Vector-borne Diseases

Disease Surveillance

Alameda County Vector Control Services District (ACVCSD) staff conducts vector-borne disease surveillance for vectors and reservoir animals. Vectors are the transmitters of disease-causing organisms from one host to another. Disease surveillance provides an early warning of a possible disease outbreak and aids in the prevention of diseases from occurring.

Vector-borne disease surveillance involves trapping and collecting vectors (arthropods, insects, rodents, or mollusk); removing/collecting the ectoparasites (e.g., fleas, ticks, mites) off the respective hosts, testing ticks and fleas for disease organisms, or taking blood samples from the host animals to detect the disease antibodies, or pathogens. The following is a brief description of some of the vector-borne diseases included in our disease surveillance program:

• Bubonic plague. Bubonic plague is a bacterial disease that occurs in certain small rodents and their fleas. People usually get plague from being bitten by a rodent flea that is carrying the plague bacterium or by handling an infected animal. Modern antibiotics are effective against plague, but if an infected person is not treated promptly, the disease is likely to cause serious illness or death.
• Hantavirus Pulmonary Syndrome (HPS). This is a viral disease carried mainly by deer mice, and occasionally other sylvatic rodents. Infected mice shed the Sin Nombre virus in its salvia, feces, and urine. Humans are infected when they inhale aerosolized microscopic particles that contain dried rodent urine or feces of an infected mouse. Presently, there are no vaccines or effective treatments for HPS; only supportive patient care.
• West Nile virus. This mosquito-borne disease was first detected in New York in 1999 and since then has spread across the contiguous United States. Most people infected with WNV are asymptomatic (showing no ill effects) while a small portion of the infected people may develop serious neuroinvasive symptoms or West Nile Fever.
• Lyme disease. This disease is caused by a spirochete (a corkscrew-shaped bacteria) called Borrelia burgdorferi and is transmitted by the Western Black-legged Tick. Lyme disease can affect many body systems. It starts as a mild flu-like illness and, over time, develops into severe chronic health problems. The early stages of the disease can include a red, expanding skin rash (called erythema migrans or EM), chills and fever, headache, swollen lymph nodes, muscle and joint pain, weakness of some muscles in the face, severe fatigue, and heart irregularities. Prompt antibiotic treatment during the early stage is usually successful. Delaying treatment can complicate, and prolong the recovery period substantially.
• Swimmer’s itch. This dermatitis is caused by the penetration of human skin by cercariae of schistosome parasites that develop in and are released from snail hosts. Cercarial dermatitis is frequently acquired in freshwater habitats, and less commonly in marine or estuarine waters. Swimmer’s itch is not a life-threatening disease and the skin itching can be treated with over-the-counter allergy medications.