Veterinary Public Health
Heartworm Disease - Case Definition
About This Case Definition
This case definition is used to evaluate and categorize cases of heartworm disease reported in animals to the Los Angeles County Department of Public Health. It was developed by public health veterinarians by reviewing published literature and reported cases of heartworm in LA County animals. Earlier case reports of this disease were reviewed and a few reclassified to meet this 2015 case definition.
Learn more about animal disease surveillance in LA County, and about cases of heartworm in animals in LA County.
Case Definition - Heartworm Disease - 2015
Confirmed
- Two positive antigen tests on two separate blood samples, or
- Positive antigen AND positive microfilaria test, or
- Parasites seen on echocardiography
Probable
- Positive antigen test, or
- Positive microfilaria test
Suspected
- Positive antibody test (feline)
- Positive antigen test, followed by a negative antigen test
Not a case
- No testing for heartworm performed, or
- Positive Antigen test followed by two negative antigen tests (i.e. false positive)
Exposure location
In general, cases are considered to be "Other" or "Unknown" unless the history indicates no travel outside of area.
- UNKNOWN - Less than 2 years of travel history available.
- LA COUNTY - Minimum of 2 years of history available, animal did NOT travel outside of LA County.
- SO CAL - Minimum of 2 years of history available. Animal did NOT travel outside of southern California.
- OTHER - Animal DID travel outside of southern California.
For the purpose of this case definition Southern California includes the following counties: Los Angeles, Orange, San Luis Obispo, Kern, Santa Barbara, Ventura, San Bernardino, Riverside, San Diego & Imperial.
Rationale for surveillance in animals
Animals cases are sentinels for the risk of mosquito borne disease in general. Wherever there are more cases, mosquito borne disease risk is higher.
References
- American Heartworm Society. Summary of the Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Dogs. Wilmington, DE 2014.
- American Heartworm Society. Summary of the Current Feline Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Cats (PDF). Wilmington, DE 2014.
- Nelson CT (2012) Heartworm Disease. In: Greene CE (Ed) Infectious diseases of the dog and cat. 4th ed. Elsevier Saunders. St. Louis, MO. 2012; 865-877.