Mosquito Disease Transmission
Jonathan F. Day, Professor of Medical Entomology
University of Florida, Florida Medical Entomology Laboratory, Vero Beach
How many bites from an infected mosquito does it take to transmit a disease? None? One? Five? Ten? The answer, you may be surprised to learn, is none.
Mosquitoes transmit a variety of diseases. Among the best known are malaria, West Nile virus, yellow fever virus, and dengue virus. Lesser known mosquito transmitted diseases include dog heartworm and filariasis (a nematode worm that causes human elephantiasis). There are two ways that a blood feeding arthropod (an insect or tick, also known as a disease “vector”) can transmit a pathogen (an organism that causes a disease): mechanical transmission and biological transmission.
In the case of mechanical transmission, the vector (mosquito) acts as a flying contaminated hypodermic needle; picking up a pathogen from an infected animal and carrying it on contaminated mouth parts to an uninfected animal where the pathogen is immediately transferred. Fortunately, this type of disease transmission is very rare with mosquitoes.
For biological transmission, the pathogen undergoes an incubation period, often lasting more than two weeks, in the body of an infected vector. During incubation, the pathogen replicates and infects many of the vectors’ organs, most notably, the salivary glands. This is the reason that an infected mosquito can transmit a disease without actually taking blood.
When a mosquito finds a suitable vertebrate host, the first thing she (male mosquitoes cannot bite) will do is cut and probe the skin looking for a source of blood that is close to the surface. During this process, saliva is introduced under the host’s skin. If the mosquito’ salivary glands contain a pathogen, that pathogen is transferred to the host as the mosquito probes. If the mosquito is disturbed while probing, she will fly off without taking a blood meal, but having infected the host as she probed. This makes infected mosquitoes extremely dangerous. If a WNV-infected mosquito finds a group of five individuals at a 4th of July block party, she could conceivably infect all five with WNV without ever taking a blood meal.
Risk of exposure to any vector-borne disease can be reduced by avoiding mosquitoes and preventing them from probing and biting. The best way to avoid mosquito probes and bites is to avoid infested areas, wear protective clothing and wear insect repellent. For more information, you can visit the UF FMEL mosquito information website at: http://mosquito.ifas.ufl.edu/Index.htm.
