Inclusion Body Hepatitis

Adenoviruses are widespread throughout all avian species ( even in healthy bird),but,  the majority of adenoviruses cause no or only mild disease. Avian adenoviruses (AAV) in chickens are the etiologic agents of 2 important diseases known as inclusion body hepatitis (IBH) and hydropericardium syndrome (HP). Although in some cases each condition is observed separately, during the last decade the 2 conditions have been frequently observed as a single entity; therefore, the name hepatitis hydropericardium has been widely used to describe the pathologic condition. The syndrome is an acute disease of young chickens associated with anemia, hemorrhagic disorders, and hydropericardium. It is a common disease in several countries, where broilers are severely affected, resulting in high mortality rates.

Etiology, Transmission, and Pathogenesis:

The AAV of group I are the etiologic agents of this condition. Although there are 12 different serotypes of AAV, the most common viruses isolated in cases of IBH/HP belong to serotypes 4 and 8. These AAV are capable of producing the disease without the immunosuppressive effects of associated viruses such as infectious bursal disease (IBDV) or chicken anemia virus (CAV) .

Horizontal( one bird to other bird) and vertical(breeder to chick) transmission play an important role in IBH/HP. Horizontal transmission happen in young chicks, infected chicks can die of peracute IBH/HP. Chicks and young chickens are commonly affected. Infection with some strains of AAV may result in minimal hepatic disease; however, if birds have been infected with immunosuppressive viruses (IBD, CAV, Marek’s disease), the clinical disease becomes evident.

Clinical Findings, Lesions, and Diagnosis:

Sudden mortality usually is seen in chickens <6 wk old and as young as 4 days of age. Mortality normally ranges from 2-40%, especially when birds are <3 wk of age. However, there have been outbreaks in which mortality has reached 80%. Mortality rates also vary depending on the pathogenicity of the virus and infection with other viral or bacterial agents. Signs associated with diseases caused by other pathogens (eg, bacteria, fungi, or viruses) commonly occur if birds are immunosuppressed.
Inclusion body hepatitis, chicken
Flocks of 3- to 5-wk-old broilers with HP may not show specific clinical signs, but abrupt onset of mortality, lethargy, huddling with ruffled feathers, and yellow, mucoid droppings may be seen. The duration of the infection usually ranges from 9-14 days with morbidity of 10-30% and a daily mortality of 3-5%. Gross lesions include up to 10 mL of a straw-colored transudate in the pericardial sac, generalized congestion, and an enlarged, pale, friable liver. Histopathologic lesions include myocardial edema in the heart with degeneration, necrosis, and mild mononuclear cell infiltration. Basophilic intra-nuclear inclusion bodies may be present in the liver. A tentative diagnosis is based on typical microscopic findings and confirmed by isolating adenoviruses from the liver. Serology, restriction enzyme analysis and PCR are used to classify adenoviruses isolated from clinical cases. This information is used for epidemiologic studies.

Treatment and Prevention:

As with many other viral diseases, there is no treatment. Antibiotics may help prevent secondary bacterial infections. Sulfonamides are contraindicated if evidence of hematologic disease or immunosuppression is seen.

Vaccines against IBH/HP are not commercially available in the USA; however, in other countries both live and inactivated vaccines are used to control the syndrome. The AAV serotypes most frequently used to prepare commercial vaccines are serotypes 4 and 8. Primary breeders with stringent biosecurity practices sometimes use autogenous inactivated vaccines to ensure the transfer of maternal immunity from breeding flocks to their progeny. In Australia, a live vaccine given via drinking water was developed for breeders between 10-14 wk of age. In other countries, including Mexico, Pakistan, and Peru, inactivated vaccines are routinely used to vaccinate breeders and broilers. When breeders are properly vaccinated, antibodies generated by the vaccine are transmitted to the progeny, providing protection against field infections and clinical disease. Broilers are vaccinated at <10 days of age when their parents either do not have serotype-specific adenovirus antibodies or maternal antibody transmission is erratic due to improper vaccination procedures that result in a suwbstantial number of unvaccinated birds.
Reference :- Merck Veterinary Manual
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