Simple goes bad

Vet Advice with Dr. Ron Clarke

Earlier this year, the World Health Organization declared the novel coronavirus, 2019-nCoV, a public health emergency. It’s just another stop on the Zoonotic Highway, a simple respiratory infection that matured into a global health emergency. Health agencies around the world have tried to smother the threat, but efforts seem flawed. History repeats itself: the novel coronavirus now enters round three and it won’t be the last outbreak to move from animals to humans.

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Science writer David Quammen says the new coronavirus, which has killed thousands in China and caused a lockdown of 56 million people, is a serious zoonosis. Its overall impact is still a big question.

The Wuhan outbreak started in a “wet market” where people pursue their desire for exotic flesh in the form of bats, snakes and civet cats. In doing so, they inadvertently become potential amplifiers of catastrophic pathogens. In the case of the new coronavirus, researchers believe that the virus may have originated with horseshoe bats in China, then potentially spread to other animals that ended up as food.

“Control of infectious agents becomes much, much more difficult when there’s an animal host,” Quammen says. “This novel coronavirus — whether or not it turns out to be a huge catastrophe, or something we can control — won’t be the last one.”

Quammen’s 2012 book, Spillover: Animal Infections and the Next Human Pandemic, traces the rise of different zoonoses around the world, including AIDS, Ebola and severe acute respiratory syndrome (SARS). He says that one of the first questions that arises with any zoonosis pertains to the animal host and how it’s being transmitted.

Coronaviruses are a large family of viruses known to cause illness ranging from the common cold to more severe diseases such as Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS). First described in detail through the 1960s, the coronavirus gets its name from a distinctive corona or crown of sugary-proteins that project from the envelope surrounding the particle. The coronavirus identified in Wuhan, China, is a new coronavirus, until now not identified in humans.

Coronaviruses are common in many non-human hosts, including camels and bats. Only rarely do these agents evolve to infect humans and then spread between humans. Recent examples include SARS-CoV and MERS-CoV.

Why only certain coronavirus species infect humans is a mystery.

The R0 or Rnaught is a mathematical term indicating how contagious an infectious disease is. The R0 is defined as the expected number of secondary cases produced by a single (typical) infection in a completely susceptible population. The R0 for 2019-nCoV is high, an indication of why China’s number of infectious cases quickly swelled. Outside China, several countries have reported cases.

One patient, admitted to a hospital in Wuhan, China, infected at least 10 health care workers and four other patients with the coronavirus that went on to sicken thousands and reach many other countries. The incident was a chilling reminder of the “super-spreaders” in outbreaks of other coronavirus diseases — patients who infected huge numbers of other people, sometimes dozens. The phenomenon is poorly understood and unpredictable, an epidemiologist’s nightmare. Super-spreaders led to considerable transmission of MERS and SARS inside hospitals.

Quammen notes that humans are the common link in all zoonoses: “We humans are so abundant and so disruptive on this planet. … We’re cutting the tropical forests. We’re building work camps in those forests and villages. We’re eating the wildlife,” he says. “You go into a forest and you shake the trees — literally and figuratively — and viruses fall out.”

Coronaviruses are not new. Coronaviruses are widespread pathogens affecting cattle (BCoV) resulting in economic losses to the beef and dairy industry throughout the world. The virus has been detected on all continents and exists serologically in over 90 per cent of cattle, suggesting most cattle are exposed through their lifetime. In a recent study, the presence of BCoV in lungs occurred second behind bovine herpesvirus (IBR).

In both beef and dairy herds, BCoV can be associated with calf diarrhea, calf respiratory disease, winter dysentery, respiratory disease in adult cattle and combined pneumonia and diarrhea in calves and adults. The clinical manifestation of disease syndromes are not solely linked to the virus itself. There are host and environmental factors at play, such as immunologic status, environmental temperature and secondary infections with other pathogens.

Two burning questions remain. First, how effective will the response to 2019-nCoV be? And how long will it take to develop a vaccine?

Critics fear lockdown measures may not be enough to control the spread. In addition to closing transportation, officials shut down a market in Wuhan selling live poultry, seafood and wild animals, which was thought to be the origin of the coronavirus, and later suspended the trade of wild animals nationwide. Schools have been closed, Beijing’s Great Wall is off limits and tourist packages from China have been halted. As always, drastic measures have unintended effects such as reducing access to hospitals, staff and supplies. China has also locked out experts who could help track the virus and prevent its spread. Travel bans and quarantines haven’t worked to contain other recent outbreaks. There is compelling evidence that if travel bans work at all, they’re less likely to work for respiratory viruses like this, because the viruses move too quickly.

A vaccine is still a year away — at minimum. Vaccines take time. After the SARS outbreak in 2003, it took researchers about 20 months to get a vaccine ready for human trials.

But with luck, researchers can work from past outbreaks to shorten the timeline. Since the Zika outbreak in 2015, researchers had brought the vaccine development timeline down to six months.

About the author

Columnist

Dr. Ron Clarke

Dr. Ron Clarke prepares this column on behalf of the Western Canadian Association of Bovine Practitioners. Suggestions for future articles can be sent to Canadian Cattlemen ([email protected]) or WCABP ([email protected]).

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