Zika: A mozzie virus hiding dark secrets

By Dr Eddy Bajrovic*

Zika. Sounds more like a DJ than a disease, right?

In fact, it’s a virus passed from a person who has it to another person who doesn’t through a mosquito bite.

The symptoms of Zika virus infection are similar to the other two better-known mosquito-borne virus infections, dengue and chikungunya, which are a risk for travellers visiting tropical and sub-tropical destinations.

Zika can cause a fever, rash and joint aches, but generally milder than those of dengue and chikungunya. In fact, many people have no symptoms and are not aware they’re infected.

So, while it’s been disconcerting to see Zika epidemics sweep through the tropical world – first through Africa and more recently the Pacific, Caribbean and the Americas – relatively few deaths were expected. Certainly less than chikungunya’s relatively modest toll and far lower than dengue, with its potentially fatal haemorrhagic version.

Risk to travelling pregnant women

However, it seems Zika may be hiding some sinister secrets.

- There are indications that it may cause the potentially severe auto-immune disease Guillain-Barre syndrome (GBS) after a small number of cases were linked to the condition, earlier in French Polynesia and now in Brazil. Sometimes triggered by an infection, GBScauses the body'simmune system to attack the body’s peripheral nerves, damaging the tissue that insulates them.

- More recently in South America, Zika infections have been linked to hundreds of cases of newborn babies with microcephaly. In October this year, the Brazil’s Ministry of Health announced a startling increase in the number of babies born with microcephaly since Zika arrived in May. Microcephaly is a neurodevelopmental disorder that leads to babies being born with smaller heads. The infant’s brain is underdeveloped, causing both intellectual and motor disabilities. There are various causes of microcephaly including transplacental infections with viruses such as rubella, herpes and the herpes-like virus, Cytomegalovirus. While it has never been linked to vector-borne diseases, samples taken from a significant number of the babies born with microcephaly have tested positive for Zika. This now raises the distinct possibility that infection during pregnancy can lead to Zika being passed to the developing foetus, causing microcephaly.

- Earlier this month, a Brazilian study revealed that Zika virus can be transmitted in blood, breast milk, and semen, providing another source of transmission which may pose an additional risk for women and couples trying to conceive.

New virus spreading rapidly

Official data from Brazil’s Ministry of Health reported this week advised that as of last Saturday (Dec 19), 2782 suspected cases of the microcephaly, including 40 deaths, had been reported by 618 municipalities in 20 of its 27 states. While the World Health Organisation is still investigating a link with Zika, Brazilian infectious disease specialists are convinced that the arrival of the virus in May and the soaring microcephaly rates is no coincidence.

Meanwhile, Zika outbreaks are raging across the Caribbean and Latin America, with one senior infectious disease physician predicting between 500,000 and 1.5 million cases in Brazil alone by the end of the year. Experts believe that, like dengue and chikungunya, it will infect millions of people (travellers have already taken it home) and become a permanent health risk for local people and travellers visiting the region. Read more

If there’s good news, it’s this: Like chikungunya (but not dengue), you can only get Zika once, although a person can get two or even three viruses at the same time.

Zika often misidentified

Let’s take a closer look at Zika and what it means to Australian travellers.

Zika is…a member of the virus family Flaviviridae. It’s related to the dengue,yellow fever,West Nile,and Japanese encephalitis viruses. In fact, it is often mistaken for its better-known, fever-causing ‘cousins’ and is frequently misidentified as dengue (and vice versa) in lab tests because of antibody cross-reactivity.

It was first identified… and named in 1947 from tests done on a sick rhesus monkey found in the Zika Forest of Uganda but a human infection wasn’t confirmed until 1968. In the following decades it has spread across much of Africa, as well as into the Pacific and parts of Asia, including India, Malaysia,the Philippines, Thailand, Vietnam,and Indonesia.

Zika’s spread by… female Aedes aegypti and Aedes albopictus Asian Tiger mosquitoes, two aggressive, daytime feeders that live close to humans, their favourite source of the blood meal they need for the development of their eggs. Able to lay eggs in a thimble-full of water, these two mozzies are also responsible for spreading dengue fever, yellow fever, West Nile fever, chikungunya, and eastern equine encephalitis, along with many other less notable diseases.

If you get infected… the symptoms of Zika can range from include dengue-like joint aches, to red eyes, headaches (particularly behind the eyes), a rash, and fever. Some Zika patients lose their appetite, have swollen lymph nodes, diarrhoea or constipation, dizziness, and abdominal and/or back pain. Males can have blood in their semen, which is capable of transmitting the virus. Get bitten by an infected mosquito early in your overseas trip and you could get sick while still travelling as illness can develop 3-12 days after the bite of an infected mozzie and last 4-7 days. The tell-tale rash usually emerges 3-5 days after the fever develops. Typically, within 2 days the rash fades and within 3 days the fever is gone. People with Zika often feel particularly tired even after the other symptoms pass. Read more

There’s no vaccine… or any preventative drug to protect against Zika. Doctors can only treat the symptoms and may recommend non-steroid anti-inflammatories and/or non-salicylic analgesics.

Zika risk areas include the Pacific, much of Asia and Africa, the Caribbean, and Central and South America, where an epidemic is gathering pace. Zika often circulates at the same time as dengue and chikungunya. Being an emerging virus, epidemics typically involve entire communities. With such intense and widespread epidemics, there’s a distinct risk of infection for visitors, even those on short stays in upmarket urban areas. This risk is now even more of a concern for pregnant travellers, who should reconsider the need to travel to regions where Zika is prevalent. If they do go, effective anti-mosquito measures are essential.

Make avoiding bites second nature

For any Aussie traveller visiting a tropical country, taking steps to avoid insect bites needs to become second nature. These include:

– Applying an insect repellent containing an effective ingredient such as DEET (30-50% formulations for adults, or 10-20% formulations for young children and infants as young as 2 months of age),   Picaridin, IR3535, or preparations containing extract of lemon eucalyptus oil when mosquitoes are about outdoors – especially at dawn and dusk when they are most active.
– Wearing long, loose-fitting, light-coloured clothing at those peak feeding times.
– Sleeping under a treated bed net if you’re staying in a tent or in budget accommodation without screened doors and windows, or air-conditioning. You can buy atreated netor purchase a DIY kit to treat both your net and clothing with permethrin, a safe contact insecticide. Used in conjunction to your personal insect repellent, permethrin creates an additional barrier that repels and ultimately kills biting bugs that land on your bed net or clothes.

If you reduce the number of times you get bitten, you reduce the chances of an insect-borne illness bringing your holiday or business trip to an abrupt end.

* Dr Bajrovic is the Medical Director of Travelvax Australia.

Routine, recommended and required travel immunisations – along with expert tailored advice and information – are available during a pre-travel medical consultation at Travelvax Australia’s clinics nationwide. For advice or to make an appointment, please call 1300 360 164  (toll-free from landlines) during business hours.