Pathogenic micro-organisms are a continuous threat to broilers as they can cause illness, immunosuppression, and poor performance. A good start of a broiler flock begins with healthy chicks in a clean house. It is important to prevent poultry from becoming infected with pathogens, especially young chicks, with cleaning and disinfection (C&D) of empty broiler houses playing an important role here.
Visual inspection doesn’t give information on the success of the disinfection. Bacterial sampling and ATP-testing provide more information about the results of the C&D regarding bacteria, but representativeness is questionable as only very small parts of the broiler house are sampled. Bacteriological testing provides also limited information about the efficacy of the C&D against viruses, especially resistant non-enveloped viruses. PCR tests can’t distinguish between inactivated and still infectious virus particles.
With a test where the broilers act as incubator, a much better indication is generated on what was still infectious in the house when the day-old chickens arrive. Viruses quite resistant to disinfectants would fit best to test for. When these resistant viruses are no longer prevalent, other less resistant pathogens will also be inactivated.
In 2019 GD launched the VIR check to assess the effectiveness of C&D in broiler houses. It uses the results of a multiplex PCR on five highly prevalent non-enveloped viruses in broiler houses: rotavirus A, rotavirus D, reovirus, Avian Nephritis Virus-3 and Chicken Astrovirus to measure the success of the C&D. Several field studies including a field study in Dutch poultry showed that nearly 100 percent of the flocks tested positive on these resistant viruses at the end of the cycle, except for rotavirus D: only 50 percent of the flocks were positive. This means that an effective C&D is needed to prevent multiple early infections in the first days post-arrival. Experimental infections in one-day-old chicks with four of these viruses showed a peak in shedding at day 6-7 of age So if you find them in the chicks, especially in high amounts around 6-7 days, it means that they must have become infected in the first few days of life.
The VIR-check formula transforms the quantitative results of the 5 qPCR’s into a VIR-check score between 0 and 200. Based on recent results of a field study, these scores are now divided into four colours: green, yellow, orange, and red. This recent field study revealed a significant correlation between the four groups within the VIR check and daily growth rates. Flocks with a yellow, orange, or red score showed a reduction of the average daily growth (ADG) of 0.8, 1.6, and 2.4 grams a day over the fattening period compared to flocks with a green score. This showed that by reducing the virus pressure in the house, on average, the flocks performed significantly better. The new VIR check score with the four categories provides farmers, veterinarians, and other involved parties further tools for a more focused approach to farm hygiene and disinfection.
The test is easy to perform. Ten cloacal swabs, taken at 6 or 7 days of age are pooled on one FTA card ring, and tested on the presence and quantity of these five non-enveloped viruses by qPCR at Royal GD. The results are transformed by a formula into the so-called VIR-check score and colour code. Due to the way, the formula is developed, vertical transmission of a virus does not influence the main score. A low VIR-check score represents a low exposure to the viruses tested, which is suggestive of a successful cleaning and disinfection procedure, including for the enveloped viruses, gram-positive and gram-negative bacteria as they are more sensitive to disinfection than the tested viruses.
