Veterinary Epidemiology and Zoonosis

Collection of sample for diagnosis of parasitic zoonoses

COLLECTION OF SAMPLES FOR DIAGNOSIS OF PARASITIC ZOONOSES

• At postmortem examination one should make an earnest attempt to collect all the parasites (ticks, mites, fleas, lice, worms and segments of tape worms).
• They should be examined beginning from outside of the body, then the subcutaneous tissue, the body cavities, internal organs, circulatory system, gastrointestinal tract and so forth.
• The collection should be carried out as systematically and completely as possible.
• Basic knowledge on the various parasites / larval stages and their location in the body adds effectiveness to the search.

Collection of faeces

• Faeces shall be collected from the rectum for parasitological examination.
• Faecal materials should be examined immediately after collection or it can be refrigerated overnight or preserved with 10% formalin to avoid hatching of eggs.

Collection of worms

• Worms seen in the faeces/rectum should be first washed in tap water and then in normal saline.
• They are fixed in 5% formalin or 70% alcohol. Worms from clear location like subcutaneous tissue, peritoneal cavity etc., can be directly fixed without washing.
• The gastrointestinal mucosa should be gently scraped for detecting minute worms / larval stages.
• If the worms are found adhering to the gut wall or firmly embedded in mucosa, they should not be pulled out.
• But the entire piece should be placed in the warm (40ºC) normal saline which detaches the worms.
• Cestodes with their scolices and trematodes are flattened by placing the parasite between glass slides and securing the ends with threads or rubber bands with gentle pressure and then they are fixed in 5% formalin or 40% alcohol.

Collection of insects and arachnids

• Parasitic insects and arachnids including fleas, ticks and mites are of significance because they are themselves directly harmful (for example, ectoparasites such as mange mites or endoparasites such as warble fly larvae) or because they transmit other disease agents. Hence, care is taken not to miss them.
• It is important to do this without causing damage, especially to the mouth parts of the tick, which will be firmly embedded in the host’s skin.
• A useful method is to grip the ‘head’ firmly, but lightly, by means of forceps and then pulled out sharply, without causing any damage to the skin.
• Where parasitic (mange) mites are concerned, a skin scraping has to be taken. Mites are found deep in the skin, so deep scrapings should be made. Shaving with the scalpel must be continued until the blood oozes freely.