PCR to Identify Gastrointestinal Nematodes in Sheep and Goats
Parasitism with gastrointestinal nematodes (worms) is common in sheep and goats.
Most grazing sheep and goats are infected with several different types of gastrointestinal worms, with different pathogenic effects.
Knowing the unique mix of gastrointestinal worms in a flock or herd means that appropriate management and treatment plans can be developed. This helps to limit the production and health impacts of worm burdens.
If the worm type is not known, the wrong anthelmintic may be administered, for example a broad-spectrum product when a narrow spectrum product would be sufficient. The pathogenicity of the worm burden may be underestimated. An example of this is when infections with highly pathogenic Haemonchus spp. are not identified in tropical and sub-tropical regions.
Traditionally worm burdens in sheep and goats have been determined manually using coprological techniques based on egg floatation, followed by larval culture techniques to identify the worm type. Larval culture techniques are:
Laborious.
Time consuming, taking up to 10 days to obtain a result.
Messy.
Have occupational health & safety risks from culturing faecal material from animals that may also be infected with bacterial pathogens (i.e., Yersinia spp., Salmonella spp.).
Require an expert skilled in identification of different worm larvae.
Limited by different egg hatching requirements of different worm types.
Require the presence of viable worm eggs.
The advent of real-time hydrolysis probe PCR is making us re-think the gold standard for diagnosis of a range of animal diseases, including parasitic disease.
Diagnostic samples from sheep and goats are often contaminated from field collection and have undergone significant delays and temperature variations during transport to the laboratory. This presents challenges that PCR can help overcome.
I have recently introduced PCR testing for three parasitic gastrointestinal nematodes of sheep and goats to my laboratory, based on the method published by Reslova et al[i].
There are numerous advantages to a molecular approach to diagnosing gastrointestinal worm infection in small ruminants. Molecular methods:
Are rapid.
Are reliable.
Can be more sensitive than egg counting methods because they detect parasite cell-free DNA, overcoming problems of intermittent egg shedding, prepatent infections and hypobiotic larvae.
Can be automated using commercially available sample processing platforms, allowing high throughput testing of samples from sheep and goats.
Do not require worm egg hatching and the culture of nematode larvae, overcoming the occupational health & safety risks from culturing faecal material from animals that may also be infected with bacterial pathogens (i.e. Yersinia spp., Salmonella spp.).
Do not require an expert skilled in identification of different worm larvae.
Are not limited by different egg hatching requirements of different worm types.
Do not require the presence of viable worm eggs.
I am currently conducting PCR testing for Haemonchus spp., Trichostrongylus spp. and Teladorsagia spp., three of the most common and pathogenic gastrointestinal nematodes of sheep and goats.
PCR testing is done on faecal samples from sheep and goats following a simple DNA extraction using a commercially available kit for extracting DNA from faecal samples.
The PCR is run as a panel, with each sample tested for Haemonchus spp., Trichostrongylus spp. and Teladorsagia spp.
Testing is performed in my in-house laboratory.
The PCR test for worm type can be requested as a stand-alone test, or combined with my Diarrhea in Goats Testing Package.
As a stand-alone test, the PCR test for worm type in sheep and goats is ideal for people who are doing their own worm egg counts, but wanting information on the unique mix of gastrointestinal worms in their flock or herd.
[i] Reslova et al. Parasites Vectors (2021) 14:391 https://doi.org/10.1186/s13071-021-04882-4