Flock production problems resembling infectious bronchitis virus (IBV) infections have been intermittently affecting egg producers’ flocks the past three years in the United States and even longer in Eastern Canada.
With no significant changes in vaccination programs, producers started seeing dramatic changes in performance. Some flocks peaked in a range of 70% to 85% and ongoing production was so low that the flock needed to be depleted for economic reasons.
When examining these flocks, many false layers were discovered, leading to the use of false layer syndrome (FLS) to describe the situation. Other flocks experienced dips during production typical of IBV infection during lay with some recovering and others not. However, both observations have appeared randomly and sporadically, not consistently affecting all flocks on a farm.
University researchers have recently been able to recreate oviduct damage associated with FLS in studies with conventional and variant infectious bronchitis viruses. Their findings have confirmed suspicions that a very early IBV challenge (within the first week of life) is causing permanent oviduct damage.
Producers had already adjusted to their IBV vaccination programs by adding a vaccination at the hatchery or soon after placement on the farm. These changes, along with other measures that need to be taken, have reduced the incidence to ensure a proper immune response is a result of vaccination.
Serological surveillance is another important tool to properly understand which infectious bronchitis viruses are in the field and to ensure proper cross-protection is offered by the vaccination program.
Dr. Jose Linares, manager of veterinarian services with Ceva Animal Health, describes the impact of early bronchitis infection. IBV establishes itself in rapidly multiplying cells such as mucosal epithelium. Although it is primarily a respiratory virus, IBV may damage the kidneys and/or the reproductive tract. For some strains, a target tissue in very young pullets is the mucosal epithelium of the oviduct. In a normal bird, only the left oviduct is functional and early IBV infection could hinder normal development, often resulting in a large cystic left oviduct. There are no outward clinical signs that can be observed, and birds mature normally.
Cystic oviduct may result from early IBV infection. (Dr. Eric Gingerich | Diamond V)
However, as a bird matures, hormones stimulate the production of ova as the ovaries are not damaged. These ova could accumulate in the abdominal cavity and create a distended abdomen. A small percentage of birds may assume a “penguin posture” and can be identified as affected.
When necropsying birds with FLS, it is easily identified by the characteristic left cystic oviduct and potentially free-floating egg yolks in the abdomen. Some IBV viruses may also cause kidney damage.
Salpingitis is sometimes seen in cases of FLS. (Dr. Sherrill Davison)
Industry veteran Dr. Sherrill Davison of the Pennsylvania Animal Diagnostic Laboratory System, University of Pennsylvania, notes that FLS from an early IBV infection is straight from the textbook, but that she never saw this syndrome in more than 35 years of practice until 2017. She added that producers in her area were able to learn from the Canadian experience, which started a year earlier.
Soon it became obvious that some flocks were also experiencing IBV infections during lay. Production drops of 2% to 14% have been reported. Some flocks recover and return to expected production levels, but others finish the lay cycle with continued lower production.
Some IBV strains infect the shell gland, resulting in wrinkled or discolored eggs.
University research
Researchers Brian Jordan and Adrea Mueller at the University of Georgia are conducting studies funded by the U.S. Poultry and Egg Foundation to confirm field observations. Their initial work has recreated permanent oviduct damage in young specific-pathogen-free (SPF) pullets challenged with either a “conventional” pathogenic Mass-41 strain or a “variant” DMV/1639 strain. The first study is ongoing as birds will continue to be evaluated at monthly time points until they reach 20 weeks of age.
Early results have shown cystic oviducts at two months post-challenge in at least one bird in each group challenged with M-41 at either three or seven days of age and with DMV/1639 at seven days of age. Other groups also were challenged with the viruses at two weeks of age and there will also be 16-week challenged groups evaluated.
Eight-week-old pullet with cystic oviduct from an early challenge. (Brian Jordan)
After the results of the first trial are reviewed, a second trial will compare vaccination strategies to protect pullets from the early challenge.
Dr. Rodrigo Gallardo has also completed studies at the University of California Davis in SPF pullets. He used a Mass-41 strain as well as a DMV-like virus that was obtained from a West Coast IBV outbreak associated with FLS.
This DMV-like virus is 91.5% genetically related to the DMV/1639 strain and 92.3% related to the PA Wolgemuth/98 strain confirming ongoing genetic mutation typical of IBV. In his study, birds challenged at three days of age started showing pathological changes as early as two days after challenge. With histopathology, he was able to observe the thickening of the oviduct, as well as damage in kidneys and the respiratory tract in chicks challenged with Mass-41 and DMV-like virus.
Vaccination
Before FLS appeared, most layer pullets received their first IBV vaccination combined with Newcastle disease between 18 and 21 days of age. Dr. Alexandra Reilley of Merck Animal Health reported that a large part of the U.S. industry is now using MILDVAC-Ma5 (Massachusetts type) in the hatchery or as part of an early vaccination program. Her colleague Dr. Denis Carrier advises most pullets get hatchery vaccination in affected areas of Canada.
For farms that have experienced issues with DMV/1639 virus, Ceva Animal Health offers Cevac IBron, which contains a Georgia serotype that has been shown to protect against GA08, GA13 and DMV/1639/11 variant IBV strains.
Linares said producers need to immunize as soon as possible, as there is a race between vaccine and field virus to infect the bird.
“We aim to help to control bronchitis as we can’t eradicate the disease,” he said. “We help our customers optimize vaccine handling, mixing and delivery, aiming to immunize the birds and minimize the consequences of IBV infection.”
Ceva offers a vaccine detection evaluation that can be used to determine a percentage of birds immunized as early as five days after vaccination.
Vaccinating a flock does not ensure birds respond with immunity from the vaccine. Dr. Keith Honegger of Elanco Animal Health works with producers to ensure the proper technique is being used by vaccination crews.
“A program is no more effective than the application,” he said. “I recommend that a vaccination method be easy to do so that it’s done right every time.”
Honegger has seen IBV breaks in flocks where the initial IBV vaccination was administered after chicks were delivered to the pullet farm. For optimal early IBV immunity, hatchery IBV vaccination is suggested.
“Use common sense to establish IBV protection,” Honegger said. He lists these recommendations:
- On a multiple-age pullet farm, assume vaccine and field viruses will be circulating between flocks.
- Be sure the flock is immunocompetent. At six weeks of age, monitor bursal health.
- Do serology at six weeks of age as high IBV titers indicate an IBV field challenge and a need for day-of-age IBV vaccination.
- Don’t forget the breeders. Be sure all chicks come from breeders properly vaccinated with inactivated vaccines for IBV, Newcastle disease virus, infectious bursal disease and reovirus. Monitor titers.
Surveillance
As IBV mutates quickly, there are many strains in the field which vary in pathogenicity. Most strains have not yet been evaluated in research studies to determine if they cause oviduct damage seen in FLS.
Davison has identified five DMV-like, two PA 1220 and one GA08 IBV strains from cases of FLS in Pennsylvania.
She assumes that she couldn’t always isolate a strain from infected birds due to timing and stage of infection when birds were evaluated.
In Quebec and Ontario, Carrier cited recent surveys that have identified DMV, 4/91 (until 2018) and CA1737/04, besides Massachusetts and Connecticut vaccine strains.
Gallardo reported that West Coast isolations in layers associated with FLS have included the DMV/1639-like virus mentioned previously, as well as a CA1737-like virus (94.5% similar to CA1737), again confirming the variable nature of IBV. He said that, to date, no FLS-associated strains have been isolated in California.
“The introduction of a new vaccine strain to control IBV variants has consequences that must be considered as the new vaccine is a potential source of genetic material for reassortment with local IBV strains and potentially creating new variants,” Gallardo said. “Using IBV vaccines as a ‘tool’ in low poultry density areas is a must – adding them in high-challenge season and pulling them out when the problem disappears. Also, when vaccinating layers, broilers and breeders housed in the area need to be considered as a possible destination of new viruses, making biosecurity a high priority.
“Selective pressure applied by homologous and heterologous vaccines increases the potential of virus mutation and recombination of existing field viruses. To ensure long-term success in a regional control program, economic considerations, different bird populations, and traffic patterns all need to be evaluated, as well as ongoing surveillance. There is no silver bullet – programs used in a specific region cannot be replicated in regions with different characteristics.”
It appears that reports of FLS are decreasing in areas where producers have responded with new control measures. However, there have been some continued issues leading to questions surrounding variants and/or vaccination techniques. Recently, there have been new reports of FLS in previously unaffected operations in the Midwest. Continued laboratory research, vaccination program adjustments, surveillance and field observation will all contribute to minimizing the impact of these IBV infections.
