Definition of the Zika Virus
The Zika Virus is a single-stranded DNA virus that belongs to the Flaviviridae family, the genus Flavivirus which also includes dengue, yellow fever, West-Nile and Japanese encephalitis viruses. These viruses are considered arboviruses, in which they are transmitted by infected arthropod vectors (such as a mosquito) when they feed on an infected host, carrying the virus in their saliva and transmitting it to another host.
History of the Zika Virus
The story of Zika virus started in April 1947, when a group of scientists were observing the temperatures of rhesus monkeys as a part of a study hunting for a yellow fever virus in the Zika forest of Uganda near Lake Victoria. One of the rhesus monkeys (identified as Rhesus 766) developed mild pyrexia (39.7°C) and was kept under observation. A blood sample was taken from Rhesus 766 and injected intracerebrally into a group of mice, where signs of sickness had been observed on them 10 days later after the injection, and a filterable transmissible agent was isolated from the brain of these mice.
In January 1948, researchers attempted to isolate the virus from trapped Aedes africanus mosquitoes in the Zika forest, and they ground them up in a blood-saline solution and inoculated it subcutaneously into Rhesus 758 where it developed a mild fever. The researchers isolated the same transmissible agent that had sickened Rhesus 766 and named later: the “Zika Virus.”
The first human case infected with the Zika virus was identified in Nigeria in 1954 during an epidemic of jaundice that was suspected to be yellow fever, where a 10 year old Nigerian female developed fever, headache, but no jaundice. The symptoms resolved spontaneously within three days. A sample of her blood was injected intracerebrally into a group of mice, later they developed signs of illness, and the Zika virus was identified in them using neutralization tests.
From 1951 to 1981, human cases of the Zika virus infection had been reported across other African countries and parts of South East Asia.
From its discovery until 2007, only 14 cases had been diagnosed with the Zika virus disease inside Africa and South Asia.
The first outbreak of the Zika virus outside Africa and Asia was reported in 2007 in the Federated Republic of Micronesia, where 49 cases had been confirmed to have the disease.
In 2013, another outbreak occurred in French Polynesia with 333 confirmed cases, and it was associated to an increase in a serious neurological disease Guillain-Barre Syndrome.
In 2015, a large outbreak of the virus was reported in North-eastern Brazil, and a few months later, clinicians started to notice an unusual increase in numbers of infants with microcephaly (small heads) that have been attributed to pregnant mothers infected with the Zika virus.
The virus started to spread from Brazil to much of South and Central America and the Caribbean.
Transmission of the Zika Virus
The Zika virus is a mosquito-borne disease which spreads mainly by the Aedes genus (Aedes aegypti and Aedes albopictus). The virus has been spreading inside many African countries and outside to America, mainly through infected mosquitoes biting healthy people. These mosquitoes are very active during the daytime, but can also bite people at night.
The main problem is that the Zika virus causes only mild flu-like symptoms that resolve spontaneously within days, therefore, infected patients may not realize they have the Zika virus in their blood. An infected individual can also be a source of infection to healthy mosquitoes.
In 2015, more than 3500 microcephalic cases have been reported in Brazil after the large outbreak of the Zika virus there, and the virus was isolated from the amniotic fluid of at least two pregnant women, suggesting a strong relationship between the Zika virus and the microcephalic infants. It was suggested that mothers infected with the Zika virus during the early stages of labor, can transmit the virus into her infants though the placenta.
There have been two reported cases of sexually transmitted Zika virus infections. It was found that the virus presents longer in semen than the blood.
There have been multiple cases reported to be infected with the Zika virus through blood transfusions in Brazil, but no cases have been reported in the United States. These reports are currently being investigated.
Clinical Manifestations of the Zika Virus
The Zika virus can either cause a mild flu-like illness or even no symptoms. About 1 in 5 people infected with the Zika virus will have non-specific symptoms, such as:
- Mild pyrexia
- Arthralgia (joint pain)
- Myalgia (muscle pain)
- Conjunctivitis (red eye)
- A headache and malaise
No incubation period has been identified for the Zika virus, and the virus usually lasts from 3 days up to 1 week, and subsides spontaneously without treatment. Infected patients usually acquire lifelong immunity against the virus.
There haven’t been reported complications with the Zika virus disease, except the large increase in cases with the neurological disease, Guillain-Barre Syndrome, during the French Polynesia outbreak in 2013, and the large increase in microcephalic babies in pregnant mothers with a history of traveling to areas endemic with the Zika virus infection.
Diagnosis of Zika Fever
The clinician should suspect the Zika virus Infection in any patient that presents with fever, rash, arthralgia, conjunctivitis and headache, with a recent history of traveling to an area endemic with the Zika virus, especially pregnant mothers due to the risk of microcephaly.
The clinical manifestations of the Zika virus disease are similar to dengue and chikungunya diseases which are also transmitted by the same mosquitoes, therefore the diagnosis can only be confirmed by the laboratory isolating the Zika virus RNA from the blood or other body fluids, such as urine or saliva.
Prevention of Zika Fever
No vaccine has been established to protect against the Zika virus disease, and the only effective preventive method is avoiding getting a bite by infected mosquitoes.
The CDC recommendations to all individuals traveling to areas where the Zika virus is endemic are:
- Wear clothes with long sleeves and pants, socks and hats to cover the whole body.
- Avoid sleeping outdoors, and sleep in a room with air-conditioning where the windows and doors have physical barriers (screens) to prevent the entry of mosquitoes inside.
- If you have to sleep outdoors, use a mosquito net to avoid getting a bite by infected mosquitoes.
- Use insect repellent.
- Covering the clothes with permethrin, but avoid applying the permethrin on the skin.
The CDC recommends postponing travel to areas endemic with the Zika virus for pregnant women due to the risk of delivering their babies with microcephaly. It was recommended to strictly apply the previously mentioned preventive methods in pregnant women who must travel to these areas, and to tell her health care provider.
Sexual transmission of the Zika virus disease has been reported in a few cases, therefore, it’s recommended to individuals traveling to endemic areas to abstain from sex, or using condoms for men.
Individuals who already have the Zika virus should avoid getting a bite by mosquitoes in the first week, as the virus exists in their blood and can be transmitted to other people.
During a Zika virus outbreak, authorities should spray insecticides to kill the mosquitoes.
Treatment of Zika Fever
The Zika virus causes a mild illness that resolves spontaneously within 3 to 7 days. There is no specific treatment for a Zika virus infection, and symptomatic treatment can only be provided to affected individuals:
- Enough bed rest.
- Analgesics and antipyretics, such as acetaminophen, to relieve the fever and the associated join and muscle pain. Avoid talking Non-Steroidal Anti-Inflammatory Drugs (NSAIDs).
- Fluid supplementation should be provided to avoid dehydration, especially in tropical areas.