Changes

There are several methods for the specific demonstration of ''Dirofilaria immitis'' in the animal. Firstly, direct microscopic examination allows rapid identification microfilariae in a drop of fresh blood as their movements can vigorously displace the surrounding red blood cells². Despite being quick, simple and inexpensive, this test is not sufficiently sensitive to provide a definitive diagnosis, particularly when there is a low concentration of microfilariae in the bloodstream. Filtration methods therefore exist to facilitate the microscopic demonstration of microfilariae^{2, 3}. These include the modified Knott's test, which involves haemolysis, centrifugation and staining with methylene blue before direct examination. Tests such as this are more sensitive than merely examining a drop of blood, and the morphology of microfilariae can be clearly seen. Sensitivity in comparison to other methos is still, however, low and so microfilarial identification tests are often reserved for confirmation of weak positive antigen tests and determination of microfilarial status prior to treatment with a microfilaricide³. Cats frequently lack circulating microfilariae, and so direct micrscopic examination is of little use in this species.

There are several methods for the specific demonstration of ''Dirofilaria immitis'' in the animal. Firstly, direct microscopic examination allows rapid identification microfilariae in a drop of fresh blood as their movements can vigorously displace the surrounding red blood cells². Despite being quick, simple and inexpensive, this test is not sufficiently sensitive to provide a definitive diagnosis, particularly when there is a low concentration of microfilariae in the bloodstream. Filtration methods therefore exist to facilitate the microscopic demonstration of microfilariae^{2, 3}. These include the modified Knott's test, which involves haemolysis, centrifugation and staining with methylene blue before direct examination. Tests such as this are more sensitive than merely examining a drop of blood, and the morphology of microfilariae can be clearly seen. Sensitivity in comparison to other methos is still, however, low and so microfilarial identification tests are often reserved for confirmation of weak positive antigen tests and determination of microfilarial status prior to treatment with a microfilaricide³. Cats frequently lack circulating microfilariae, and so direct micrscopic examination is of little use in this species.

Tests also exist to detect ''D. immitis'' antigens. ELISAs specific for proteins released from the reproductive tract of adult female worms are available for in-house use². Sensitivity and specificity are excellent, but small worm burdens and the

ELISA antigen tests detect specific circulating proteins

presence of immature female- or male-only infections can give low antigen titres hence false negatives. This is especially common in cats. Specific agglutination and immunochromatography techniques are also available for use in dogs. Any antigen test performed in the first six months of infection may give false negative results as levels of circulating antigen are initially low while female worms mature.  

released by the reproductive tract of mature female

worms. These are available as either in-house or laboratory

tests and their sensitivity and specificity approach

the response to treatment. Small worm burdens, the

presence of immature females or male-only infections

are common causes of low antigen titres and false

negative results, especially in cats, where these circumstances

occur more frequently. In dogs, specific agglutination and immunochromatography techniques are also

available. An antigen test performed too soon after infection

(first six to seven months) may yield false negative

results because of the low antigen levels in the circulating

blood.

Antibody tests are currently available for routine screening

Antibody tests are currently available for routine screening