The Zika virus and risks of retinopathy
What is the Zika virus?
Why is everyone talking about the Zika virus? It cannot just be the Rio games. As ophthalmologists, we are just beginning to be aware of this virus, as it can cause a retinopathy which significantly affects the vision.
The Zika virus belongs to the Flaviviridae family, similar to Dengue virus, or Yellow Fever. It is passed on by the bite of an infected female Aedes species mosquito.
Although it was first described in Uganda in 1947, the first outbreak of the infection outside Africa was only documented more recently in Micronesia in 2007, and then there was an outbreak in French Polynesia in 2015. Brazil reported its first case of the Zika virus in 2013.
How did the Zika infection spread so quickly?
Because the population in those areas had not previously been exposed to the Zika virus, they did not have any immune defences against the infection. Because of the particular mosquito, the Aedes Aegypti, is found in those regions, it rapidly spread.
In October 2015, the health authorities in Brazil reported a significant increase in the number of babies born with microcephaly and raised the possible association of that observation with the outbreak of the Zika virus. In February 2016, the WHO declared the Zika virus infection a global emergency. Below you will find a summary of what we know about the potential impact of the virus on pregnant women:
- The Zika virus infection is asymptomatic in almost 80% of people.
- In 20% of individuals, the symptoms will be similar to a mild case of the flu.
- Cases of temporary loss of sensitivity and sometimes motor impairment in the hands and feet, called Guillain-Barre syndrome, have been described. These symptoms are usually mild and treatable. Guillain-Barre syndrome in itself can have complications in 10% of patients, especially if they have had previous Dengue fever.
- Symptoms usually appear 3-12 days after the bite and last one week at most.
- There is no evidence that pregnant women are more susceptible to get the infection, or that it is more dangerous for them.
- It is true that the Zika virus can be passed on to the foetus through the placenta.
- Transplacental infection probably has a higher risk in the first and second trimester.
- The primary foetal defect described is microcephaly, where the head circumference is two standard deviations lower than it should be for its gestational age.
- There are also cases of enlarged ventricle dilation, intracranial calcification, problems with the development of the neurones and retinopathy with a significant effect on the eyes.
It is that last point that we as ophthalmologists are concerned with.
For those babies that survive, they will clearly be mentally very subnormal but their eyes may also be affected. Although this is currently not a problem of any major importance in London, we are gradually seeing cases in Europe, where people have travelled to South America. Therefore, ophthalmologists over the next few years may well be seeing more patients with Zika virus.
At Clinica London, we have the well-known paediatric ophthalmologist, Ms Naz Raoof. She works very closely with two orthoptists, Gina Harris and Joe McQuillan, who help to measure the vision and she assesses the retina.
We also have Professor Michel Michaelides who is trained in inherited retinal disease and congenital retinal infections, which now includes Zika virus.