I’ll take a break from writing about widespread canine infectious respiratory disease complex (CIRDC) in North America to talk about a single case of a rare disease in a dog. Wageningen Veterinary Research has reported a case of Bluetongue infection in a dog in the Netherlands, a disease of significant consequence to livestock that’s recently been found again in the country.
Bluetongue is a viral disease caused by the unoriginally named bluetongue virus (BTV), which is endemic in many parts of the world, especially tropical and subtropical countries. However, a lot of countries put in significant effort to control this virus and maintain disease-free status, because it has major impacts on food animals. The infection often kills sheep, and while it doesn’t usually kill cattle, infection can cause a major drop in milk production. A single case of bluetongue in a previously disease-free country can result major livestock export restrictions. The Netherlands managed to control bluetongue since their last outbreak in 2007, but it was found again in the country earlier this year; based on the strain, it’s suspected the virus may have been imported from Italy.
The bluetongue-affected dog in this report was a 3.5-year-old pregnant dog from a Dutch dairy farm. The dog had severe signs of illness, including shortness of breath, pulmonary edema, severe emaciation and lethargy. It’s interesting that someone considered bluetongue and tested the dog, especially since the disease wasn’t known to be present in cattle on the farm, though it was subsequently identified in two cattle after the dog’s diagnosis. Thanks to an astute vet and access to testing, a diagnosis of bluetongue was made through detection of BTV by PCR. Not surprisingly, it was the same strain of BTV that’s been circulating in sheep and cattle in the Netherlands.
There’s no mention of whether the dog survived and/or if it was treated. For something like this, we’d be focusing on supportive care and treating the consequences of the infection, while the dog hopefully fought off the virus itself, since we don’t have a specific antiviral treatment for BTV (or at least not one that we know is safe and effective in a dog).
This isn’t the first case of bluetongue in a dog, but it’s a very rare diagnosis. Interestingly, most of the reported canine cases have been in pregnant dogs. We don’t know why that is, but it could be for a number of potential reasons, or a combination thereof, including:
- Just a coincidence
- Greater likelihood of testing a sick pregnant dog
- Increased susceptibility of dogs to infection during pregnancy
How was the dog infected with BTV?
Livestock-to-livestock transmission of BTV is mainly by biting midges (little insects), so the virus can move with infected sheep and cattle, infected midges (blown off course by storms or hitching a ride in a vehicle), or contaminated raw food items that somehow end up being fed to livestock (e.g. food scraps).
How this dog was infected isn’t clear. Contact with or ingestion of colostrum, fetal fluids or fetal membranes, raw meat or blood from an infected ruminant are considered the most likely routes of transmission. However, spread by infected midges can’t be ruled out. This dog lived on a dairy farm, had direct contact with cattle and their environment, and may have had access to high-risk tissues like placentas, so there were a variety of potential sources of exposure.
Does/did this dog pose a risk to other animals?
Presumably not. It’s assumed that dogs are “dead end hosts” for BTV. Dead end hosts can have serious disease but usually don’t produce or excrete enough virus to pass infection on to others. But that is an assumption here, and especially with a rare infection like BTV in a dog, we can’t have complete confidence in assumptions.
Does this case change anything in the big picture?
Probably not much. It’s a reminder of the unpredictability of infectious diseases, the need to consider the whole human/animal/environment ecosystem (versus having tunnel vision about certain species), and that spillover of infections from the main host to others probably occurs a lot more than we recognize for a wide range of infectious diseases.