PIC Update: IBH in Ontario Broilers

Inclusion Body Hepatitis (IBH) is a viral disease of poultry (mainly
chickens) caused by specific strains of Fowl Adenoviruses (FAdV) and
first identified in the United States in 1963.

By Dr. Babak Sanei, Ontario Ministry of Agriculture, Food, and Rural Affairs

Inclusion Body Hepatitis (IBH) is a viral disease of poultry (mainly chickens) caused by specific strains of Fowl Adenoviruses (FAdV) and first identified in the United States in 1963. There is no public health or food safety concern with respect to the IBH cases in chickens; however, the disease can cause morbidity and mortality within flocks, contributing to financial losses.

The average age of broilers affected by IBH in Ontario is around 15 days. The first indication of the disease is a sudden marked increase in mortality. During an outbreak, birds may be observed sitting in a crouching position with ruffled feathers. Clinical diagnosis of IBH in an infected flock will confirm typical liver lesions and microscopic changes within the liver cells, specifically, inclusion bodies (shown above).

In addition to chickens, FAdVs have also been isolated from both healthy and sick birds in other bird species such as turkeys, pigeons, mallard ducks and geese. FADVs are common within the poultry environment, and normally do not cause disease in birds.
 
Specific types of FAdVs, however, have been associated with inclusion body hepatitis (IBH) in broiler flocks. In a recent study, three main virus types (serotypes 11, 8a and 2) were found to be associated with the majority of IBH cases in Ontario. If you suspect IBH in your flock, it is important to determine the strain(s) causing the clinical IBH, to ensure the proper course of action for management of the disease.

Economic Impact
There has been no comprehensive study Conducted in Canada to date to determine the true economic impact of IBH, although baseline data is available. Data collected at major broiler hatcheries from January 2007 to June 2009 on IBH incidence and impact suggest that annual loss in Ontario due to IBH is close to 105,000 broilers. This is equivalent to approximately 210,000 kilograms of live body weight, and translates to a financial loss in the order of $300,000.

Clinical Picture
IBH has been reported in birds as young as seven days and as old as 20 weeks. The average age of broilers affected by IBH in Ontario is around 15 days. The first indication of the disease is a sudden marked increase in mortality. During an outbreak, birds may be observed sitting in a crouching position with ruffled feathers. Clinical diagnosis of IBH in an infected flock will confirm typical liver lesions and microscopic changes within the liver cells, specifically, inclusion bodies. Inclusion bodies are abnormal structures inside cells having characteristic staining properties and associated especially with certain viral infections. Losses usually peak within four or five days after the onset of clinical disease. Mortality in IBH cases varies significantly in affected flocks due to the type of virus, age of the flock and presence of immunosuppressive diseases (e.g., IBD, CAV).

One study in Ontario showed the overall course of IBH cases in affected broiler flocks to be between six and 13 days. Average mortality was 3.1 per cent, ranging from 0.37 per cent to 11.3 per cent, although higher mortality rates in broilers have been reported.

Epidemiology
Both vertical transmission (from breeders to offspring), and horizontal transmission (from flock to flock) are possible.

Timing of exposure to the virus plays an important role in vertical transmission; if a breeder flock is exposed to pathogenic IBH virus prior to the onset of production, the birds will produce antibodies that can protect offspring through passive immunity. On the other hand, if a naive breeder flock is exposed to pathogenic IBH virus after the onset of egg production, the virus can be transmitted to offspring over the course of five to nine weeks and possibly result in IBH outbreaks in broiler flocks.

Horizontal transmission is also an important factor in spreading the virus to susceptible broiler flocks at early ages. The peak of virus shedding by infected broiler flocks occurs between four and six weeks of age and is a potential source of disease for other broiler flocks. 

If day-old broilers from various breeder sources are mixed, cross infection of pathogenic types of IBH can occur. This scenario may result in only a portion of the flock becoming sick, because only a portion of the flock may be naive to the virus (i.e., have no maternal immunity).

It has also been suggested that an infected but immune breeder flock might shed the virus to its offspring, especially during times of stress such as peak of production. While the offspring of the breeder flock might be immune to the disease, other broilers raised in the same barn but sourced from different breeder flocks may be naive to the virus and become sick due to horizontal transmission.

What Can be Done?
Management Interventions at the Broiler Breeder Level:

IBH doesn’t cause disease in mature breeder flocks; however, an active immunity against IBH prior to the onset of production can establish maternal immunity in broiler offspring.

Not all breeder flocks will be naturally exposed to the pathogenic strains of IBH virus prior to the onset of production. Therefore, the ideal approach is to vaccinate all breeders on two occasions during the pullet stage. This approach can induce adequate maternal immunity at broiler levels.

• Commercial live and inactivated vaccines are not available in Canada, but they have been successfully used in some other countries (e.g., Australia, Mexico and Pakistan).
• Recently, at a limited geographical scale, autogenous inactivated products have been used in Canada to ensure the transfer of maternal immunity from breeding flocks to their progeny. (Autogenous inactivated products are prepared from the endemic strains of the virus isolated from the infected flocks and are the cause of the current IBH cases in the region.)

If vaccination of all breeders in the region is not feasible, an alternative approach is to identify breeder flocks that have not been exposed to the pathogenic virus between the ages of 12 and 16 weeks and vaccinate only the naive target breeder flocks.

Some immunosuppressive viruses such as Chicken Infectious Anaemia (CIA) virus and Infectious Bursal Disease can act as predisposing factors for IBH outbreaks in broilers. A proper vaccination of breeder flocks against CIA can induce sufficient maternal immunity in broiler progenies against this disease.

Addition of spiking males to a naive breeder flock during the production has the potential to introduce the pathogenic strains of IBH and subsequent vertical transmission. It is important to determine the level of exposure of spiking males and breeder flocks to IBH strains prior to this management practice.

Management Interventions at the Broiler Level:

 IBH is a viral disease and antibiotics are not effective against viruses; however, antibiotics may be used for treatment of other potential concurrent bacterial infections.

If you are dealing with an infected IBH flock, the following should be considered:

If an outbreak of IBH has occurred in a broiler flock, there is not much that the producer can do to reduce the impact of the infection.

Infectious Bursal Disease (IBD) has been shown to predispose birds to become more susceptible to pathogenic strains of IBH. If needed, a proper vaccination program should be developed in consultation with your veterinarian to protect against this disease.

Infected IBH broiler flocks can shed the virus, mainly from week 3 post infection, and can be a source of horizontal transmission to other naive broiler flocks. Application of proper biosecurity programs for broiler flocks at all times, and during the early stages of bird placement, is very important.

A complete cleaning and disinfection of the barn is strongly recommended. This is because FAdVs are hardy viruses and can survive in the barn and result in recurrent outbreaks in newly placed flocks. These viruses are resistant to lipid solvents such as phenol- and alcohol-based disinfectants, but can be inactivated by formaldehyde.

Dealing with IBH in Ontario requires a collaborative approach at different levels within the poultry industry. At the breeder level, effective immunization of breeder flocks against pathogenic serotypes of IBH can minimize the impact of vertical transmission. At the broiler level, application of adequate biosecurity measures is the best approach to reduce the horizontal transmission to other naive broiler flocks. Other concurrent infection with immunosuppressive diseases (e.g., IBD) should also be addressed.