A few weeks ago, I did a talk about Schmallenberg virus for a government group. It was an unusual talk for me since it was about a disease that I’ve never seen, and a virus that as far as we know is not even present in North America. While I’ve been monitoring the issues with Schmallenberg virus in Europe, it was a good opportunity for me to look into the subject more thoroughly. One reason to do so is just academic interest, as someone who deals with infectious diseases. Another is because foreign diseases have a habit of becoming non-foreign, and that’s a serious concern with Schmallenberg.
Schmallenberg virus was first identified in 2011 along the Dutch-German border, so it’s a "new kid on the block." The virus is spread by insects called biting midges, and the disease affects ruminants (mainly cattle, sheep and goats). It causes two main problems: 1. diarrhea and decreased milk production in adults, and 2. adverse effects on the developing fetus in pregnant animals (causing abortion, stillbirths, and deformed calves/lambs/kids). The virus has rapidly spread across all of Europe and is now a major issue in some regions.
One important question about this virus is from where did it come? The answer is not clear. It’s important to figure this out to help determine where the virus might go. A midge hitch-hiking on a plane could be one way for the virus to make it to North America. However, a recent report from Sweden raises a few interesting questions.
Researchers at the Swedish Institute of Agricultural Sciences tested blood samples from 100 dogs. They found antibodies against Schmallenberg virus in 2 of them, and both positive samples were from the same dog that lived in an area where the virus has been found in ruminants.
What does this mean? It’s not clear yet.
- It might be of no consequence at all. It could just mean that an infected midge bit the dog and the dog’s immune system mounted an immune response to kill the virus.
- It can’t be dismissed that it could cause similar disease in dogs as in ruminants. I think that’s unlikely but it’s possible.
- Another concern is if, after being bitten, the virus can reproduce and reach reasonable levels in the dog’s blood (like it does in ruminants), then the dog could be another source of virus for more midges. It might not mean much in endemic areas where there are already lots of infected ruminants harbouring lots of virus. However, dogs travel more than ruminants, and if the virus can live in this species (whether or not it causes disease), then an infected dog could carry the virus to another country or continent. That’s my concern.
It’s incredibly easy to get a dog into Canada. That’s why we’re seeing various imported diseases in dogs, such as leishmaniasis. There’s not even a basic requirement (as in some countries) to mandate treatment for the concerning parasite Echinococcus multilocularis. So, there’s certainly going to be no testing for Schmallenberg virus (nor would this be practical). If European dogs can become infected and be infectious for a period of time, it’s quite plausible that dogs could be a source of international transmission. Fortunately, infected ruminants only shed the virus for a short period of time, so if dogs can be infectious, they’d hopefully following the same course. However, ever if they only shed for a few days, it’s still possible that they could be shipped across the ocean and find a waiting midge. Stranger things have happened with infectious diseases.