Everyone around is so worried about mosquito bites leading to malaria or dengue fever. Not even roaches draw that kind of attention these days. Like the scare of malaria and dengue isn’t enough, there is another fever emerging which is slowly making room for itself amongst us. Ever heard of Zika virus? It causes a disease called, “zika fever” or “zika disease” in humans. This disease was first discovered in 1952 when a caged rhesus monkey in the zika forest near the East African Virus Research Institute in Uganda, was seen to develop a fever. They could isolate the transmissible agent which was found to be zika virus. It was originally thought to be confined to parts of Asia and Africa. It was rediscovered in 2007 in a patient in Yap, Federated States of Micronesia. Aedes aegypti mosquito is the known vector of this virus. The virus can be transferred between human-human through sexual contact and also through blood transfusion. Detection of zika virus RNA in amniotic fluid suggests that it can be transferred vertically and that it can cross the placental barrier and can also affect the fetus. The Pan American Health Organization (PAHO) has confirmed its presence in parts of Panama and Venezuela in December 2015.
Symptoms of zika fever
Not everyone who is infected with zika virus develops the disease. According to CDC, 1 in 5 people develops zika fever. The incubation period of the disease is between 3 to 12 days. During this period, people show the following symptoms- fever, rashes, headaches, conjunctivitis/red eyes, muscle pain, and vomiting. The disease is mild and there are no reports of hospitalization or death. The illness starts to lose its hold within 4-7 days. The rashes are called maculopapular rashes. They start at the face and then proceed to form all over the body. This disease is not seen to cause any further complications. However, infection with zika virus during pregnancy has raised red flags. Certain autoimmune, neurological and neurodevelopmental conditions like microcephaly and Guillain-Barre syndrome in newborns who are infected with ZIKV has been noticed. In 2015, Zika virus has been isolated from a newborn in Ceara, Brazil. This child was born with microcephaly. Following this, there were about 739 cases of infants being born with congenital neurological disorders. As of December 1, 2015, the ministry of Brazil has confirmed the virus to be responsible for microcephaly in infants. 1,248 cases with 7 fatalities were reported in 14 States of the country.
Above is an image of the structure of the Flaviviridae virus (Source: lookfordiagnosis).
The zika virus belongs to the family Flaviviridae like its counterparts causing dengue, yellow fever, West Nile and Japanese encephalitis. The virus is icosahedral in symmetry which is due to the arrangement of the surface proteins. It has a positive sense single-stranded RNA genome that is 10794 kb in length and unsegmented. There are two flanking coding regions that are cleaved into capsid, the precursor of the membrane (prM), envelope (E) and seven non-structural proteins (NS). It has a nucleocapsid and is enveloped by a host-derived lipid bilayer consisting of the E and M proteins.
The virus enters the host cell by attaching itself to the host cell receptors. This is brought about by the envelope proteins of the virus which induce endocytosis in the virion. Upon the fusion of the virus membrane with the endosomal membrane of the host, the ssRNA is released into the host cell. The ssRNA gets translated to a polyprotein and then differentiates into structural and non-structural proteins. The viral factors responsible for the replication of the viral genome carry forward their task and these factors along with the endoplasmic reticulum of the host form dsRNA. The genome is then assembled in the ER of the host cell and then to the Golgi complex. From here, they exit into the intracellular space and continue to infect other host cells.
1. PCR is performed to detect the presence of the viral DNA.
2. ZIKV antibodies (IgM) are detected in the serum. Though the ZIKV antibodies are detectable after 3-5 days of infection, cross-reactivity with dengue, West Nile, and Japanese encephalitis is commonly seen. However, the cross-reactivity was seen in people who were previously exposed to viruses belonging to Flaviviridae. Patients infected with ZIKV for the first time did not show such cross-reactivity. CDC has developed an ELISA to detect the ZIKV IgM.
3. Urine samples are analyzed for the virus as the RNA is present in the urine up to 10 days of infection.
4. Differential clinical diagnosis is advised as there can be chances of co-infection with dengue or chikungunya and malaria which are also transmitted through mosquito bites.
Since the disease is self-limiting and mild, there is no vaccine or specific treatment which has been developed. Patients are suggested to rest and keep themselves hydrated. Medications are usually prescribed against the symptoms like fever, vomiting, headaches and muscle pains. Antihistamines are prescribed for pruritic rashes. Also, the healthcare provider should be cautious while administering drugs as certain drugs like non-steroid anti-inflammatory agents and acetylsalicylic acid can cause side effects like hemorrhages in the patients infected with a Flaviviridae group of viruses.
Above is an image of the health advisory issued by the Ministry of Health, Brazil in the efforts to convey the steps to prevent the disease (Source: Guardian).
Since the disease is transmitted through a vector, the preventive measures usually focus on not giving a chance to the vector to transmit the virus to the host.
1. Keeping the surroundings clean by reducing the breeding ground for mosquitoes helps majorly in the prevention of this disease.
2. Protecting oneself from a mosquito bite is of importance to prevent the infection.
3. Wearing long sleeved clothes, during the highest hours of mosquito activity.
4. Travelers are advised to find out the diseases which are endemic to the place and go about protecting themselves accordingly.
5. A person infected with zika virus is advised to follow safe sex practices or to avoid sexual contact until the healthcare provider gives clearance.
Zika virus is slowly emerging as a pathogen. Since the virus causes mild infection in humans, it hasn’t been studied for its potential to be a disease causing agent.