WHAT HAPPENED IN WUHAN?
People visiting a seafood and wild animal market a few weeks ago almost certainly picked up a species of virus from live wild animals on sale. This virus, a member of the Coronavirus family, causes fever, a cough and sometimes pneumonia.
It seems to be relatively easy to transmit between people and identified cases have risen sharply to well over 10,000 in a few weeks, most in the city of Wuhan with a few (so far) in other towns and countries.
Each infected individual is estimated to be infecting about three others. This rate needs to be reduced to near zero to eliminate the disease, but the incubation period is up to two weeks, during which time the virus can unwittingly be passed on.
In most people, the disease is mild, but there have been getting on for 300 deaths, mainly in those with compromised health. Although the fatality rate is only about 2% (compared with 70% for Ebola), an epidemic affecting, say, one million people could still result in 20,000 deaths.
It’s obviously important to interrupt its spread, hence the various steps that have been taken, including travel bans and quarantine for exposed individuals. The WHO has acted fast and declared an international health emergency (which it didn’t for nearly a year after the Ebola outbreak).
WHAT IS A VIRUS?
Viruses consist essentially of small amounts of genetic material, DNA or RNA, coding for a few genes, all wrapped in a protective coat of protein. They are not alive because they lack the machinery of cells that enables growth and reproduction but they can use the machinery of cells that they infect to reproduce. Viruses are therefore parasites on living organisms, from bacteria to whales.
There are about 1031 (1 followed by 31 zeroes) viruses on Earth, some 1021 times more than there are humans on the Earth.
HOW DO VIRUSES INFECT PEOPLE?
Once a virus is released from its host, it must survive long enough to reach another host and then be able to enter its cells. Some are transmitted by insect bites (e.g. yellow fever), others have to be transmitted in shared body fluids (e.g. HIV), while still others are capable of surviving on surfaces, such as skin (flu) or in fluid droplets from coughs and sneezes (colds).
The virus must enter the cells of its host to be able to reproduce and this relies on the coat proteins being able to attach to a protein in the cell membrane. Most viruses can only infect the limited range of hosts whose cells they have evolved to “recognise.” They can only jump the species barrier if the new host has cell proteins similar to those of their natural host.
HOW SERIOUS IS A VIRAL INFECTION?
The effect viruses have on their hosts ranges from mild (almost symbiosis) to lethal: it is a matter of what benefits the spread of their genes. For animal (including human) pathogens, the best solution seems to be for the virus to cause a mild infection that allows the host to pass on the virus to close contacts. Of course, even a mild infection can be serious for vulnerable individuals.
Some cause acute illnesses which may or may not be serious (e.g. common cold, flu, Ebola). Others can lie dormant, sometimes by incorporating their genetic material with that of their host, re-emerging from time to time to cause illness (e.g. shingles, cold sores); some cause or increase the likelihood of developing certain cancers (e.g. cervical cancer from human papilloma virus, liver cancer from Hepatitis C virus).
Most viruses co-exist with their hosts and cause few or no problems: viruses and hosts co-evolve so that both survive to pass on their genes. The major problem is when a virus jumps from one species to another which has not had time to evolve defences. Then the infection can be very severe, even life threatening. An example is myxomatosis in European rabbits.
In the 1950s, this killed over 95% of rabbits infected but resistance evolved in the surviving rabbits, while the virus evolved to become less virulent. It doesn’t help the survival of the virus if the host dies out.
WHAT ARE CORONAVIRUSES?
Coronaviruses (CoVs), discovered over 50 years ago, are a family of viruses that cause zoonotic diseases (diseases in humans caught from animals). Other viruses that can jump the species gap and cause illness in humans include influenza viruses, as well the Ebola virus and HIV.
The family of CoVs seem to infect various populations of wild animals, often birds or bats, and some domesticated species. CoVs cause a significant proportion of common colds in humans. Other CoVs affecting humans include SARS and MERS, which both cause serious lung problems with high rates of fatality. The Wuhan virus is new to science and is known as novel coronavirus (2019-nCoV).
WHERE DID NCOV COME FROM?
The coronavirus outbreak in humans seems to have started in the Wuhan market, where many wild animals are sold (for food or traditional Chinese medicine), including bats, the probable natural host for nCoV. Many of the animals on sale, when tested, were found to be carrying the virus.
It is logical to assume that all the human cases can be traced back to this source, though infection could have arisen through contact with wild bats when capturing them. Habitat encroachment and destruction may also be routes for humans to be exposed to diseases endemic to wild animals (suggested in the case of Ebola).
TREATMENT OF NCOV INFECTIONS
There is no treatment for virus infections in general but vaccination works against specific viruses, such as smallpox. Research groups have been working on vaccines against viruses since the Ebola crisis and therefore have a bit of a head start in developing one for 2019-nCoV.
In this research, they have been supported by the Coalition for Epidemic Preparedness Innovations (CEPI), funded by governments and philanthropic organisations. It is difficult to see how this sort of vaccine would ever be developed by private drug companies reliant on profits.