The Killing Fields

With the majority of affected areas concentrated in Asia, other regions were spared the devastation of SARS and MERS

Revisited

No.110 Issue 2/2015

Title

The Smallest Slayers

Contagion in our midst

Text

Stanley Perlman, MD, PhD Human beings have been infected with viruses probably since we first evolved as a species. But as viruses are extremely small, it is only in the last 50 to 100 years that they were even characterised to a significant extent. However, the relationship between humans and viruses has changed over the past few years and some viruses that previously infected only wild or domesticated animals have now jumped the species barrier to infect humans (zoonotic viruses). This occurred partly because humans have invaded the habitats of different animals. In addition, healthcare providers have become better at diagnosing these virus infections. Two of the most striking examples of this species jumping are Severe Acute Respiratory Syndrome CoV (SARS-CoV) and Middle East Respiratory Syndrome CoV (MERS-CoV). Both of these coronaviruses originated

in bats, where they cause mild or subclinical infections. Both then infected an intermediate host, which probably served as the source for human infection.

SARS-CoV spread from bats to infect animals such as Himalayan civets and raccoon dogs in wet markets in China, and subsequently to human populations. It took a confluence of (unlucky) events for SARS-CoV to become as severe a human infection as it did and to spread to places all around the world. SARS-like CoV probably crossed into human infections many times in the Chinese wet markets, but widespread transmission required infection of a highly susceptible individual, who spread the virus to others. Molecular epidemiological studies showed that the virus was rapidly adapting to the human host during the 2002–2003 epidemic before it was controlled.