Changes

[[Image:dirofilariasis.jpg|right|thumb|200px|Dirofilariasis. Courtesy of T. Scase]]

[[Image:dirofilariasis.jpg|right|thumb|200px|Dirofilariasis. Courtesy of T. Scase]]

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 of 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. However, sensitivity in comparison to other methos is still 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.

[[Image:dirofilariasis 2.jpg|right|thumb|200px|'''Dirofilariasis'''. Courtesy of T. Scase]]

[[Image:dirofilariasis 2.jpg|right|thumb|200px|'''Dirofilariasis'''. Courtesy of T. Scase]]

Tests 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

Tests 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

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. In-house tests are also available to detect antibody against ''Dirofilaria immitis''. The presence of antibodies confirms exposure, but does not necessarily provide information about current infection. These tests are therefor most useful for ruling out infection. ''D. immitis'' antibody tests have a low specificity² and so have largely been superceded by tests for antigen.

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. In-house tests are also available to detect antibody against ''Dirofilaria immitis''. The presence of antibodies confirms exposure, but does not necessarily provide information about current infection. These tests are therefore most useful for ruling out infection. ''D. immitis'' antibody tests have a low specificity² and so have largely been superceded by tests for antigen.

PCR-based tests are highly sensitive and specific for the diagnosis of immature and adult heartworms, and are especially useful in unconventional (e.g. wildlife) hosts². At present, these tests are not widelt available for the diagnosis of ''Dirofilaria immitis''.

PCR-based tests are highly sensitive and specific for the diagnosis of immature and adult heartworms, and are especially useful in unconventional (e.g. wildlife) hosts². At present, these tests are not widely available for the diagnosis of ''Dirofilaria immitis''.

===Pathology===

===Pathology===