The Zika virus, a member of the Flaviviridae family, was first identified in 1947 in a rhesus macaque monkey in the Zika Forest of Uganda. Sporadic human infections were noted across Africa and Asia in subsequent decades. However, it was not considered a significant health threat until widespread outbreaks began in 2007, particularly in the Pacific Islands and later in the Americas, leading to its declaration as a Public Health Emergency of International Concern by the World Health Organization (WHO) in February 2016 due to its rapid emergence and associated complications.
Mosquito-Borne Transmission
The primary method of Zika virus spread is through the bite of infected mosquitoes. The main vector responsible for transmitting the virus to humans is Aedes aegypti, a mosquito species known for its preference for urban environments and daytime biting habits. This mosquito commonly breeds in domestic water-holding containers such as flower pots, buckets, and discarded tires.
A secondary vector, Aedes albopictus, also contributes to Zika transmission. The transmission cycle begins when an Aedes mosquito bites a person infected with Zika, acquiring the virus. After an incubation period within the mosquito, typically lasting several days, the infected mosquito can then transmit the virus to other uninfected humans through subsequent bites.
Non-Mosquito Transmission Routes
Zika virus transmission extends beyond mosquito bites, encompassing several other significant routes. One prominent non-mosquito route is mother-to-fetus transmission, where a pregnant person passes the virus to their developing fetus. This can lead to congenital Zika syndrome, a condition associated with severe birth defects such as microcephaly, characterized by an abnormally small head due to impaired brain development.
Sexual contact is another documented route of Zika transmission. The virus can spread through vaginal, anal, and potentially oral sex. Zika virus has been detected in semen and vaginal fluids for extended periods, highlighting the potential for prolonged sexual transmission.
Transmission through blood transfusions is possible but considered rare. Similarly, organ transplantation is an extremely rare route of transmission.
Protecting Against Transmission
Preventing Zika virus transmission involves a multi-faceted approach addressing all known modes of spread. To protect against mosquito bites, individuals should use insect repellents containing active ingredients like DEET, picaridin, IR3535, or oil of lemon eucalyptus, applying them to exposed skin and clothing. Wearing long-sleeved shirts and long pants can also reduce skin exposure to mosquitoes, which are most active during daylight hours.
Eliminating mosquito breeding sites is another effective measure; this involves regularly emptying or covering containers that can hold standing water around homes, such as flower pots, buckets, and bird baths. For water sources that cannot be emptied, like ponds, larvicides can be used to kill mosquito larvae.
For those who have traveled to Zika-affected areas or whose partners have, practicing safe sex is recommended to prevent sexual transmission. This includes consistent and correct use of condoms or abstinence. Before traveling, it is advisable to check health advisories from organizations like the Centers for Disease Control and Prevention (CDC) or the World Health Organization (WHO) to be aware of regions with active Zika transmission. Public health agencies also screen blood and organ donations to reduce transmission risk.
Recognizing Zika: Symptoms and Diagnosis
Recognizing Zika virus infection can be challenging because many individuals, approximately 80%, remain asymptomatic or experience very mild symptoms. When symptoms do occur, they typically appear 3 to 14 days after exposure and usually last for several days to a week. Common symptoms include fever, a maculopapular rash that can spread across the face, trunk, and extremities, joint pain, and non-purulent conjunctivitis (red eyes). Other reported symptoms include muscle aches and headaches.
The overlap in symptoms with other mosquito-borne illnesses, such as dengue and chikungunya, makes clinical diagnosis based solely on symptoms difficult. Therefore, laboratory testing is often necessary to confirm a Zika infection. Diagnosis typically involves molecular tests, like real-time reverse transcription polymerase chain reaction (RT-PCR), which can detect viral RNA in blood or urine samples, particularly within the first seven days of symptom onset.
If more than seven days have passed since symptoms began, or if PCR results are negative, antibody testing (serology) may be performed to detect Zika virus-specific IgM antibodies, which can remain for up to 12 weeks. A person’s recent travel history to areas with active Zika transmission is an important piece of information that healthcare providers consider when evaluating potential cases.