By Siouxsie Wiles 26/01/2016


A virus spread by mosquitoes and which has been linked to babies being born with smaller heads and brains in Brazil is making the news. Here’s a quick FAQ to bring you up to speed.

What is Zika and where has it come from?

Zika is an RNA virus that was first identified in monkeys in Uganda in 1947. The first human cases were reported in 1952 in Uganda and Tanzania. There were only a small number of reported cases after that, until the first documented outbreak in Yap in Micronesia in 2007. There was another outbreak in the Pacific in 2013. From the Pacific, Zika seems to have spread to the Americas via Easter Island, appearing in Brazil in April 2015. There is some mention online that Zika might have entered Brazil during the FIFA World Cup in 2014. Since April 2015, it’s estimated that between 440,000 to 1.3 million people in Brazil have been infected with the virus. The World Health Organisation (WHO) now lists Zika virus also present and locally transmitting in Barbados, Bolivia, Colombia, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Saint Martin, Suriname and Venezuela.

Update: Just found this reference that suggests entry of Zika to Brazil was via the Va’a World Sprint Championship canoe race, in which four Pacific countries, which had cases of Zika during the 2013/2014 outbreak, competed.

How is Zika virus transmitted?

The Zika virus is mainly transmitted to people by mosquito bite, although there are some reports of sexual transmission through the semen of infected men. Mosquitoes of the Aedes family are the culprits here. They can also transmit other viruses, including West Nile virus, Dengue and Chikungunya, but not the malaria parasite. That’s a different mosquito. Adult Aedes mosquitoes can live for 2-4 weeks depending on the environmental conditions. Female Aedes mosquitoes are daytime feeders; after taking a blood meal, a female will produce on average 100 to 200 eggs, depending on the size of the blood meal. A  female Aedes mosquito can produce up to five batches of eggs during her lifetime. The female mosquitoes pick up the Zika virus when feeding on an infected person, and then go on to transmit the virus to other people when they feed again.

What are the symptoms of Zika infection?

Until recently, the Zika virus was thought to give people a mild infection. About 2-7 days after a mosquito bite, 1 in 4 people develop symptoms which could include a mild fever, conjunctivitis, a headache, joint pain and a rash. But since October 2015, there have been over 3,500 babies born in Brazil with microcephaly – a quite uncommon complication of pregnancy in which babies brains don’t develop properly and they are born with a smaller head and brain. Microcephaly can cause convulsions, difficulty feeding and developmental delays. The rise in the number of cases correlates with the rise in cases of Zika infection in the general population. Researchers have also isolated Zika RNA from the placenta of a woman with a foetus with microcephaly, suggesting the virus can cross the placental barrier, and the amniotic fluid of two other pregnant women whose foetuses were diagnosed with microcephaly by ultrasound (1). The virus was also found in the blood and tissues of a newborn that died of microcephaly. It’s thought that women who are infected with the virus during early pregnancy are most at risk of transmitting it their developing baby.

The WHO is also investigating an increase of Guillain-Barré Syndrome (GBS) cases in El Salvador. GBS is an autoimmune disease caused by the body’s immune system mistakenly attacking the peripheral nerve. Symptoms include numbness, tingling, and pain, muscle weakness and, in severe cases, trouble breathing. The average number of GBS cases a year is usually 169, but in between the 1st December 2015 and the 6th January 2016, El Salvador reported 46 GBS cases, including 2 deaths.

What’s the treatment for Zika?

There is currently no treatment or vaccine for Zika. The main way to avoid infection is to prevent being bitten by mosquitoes and to try to stop Aedes mosquitoes breeding. Women in outbreak countries are currently being advised to delay getting pregnant.

How far is Zika going to spread?

One of the main ways Zika has spread is when infected people have traveled and been fed on by local Aedes mosquitoes, which then go on to infect other people. Bogoch and colleagues have made a model of where Zika might go next based on people leaving Brazilian airports. Their paper has just been published in the Lancet (2). Between September, 2014, and August, 2015, 9·9 million travellers departed from Brazilian airports for international destinations. The majority of these (65%) travelled to the Americas, while 27% travelled to Europe and 5% to Asia. The model suggests that Argentina, Italy, and some parts of the USA could start seeing seasonal transmission of Zika virus, while over 70 million people are living in the parts of Mexico, Colombia, and the USA that could see year round transmission of the virus. The fact that Brazil is set to host the summer Olympic Games in August this year is starting to worry some people.

Final destinations of travellers departing Brazil by potential for Zika transmission (from Bogoch et al).
Final destinations of travellers departing Brazil by potential for Zika transmission (from Bogoch et al).

What’s the risk to NZ?

According to the Ministry of Health website, we don’t have the right mosquitoes in New Zealand for the Zika virus to flourish here. The main risk to New Zealanders is travelling to countries with widespread Zika transmission. This list of countries seems to be growing by the day, but most relevant to New Zealanders is probably Samoa. The CDC is advising women who are pregnant, or trying to get pregnant, to postpone travelling to countries with Zika, and if this can’t be done, to take all precautions to avoid being bitten by mosquitoes. This means using mosquito nets, covering up arms and legs with long clothing, and using proper insect repellents that contain DEET or picaridin. Now is not the time to be relying on ‘chemical-free’/homeopathic repellents or nonsense vitamin B patches.

References:

  1. Oliveira Melo et al (2016). Zika virus intrauterine infection causes fetal brain abnormality and microcephaly: tip of the iceberg? Ultrasound in Obstetrics & Gynecology. DOI: 10.1002/uog.15831
  2. Bogoch et al (2016). Anticipating the international spread of Zika virus from Brazil. Lancet. pii: S0140-6736(16)00080-5. doi: 10.1016/S0140-6736(16)00080-5.