Acetic acid as an alternative reagent in the modified Knott test

• Published in: Veterinary parasitology 2019-12, Vol.276, p.108975-108975, Article 108975
• Main Authors: Evans, Christopher C., Bradner, Jenna L., Savadelis, Molly D., Nelson, C. Thomas, Moorhead, Andrew R.
• Format: Article
• Language: English
• Subjects: Acetic Acid; Animals; Diagnosis; Dirofilaria immitis; Dirofilariasis - diagnosis; Dirofilariasis - parasitology; Dog Diseases - diagnosis; Dog Diseases - parasitology; Dogs; Formaldehyde; Hemolysis - drug effects; Indicators and Reagents; Knott test; Microfilaria; Microfilariae - growth & development
• ISSN: 0304-4017; 1873-2550
• DOI: 10.1016/j.vetpar.2019.108975

[Display omitted] •The modified Knott test is an important tool in heartworm diagnosis.•Acetic acid was tested as a safer alternative to formalin in the test.•Knott tests performed with acetic acid yielded similar results to the standard test.•Morphology was found to be altered in a way that may affect species ID. The suitability of acetic acid as a safer alternative to formalin in the modified Knott test was evaluated for the diagnosis of canine heartworm (Dirofilaria immitis). Microfilaria concentration was measured by both methods and found to agree within reasonable limits (−5.84 % bias; −88.1–76.4 % limits of agreement). The level of agreement was lower when samples were prepared with a 24 h delay, but this was due to the formalin method tending to yield lower counts (−20.1 % bias; −90.5–50.2 % limits of agreement). Clearing the sample of hemoglobin improves readability and is a key feature of the modified Knott test. Hemolysis was significantly lower in the acetic acid method than the formalin method as measured by red blood cell count (6.83 × 106 and 8.79 × 106 cells/ml, respectively; p =  0.015) and absorbance at 415 nm (33.20 and 34.75, respectively; p