Assessing the awareness of Onchocerca cervicalis amongst equine veterinary surgeons in the UK

30 Nov 2020


By Victoria Lindsay

Take home message: There may be a lack of awareness and understanding of onchocerciasis (caused by nematode Onchocerca cervicalis) amongst UK equine veterinary surgeons despite increasing disease prevalence, impacting equine health and welfare.

Onchocerca cervicalis (OC) is a parasitic nematode of horses that causes a clinical syndrome known as onchocerciasis. Affected horses present with itching and skin inflammation, and often insect bite hypersensitivity (IBH) is a differential diagnosis. Anthelmintics such as ivermectin and moxidectin are the primary treatments, and due to the widespread use of these treatments for other parasites, this syndrome is often assumed to be well controlled in the general population. This study aimed to establish how aware equine veterinary surgeons are of this parasite, how commonly vets encountered unresponsive dermatosis/IBH cases (that could be caused by onchocerciasis), and to determine whether the use of ivermectin and moxidectin by veterinary surgeons is declining in the UK.

A questionnaire-based study was conducted using an online survey platform, collecting both quantitative and qualitative responses from currently practising equine veterinary surgeons on their awareness and knowledge of OC, whether they had diagnosed cases and why/why not, and on usage of ivermectin and moxidectin by their clients. 88 responses were received (response rate of 4.89%), and ‘knowledge scores’ were given based on participant answers to the four questions on parasite class, intermediate host, clinical signs and lifespan of OC.

Whilst the majority of survey respondents were aware of OC (78.4%), only six had previously diagnosed a case, and only one had this confirmed using diagnostic testing. When ‘aware’ respondents were tested using four knowledge questions, 49.3% answered fewer than two questions correctly, indicating that understanding was lower than respondents believed it to be. Furthermore, whilst a median of 25% of annual IBH cases were not responsive to standard treatments, a majority of respondents (83.7%) did not consider onchocerciasis as a differential diagnosis in those cases. 12.5% of respondents who did not consider OC as a differential diagnosis believed that OC is not present in the UK equine population. Together, these results imply UK equine veterinary surgeons lack knowledge of OC that may be detrimental to equine health.

Whilst median annual usage of ivermectin or moxidectin was 81-90%, 60.2% of respondents believed usage of these drugs would decrease over the next decade due to developments in diagnostic testing, increased usage of faecal egg counts, and increasing awareness of resistance to anthelmintic drugs in owners. Should usage of these anthelmintics decrease as respondents predict, prevalence of OC is likely to increase, and thus the importance of veterinary awareness of this parasite and the associated clinical disease is highlighted.

The study was carried out by Sarah Mansell, studying Bioveterinary Science at Harper Adams University, and has been highly commended in the 2020 BSAS Undergraduate Thesis of the Year Award. “I was delighted to be nominated for the thesis of the year award,” says Sarah, who is now studying for an MSc in Animal Nutrition at the University of Nottingham, “Nutrition is an area of animal science I am particularly passionate about, and I spent my undergraduate placement year working in the nutrition industry”. Sarah hopes to pursue a career in research and development in the areas of animal health, welfare and food supply.

Victoria Lindsay, Royal Veterinary College PhD Student

Victoria has been a member of the BSAS Early Careers Council for two years, and is in the final year of her PhD at the Royal Veterinary College studying the genetic architecture of exertional rhabdomyolysis in horses.