Diagnostic tests are often used to provide confidence in vaccine uptake and to demonstrate disease-free health status
In a rapidly changing poultry production environment, being able to identify and prevent disease is an increasing priority for producers. Katie Pitman, technical services adviser at MSD Animal Health UK, explains why laboratory diagnostics play a crucial role in helping safeguard the health of UK poultry flocks, while also discussing what tests are available and the benefits these bring to producers.
“Diagnostic tests are extremely important for poultry producers as they can be used to confirm or exclude a disease, or as a surveillance tool to identify a field virus that may be affecting birds. “Gaining an awareness of potential disease pressures, and circulating pathogens, can help determine action in the current flock and form a disease prevention strategy for the next bird intake,” says Pitman.
“In addition, diagnostic tests are often used to provide confidence in vaccine uptake and can also be used to demonstrate disease-free health status, which is a requirement for food standard regulations, or when exporting birds.”
Producers have access to a broad platform of diagnostic tests, the choice of which is largely dictated by what clinical signs are observed and which parameters need to be monitored. “To get the best value out of the tests, the number of samples collected is particularly important, to gain representative results and this will differ slightly according to test type.
“When testing for vaccinal response, we would recommend taking samples from 20 birds per flock, and for export and health monitoring programmes, samples from 60 birds are advised,” she says. There are many different types of diagnostic tests available, the most common of which are polymerase chain reaction testing, antibody testing, parasitology testing, and histopathology testing.
POLYMERASE CHAIN REACTION (PCR) TESTING
This process involves the amplification of small segments of DNA to allow detailed molecular or genetic analysis of a virus, for example, so we can identify which specific strain of a virus is infecting a bird at that point in time. “We often use this method to identify the virus infectious bronchitis (IB) within a flock, but it can be used to identify other viruses such as Mareks disease and Gumboro disease, plus infectious laryngotracheitis and Mycoplasma, Salmonella and Reovirus, to name a few,” says Pitman. When viruses infect an animal, they embed their genetic material in the DNA, meaning that PCR testing can identify the presence of a virus in animal tissue or mucus from the trachea, for example.
This form of testing can be used as an aid for disease diagnosis, monitoring flock health and performance, and to evidence vaccine response. Antibody testing involves the collection of blood samples (serology) from birds. It determines the presence or absence of antibodies to a specific disease. “The level of circulating antibodies in the blood will differ depending on whether the bird has had a vaccine, or been exposed to a field virus. A rising level of antibodies, identified from paired samples taken a number of weeks apart, indicate seroconversion and this can be correlated with clinical signs that are observed,” she adds.
Pitman explains that parasitology is the study of parasites, and is a popular technique commonly used in commercial livestock production, particularly in worm and coccidiosis quantification and speciation. “In this test, faecal samples are collected for laboratory analysis at specific time points. The results will help to determine the most appropriate worming programmes, and also look at product efficacy against the target species. In the case of coccidiosis oocyst counts, we can learn about coccidial oocyst cycling, product efficacy and house hygiene.”
This involves microscopic examination of diseased cells or tissue retrieved during postmortem examination to show common changes that occur during a disease. Histopathology can be useful to confirm diseases, for example infectious laryngotracheitis (ILT) and Marek’s disease. Usually further tests are utilised to confirm viral and bacterial causes of the gross pathology. “In conjunction with good biosecurity and disease prevention methods such as vaccination, diagnostic tests are a great tool that producers can use in a bid to help to keep birds healthy, and to proactively identify potential risks to current and future crops,” says Pitman.