The Schmallenberg Virus Raises New Concerns About Food Safety

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Experts are keeping close watch on a virus spread by biting bugs that is causing congenital defects in cattle and small ruminants.

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As if we weren't concerned enough over safety issues with food and dairy animals, there's a new virus across the pond that experts are keeping watch on. Likely, it's nothing to worry about, for a number of reasons, but it makes you wonder whether there's something fundamentally wrong with our food practices today.

The first official confirmations of the virus occurred in the German town of Schmallenberg back in November, and it has since spread to Belgium, France, the Netherlands, and the United Kingdom. It affects cattle and small ruminants -- sheep and goats. Its spread is not through animal-to-animal contact, but by mosquitoes and midges (other biting bugs).

The symptoms aren't terribly severe, if they show up at all: They usually consist of fever, loss of appetite, diarrhea, and significantly decreased milk production, and generally go away by themselves after a week or so. Deaths have not been associated with the virus, making it somewhat less concerning for the host than other recent outbreaks like the foot-and-mouth and bluetongue diseases.

The bottom line is that no one really knows how many animals it will affect, or what its course will be.

The curious symptom, however, is that the offspring of infected animals can have congenital defects. Animals who are infected before they get pregnant seem to be OK -- but there's a brief critical period during gestation where if a pregnant animal is infected, the calf, lamb, or kid can have significant physical deformities. It's not clear what this sensitive period is with the Schmallenberg virus itself, but in related viruses it's between days 28 and 36 in sheep and days 75 and 110 in cattle.

According to a report (PDF) recently released by the European Food and Safety Administration (EFSA), the most common malformations of affected offspring are "severe arthrogryposis, torticollis, brachygnathia, hydrocephalus, and other severe brain malformations," or, in other words, limb malformations, bent necks, jaw deformities, and dangerous fluid accumulation on the brain. Because of the deformities, there is a higher rate of stillbirths, which can be a concern both clinically and economically.

Because some of the affected animals are pregnant presently, officials expect to see a jump in affected offspring in the coming months. The EFSA report outlines the possible trajectories for the virus, based on models of earlier related viruses, which take into account affecting changes in temperature (warmer is worse for its spread), the number of vectors (how many bugs bite the host), and whether or not the animal population might have been exposed in the past and developed immunity to it. No one really knows how many animals it will affect, or what its course will be. The EFSA proposes, of course, that European Union member states should work together to share information and track the virus in the coming months and years.

Luckily, the virus does not seem capable of infecting humans. According to the European Centre for Disease Prevention and Control (ECDC), the closest relatives of the Schmallenberg virus are the Shamonda, Aino, and Akabane viruses, which only affect livestock. On the other hand, the Schmallenberg virus is a member of the Orthobunyaviruses family, of which about 30 are known to infect humans. The official stance among European officials is that there's little evidence that it could be a concern to us. Says the EFSA: "As the genetically most related viruses do not cause disease in humans, it is unlikely that this new virus will cause disease in humans but it cannot be excluded at this stage." Whether eating infected meat or drinking affected milk is unclear, but it seems unlikely if unappealing.

Russia and Mexico have banned the imports of animals and animal products from affected regions. The United States has not yet made moves to do the same, but the United States Department of Agriculture (USDA) says it will continue to work closely with European officials to monitor the situation.

The British publication Farmers Weekly has been tracking the virus and periodically commenting on the concerns about its spread. The first cases of bovine infection have just been reported in Britain, where it had previously been confined to sheep. The main concern among dairy farmers is for the loss of milk production that comes when a cow loses her calf: this can lead to financial ruin if multiple animals are affected. Sheep farmers have apparently also had it rough, given recent, albeit more severe, viruses like those mentioned earlier. According to one commentary, if sheep farmers see a loss of 25 percent of production rates, they will have no profit at year's end.

The bottom line is that the virus remains largely an unknown in this early stage. Because it's spread by a bug vector, the virus may be somewhat more difficult to contain than if it was spread by direct contact. Officials will be keeping a watchful eye on its sweep, and hopefully the least damaging scenario will play itself out, which won't, we hope, involve a leap across the Atlantic.

Image: James Thew/Shutterstock.

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Alice G. Walton, PhD, is a health journalist and an editor at The Doctor Will See You Now.

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