Zika virus has been all over the news recently. This is due to its rapid spread to countries which has never had to deal with the potentially devastating virus. In fact, on February 1, 2016, the World Health Organization (WHO) declared Zika virus a Public Health Emergency of International Concern (PHEIC).
So, where did this virus originate and why is it suddenly spreading?
Origins of Zika Virus
Zika virus was discovered in 1947 in samples taken from a rhesus monkey. Its name derives from the location it was found, the Zika forest in Uganda. Soon after, it was discovered that the Aedes aegypti mosquitos were a vector for the virus. The first human cases of Zika were detected in 1952 and have since been reported in Africa and Southeast Asia.
In 2007, Zika spread across the Pacific to the island of Yap, resulting in a large outbreak. The first reports of locally transmitted infection in South America came from Brazil in May 2015. The virus then spread to other South American countries rapidly, through the range occupied by Aedes mosquitos.
On the last day of 2015, the United States reported the first confirmed case of locally acquired Zika infection in Puerto Rico. The first known case of Zika virus transmission in the United States was in February of 2016. To date, there have been over 500 cases of Zika reported in the United States, all of which were travel-associated.
Transmission of Zika
By now, it is well accepted that the main method of Zika transmission is through the Aedes aegypti mosquito. These mosquitos can bite up to five people in one blood meal, lending to the rapid spread of the disease. Though these mosquitos can travel several hundred kilometers over the open ocean, Zika virus infections are expected to be carried worldwide by international travel or trade involving an infected person or mosquito.
Surprisingly, the virus has also been confirmed to be sexually transmissible. This was found as individuals who have not travelled outside of the United States contracted the virus upon being intimate with their (male) partners who have travelled to Zika-infected countries. It’s currently unknown whether or not Zika can be transmitted through saliva or vaginal fluids.
The most common symptoms of Zika are fever, rash, joint pain, or conjunctivitis (red eyes), muscle pain and headache. Most people won’t present with any symptoms at all, but for those that do, the illness typically subsides within a week.
Link to Brain Damage in Infants
The common symptoms of Zika virus infection don’t sound so bad, but for couples expecting a child, the effects of Zika are frightening. In April 2016, it was confirmed that Zika virus infection is the direct cause of the Brazil’s outbreak of microcephaly, a condition in which infants are born with an abnormally small head. Microcephaly can result in cognitive deficits, developmental delays, and dwarfism.
For some babies in utero, Zika virus infection has been shown to result in the absence of convolutions (folds) in the brain. This is significant as the folds are what increase the surface area of the brain, allowing more neurons to exist. The virus can also cause underdevelopment of the corpus callosum, the structure in the middle of the brain that allows communication between the two hemispheres. As you can imagine, this can cause motor difficulties and loss of hand-eye coordination.
When a pregnant woman is infected with Zika, it can also cause a range of developmental problems in the child. For example, the child may have abnormalities in vision and hearing, even without microcephaly. Unfortunately, these neurological effects are permanent, though early childhood intervention programs may be able to help strengthen the child’s abilities. Not every pregnant woman infected with Zika will deliver a baby with these problems, but they are at an increased risk.
Link to Brain Damage in Adults
Also discovered in April 2016, was that Zika virus can cause a rare autoimmune disorder that attacks the brain and spinal cord in adults. Autoimmune disorders occur when the immune system overreacts and begins to attack the body’s own tissues, resulting in inflammation. Zika causes acute disseminated encephalomyelitis, or ADEM, which can lead to the destruction of white matter in the brain. The symptoms of ADEM resemble those of Multiple Sclerosis (MS) and include loss of vision, weaknesses and loss of balance.
The question now remains as to why Zika virus has such a strong link to disorders of the brain. Hopefully, future research will help to shed some light on the underlying mechanisms regarding the issue.
Currently, there is no vaccine to prevent or medicine to treat Zika virus. However, many scientists are working on the development of a vaccine. In the meantime, treatment is focused on treating the actual symptoms of the infection. For example, since Zika may cause fever or pain, it’s important to stay hydrated, take acetaminophen and get plenty of rest.
On an individual level, the most obvious answer to the question of prevention of Zika virus is to avoid being bitten by mosquitos carrying the Zika virus. Of course, avoiding Zika-affected countries is probably your best bet for doing this, but sometimes, we can’t avoid travelling to these areas. Thankfully, there are several measures which can be taken to prevent mosquito bites, including using effective insect repellent and wearing clothing that fully covers your arms and legs.
Since Zika virus can also be spread through semen, it’s important that couples take caution to practice safe sex. It has been advised that men who know they’ve probably been infected with Zika should not have sex without wearing a condom for six months.
The outlook with regard to the current Zika virus outbreak in the Americas is uncertain. Herd immunity, which is the indirect protection that occurs when a large proportion of the population has become immune to an infection, will eventually slow the spread of the disease. However, there will still be a need for immediate and long-term prevention and control strategies. Currently, there are a large number of drug manufacturers and research institutions who are working on a vaccine but it’s at least a year away.
We also need to consider the changes in weather patterns and the environment that may influence Zika infections by affecting how quickly Zika virus replicates in its mosquito host, the life cycles of mosquito vectors and the distribution of the mosquitos themselves. The Southern states are more vulnerable to Zika virus as they are warm and humid.
Some experts are concerned that as summer nears, we may have local transmission of Zika virus. That is, people may get bitten and infected by a mosquito carrying Zika virus without leaving the United States. To prepare for this, it’s recommended that individuals install screens in their homes and limit mosquito breeding grounds (i.e. standing water) in their backyards.