Surveillance of Culex spp. vectors and zoonotic arboviruses at a zoo in the United Kingdom

The emergence of several zoonotic mosquito-borne pathogens in Europe, including West Nile virus, Sindbis virus and Usutu virus, has emphasised the importance of consistent surveillance. Considerable fieldwork effort is usually needed to detect low-prevalence pathogens in mosquitoes and screening vertebrate hosts and reservoirs is rarely done simultaneously with mosquito sampling. Zoological gardens offer an opportunity for the surveillance of pathogens, mosquitoes, hosts, and reservoirs concurrently; thus, the aim of this study was undertaking integrated surveillance for mosquito-borne pathogens of wild birds and mosquitoes in Chester Zoo (Cheshire) in the United Kingdom. Mosquitoes were collected in September 2020 and tested for zoonotic bird-hosted arboviruses (i.e., West Nile virus, Usutu virus and Sindbis virus) using RT-qPCRs. Of the 3316 mosquitoes trapped, 98% were identified as Culex spp. The average minimum prevalence of the viruses found in the literature was used to calculate the sample size needed for detecting these viruses with 99% confidence. The testing of 2878 Culex females found no evidence of presence of the three viruses. Significant differences were found in mosquito abundance per sampling site and collection date; furthermore, important sources of immature and resting mosquitoes were found near aviaries. Eighteen wild birds belonging to 11 species were found dead in the zoo from May to December 2020 and were RT-qPCR tested for West Nile virus and Usutu virus; all samples resulted negative for viral infection. It is unlikely that these viruses were present in the zoo during the sampling period; however, since they circulate in Europe and Usutu virus has been isolated in the United Kingdom and may overwinter here, continued monitoring of mosquitoes and wild birds is recommended as virus introduction and dissemination are possible. This study highlights the importance of regular and integrated arboviral surveillance of zoonotic pathogens in zoos providing baseline information to that end.

Field-based assessments of the seasonality of Culex pipiens sensu lato in England: an important enzootic vector of Usutu and West Nile viruses

BACKGROUND

Usutu virus (USUV), which is closely related to West Nile virus (WNV), sharing a similar ecology and transmission cycle, was first reported in the UK in the southeast of England in 2020. Both USUV and WNV are emerging zoonotic viruses hosted by wild birds. The 2020 finding of USUV in England raised awareness of this virus and highlighted the importance of understanding the seasonality of Culex pipiens sensu lato (Cx. pipiens s.l.), the main enzootic vector of these viruses. Zoos are prime locations for trapping mosquitoes because of their infrastructure, security, and range of vertebrate hosts and aquatic habitats.

METHODS

Three independent zoo-based case studies at four locations that cover the seasonality of Cx. pipiens s.l. in England were undertaken: (i) London Zoo (Zoological Society London [ZSL]) and surrounding areas, London; (ii) Chester Zoo (Cheshire); (ii) Twycross Zoo (Leicestershire); and (iv) Flamingo Land (zoo; North Yorkshire). Various adult mosquito traps were used to catch adult Cx. pipiens s.l. across seasons.

RESULTS

High yields of Cx. pipiens s.l./Culex torrentium were observed in Biogents-Mosquitaire and Center for Disease Control and Prevention Gravid traps in all studies where these traps were used. Mosquito counts varied between sites and between years. Observations of adult Cx. pipiens s.l./Cx. torrentium abundance and modelling studies demonstrated peak adult abundance between late July and early August, with active adult female Cx. pipiens s.l./Cx. torrentium populations between May and September.

CONCLUSIONS

The information collated in this study illustrates the value of multiple mosquito monitoring approaches in zoos to describe the seasonality of this UK vector across multiple sites in England and provides a framework that can be used for ongoing and future surveillance programmes and disease risk management strategies.

JMM Profile: Usutu virus

Usutu virus (USUV) is an emerging arbovirus belonging to the family Flaviviridae, genus Flavivirus. It is maintained in an enzootic cycle, with mosquitos as the vector and birds as the main amplifying host. Humans, and other mammals such as horses, are dead-end hosts. The virus was originally detected in sub-Saharan Africa, but in the past two decades has spread across Europe. In certain bird species, such as the Eurasian blackbird (Turdus merula), USUV is extremely virulent and can be fatal. Human infection is rare and often asymptomatic, but multiple short-term neurological diseases have been reported, highlighting its public-health risk.

Impact of research on contagious ovine digital dermatitis on the knowledge and practices of UK sheep farmers and veterinarians

BACKGROUND

Contagious ovine digital dermatitis (CODD) is a common foot disease of sheep which causes a severe form of lameness and can be difficult to control. Recent research has provided evidence-based guidance on diagnosis, treatment and farm management control. The aim of this study was to determine the uptake of this guidance on the knowledge and practices of UK sheep farmers and veterinarians and identify priorities for future research.

METHODS

Data were collected in 2019-2020 by electronic surveys of UK sheep veterinarians and farmers distributed through sheep industry organisations and social media.

RESULTS

Two hundred eight-four sheep farmers and 77 veterinarians responded to the surveys. Fifty-two per cent of farmers and 70% of vets considered that their management of CODD had improved as a direct result of recent research evidence on the disease. The principle areas improved for both sectors were biosecurity advice and use of antibiotic treatments. Farmers and veterinarians reported that the priorities for future research should be in therapeutics, vaccine development and the understanding of disease transmission.

CONCLUSION

There has been strong uptake of recent evidence-based veterinary medicine by farmers and veterinarians for the management of CODD, particularly in the areas of biosecurity and responsible antibiotic use.

Novel ulcerative leg lesions in yearling lambs: Clinical features, microbiology and histopathology

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An outbreak of an infectious dermatological disorder of unknown aetiology in a flock of yearling lambs was investigated.

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Lesions occurred on the distal limb between the coronary band and carpel joint as a circular ulcerative dermatitis.

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Treponema spp., Dichelobacter nodosus, Staphylococcus aureus, Dermatophilus congolensis and poxvirus screens were negative.

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Fusobacterium necrophorum and Streptococcus dysgalactiae were detected in the majority of lesions examined.

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An aetiology involving bacterial infection with F. necrophorum and S. dysgalactiae was implicated.

Here we report an outbreak of an atypical, ulcerative dermatitis in North Country mule lambs, located in South Gloucestershire, UK. The lesions, which appeared to be contagious, occured between the coronary band and the carpal joint as a focal, well demarcated, circular, ulcerative dermatitis. Histopathological examination of the lesion biopsies revealed areas of ulceration, epidermal hyperplasia, suppurative dermatitis and granulation tissue. Clumped keratohyalin granules and intracellular keratinocyte oedema (ballooning degeneration) were evident within lesion biopsies, consistent with an underlying viral aetiology. A PCR-based microbiological investigation failed to detect bovine digital dermatitis-associated treponeme phylogroups, Dichelobacter nodosus, Staphylococcus aureus, Dermatophilus congolensis or Chordopoxvirinae virus DNA. However, 3 of the 10 (30 %) and 6 of 10 (60 %) lesion samples were positive for Fusobacterium necrophorum and Streptococcus dysgalactiae DNA, respectively. Contralateral limb swabs were negative by all standard PCR assays. To better define the involvement of F. necrophorum in the aetiology of these lesions, a qPCR targeting the rpoB gene was employed and confirmed the presence of F. necrophorum DNA in both the control and lesions swab samples, although the mean F. necrophorum genome copy number detected in the lesion swab samples was ∼19-fold higher than detected in the contralateral control swab samples (245 versus 4752 genome copies/μl, respectively; P < 0.001). Although we have not been able to conclusively define an aetiological agent, the presence of both F. necrophorum and S. dysgalactiae in the majority of lesions assayed supports their role in the aetiopathogenesis of these lesions.