Testing for Zika in clucky couples
Zika virus was first identified 70 years ago but largely flew under the medical radar because the symptoms were generally mild and self-limiting.
Then in 2015, an outbreak in Brazil appeared to be accompanied by a spike in Guillain–Barré syndrome.
Later that year, Brazilian researchers reported another alarming association when they linked Zika infection during pregnancy to microcephaly in newborns.
By May 2016, the WHO had concluded that there was sufficient evidence that Zika infection was a likely cause of congenital brain abnormalities, including microcephaly.
As a result, doctors need to understand the clinical implications of potential infection during pregnancy, and to provide appropriate counselling and referral for patients at risk of contracting Zika during their reproductive years.
Take, for example, the case of Melanie and Mark. Thirty-year-old Melanie was diagnosed with endometriosis in her teens.
She and her partner Mark had trouble falling pregnant, and after trying for several years, sought advice from an assisted fertility unit.
Their daughter is now two years old, and the couple recently made arrangements to begin another round of treatment in a few weeks in order to try for another pregnancy.
Mark works for a large pharmaceutical company and, last month, had a two-day business trip to Rio de Janeiro.
It was only after Mark returned, and his brother asked him jokingly whether he had picked up Zika virus, that Melanie and Mark realised the trip might impact on their pregnancy plans.
What is Zika virus?
Zika virus is a mosquito-borne flavivirus first identified in monkeys in Uganda in 1947.
It is transmitted via the bite of an infected mosquito from the Aedes genus, mainly Aedes aegypti.
These are the same mosquitoes that act as vectors for dengue, chikungunya and yellow fever. They differ from the mosquito species that carries malaria since they prefer to feed during the daylight hours.1
The female mosquitoes feed almost exclusively on humans, whereas male Aedes mosquitoes feed only on fruit and therefore do not spread disease.
Females require the nutrients present in blood to produce their eggs and a single female produces up to 500 eggs over her two-week life span. She lays these in water — sometimes as little as it takes to fill a bottle top — and the eggs can remain dormant for up to six months.
When not feeding, the Aedes mosquito likes to rest in cool, dark places. Humans have provided an ideal environment for them within their houses and shaded gardens.2
Where does Zika virus occur?
Outbreaks of Zika virus in humans have been reported in tropical areas throughout Africa, the Americas, Asia and the Pacific. Zika virus was recently found in mosquitoes in Fiji.
Up until December 2017, a total of 134 cases of Zika virus had been reported in Australia, with 102 of those cases notified in 2016.3
The WHO publishes a regularly updated table, categorising countries according to the status of Zika virus transmission (see online resources box).
According to the Australian Department of Health, travellers should be advised a country is “Zika affected” if it is WHO category 1 (where Zika has recently first occurred and is spreading currently) or WHO category 2 (where Zika has been present for a longer time, and cases may or may not be reported, but there is no evidence that the virus has gone — see table.)
Please click to expand the table:
Zika virus transmission
Once the Aedes mosquito consumes blood from a human who has Zika virus, they can potentially transmit the virus to anyone else on whom they feed.
In addition to transmission via mosquitoes, sexual transmission of Zika virus has also been documented.
There is growing evidence that Zika virus is present in the semen and urine for a lot longer than it can be detected in the blood.4
In one case report, Zika virus was not cleared from the semen of a man with a confirmed infection until nearly six months after his acute illness had resolved.5
This means that an infected male can potentially transmit the virus to an uninfected partner for up to six months.
Women appear to clear the virus more quickly, being free from the virus within two months.
Therefore, current advice is that women delay pregnancy for two months after returning from a Zika-prone area regardless of whether they have symptoms.6
Symptoms of Zika
Eighty per cent of those infected with Zika virus are completely asymptomatic.7
The remaining 20% will usually develop a mild flu-like illness and may be symptomatic for up to a week.
The viral incubation period is typically 3-12 days.
Symptoms may include low-grade fever, fatigue, maculopapular rash, arthralgia/myalgia, headache and conjunctivitis.
Most patients with a suspected Zika virus infection require only supportive treatment, rest, fluids and analgesia.8
Protection against mosquito bites is a key measure to prevent Zika virus infection in countries where the infection is endemic.
Preventive measures include wearing long-sleeve shirts, long pants, socks and shoes, and frequently applying repellents — such as DEET and picaridin — to exposed skin.
Clothing can be treated with permethrin, which should be reapplied after laundering. Sleeping in air-conditioned rooms or under nets provides additional protection.8
In Australia, the Aedes mosquito is only seen in Queensland.9
This makes it extremely important that travellers from high-risk Zika virus areas returning to Queensland maintain strict protection against mosquito bites for four weeks after their return so as to minimise the risk of carriage in local mosquitoes and an outbreak in that state.8
There is no vaccine as yet, but a purified inactivated virus vaccine has recently entered phase I clinical trials to test safety and efficacy.
Testing for Zika virus is performed at all state public health laboratories in Australia.
If Zika virus infection is suspected, it is important to seek expert advice from the pathology provider and an infectious disease specialist since testing algorithms are fairly complex.
The Department of Health and WHO have published guidelines to assist practitioners in making investigative and treatment recommendations (see online resources box).
All symptomatic patients who have recently travelled in a Zika virus-prone area should be tested for the virus.
This is even more important if that traveller is pregnant or part of a couple planning a pregnancy.
If a patient presents within a week of symptom onset, serum and urine nucleic acid testing (for example, PCR) provides the most reliable diagnosis, although WHO testing guidelines also recommend performing serology to establish a baseline (see online resources at the end of this page).
Perform concurrent serological and PCR testing for other mosquito-borne infections, such as dengue and chikungunya, since cross-reactivity with Zika tests can occur.
Levels of Zika virus in the blood fall rapidly and from seven days after symptom onset, a negative Zika virus serum PCR test cannot reliably rule out infection, although the virus is generally detected in the urine for longer.10
One week after symptom onset, the diagnosis of Zika becomes dependent on serological testing.
In general, the detection of IgM to Zika virus in the absence of IgM to dengue or other cross-reactive viruses is suggestive of recent infection, but in some people, IgM persists for several months.
However, in the case of recent exposure, a significant rise in Zika virus IgM in convalescent serum (two weeks after first sample) provides additional confirmation.
It is important that the pathologist is provided with any history of previous flavivirus vaccination (such as Japanese encephalitis or yellow fever) or previous flavivirus infection (such as dengue) to aid them in the correct interpretation of the test results.10
So how to advise Melanie and Mark?
If this couple were not imminently planning a pregnancy, the advice would be that no testing is needed, but that they should initiate safer sex practices (use of condoms for any penetrative intercourse), as well as an effective method of contraception in order to avoid falling pregnant for six months.
Because this couple is planning a pregnancy within that time frame, arranging Zika virus testing for Mark can be justified.
As always, history is important. In this case Mark and Melanie are both well and report no symptoms suggestive of Zika virus infection. Mark reports never previously having had a flavivirus infection or vaccination.
On questioning, the couple has had unprotected intercourse on several occasions since Mark’s return, but Melanie’s pregnancy test is negative.
Perform a repeat pregnancy test three weeks after their last unprotected intercourse in order to rule out a very early pregnancy.
Despite the fact Melanie has had difficulty falling pregnant in the past, it is still important to advise that protected sex continues until Mark tests negative for the virus.
Mark undergoes PCR testing for Zika virus on both blood and urine specimens, as well as serology at four and six weeks after his last potential exposure to the virus.
Thankfully, he is negative to Zika virus on all serological and PCR tests, making transmission to a sexual partner unlikely.
Had Mark tested positive, then Melanie would also have been counselled to consider testing.
Although an infectious diseases specialist advises their risks are low, in the end the couple decides that they will wait the six months before proceeding with their plans for pregnancy.
Dr Foran is a sexual health physician and co-ordinator of undergraduate and postgraduate courses in women’s health at the University of NSW.
References (accessed February 2018)
- WHO. Media Centre Fact Sheet.
- Oxitec Corporation. Five Facts You Need to Know About Aedes Aegypti.
- Department of Health. Summary Information About Overseas-Acquired Vector-borne Disease Notifications in Australia.
- Lancet Infectious Diseases 2016; 16:1106-07.
- Eurosurveillance 2016; 21.
- CDC. Zika and Pregnancy. Women and Their Partners Trying to Become Pregnant.
- New England Journal of Medicine 2009; 360:2536-43.
- Department of Health. Zika Virus. Information for Clinicians and Public Health Practitioners.
- Medical Journal of Australia 2009; 190:265-68.
- WHO. Laboratory Testing for Zika Virus Infection.