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IDEXX has developed a new test kit to detect avian pneumovirus

A broader and effective tool to detect avian pneumovirus in chickens and turkey operations
The most common and prevalent types of avian pneumovirus (APV) are A and B, but there is an increasing concern among epidemiologists for the potential spread of APV type C from wild flocks to the poultry industry. This phenomenon already occurs in the U.S. poultry market, where APV type C is the most prevalent and distributed APV in turkey flocks in certain states.³ For this reason, it is important to have a diagnostic test kit that is able to detect all three APV strains in the commercial chicken or turkey industry.

Infection with APV damages the cilia of the upper respiratory tract or trachea, which may lead to upper respiratory clinical signs such as coughing, sneezing, swollen head and more complicated respiratory problems (the most likely situation in turkeys and broiler breeders). This stress on the cilia and upper respiratory tract can facilitate the multiplication of E. coli and other bacteria infections such as Mycoplasmas, Bordetella sp., etc. that lead to a respiratory syndrome called swollen head syndrome (SHS). SHS tends to be the most likely situation in commercial layers and broilers. Jones RC et al demonstrated co-infection with two bacterial infections.⁴ Furthermore, APV plays a role in the multiplication of infectious bronchitis virus (IBV) in the upper respiratory tract that can facilitate an IBV vaccine rolling.

APV can colonize the mucosa surface (affecting the small glands that excrete calcium and pigments during the egg formation) in turkey breeders, broiler breeders and layers. Reproductive tract lesions can cause a lack of pigmentation on the eggshell, increase in the percent of egg abnormalities ^1,2, and an increased susceptibility to bacteria penetration through developing eggshell cracks. All three can lead to a decrease in egg production.

IDEXX has produced a new quantitative indirect ELISA test for the detection of any A, B and/or C APV types in chicken and turkey flocks that have faced a natural field exposure or have been vaccinated against APV. With this ELISA test kit and the xChek software, customers can screen SPF populations or monitor flocks that have been vaccinated with any live or inactivated APV vaccines. IDEXX recommends building a baseline for your company based on the vaccination program in place or any field virus exposure. By doing this, production managers and veterinarians can monitor new outbreaks and changes in vaccine performance. Companies will be able to assess the need for changing or adding vaccines to their monitoring program.

FlockChek* APV Ab ELISA Test Kit

• Detects A, B and C avian pneumovirus types
• Detects vaccine immune response 16 days after vaccination
• Designed for chicken and turkey serum samples
• 98% specificity in SPF populations
• Indirect—quantitative ELISA

Specificity in Chickens
Comparing the FlockChek APV Ab Test Kit to a competitor's blocking format or competitive ELISA (gold standard for specificity), the FlockChek APV Ab Test Kit performed better than the competitor's blocking ELISA; 98.4% specificity vs. 96.9% specificity, respectively (Graph 1 and Graph 2).

Specificity in Turkeys
The FlockChek APV Ab Test Kit showed better specificity in a negative U.S. turkey population as compared to a competitor's ELISA, 100% vs 51.3% specificity (Graph 3 and Graph 4). The FlockChek APV Ab Test Kit exhibits a tight population distribution (Graph 3). The cutoff in Graph 3 for the FlockChek APV Ab Test Kit is 0.2; the arrows in Graph 4 indicate the suspect zone for the other indirect ELISA test kit.

Sensitivity in Chicken Vaccinated with APV Types A or B
In this study, 18 chickens were vaccinated with commercially available inactivated vaccines types A or B. The first group was vaccinated with inactivated type A vaccine, and two other groups with type B vaccines. The last group was a nonvaccinated control group. Serum samples were taken at various intervals, including the day of vaccination and up to the forty-third day post-vaccination. The mean titer and percentage of seroconvert for each group can be seen in Graph 5 and Graph 6.

FlockChek APV Ab Test Kit was able to detect antibodies at 16 days post-vaccination. The type B vaccinated group reached up to 100% of seroconversion with mean titers between 1,500 and 2,500. The groups vaccinated with A and B1 had seroconversion between 60% and 80%, and mean titers between 1,000 and 2,000. A decline in antibodies was seen at 43 days post-vaccination in all the groups. This study demonstrates that the FlockChek APV Ab Test Kit was able to detect antibodies from all three commercially available inactivated vaccines against APV 16 days post-vaccination and up to 43 days post-vaccination.

Sensitivity in Turkeys
In this study, turkeys were vaccinated with live vaccines against APV types A or B. Vaccination was given to day-old turkeys; and serum samples were collected at various time intervals. The first set of serum samples (sample size = 23 serum samples) were collected at three weeks of age. After an additional live vaccination (boost) was given, new serum samples were taken at six weeks and 12 weeks of age. One final serum collection was completed after an inactivated vaccination at 33 weeks of age.

Graph 7 indicates a large percent of positive serum samples from turkeys vaccinated at one-day-old with the live vaccine type B. At three weeks of age, there is low seroconversion that is likely due to maternal antibodies interference. In Graph 8, after an additional live vaccination type A (boost) was given, the turkeys showed an increased titer at six weeks of age and 12 weeks of age. At six weeks of age, the percent of seroconversion remains high, and then starts to decline at 12 weeks of age.

In conclusion, FlockChek APV Ab Test Kit is able to detect antibodies in turkeys vaccinated with live APV vaccines against types A or B.

Sensitivity in Chickens Vaccinated with APV Type C
In this study, seven chickens were vaccinated with an inactivated vaccine containing type C APV. Serum samples were collected twice a week for four weeks post-vaccination. The FlockChek APV Test Kit detected antibodies against APV type C eleven days post-vaccination. The rate of seroconversion and mean titer are shown in Graph 9. At day fourteen, all birds had seroconverted with a mean titer of 1,400, which increased over time 7,400 at day 28.

Sensitivity in Chickens Vaccinated with APV Type A Vaccine Compared to Field Challenged Chickens
In this study, chickens were vaccinated with live and/or inactivated APV vaccine type A and compared to nonvaccinated chickens that faced field challenge. At this testing site, the vaccination programs were monitored using an indirect ELISA test kit (competitors test kit). Table 1 shows 140 serum samples tested with FlockChek APV Ab Test Kit compared to the competitor's indirect ELISA test kit. The FlockChek APV Ab Test Kit showed a higher seroconversion rate (100% positives) and a good titer level, which is beneficial for baselines purposes. The presence of antibodies even in nonvaccinated birds is due to a nonpathogenic strain of APV present in the flocks (according to information from this poultry company).

Table 1. Field trial comparison

Detectibility
Analytical sensitivity was compared between the FlockChek APV Ab Test Kit and four commercially available competitors' kits by analyzing a dilution series of types A, B and C specific sera. Each sera was strong in the respective subtype, but they were not matched by titer level to each other. The titer of the most diluted sample that came up positive can be seen in Table 2.

Table 2. Minimum level of antibody detection against A, B or C avian pneumovirus antigens

The FlockChek APV Ab Test Kit was able to detect antibodies against APV type A at the 1:256 dilution. Only competitor A had similar results. APV type B sera could be detected at the 1:128 dilution by the FlockChek APV Ab Test Kit and only competitor D matched these results. Finally, the FlockChek APV Ab Test Kit is the only one that claims to detect strain C APV.

Conclusion
The FlockChek APV Ab Test Kit offers many advantages over current competitor's APV test kits. They include:

• The FlockChek APV Ab Test Kit has better specificity compared to a competitor's ELISA with a blocking format that is considered the gold-standard reference for negative chicken and turkey populations. By using the FlockChek APV Ab Test Kit, poultry customers will have more confidence in monitoring APV and/or naive populations.

• The FlockChek APV Ab Test Kit can detect the presence of all three strains of APV (A, B or C). Current commercially available ELISAs do not have claim to detect strain C.

• The FlockChek APV Ab Test Kit can detect immuno response to the most common commercially available live or inactivated vaccines against APV that contained A, B or C antigens in its formulation.

• The FlockChek APV Ab Test Kit can be used with IDEXX xChek* software to generate baselines and be able to monitor vaccination programs and field-challenge interaction.

• The FlockChek APV Ab Test Kit had a good balance of sensitivity for detection of A, B or C avian pneumovirus types.

• The FlockChek APV Ab Test Kit has: same sample diluent and test protocol as the other IDEXX poultry test kits.

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