Hemorrhagic enteritis (HE) is an acute disorder affecting young turkeys ≥4 weeks old. In its most severe form, it is characterized by depression and hemorrhagic droppings. Mortality may be increased; however, this is rare because of the extensive use of vaccines. Marble spleen disease (MSD) is an acute respiratory disease of pheasants characterized by depression, enlarged mottled spleens, pulmonary congestion, and death. Both diseases are caused by related viruses. Species-specific differences in the clinical response are thought to be related to differences in the target organs for anaphylaxis and variation in viral pathotype. Infection with less virulent pathotypes in either host often may go undetected until secondary bacterial infections begin to develop as a result of viral-induced immunosuppression.
Similar diseases have been seen sporadically in other species of birds, such as chickens (avian adenovirus splenomegaly [AAS]), guinea fowl, peafowl, and chukar partridges. Other siadenoviruses have also been reported to cause disease in various psittacine species, pigeons, finches, and penguins.
The etiologic agent of hemorrhagic enteritis and related infections such as marble spleen disease is a nonenveloped, icosahedral DNA virus, 70–90 nm in diameter. It is a member of the family Adenoviridae and the genus Siadenovirus, species turkey adenovirus 3 (TAdV-3) Based on differences in presentation within host species, numerous viral pathotypes appear to exist. These differ slightly at the DNA level but are indistinguishable serologically.
HE, MSD, and AAS are geographically widespread and considered endemic in areas where turkeys, pheasants, and chickens are raised commercially. Due to the widespread use of HE vaccines in turkey-producing countries, clinical HE is less frequently observed; however, HE virus (HEV)-associated immunosuppression may still be prevalent, with subsequent losses due to secondary infections. The usual route of HEV infection is fecal-oral/cloacal ("cloacal drinking"), and the virus is often introduced onto previously uninfected premises via personnel or equipment contaminated with infectious feces. In the case of MSD, aerosol-based transmission cannot be ruled out. As infection begins to cycle through a flock, large quantities of the virus are shed in the feces, which facilitates rapid spread to susceptible birds. Persistent infections may be detected with latent shedding by clinically recovered birds.
Turkey poults and pheasants younger than 3–4 weeks old normally do not develop clinical disease because of age-related resistance or, more commonly, the presence of maternally derived antibodies. The virus may survive under moist conditions (ie, in litter) well beyond the refractory period.
Morbidity usually approaches 100% for both hemorrhagic enteritis and marble spleen disease. In commercial operations, HE typically affects turkeys 6–12 weeks old but is most common between 7–9 weeks of age, when maternally derived HE-antibodies have waned. In outbreaks involving virulent pathotypes, clinical signs can include depression, pallor, and bloody droppings, which are observed within 5–6 days after oral infection and progress quickly. Acute mortality can range from 1%–60%, with an average of 10%–15% throughout a 2-week period.
Birds that survive the acute phase experience a transient immunosuppression related to the lymphotrophic, lymphocytopathic nature of the virus. This often manifests itself in the form of secondary bacterial infections, eg, colibacillosis ~10–14 days after exposure to the virus. Thus, a second peak in mortality, potentially overlapping the first, may be seen and, in less virulent outbreaks, may actually dominate the clinical picture. The second wave of mortality often lasts 2–4 weeks and is characterized by lesions commonly associated with bacterial respiratory disease or septicemia, eg, fibrinopurulent pneumonia, airsacculitis, pericarditis, peritonitis, perihepatitis, hepatomegaly, and splenomegaly. Concomitant or prior exposure to necrotic enteritis, coccidiosis, Newcastle disease virus, Bordetella avium, or Mycoplasma gallisepticum and M synoviae can exacerbate the problem. Similar multiple agent interactions have been implicated in mortality associated with the use of live vaccines for hemorrhagic enteritis.
MSD typically affects pheasants kept in captivity when 3–8 months old. Onset is acute, with dyspnea, asphyxiation, and sudden death occurring as a result of pulmonary congestion and edema. Mortality is commonly 2%–3% but can reach 15%. Secondary bacterial infections as a result of immunosuppression have also been noted.
Necropsy of moribund or dead birds infected with hemorrhagic enteritis virus reveals gross congestion and occasional intraluminal hemorrhage in the proximal small intestine. The spleen is usually enlarged, friable, and mottled white, except in birds that have hemorrhaged extensively. Hemorrhage in the intestine is not common in field cases. Histopathologic changes in the duodenum include congestion, hemorrhage, and necrosis of the intestinal epithelium. This lesion in particular is thought to be the result of a virally induced, cytokine-mediated anaphylactic reaction, with the GI tract being considered the target shock organ in turkeys. Basophilic intranuclear inclusions can be found in lymphocytes and macrophages in a variety of tissues (eg, intestine, liver, and lungs) but predominantly in the spleen, where lymphoreticular hyperplasia and lymphoid necrosis are noted. Intranuclear inclusions in the renal tubular epithelial cells of the kidneys can be seen in turkeys that have recovered from hemorrhagic enteritis.
On histopathologic evaluation of pheasants with MSD, flooding of the atria and tertiary bronchi with fibrin and RBCs, as well as generalized vascular congestion and focal necrosis, are often seen in the lung. As with HE, this response may be anaphylactic in nature, with the lung being considered the target shock organ in the pheasant. Splenomegaly with lymphoreticular hyperplasia and lymphoid necrosis also occur and are the characteristic lesions for which marble spleen disease is named. Basophilic or magenta-colored intranuclear inclusions may be found in a variety of tissues excluding the GI tract, with the highest concentration of virus found in the spleen.
Diagnosis of virulent outbreaks of hemorrhagic enteritis or marble spleen disease can often be made based on clinical signs and gross lesions. Confirmation is by histopathology and the presence of seroprecipitating virus in the spleen as determined by agar gel immunodiffusion. HEV propagation in the cell line MDTC_RP19, spleen or B cell suspension cultures, or naive birds (turkeys as well as chickens) is possible but time consuming.
Various PCR techniques to detect viral DNA in tissue have also been described and are in regular use. Sequencing approaches can be used to differentiate vaccine and virulent field strains, but differences at the nucleic acid level are minor, so sequencing must go beyond the sequence of the hexon protein. To determine whether HEV or MSD virus is a predisposing factor in cases of bacterial respiratory disease or septicemia, or to verify a primary diagnosis, acute and convalescent sera (3 weeks apart) can be tested using either agar gel immunodiffusion or ELISA, the latter being also commercially available.
In turkeys, differential diagnoses include colibacillosis, pasteurellosis, paratyphoid, and erysipelas. Reticuloendotheliosis or lymphoproliferative disease should be considered when lymphoreticular hyperplasia is the predominant lesion. GI lesions without splenic involvement should evoke consideration of other viral, bacterial, parasitic, and toxic enteritides of turkeys. In pheasants with acute respiratory disease, differential diagnoses include Newcastle disease, avian influenza, Syngamus trachea, and in the case of birds reared in confinement, gaseous toxins.
Prevention of hemorrhagic enteritis or marble spleen disease normally relies on the use of live vaccines administered in the drinking water at ~4–5 weeks of age, when maternally derived antibodies are below the breakthrough level of the vaccine. Tissue culture products and crude splenic preparations containing avirulent isolates produce lifelong protection, possibly due to virus persistence, and are licensed in different countries. A subunit vaccine as well as a full-antigen inactivated vaccine to prevent HE in turkeys have been described in Europe. Antibodies have been suggested to be the main determinant of protection, but cell-mediated immunity also has been shown to be stimulated after infection. Virus-neutralizing epitopes have been identified within the hexon protein, and protection is not strain-specific. Vaccine-driven antigenic drift of field strains cannot be excluded.
Vaccines intended for use in turkeys should not be used in pheasants, and vice versa, because the avirulent isolates used for vaccinating one species are typically virulent in the other. Because of the potential for interaction with other agents, including live vaccines, regular disease monitoring and careful integration of HE and MSD vaccines into flock vaccination protocols is encouraged. Intuitively, vaccines should not be administered to birds exhibiting signs of illness or within 2 weeks of any other vaccination.
Secondary bacterial infections may be treated with antibiotics based on the resistance profile of the bacterial isolates. Vaccination must be accompanied by biosecurity and hygiene measures. Chlorine, iodine, and quaternary ammonium-based disinfectants may be effective against the nonenveloped viruses. All-in, all-out management practices may help reduce the risk of transmission between flocks, but elimination of the virus on multi-age farms seems difficult.
In the past, HE outbreaks have also been successfully treated and controlled by injection of exposed birds with 0.5–1 mL of antiserum obtained from recovered flocks. It is presumed that a similar approach may be effective for pheasants. Due to high labor costs, this is rarely used.
Vaccination in combination with hygiene measures are important for the control of HE and MSD.
Maternal antibodies may interfere with the vaccine response, and therefore, at the time of vaccination, must be below the breakthrough level of the vaccine.
Revaccination may not be necessary because life-long immunity is assumed. In the case of high variation in maternally derived antibody levels within a flock, a second vaccination may be necessary to achieve sufficient protection.
Pierson, F. W., and S. D. Fitzgerald. 2013. Hemorrhagic enteritis and related infections. In: Diseases of Poultry, 13th ed. D.E. Swayne, J. R. Glisson, L. R. McDougald, L.K. Nolan, D. L. Suarez and V. Nair, eds. Wiley-Blackwell, Ames, Iowa, USA, pp. 309-331. (new edition in 2021)
Dhama, K., Gowthaman, V., Karthik, K., Tiwari, R., Sachan, S., Kumar, M. A., Palanivelu, M., Malik, Y. S., Singh, R. K., Munir, M. 2017. Hemorrhagic enteritis of turkeys - current knowledge. Veterinary Quarterly, 37:1, 31-42.