Zika virus is a mosquito-borne illness that can lead to significant health issues. Infection during pregnancy may result in infants being born with microcephaly and other congenital malformations. In adults and children, it is associated with neurological conditions such as Guillain-Barré syndrome. The virus spreads through a biological “vector,” an organism that transmits an infectious agent from one host to another. In the case of Zika, mosquitoes serve as the primary vectors, carrying the virus between people.
Identifying Zika-Carrying Mosquitoes
The principal mosquito that transmits the Zika virus is Aedes aegypti. This species is visually distinct, characterized by its dark body and white markings. A notable feature is a lyre-shaped pattern of white scales on the upper surface of its thorax. White bands are also present on its legs.
This mosquito shows a strong preference for feeding on human blood and often ventures indoors to find its meals. Its tendency to live in close proximity to people makes it an efficient spreader of disease in urban and suburban areas. Another species, Aedes albopictus, commonly known as the Asian tiger mosquito, can also transmit the Zika virus, although it is considered a secondary vector.
Aedes albopictus is recognizable by its black body and a single white stripe running down the center of its thorax, in addition to banded legs. Unlike Aedes aegypti, the Asian tiger mosquito is not as exclusively focused on humans for its blood meals and will also feed on animals. This behavior can lessen the probability of it transmitting the virus from one person to another. It is also known to bite outdoors, expanding the range of environments where people might be at risk.
Global Spread and Breeding Grounds
The mosquitoes that carry the Zika virus, particularly Aedes aegypti and Aedes albopictus, are found in tropical and subtropical regions around the world. Their geographic range has been expanding, aided by factors like global trade and climate warming, which creates more suitably warm and humid environments for them to survive and reproduce.
A defining characteristic of these mosquitoes is their reliance on standing water for breeding, specifically in containers. They do not lay eggs in large bodies of water like ponds or marshes. Instead, they seek out artificial containers commonly found around human dwellings, such as discarded tires, flower pots, buckets, and even small bottle caps that collect rainwater.
The close relationship between these mosquitoes and human settlements is a direct result of urbanization providing abundant breeding sites. The desiccation-resistant nature of their eggs allows them to survive dry periods and hatch once they are submerged in water again, contributing to their persistence and spread.
Virus Transmission by Mosquitoes
Zika virus transmission begins when a female mosquito bites an actively infected person and ingests the virus. The virus must then survive and replicate within the mosquito in a process known as the extrinsic incubation period. This is the time required for the virus to infect the mosquito’s midgut, multiply, and then spread to its salivary glands.
This internal replication process takes around 10 days, although the exact duration can be influenced by environmental factors like temperature. Once the virus has reached the salivary glands, the mosquito can transmit it to another person during a subsequent blood meal via its saliva.
A person infected with Zika has a high enough level of the virus in their blood to be contagious to mosquitoes for about a week after symptoms begin.
Controlling Mosquitoes and Preventing Bites
Effective management of Zika-carrying mosquitoes involves targeting their breeding sites. A primary strategy is source reduction, which means regularly inspecting property for and eliminating any stagnant water. Homeowners should empty, clean, or cover items like buckets, planters, and birdbaths, and properly dispose of trash that could collect water.
Protecting oneself from bites is another line of defense. Key strategies include:
- Using EPA-registered insect repellents containing ingredients like DEET, picaridin, or oil of lemon eucalyptus.
- Wearing long-sleeved shirts and long pants to reduce the amount of exposed skin.
- Installing or repairing screens on windows and doors to prevent mosquitoes from entering homes.
- Sleeping under mosquito nets, which is important for those who nap during the day, such as young children and the elderly.
In areas with active virus transmission, public health agencies may conduct community-wide control measures, such as applying larvicides to water-holding containers or spraying insecticides to reduce adult mosquito populations.