Species Susceptibility to Bluetongue in European Zoos During the Bluetongue Virus Subtype 8 (BTV8) Epizootic August 2006–December 2007
Bluetongue is a serious viral disease of domestic livestock, principally sheep. However, little is known about the susceptibility of non-domestic ruminants to the disease. Though all ruminants are thought to be susceptible to infection, clinical expression is highly variable. It can range from subclinical infection, to fever, coronitis and laminitis, ulceration of the mucous membranes of the oronasal cavity, oedema of the head and neck, cyanosis, and death. Clinical expression is dependent on species, breed/race, subtype of virus, previous exposure, stressors, environmental conditions, and behaviour of the culicoid midge vector.2
European zoos are in a unique position to contribute to knowledge on disease caused by bluetongue virus subtype 8 (BTV8) in non-domestic ruminants, as they house and monitor a wide range of ruminant species that can be assumed to have been naïve to infection prior to the BTV8 epizootic in northwestern Europe that began in August 2006. A web based survey was produced and received endorsement by the EAZA veterinary committee and the Infectious Disease Working Group of EAZWV. The survey was circulated in December 2007 to all EAZA and WAZA collections in the region and to other zoos via EAZWV and the regional zoo vet associations.
One hundred forty-six responses were received, representing over 50% of EAZA collections. Of these, 49 zoos were within 20 km of confirmed BTV8 cases and could be classified as at risk of infection. These 49 zoos held over 1000 susceptible individuals of 53 different species and seven ruminant families indigenous to Europe, North and South America, Africa, and Asia. Clinical disease was seen in 62 individuals (6% of the at-risk population), in 13 zoos (27% of at-risk collections).
Preliminary analysis suggests that the Bovidae are the most susceptible family of ruminants to clinical disease, with four species showing morbidity of greater than 20% and mortality of greater than 10%. The average case fatality rate for the affected Bovidae species was 69%. All the affected ruminant species in this study were indigenous to Europe, Asia, or the Americas. Clinical signs in these species are consistent with those recorded for BTV8 infection in domestic livestock.1 It is noteworthy that none of the over 200 African ruminants of 20 species being held by zoos in at-risk areas were reported to be clinically affected. Follow-up of the affected animals is planned to confirm the data presented here and to establish the proportion of animals listed in which a definitive diagnosis of BTV8 infection was established.
In conclusion, BTV8 infection can cause significant mortality or morbidity in some ruminant species, particularly of those members of the family Bovidae indigenous to Europe and Asia. Zoo managers should focus protective measures on these susceptible species as a priority. Protective measures might include housing, use of insecticide, midge control, and vaccination. Species not showing clinical disease may well act as reservoirs and multiplier hosts for BTV and managers should also consider instituting protective measures for these species. Investigation of levels of viremia in different species would help determine which of them posed the greatest risk. Further data collection over the coming midge season is planned and should help improve the accuracy and validity of this study.
This material was first presented at the EAZWV meeting in Leipzig, May 2007. Its presentation at AAZV also is fully endorsed by EAZWV.
We thank European Association of Zoos and Aquariums (EAZA) and European Association of Zoo and Wildlife Veterinarians (EAZWV) Infectious Disease Working group for their support of this survey and all the respondents for their assistance.
1. Elbers ARW, Mintiens K, Staubach C, Gerbier G, Meroc E, Ekker HM, et al. Epidemiological analysis of the 2006 bluetongue virus serotype 8 epidemic in northwestern Europe: nature and severity of disease in sheep and cattle. In EFSA scientific report: Epidemiological analysis of the 2006 bluetongue virus serotype 8 epidemic in northwestern Europe. http://www.efsa.europa.eu/EFSA/1178620925100/efsa_locale-1178620753812_Bluetongue.htm. Accessed 2007. (VIN editor: link was not accessible as of 1/15/2021.)
2. Verwoerd DW, Erasmus BJ. Infectious Diseases of Livestock. In: Coetzer JAW, Tustin RC, eds. Oxford University Press; 2004;1201–1220.