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707-285-2210 (fax)

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Cotati, California
94931-9736

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Featured vector borne diseases (below)
1. West Nile Disease
2. Viral encephalitis
   • Encephalitis virus in California - Summers 1997 & 1998
3. Malaria
4. Lyme Disease
5. Ehrlichiosis
6. Babesiosis
7. Plague
8. American Trypanosomiasis
Disease surveillance

VECTOR BORNE DISEASES

The vector-borne group of diseases is made up of organisms that spend part of their life inside a mosquito, flea, tick or other arthropod, and the other part inside a vertebrate. The arthropod (or "vector") picks up the disease agent when it bites a sick or infected host, and then carries it to one or more new hosts during its next blood meals.

Mosquitoes were already feeding on blood during the days of the dinosaurs. Many viruses, bacteria, protozoans, worms and other parasitic organisms have spent millions of years adapting their own life cycles to the intimate relationships between biting arthropods and their hosts. In a kind of lottery-of-life, every successful agent has evolved and fine-tuned each detail of its existence to the ecology and natural history of its two very different kinds of hosts.

These blood-feeding arthropods (a mosquito, a flea and a tick) were caught in sticky tree sap on the Caribbean island of the Dominican Republic 20 to 30 million years ago. The sap later hardened into amber. They can now be seen at the American Museum of Natural History in New York.

Vector-borne diseases that affect agriculture, like equine encephalitis, canine heartworm, or bluetongue of sheep, have received a lot of attention by scientists. The vast majority affect only wildlife populations and are still very little known. Some bacterial and viral agents have only recently been discovered, when new diagnostic tools identified a previously unrecorded organism in a human patient.

The normal vertebrate hosts of most vector borne diseases of man (malaria is now almost an exception) are wild or domestic animals. Humans usually become infected only when they step into an already existing natural, or "enzootic" cycle. Diseases caused by organisms currently exploring these newly opened transmission routes to man have been called "emerging infectious diseases".

Many parasites of man and domestic animals are not currently found in California, but are widespread elsewhere. California does have potential arthropod carriers for these agents if they ever are introduced. Any relaxing or abandonment of the current levels of surveillance, quarantine and vector control could have huge repercussions.

Internet References:

• Vector borne diseases in California.   A series of brochures by the California Department of Health Services. [Go to "Publications"]
• Resurgent Vector-Borne Diseases as a Global Health Problem   Funds available to Federal and State health agencies and medical schools for prevention and training in vector-borne diseases have fallen drastically in recent years, leaving regional mosquito and vector control districts with greater responsibility for handling emergency situations. (An report in the journal Emerging Infectious Diseases. Vol.4(3):442-50, 1998)