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Equine Severe Combined Immune Deficiency (view source)
Revision as of 11:52, 25 August 2010
, 11:52, 25 August 2010no edit summary
==Diagnosis==
==Diagnosis==
Diagnosis may not be straigtforward as the clinical signs may resemble those of many other infections occurring in foals. The antemortem diagnosis of SCID is usually based on three criteria; a) a persistent lymphopaenia (occurring over 1-2 weeks) with less than 1000 lymphocytes per ml, b) a lack of serum IgM in foals over four weeks of age and c) lymphoid hypoplasia. Affected foals may also develop anaemia late in the course of the disease.
Diagnosis may not be straigtforward as the clinical signs may resemble those of many other infections occurring in foals. The antemortem diagnosis of SCID is usually based on three criteria; a) a persistent lymphopaenia (occurring over 1-2 weeks) with less than 1000 lymphocytes per ml, b) a lack of serum IgM in foals over four weeks of age and c) lymphoid hypoplasia. Affected foals may also develop anaemia late in the course of the disease.
The intradermal phytohemagglutinin (PHA) test may be used as a test for immunocompetence and assesses T lymphocyte function. It can be performed in foals of all ages as the test is not affected by maternal antibodies. Intradermal PHA causes a delayed hypersensitivity reaction, resulting in a skin swelling. A foal suffering from SCID fails to respond to intradermal PHA.
Blood or cheek swabs may be submitted for PCR to identify the mutant allele of the DNA-PK gene in order to obtain definitive diagnosis. The test also identifies carriers of the disease which is important for screening prior to breeding. Additionally, post mortem findings of a small thymus and/or absent lymph nodes combined with the presence of opportunistic infections support a diagnosis of SCID. Histologically, lymph node follicles and germinal centres are absent with severe cellular hypoplasia of the thymus and lymph nodes.
Blood or cheek swabs may be submitted for PCR to identify the mutant allele of the DNA-PK gene in order to obtain definitive diagnosis. The test also identifies carriers of the disease which is important for screening prior to breeding. Additionally, post mortem findings of a small thymus and/or absent lymph nodes combined with the presence of opportunistic infections support a diagnosis of SCID. Histologically, lymph node follicles and germinal centres are absent with severe cellular hypoplasia of the thymus and lymph nodes.