South America… With the promise of ruins, culture, and natural wonders, it is a popular destination on backpackers bucket lists. For decades, it has delighted travelers with mountains, rainforests, deserts, salt flats and enchanting festivals. Now many countries in South America have been infested by the Zika virus epidemic. In April 2015, the virus broke out in Brazil and quickly spread to neighboring countries in South America (Figure 1). In 2015, the epidemic affected over 50, 000 people in Brazil, and over 20, 000 in Columbia. I will be traveling to South America this coming summer. Like many backpackers, I am worried about contracting the Zika virus and the possible link to microcephaly.
Figure 1. Areas experiencing an outbreak of the Zika virus.
The Zika Virus
The virus is spread through mosquitos from the Aedes family. Infection leads to the formation of rashes, fever, joint/muscle pain, and inflammation of the eyes (conjunctivitis). The symptoms are relatively mild: only 20% of people infected show symptoms, symptoms rarely require hospitalization, and very rarely do people with the virus die Despite these mild consequences, there are a few reasons for concern:
- The Zika virus could potentially be an international problem due to the ease that it is transmitted via the Aedes
- The Zika virus is not curable. There is currently no immunization or antiviral medication to offer those that are infected. Therefore, treatment is focused on relieving symptoms.
- Diagnostic test are slow
- The warmer weather (due to El nino) has led to larger mosquito populations. Therefore, there are more potential carriers for the Zika virus.
- The Zika virus as been linked to birth defects and developmental problems associated with microcephaly. Although this has not been confirmed, pregnant women are cautioned to take extra precautions.
This is a condition where babies are born with smaller then normal heads and brain defects. At birth, babies with microcephaly have a head circumference of less then 32cm and are often still born or die shortly after birth (Figure 2). The disease has been known to causes seizures, facial deformities and lead to problems in speech, learning, vision and motor function. Therefore, if the child survives, he/she suffers from mental disabilities, and delays in development.
Figure 2. Baby showing microcephaly phenotype
Microcephaly is a congenital disease, which means that the defect is present prior to birth. The disease arises from a gene mutation, which disables the brain and scull from properly maturing during fetal development. Mutations on any one of seven genes (most commonly on the ASPM gene) have been shown to lead to microcephaly. Evidence shows that the proteins made by these genes are important cell division regulators that are required for proper brain development. The lack of regulation results in infants having smaller brains, smaller sculls, and brains containing fewer then normal neurons. In addition, the presence of multiple centrosomes has been shown to be associated with microcephaly. The presence of too many centrosomes can lead to the stalling of mitosis and induction of apoptosis though the caspase cascade. This increase in apoptosis has been shown to lead to a decrease in neural cell production and reduced brain cells seen in microcephaly.
Microcephaly is an autosomal recessive disease. Due to this pattern of inheritance, microcephaly is not common. Prior to the outbreak in 2014 only 150 babies were born with microcephaly in Brazil. After the outbreak of the Zika virus in Brazil, there was a sudden increase in the number of babies born with microcephaly. Microcephaly has continued to climb since the outbreak of the Zika virus with over 3, 500 infants being born with microcephaly since October 2015.
The jump from 150 children being born with microcephaly in one year to 3, 500 in less then a year cannot be explained using inheritance patterns and genetics. There must be another cause for the increase in microcephaly. The strong correlation between the appearance of the Zika virus and increase in microcephaly indicates that the two are related. Even though this has not been proven scientifically, I believe that the evidence is strong enough to warrant the recent explosion in the media and scientific community on the possible link between Zika and microcephaly.
In the past, the Zika virus has not been a focus for scientific inquiry. Therefore, the long-term effects and mechanisms of infection are unknown. Despite this concern, for non-pregnant women there is currently no reason to avoid travel to areas experiencing the Zika Virus epidemic. It certainly won’t stop me.