic potential of AP isolates present in Scotland.

Questions

Solutions

This project adopts a One Health approach to focus on the protection of public and animal health by further understanding and controlling key zoonoses of livestock and wildlife. This is being achieved through several objectives including the investigation of zoonotic tick, water and food-borne infections in livestock, wildlife, and ticks to discriminate between the presence of zoonotic and non-zoonotic variants and the development of novel tick-borne disease (TBD) transmission-blocking strategies.

Zoonotic tick-borne Babesia infections in livestock and wildlife

We are sequencing the whole genome of B. venatorum-positive samples from naturally infected livestock species to allow antigen identification and to develop serological assays to discriminate between zoonotic species (B. venatorum and B. divergens). This is allowing us to assess the prevalence of these parasites in Scotland. Concurrently, we are developing polymerase chain reaction (PCR)-based detection methods to distinguish between these Babesia species and applying these to Scottish tick collections. We are then testing samples from geese to identify the Babesia species present and the potential of migratory birds to introduce new species into Scotland.

Anaplasma phagocytophilum (AP) genotyping for the detection of zoonotic isolates in ticks, livestock, and wildlife

Our previous research led to the development of a diagnostic test for infection caused by Anaplasma AP in livestock, wildlife, and ticks. Building on this work, we are characterising existing AP-positive archive material from different species from samples submitted for routine diagnostic testing. Several sequencing approaches are being utilised and the detection of different isolates in different species is shedding light on the possibility of zoonotic transmission and assisting in evaluating the risk for human disease because of tick bites.

Development of tick-borne disease (TBD) transmission-blocking strategies

We are also establishing novel preventative approaches to TBDs by establishing both the potential for vaccination and the effects of the tick microbiome on vector competence. We are combining a vaccine to control louping-ill virus (LIV) with a co-delivered vaccine to prevent onward transmission of this and other TBPs by increasing the mortality and inhibiting the further development of larval ticks feeding on the vaccinated host. We are then measuring the potential impacts of such a transmission-blocking vaccination strategy.

Using next-generation sequencing among other approaches, we are determining the microbiome of Scottish tick populations in conjunction with monitoring the ticks for known tick-borne pathogens (TBPs) to determine the association of endosymbionts with TBPs. If successful, this will provide baseline data for future work aimed at targeting endosymbionts to control ticks.

Investigate the role of wildlife as a source of protozoan diseases (Cryptosporidium and Giardia) threatening livestock and human health

Finally, we are investigating whether wildlife species (rabbits, geese, and possibly pheasants) are infected with Cryptosporidium and Giardia and if they can be sources of infection for livestock or humans. Preliminary data indicate that rabbit faeces can contain Cryptosporidium oocysts and Giardia cysts and that pheasant and goose faeces can contain Cryptosporidium. The presence of Giardia in pheasants and geese is currently unknown. We are collecting rabbit and pheasant faecal samples, speciating and genotyping any positive Cryptosporidium as well as detecting, speciating and genotyping Giardia positive samples. We are determining if human and livestock infectious Cryptosporidium and Giardia species and assemblages are present in the host species and if these can amplify the parasites, therefore acting as a significant source of human and livestock infectious protozoa in Scotland.

Project Partners

Progress