THE ZIKA VIRUS II - ZIKA DISEASE
The first brief in this series described the geographical distribution of the Zika virus. This brief deals with the symptoms which result from infection.
Introduction
The Zika virus continues and has been found in 70 countries so far. The Zika illness is generally mild, with symptoms including a slight fever or rash, appearing a few days after a person is bitten by an infected mosquito. Many will not develop any symptoms at all, but some may also suffer from conjunctivitis, muscle and joint pain, and feel tired. The symptoms usually last from 2 to 7 days. They can be treated with common pain and fever medicines, rest and plenty of water.
Diagnosis is based on symptoms and the person’s recent history (e.g. mosquito bites, or travel to an area where the Zika virus is present). Laboratory testing can confirm the presence of the Zika virus in the blood. However, the diagnosis may not be reliable, as the virus could cross-react with other related viruses such as the dengue, West Nile, yellow fever and Japanese encephalitis viruses, carried by the same mosquitoes.
Complications
However, more serious effects of Zika infection have been identified recently. There is now scientific consensus that infection in a pregnant mother can cause congenital brain abnormalities, including microcephaly – birth with an unusually small head – in her infant. In January 2016, ophthalmological abnormalities were reported in three children with microcephaly and cerebral calcifications detected by CT scans and presumable intrauterine Zika infection. More recently, the WHO has reported a wider range of manifestations in infants: craniofacial distortion, spasticity, seizures, irritability, brain stem dysfunction, cortical disorders and ventriculomegaly (enlargement of the ventricles in the brain).
There is also consensus that infection can trigger Guillain-Barré syndrome. Guillain-Barré syndrome is a disorder in which the body's immune system attacks part of the peripheral nervous system. It creates weakness, first in the legs, and then in the arms and upper body. In severe cases, it can result in almost total paralysis, and is life threatening. It can last for several weeks. Most individuals recover from even the most severe cases of the syndrome, although some continue to have a certain degree of weakness. But between 3.5 and 12% of patients die from complications during the acute phase: sepsis, pulmonary embolism or cardiac arrest.
The Zika virus can cause other neurological syndromes: meningitis, meningoencephalitis, myelitis and Fisher syndrome. Meningitis is a serious disease in which there is inflammation of the meninges, caused by viral or bacterial infection, and marked by intense headache and fever, sensitivity to light, and muscular rigidity. Meningoencephalitis simultaneously resembles both meningitis and encephalitis, which is an infection or inflammation of the brain. Myelitis is inflammation of the spinal cord. Fisher syndrome is characterized by impairment of eye movements, abnormal coordination and loss of tendon reflexes.
In rare cases, the Zika virus can cause uveitis (inflammation of the middle tissue of the eye) which can lead to pain, blurred vision and, in severe cases, blindness.
Recent research
Fundamental research on the Zika virus and its effects has started to appear. The May 2016 edition of Science Magazine reported that experiments with mice show precisely how the virus slows foetal growth, damages the brain and leads to miscarriage. Studies of monkeys naturally infected with Zika are under way.
A Science News Bulletin from Rockefeller University on 18 August 2016 indicated, based on mice studies, that certain adult brain cells may be vulnerable to infection, as well as brain cells in foetuses. Among these are populations of cells that served to replace lost or damaged neurons throughout adulthood. These cells are also thought to be critical to learning and memory. Particularly vulnerable are the sub-ventricular zone of the anterior forebrain and the sub-granular zone of the hippocampus. The hippocampus is situated in the medial temporal lobe of the brain. It is just below the amygdala which is responsible for detecting fear and dealing with emergency events.
For a diagrammatic representation of the hippocampus see below:
The 6 September 2016 edition of LiveScience reported that mice studies show that genetic material from the virus can find its way into tears, raising the possibility of infection through contact with them.
Findings from mice and monkeys, though suggestive, do not automatically imply the same effects in humans. The vulnerability of human foetuses to the Zika virus is clearly established, but it may well be that infection has long term degenerative effects on children and adults as well.
Conclusion
The adverse impact of the Zika virus may stretch well beyond any mild immediate illness resulting from infection. In the view of the WHO, Zika virus infection and its associated congenital and other neurological disorders continues to be a Public Health Emergency of International Concern.
The final brief in this series will discuss what the World Health Organization and the United States Centre for Disease Control are currently doing to keep the infection rate under control.
Arvitha Doodnath
Legal Researcher
Helen Suzman Foundation
arvitha@hsf.org.za