Disease Topics

DISEASE TOPICS

With its varied coastal, mountainous, urban and rural habitats, the South Coast area of Santa Barbara County provides for an abundance of vectors consisting of ticks, rodents, mosquitoes, fleas and stinging and venomous insects. Etiologic agents associated with these vectors are the source for Lyme Disease, Hantavirus Pulmonary Syndrome (HPS), the encephalitis viruses, sylvatic plague, and various allergic reactions and insect envenomizations. The Mosquito and Vector Management District routinely carries out an ongoing vector-borne disease surveillance program to determine the distribution, epidemiology and confirmation of human cases of vector-borne diseases within the District. The following is a synopsis of the microorganisms and their associated vectors covered under the Districts' vector-borne disease surveillance and control program:

Mosquito-borne Encephalitides
Mosquito-borne arboviruses capable of causing human disease within the District consist primarily of the Encephalitis viruses, namely the Western Equine Encephalitides (WEE), the St. Louis Encephalitides (SLE), and the California Encephalitides and most recently, West Nile Virus. The most common vector of the encephalitis viruses is the Culex tarsalis mosquito. There are several other fresh water mosquito species found in the District that are slightly less efficient vectors of encephalitis viruses, namely the Southern House Mosquito (Culex quinquefasciatus) and the Northern House Mosquito (Culex pipiens). Evidence suggests that the California Salt Marsh Mosquito (Aedes squamiger), also found in the District, vectors California Encephalitides.

The District monitors the presence of the viruses through the use of sentinel chicken flocks and insect trapping. Chicken flocks are located in sites within the District to mimic the transmission of mosquito borne encephalitis within the wild bird population. Bi-monthly chicken blood samples are analyzed for virus antibody. Insect trapping on a bi-monthly basis utilizing CDC CO2 traps are used to trap blood meal seeking female mosquitoes. Trapped mosquitoes are anesthetized, sorted and processed for lab analyses of active encephalitis viruses.

Dog Heartworm Mosquitoes in the area can also vector Canine (Dog) Heartworm Disease. Although many species of mosquitoes fed on dogs, the Western Treehole Mosquito is the primary vector of Dog Heartworm in California. The Western Treehole Mosquito is so named because its immature stages frequently develop in rot holes of trees such as oaks, laurels, eucalyptus, sycamores, etc. Immatures can also live in old tires, cans buckets, especially if there are under a tree canopy. In Santa Barbara County, this includes many foothill areas, riparian (streamside) areas, and other heavily wooded places. Adult Western Treehole Mosquitoes are present in California from March through August, depending on rainfall levels and temperature. Adults are active at sunset and sometimes during the daytime. They are small mosquitoes that often can squeeze through window screens. If you live in an area where Treehole Mosquitoes may occur, consult a veterinarian for prevention and treatment of Dog Heartworm. Drugs are available to prevent the disease. Dog Heartworm is highly curable if diagnosed in its early stages.

Tick-Borne Diseases
The primary tick-borne disease of concern to the District is Lyme Disease, which is vectored by the Pacific Black-Legged tick (Ixodes pacificus). Periodic insect collection surveys of coastal woodlands and foothill areas within the District are carried out to determine the presence of the microbe Borrellia burgdorferi. When discovered, tick samples are processed and sent out for lab analysis. Another emerging tick-borne infectious agent causing Human Granulocytic Ehrlichiosis, or HGE, is also of increasing concern to the District as it appears to be vectored by the same tick species that causes Lyme Disease.

Sylvatic Plague
Naturally occurring sylvan rodents in all areas of the District have the potential to carry and harbor the oriental rat flea (Xenopsylla cheopis) which is known to vector human plague. Ongoing rodent plague surveillance studies are periodically performed to determine plague infections and overall adult flea populations hosted by the California Ground Squirrel (Spermophilus beecheyi), and chipmunks (Tamias sp.). Areas that exhibit high squirrel populations with accompanying high flea indices are treated with pesticide to control the fleas.

Hantaviruses
As a relatively new emerging disease, Hantavirus Pulmonary Syndrome (HPS) is vectored by the deer mouse (Peromyscus maniculatus) which has been established to carry the Sin Nombre strain of hantavirus. Several other hantavirus strains have been discovered in the Santa Barbara South Coast from two different mouse species. The other mice species are the California Meadow Vole (Microtis californicus) and the Western Harvest Mouse (Reithrodontomys megalotis), each carrying the El Morro and Isla Vista strains of hantavirus, respectively. The District periodically conducts disease surveillance to determine the hantavirus infected rodent species and disease foci.

Envenomization
The District is involved with the epidemiology of reports of insect envenomizations involving spiders, wasps, centipedes, scorpions and others. Human cases are confirmed through entomological and field studies. Additionally, as the Africanized Honey Bee (AHB) becomes established in the South Coast, the District is prepared to respond to calls for assistance in the control and identification of the AHB.

INFORMATION ONLINE

Disease Surveillance Data Fact Sheet

This is an informational Bulletin on the District' current disease surveillance data.

Monthly Disease Surveillance Report This is a monthly report on the District's disease surveillance activities.

Santa Barbara Coastal Vector Control District

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