Zika Virus: A Reminder of the Importance of Emerging Disease Detection
By now most people have heard of the exotic-sounding Zika virus. The emergence of this exotic-sounding disease has been garnering attention, even prompting some health officials to advise people to change travel plans.
Overview & Symptoms
Zika virus, a tropical mosquito-borne disease, has recently emerged in many South American and Central American countries after having first been characterized in Africa and Asia. Travelers to those parts of the world have brought the disease back with them, including several returning to the United States. The vast majority of people exposed to the virus never know they have the disease. Some develop vague symptoms such as fever, rashes, and body aches. The more troublesome aspect of the disease is its recent association with birth defects in babies. Some of these children have been born with microcephaly, where the baby’s head is smaller than normal, along with brain defects.
The possibility of these dramatic outcomes has led officials to advise pregnant women not to travel to certain parts of South America, Central America or the Caribbean, areas of active infection. Luckily for us in the Northern Plains, the mosquito species adept at spreading the virus is not found here. Even in the case of infected travelers returning here, spread beyond them is not likely.
Zika virus has no known connection with animals; so far the transmission routes appear to be exclusively human-to-human with the necessary help from the right mosquito species. Yet, its association with birth defects brings to mind some viruses that can affect our livestock.
It was Cache Valley Virus infection that had the attention of sheep producers several years ago. Infected ewes were giving birth to lambs with severe birth defects – problems in the brain as well as fused leg joints and other developmental problems. Cache Valley and Zika virus infections have more than a few similarities. Both are transmitted by insects. They cause mild or no illness in the infected mothers, and both can cause birth defects.
Viruses typically have a hard time navigating a pregnant female to infect the developing baby. The virus has to evade the mother’s immune system in high enough numbers to make it through her bloodstream, across the placenta, and infect the fetus. If the fetus’s immune system isn’t developed enough to clear the virus, the virus can then infect and damage target cells in the fetus.
Some viruses are exquisitely specific about the types of cells they like to infect – for example, the developing brain cells of a human fetus (or a lamb fetus, for that matter). Hence, we get birth defects affecting a very specific part of the brain, or the joints, for example. Bovine Viral Diarrhea Virus is another example of a birth-defect causing animal virus, causing a brain defect called cerebellar hypoplasia. This is where just one part of the brain– the part responsible for muscle coordination – doesn’t form.
It’s important to realize that not every birth defect – in people or animals – results from a viral infection. Genetic mishaps in development are more common causes. Instances of animal birth defects should be investigated by a veterinarian with a good relationship with their diagnostic lab, so that infectious causes can be differentiated from the random causes.
The Importance of Early Detection
Zika virus’s emergence also brings up an important aspect of disease detection. Zika virus is not new, having first been investigated by scientists in the 1940’s. Tests were developed and largely sat on the shelf while the virus disappeared into obscurity. Now, when people movement and insect survival have changed enough to create the right conditions for the disease to explode, that prior knowledge and tests were already there for scientists to call upon.
Like those Zika virus-discovering scientists, we’re still discovering novel new animal diseases that – right now – seem relatively obscure. Some recent examples are the characterization of a new form of influenza, Influenza D, at SDSU, and Kansas State’s recent discovery of a new virus that causes tremors in baby pigs. Neither one of those issues seems to have a significant effect on animal production – yet. If they ever do, though, we will already have access to diagnostic tests that can rapidly detect the disease, so big problems can be quickly stopped before they get out of hand. Continual discovery and monitoring of novel germs is important so we have the tools at the ready should they change enough to cause real problems in animals, people – or both.
Source: Russ Daly, DVM, South Dakota State University