Anyone watching the news at the moment would think that Zika virus has just been discovered and is about to cause widespread panic in the way that Ebola did in 2014. However Zika virus is not new, it was first discovered in the Zika forest in Uganda in 1947; apparently Zika means “overgrown” in the local Luganda language. However the Spice Girls seem to coin the term in “Wannabe”...I can’t get that tune out of my head since every sound-bite is on Zika virus!
In fact the CDC list many tropical islands and countries including 23 in Central and South America as having the virus http://www.cdc.gov/zika/geo/. This is not particularly surprising given that Zika Virus is transmitted by the same day biting mosquito species (Aedes spp.) that transmit Dengue and Chikungunya and these viruses are also endemic in these countries. Aedes mosquitoes breed in standing water such as water storage tanks and containers full of rain water. What I find surprising is that the rest of the known Dengue and Chikungunya regions do not have Zika virus outbreaks but I wonder if this is a case of if you don’t look for it you won’t find it!?
So what has changed, why is the media in a spin about Zika? It has been suggested that Zika Virus infection might be linked to birth defects in humans, in particular with microcephaly (abnormal brain development). Brazil reported its outbreak in April 2015 but more recently announced that they believe there is an association between the outbreak and a rise in birth defects. This possible effect on babies and its emotive imagery is the reason it has hit the headlines.
Zika virus infection is asymptomatic in 75-80% of people. Other people develop a low grade fever of 38-38.5oC (Dengue and Chikungunya tend to cause very high fevers of 40oC or more), a maculopapular rash, non-purulent conjunctivitis and arthralgia in the small joints of the hands and feet (as opposed to the large joints such as the knees with Chikungunya). Headaches and muscle pains are also common. It is uncommon for patients with Zika virus infection to require hospital treatment and deaths are very rare. The incubation period varies from 2 to 12 days.
Infections in pregnancy
As yet, no direct cause has been proven between Zika virus and microcephaly, although absence of evidence is not evidence of absence. The possible association between infection in pregnancy and the development of microcephaly in babies in Brazil is suggested by the increased number of cases of microcephaly during the current outbreak of Zika virus. So far there have been 180 cases of microcephaly reported in the 3 months from October 2015 to January 2016 compared to an average of 200 cases per year before this time; an approximately four-fold rise. However it must be remembered that this increase in documented cases is in the context of heightened awareness. There may be other reasons for the potential link e.g. what is the potential effect of the chemicals being used to control mosquitoes? Are case demographics suggestive of contaminated living conditions, poor nutrition, other infection or even medication etc? There is no information whether normal babies from similar demographic backgrounds have also been exposed to the virus. Further work must be done to show cause and effect.
No association has been detected previously in other outbreaks such as in French Polynesia in 2014, but this is the first time that a country with a large population and good surveillance infrastructure has been affected. Brazil therefore provides an opportunity to prove or disprove a link. It is worth remembering that there is an association between other viruses and fetal abnormalities e.g. Rubella causing heart defects, congenital cataracts and microcephaly and therefore it is entirely plausible that Zika virus might also cause microcephaly.
How is Zika virus infection diagnosed?
Zika virus infection is detected by either finding evidence of the virus or the immune response to the virus.
If a patient presents within 7 days of the onset of symptoms consistent with Zika virus (see above) who has been to a country where Zika virus is known to be circulating then a serum or EDTA sample can be tested by PCR for the virus. If the patient presents later than 7 days then serum can be tested for the presence of antibody against the virus. However there can be some cross reaction to other viruses such as Dengue and West Nile viruses.
If the patient is pregnant then Public Health England recommends fetal ultrasound (repeated after 4 weeks if initially normal) and serum/EDTA/urine for PCR. If the PCR is positive or inconclusive or the ultrasound is abnormal then the patient should be referred to fetal medicine specialists
There is no specific treatment for Zika virus, and no interventions that have been shown to prevent mother to fetus transmission.
The current strategies to prevent possible fetal abnormalities as a result of Zika virus infection are:
- Pregnant women should avoid travel to areas where Zika virus outbreaks are occurring
- If in an area with ongoing Zika virus transmission then take precautions to avoid being bitten by the Aedes mosquitoes such as covering up in the daytime, using insect repellents during the daytime and eliminating standing water.
So what should I do for my patients?
There are a number of areas where we should advise and manage patients in regards to possible Zika virus infection:
- Travel advice – warn pregnant patients to avoid travelling to areas with Zika virus outbreaks unless it is essential as per Public Health England guidance and give clear instruction to all patients in how to minimise the risk of being bitten by daytime biting Aedes mosquitoes as we would for Dengue or Chikungunya
- Reporting illness – provide information to travellers about the symptoms and signs of Zika virus infection
- Pregnancy – be alert to the possibility of Zika virus exposure, ask pregnant patients for a travel history and follow the PHE guidance for investigating at risk pregnant women
It is important that we don’t go overboard with our response to Zika virus. At the time of writing, only a total of 6 cases of Zika virus have been identified in the UK and no associated cases of fetal abnormalities have been reported. We do not have the Aedes mosquitoes capable of transmitting Zika virus in the UK so whilst we might “import” the occasional patient we won’t get ongoing transmission as it is not normally spread from person to person. The important point is to spot the returning traveller who might be pregnant and start investigating and managing them.
Whilst Zika virus may eventually be shown to cause microcephaly, it is worth keeping our response in perspective at the moment. In 2015, malaria killed an estimated 306,000 under-fives globally, including 292,000 children in the African Region, there were 3 million cases of Dengue globally last year with about 1% mortality (30,000 deaths) and in the Ebola outbreak in West Africa there have so far been 28,638 cases and 11,316 deaths.