The new threat
As countries in Latin America rush to contain the spread of the Zika virus, Wency Leung and Ivan Semeniuk take a look at the pandemic and the virus carrier
The Zika virus was first identified in rhesus monkeys in Uganda in 1947, and it was found in humans five years later, according to the World Health Organization. While there have been occasional outbreaks since, mostly in Africa and Asia, the latest rapid spread of the virus in the Americas has been explained, in part, by the proliferation of its carrier, the Aedes aegypti mosquito.
The virus is a flavivirus, related to dengue. Symptoms of a Zika virus infection are mild – it's estimated 80 per cent of those infected experience no symptoms at all – and deaths are extremely rare. However, its possible link to a spike in babies born with microcephaly, or abnormally small heads, has prompted widespread concern.
What does it do inside the body?
The Zika virus enters the blood with a mosquito bite. Like any virus, it can't replicate on its own. But, once it gets inside the host's cells, it hijacks the host's machinery for making nucleic acid and protein, and then creates copies of itself, explains David Patrick, director of the school of population and public health at the University of British Columbia.
As with any virus, he says, the illness the host experiences is a combination of the body's immune response and what the virus does to the cells while it's replicating.
Symptoms of a Zika infection include low-grade fever, headache, skin rashes and conjunctivitis, or redness and inflammation of the eyes.
The World Health Organization says while there's increasing evidence of an association between the Zika virus and microcephaly in babies, it's still not clear whether the virus is to blame.
Mario Tama/Getty Images
How long does the virus last inside the body?
Zika and related viruses do not survive long. Symptoms typically last between two to seven days.
"They're not like a chronic viral infection in the body," Dr. Patrick says, noting they tend to last only weeks before the infected person's immune system fights them off.
Is it sexually transmitted?
Sexual transmission of the Zika virus has been reported in two cases, according to the European Centre for Disease Prevention and Control. The WHO also notes there is some evidence that it can be passed from person to person through blood transfusions and during childbirth. These modes of transmission, however, are very rare.
What's required to make a vaccine?
Scientists would first need to identify the Zika strains and then understand what parts of the immune system are protective against the virus, in order to design a vaccine that would stimulate that immune response and then to put the vaccine through safety trials, Dr. Patrick says. The Butantan Institute in Sao Paulo is leading the research to develop a vaccine, which could take three to five years, reports Reuters.
– Wency Leung
No one thought the most nerve-racking part of pregnancy would be the babymoon. But many parents-to-be are torn after warnings last week about the mosquito-borne Zika virus, which is likely to spread to all countries in the Americas except for Canada and Chile, the World Health Organization said on Monday.
Hardy and resourceful Zika-carrying mosquito has adapted to live off humans
When you look up close, there's no denying that Aedes aegypti is one sharp-looking insect, sporting a distinctive pattern of white-on-black markings.
"It's actually a beautiful mosquito," says David Severson, an entomologist at the University of Notre Dame who specializes in mosquito genetics.
But while the bug that carries the Zika virus, among other diseases, has few fans, it absolutely adores humans – so much so that it has adapted itself to living off of us entirely.
As mosquitoes go, it is an astonishingly hardy and resourceful species. A few thimblefuls of water here or there is all it needs for a breeding site. And, if the water dries up, Aedes aegypti eggs can survive in a dormant phase for months at a time. Just add water and voilà: instant mosquito larvae.
A "day biter" that is most active when its hosts are out and about, Aedes aegypti is not the kind of mosquito that people encounter only while trekking through the rain forest. It prefers to live where humans do and where it's not too cold or too arid. That includes just about every urban environment in the tropics and sub-tropics, a perfect set-up for transferring viruses such as Zika each time a female mosquito fills up with human blood.
In the Western hemisphere, where Aedes aegypti is thought to have arrived with the slave trade, only Chile and Canada are considered entirely free of the species for reasons of climate. By the 1960s, a massive campaign to bombard mosquito breeding areas with pesticides had achieved eradication in many Latin American countries, but since then, Aedes aegypti has roared back. Now, there are strains of the species with an inbuilt resistance to the chemicals that were once so effective against it.
And there are signs it is spreading. Dr. Severson was among the researchers who recently identified a population of Aedes aegypti living in Washington. And even with the U.S. capital blanketed by a record snowfall this week, there's little doubt that the local Aedes aegypti are biding their time – possibly by hiding out in the city's subway system or some other underground refuge – and looking forward to a warm, wet D.C. spring.
With climate change expanding the ranges of many tropical insects, it's possible Aedes aegypti will get closer to Canada in the future. By then, proposed measures to control the insect with genetic engineering may be in effect. In the meantime, any Canadian heading south is advised to remember he or she is a walking buffet for Aedes aegypti, the mosquito that loves only people.
– Ivan Semeniuk