Hitch-hiking mosquitoes and emerging diseases

Authorities in Hawaii are advising people in Oahu to eliminate standing water as a mosquito control measure. While it's always a good idea, it's of particular concern in this case bacause a rare type of mosquito, Aedes aegypti, was found around the Honolulu International Airport. This mosquito species is a highly effective vector for various infectious diseases, including dengue fever and yellow fever.

What does this have to do with companion animal disease? Well, nothing directly, but it's a good reminder of how infectious diseases can easily reach a distant area (even Hawaii) in a short period of time.

There are a plethora of mosquito-borne diseases out there, and presumably we don't even know about many of them. Mosquitoes don't fly very far, which helps contain these diseases to certain areas. However, mosquito-borne diseases can still spread over wide ranges if either the pathogen or the mosquitoes are hitch-hiking.

A common way for pathogens to travel is in various kinds of animals (especially birds) that can harbour the pathogen (usually a virus) and infect mosquitoes in distant areas.

Modern transportation can be an effective vehicle for pathogen-laden mosquitoes. Theoretically, all it takes is for a single infected mosquito to hop onto a plane and survive the flight to a new region. If the mosquito bites a susceptible host, it can cause a rare disease - that's of particular concern since it's unlikely that an exotic foreign disease in someone who has not left the country would be promptly diagnosed (and therefore promptly treated). Even worse, the disease could establish itself in the new region if a series of things happen:

  • The mosquito has to bite something or someone.
  • That something or someone has to be susceptible to the pathogen and that pathogen needs to grow inside the host's body to high enough levels that it can infect another mosquito.
  • Another mosquito that can carry the pathogen must come along, bite the infected individual and acquire the pathogen.
  • The new mosquito must then find another susceptible host to bite.
  • The above needs to be repeated enough times that the pathogen establishes a foot hold in the area and starts causing disease.

Is this common? No.

Is it possible? Yes.

West Nile virus is an example of what can happen. This mosquito-borne virus came out of nowhere in North America in the early 2000's and caused widespread illness and death in humans, horses and various other species. Did it arrive via a mosquito on a plane? No one knows, but it's certainly a possibility.

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