The new Zika virus threat has caused alarm among pregnant women around the world, due to the threat of those infected giving birth to babies with microcephaly, or small brain, which can cause brain damage and mental incapacity.
Zika virus has caused a rise of microcephaly in Brazil from 150 cases a year to 3700 cases since October last year. Zika virus has been implicated in other tragic pregnancy and neurological outcomes. These include miscarriages, stillbirths and neurological conditions such as Guillain–Barré syndrome, a creeping paralysis caused by an autoimmune disease that attacks the nerves.
There was a similar rise in the number of cases of post-viral infection of Zika virus survivors with Guillain–Barré syndrome in Brazil and El Salvador.
Zika virus was found by amniocentesis (amniotic fluid tests) in two pregnant women who had babies with microcephaly in Paraiba State in Brazil. The women had been infected during pregnancy.
However, as yet there is no definite proof that the Zika virus causes microcephaly. This requires further testing, but the virus is implicated.
Brazilian paediatrician Dr Vanessa van der Linda Mota, who was one of the first neurologists to suggest a link with Zika virus, said it may also be associated with malformation of the limbs, especially arthrogryposis, in which the joints are malformed so that arms and legs cannot fully extend.
Mosquitoes infected with Zika virus have been found in Puerto Rico, the Caribbean and Mexico. The virus has now spread to 22 countries beyond Brazil.
The World Health Organisation has declared Zika virus now constitutes a public health emergency of international concern. WHO director Margaret Chan said it would dedicate resources towards a huge effort to prevent pregnant women from becoming infected, as well as research to confirm the link.
The Zika virus is transmitted by a mosquito that has bitten an infected person. If someone becomes infected while travelling overseas, on returning to their own country the virus can transmitted when the infected mosquito bites to a whole new population.
So in poor living conditions it can spread like wildfire. The Zika virus is frightening as there is no vaccine and the only preventive measure is to not be bitten by mosquitoes.
There is only one genus of mosquito that can carry the virus, Aedes, however there are several species — Aedes aegypti, A. africanus, A. luteocehalus, A. albopictus and A. hensilli. They are aggressive daytime biters, prefer to bite people rather than animals, and live near people both indoors and outdoors. These mosquitoes typically lay eggs in and near standing water, in things such as buckets, bowls, animal dishes, flower pots and vases.
The Aedes aegypti species does not belong in the Americas. It is native to Africa, and was introduced to the Americas when Europeans invaded the New World. In the 20th century, mosquito control programs nearly eradicated the unwelcome menace from the Americas. As late as the mid-1970s, Brazil and 15 other nations were free of Aedes aegypti.
But despite the successes, eradication efforts were halted, allowing the mosquito to regain its lost territory. As we all know, it is very difficult to prevent being bitten by any mosquito, as often they can bite through long sleeved shirts and thin cotton clothing. In Australia, Aedes is only one of 300 types of mosquitos and is present in North Queensland, where outbreaks of Dengue fever have occurred.
Nature and history
Zika virus is related to Yellow Fever virus, Dengue virus, Spondweni virus, Japanese encephalitis and West Nile virus.
About 80% of people infected by the virus never know it as they have no symptoms. The other 20% have symptoms that appear 3 to 15 days after exposure to the virus.
Initially viewed as an innocuous and mild disease, the symptoms, which last from one-to-five days, include muscle pain, fever, headache, a skin rash, conjunctivitis or red eyes. It is the post-viral effects that are a worry, as the virus can be transferred to a developing foetus by an unknown mechanism.
It is rare for a virus to cause effects on the foetal brain, but a few are well known, such as cytomegalovirus, herpes, syphilis, rubella and toxoplasmosis.
Zika virus is not new, having been identified in rhesus monkeys in the Zika Forest in Uganda in 1947, again in 1948 in the mosquito, Aedes africanus and was first reported in humans in 1952 in Uganda and Tanzania. It was found in Nigeria in 1968.
Little was heard of the virus until 2007 when an outbreak of Zika virus was reported on Yap Island in Micronesia — 75% of the population were affected over 13 weeks with 185 suspected cases.
The Zika virus also caused a major epidemic in French Polynesia in 2013–14 with 10,000 cases together with Dengue and chikungunya, another emergent virus. This outbreak resulted in 100 cases with severe neurological and autoimmune complications.
New Caledonia reported cases that had been imported from French Polynesia in 2013. Genetic analysis of the virus revealed that the strain in Brazil was most similar to one that had been circulating in the Pacific Islands.
It has also been reported that the Zika virus can be sexually transmitted. Clinical and serologic evidence indicated that two American scientists contracted Zika virus infections while working in Senegal in 2008. One of the scientists transmitted Zika virus to his wife after his return home.
There is no evidence that it can be transmitted by breast feeding.
Zika virus symptoms are similar to other insect-borne viruses, Dengue fever and Chikungunya virus, so confirmation has to be done by molecular diagnosis.
Brazil had been on alert for an introduction of a new virus following the 2014 FIFA World Cup, because the event concentrated people from all over the world. However, no Pacific island nation with Zika transmission had competed at this event, making it less likely to be the source.
Zika virus may have been introduced after an international canoe event held in Rio de Janeiro in August 2014, which hosted competitors from various Pacific islands. Another possible route of introduction was overland from Chile, since that country had detected a case of Zika disease in a returning traveller from Rapa Nui (Easter Island).
There are now fears for the coming Olympic Games, to be held in August in Rio de Janeiro, with the prospect that the Zika virus will discourage thousands from attending.
Environmental damage, abortion laws worsen threat
Health Officials from El Salvador, Colombia, Ecuador, Brazil and even Jamaica, even though there are no reported cases there yet, have advised women to delay pregnancy for six months to two years to avoid a Zika infection.
The World Health Organization says it is likely that the virus will spread, as the mosquitoes that carry the virus are found in almost every country in the Americas.
Will this lead to a change in abortion laws, which are overwhelmingly restrictive, in these countries? El Salvador, for instance, does not allow abortion under any conditions, even rape. Colombia's national health institute reported there are 2116 pregnant women who are infected by the Zika virus. Abortion is banned in the country except in specific circumstances, such as a threat to the life of the mother.
How Zika virus might affect the brain is unclear, but a study from the 1970s revealed that the virus could replicate in the neurons of young mice, causing neuronal destruction. It is puzzling as to why no cases of microcephaly appeared during the outbreak of Zika virus infections in Polynesia.
Recent genetic analyses suggest that strains of Zika virus may have undergone mutations, possibly accounting for changes in its ability to infect mosquitoes or hosts.
Vast environmental changes are the cause of the spread of the virus. Deforestation, followed by agriculture and regrowth of small low-lying bushes, has provided a more suitable environment for the Aedes mosquito than that offered by pristine forests.
Increasing urbanisation, poverty and greater global travel have also created a fertile breeding ground. Climate change has also raised temperatures and humidity levels in areas that were previously below the threshold for mosquitos to thrive. For example, A. aegypti and A. albopictus have expanded their geographic range in the past 20 years.
In California, A. aegypti species was first detected in 2013 and their number has now tripled. There is little doubt that the virus can make it to Australia.