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By Dr. Ibne Ali, IMN PyrophosUpdated October 20268 min read
Adenovirus - IBH Infection in Poultry

Understanding Avian Adenovirus Infections in Chickens: A Comprehensive Guide

Avian adenovirus infections are a common concern in poultry, particularly affecting chickens worldwide. While many infections can be subclinical or associated with nondescript syndromes, certain adenoviruses are significant primary pathogens causing distinct and economically important diseases. Understanding these infections is crucial for maintaining flock health and productivity.

What are Avian Adenoviruses in Chickens?

Adenoviruses are DNA viruses that replicate and produce characteristic inclusion bodies in the nuclei of infected cells. They are non-enveloped and range in size from 70 to 90 nm. In poultry, adenoviruses are classified into three genera, with those affecting chickens primarily belonging to:

  • Aviadenovirus (Group I Avian adenoviruses): This genus includes Fowl adenoviruses (FAdV) with 12 serotypes (FAdV-1 to FAdV-11) assigned to five species (A-E).
  • Siadenovirus (Group II Avian adenoviruses): Turkey adenovirus A (TAdV-3), which causes Marble Spleen Disease in pheasants, can also cause Avian Adenovirus Splenomegaly in chickens.
  • Atadenovirus (Group III Avian adenoviruses): Duck adenovirus-1 (DAdV-1) causes Egg Drop Syndrome (EDS) in chickens.

How do Chickens Get Infected?

Adenoviruses can spread through both vertical and horizontal transmission.

  • Vertical Transmission: Infected breeders can transmit the virus through eggs to their progeny. This can lead to outbreaks in young birds or latent infections that reactivate later, particularly during stress or peak egg production.
  • Horizontal Transmission: The virus is shed in feces, making the fecal-oral route a primary mode of spread. Contaminated environments, fomites (such as egg trays and transport vehicles), personnel, and even dust created during cleaning can facilitate spread between farms or within flocks. Some adenoviruses, like FAdV-4, can also spread via aerosol transmission.

Major Adenoviral Diseases in Chickens and Their Lesions

The lesions associated with avian adenovirus infections vary significantly depending on the specific virus or syndrome involved. Here's a breakdown of the key diseases in chickens:

1. Inclusion Body Hepatitis (IBH)

  • Definition: IBH is a disease of young chickens characterized by sudden onset, increased mortality, and hepatitis with intranuclear inclusion bodies.
  • Causative Agents: Most commonly caused by FAdV-2, FAdV-8 (8a and 8b), and FAdV-11, but also by FAdV-4 (as part of HPS) and FAdV-6.
  • Occurrence: Worldwide distribution, typically seen in 2 to 5-week-old broilers, but can affect younger or older birds, layers, and breeders.
  • Clinical Signs: Often, the first sign is a sudden marked increase in mortality (up to 30%, but typically lower). Affected birds may be depressed, listless, pale (comb, wattles, facial skin), and show ruffled feathers or huddling. Yellow, mucoid droppings may also be observed.
  • Gross Lesions:
  • Liver: Consistently affected, appearing swollen, enlarged, pale pink to tan, yellow, or mottled. It may have focal soft areas or petechial and ecchymotic hemorrhages under the capsule and in the parenchyma.
  • Kidneys: Frequently swollen, pale, or mottled.
  • Bursa of Fabricius: Can be reduced in size.
  • Other: Mild hydropericardium, necrotizing pancreatitis, pale skin, yellow discoloration (jaundice), petechial hemorrhages in skeletal muscles (legs, breast), anemia, icterus of skin/subcutaneous fat, and bone marrow degeneration may occur. Gizzard erosions can also be seen.
  • Microscopic Lesions:
  • Liver: Multifocal to locally extensive degeneration and necrosis of hepatocytes. The hallmark is the presence of large basophilic intranuclear adenoviral inclusions within hepatocytes, especially at the periphery of necrotic foci.
  • Kidneys: Membranous and membranoproliferative glomerulitis, less frequently cortical tubular degeneration and necrosis.
  • Bursa: Reduced follicular size with lymphoid depletion.
  • Pancreas: Necrotizing pancreatitis with intranuclear inclusions.
  • Gizzard: Necrotic focal lesions.

2. Hydropericardium/Hepatitis Syndrome (HPS)

  • Definition: Similar to IBH, but with a more acute course and higher mortality, characterized by significant fluid accumulation around the heart.
  • Causative Agent: Caused by virulent FAdV-4 strains.
  • Occurrence: Mainly affects 3 to 6-week-old broiler chickens, but also reported in layers and breeders.
  • Clinical Signs: Rapidly increasing mortality (20-80%), dullness, depression, ruffled feathers, huddling, ventral recumbency, and closed eyes in later stages.
  • Gross Lesions: The striking feature is the accumulation of up to 10 ml of serous fluid in the pericardial sac (hydropericardium). The liver is discolored, enlarged, and may show focal necrosis and hemorrhage. Lungs can be edematous and congested, and kidneys may be pale with enlarged tubules due to urate deposits.
  • Microscopic Lesions: Marked necrotizing hepatitis with intranuclear inclusion bodies in hepatocytes, similar to IBH. Also, viral tropism for lymphoid tissues leads to degeneration of lymphoid organs and lymphocyte depletion (lymphocytolysis) in the bursa, thymus, and spleen.
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3. Gizzard Erosion and Ulceration Syndrome (GEU)

  • Definition: A significant cause of economic losses due to gizzard lesions.
  • Causative Agent: Caused by FAdV-1.
  • Occurrence: Emerged in the last 20 years, affecting broilers, pullets, broiler breeders, and commercial egg-laying flocks. Can occur sporadically or in outbreaks.
  • Clinical Signs: Affected birds may die with no evident clinical signs. Losses are mainly due to reduced growth rate, increased mortality, and condemnation of gizzards at slaughter.
  • Gross Lesions: Gizzards may be dilated or contain brown sanguineous fluid. There are variably sized brown-black discolored areas of koilin, with erosions, ulceration, and inflammation extending to the deeper mucosa.
  • Microscopic Lesions: Basophilic intranuclear inclusions typical of adenoviruses are commonly, but not always, detectable in the glandular epithelial cells. There is also thickening and vacuolation of the koilin layer due to inflammation and degeneration.

4. Egg Drop Syndrome '76 (EDS'76)

  • Definition: An infectious disease of laying hens characterized by a loss of color in pigmented eggs and failure to achieve production targets, or by the production of thin-shelled, soft-shelled, or shell-less eggs in otherwise healthy-looking birds.
  • Causative Agent: Caused by Duck adenovirus-1 (DAdV-1), an Atadenovirus.
  • Occurrence: Widespread globally, but not historically described in North America until recently (first reported in USA in 2019).
  • Clinical Signs: Primary signs are associated with egg quality issues: loss of color in pigmented eggs, thin-shelled, soft-shelled, or shell-less eggs. Egg production may drop rapidly or fail to reach expected peaks. Other mild signs can include transient dullness, watery droppings (due to oviduct fluid secretion), small eggs, watery albumen, or delayed onset of lay.
  • Gross Lesions: Often minimal in natural infections. May include inactive ovaries and atrophied oviducts, though these are not consistently present. Experimentally, edema and swelling of uterine mucosal folds and exudate in the shell gland lumen have been described.
  • Microscopic Lesions: In experimentally infected hens, oviduct changes include proprial edema, infiltration of inflammatory cells, atrophy of tubular glands, and degeneration/desquamation and attenuation of uterine epithelium. Intranuclear adenoviral inclusions may be seen in epithelial cells of the uterus, isthmus, and vagina. However, these acute inflammation, necrosis, or viral inclusions are rarely identified in naturally occurring outbreaks because the lesions are transient.

5. Avian Adenovirus Splenomegaly (AAS)

  • Definition: A disease in chickens caused by Siadenoviruses. While details on specific chicken lesions are less emphasized, Siadenoviruses (Turkey siadenovirus A) are known to cause splenomegaly (enlarged spleen) in pheasants (Marble Spleen Disease) and turkeys (Hemorrhagic Enteritis), both of which show characteristic intranuclear inclusions in splenic cells.

Diagnosing Adenovirus Infections in Chickens

  • Histopathology: The demonstration of characteristic intranuclear inclusion bodies in affected organs (e.g., liver for IBH/HPS, gizzard for GEU, oviduct for EDS) is a key diagnostic method. For IBH, HPS, and GEU, inclusions are usually readily detected.
  • Virus Isolation: Isolation of the specific FAdV from affected organs (e.g., liver for IBH) can confirm the diagnosis. For EDS'76, duck/goose embryonated eggs or cell cultures are used.
  • Molecular Methods (PCR): Detection of adenoviral DNA (e.g., FAdV DNA in liver for IBH) by PCR is a method of choice for direct identification and genotyping.
  • Serology:
  • For IBH, seroconversion to associated serotypes (FAdV-2, -8, -11) can be detected by micro-neutralization assays. However, general serological tests for group antigens are of limited value due to widespread infection and inability to differentiate pathogenic from non-pathogenic strains.
  • For EDS'76, serological tests like hemagglutination inhibition (HI) are very helpful, especially in unvaccinated flocks, as infected hens typically seroconvert by the time abnormal eggs are produced.
  • Electron Microscopy: Can augment routine diagnosis.

Control and Prevention in Chicken Flocks

There is no specific treatment available for avian adenovirus infections. Control strategies primarily focus on prevention:

  • Biosecurity: Strict biosecurity practices are essential, including proper disinfection of barns and equipment, and good ventilation. This helps prevent horizontal spread, especially since adenoviruses are resistant to environmental factors.
  • Vaccination:
  • IBH/HPS: Inactivated vaccines, sometimes derived from liver homogenates of infected birds or cell cultures, are available in some countries. Live-licensed vaccines (e.g., against FAdV-8b in Australia) and autogenous vaccines (often bivalent, containing FAdV-8 and FAdV-11) are also used. Control of immunosuppressive viruses like Infectious Bursal Disease Virus (IBDV) and Chicken Anemia Virus (CAV) is also important to prevent severe IBH outbreaks, as they can enhance adenovirus pathogenicity.
  • EDS'76: Inactivated vaccines, typically administered before the onset of lay, have been very successful in controlling clinical EDS. Eradication programs are also used. Minimizing contact with wild waterfowl (natural hosts) and using treated water sources are also recommended.
  • Breeding Stock Management: To avoid vertical transmission, eggs from primary breeding flocks with a history of recurrent IBH in their progeny should not be used for hatching. For EDS'76, eradication has been achieved in some primary breeders.
  • Environmental Resistance: Adenoviruses are relatively resistant to physical and chemical factors, making environmental persistence a challenge.

By implementing robust biosecurity measures and considering vaccination strategies where available, chicken farmers can significantly reduce the impact of these challenging adenovirus infections. IBH Infection ibh in poultry

Problem in your flock? Send photos of the birds and droppings on WhatsApp for a first opinion from Dr. Ibne Ali.

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