Signalment: Approximately 5-month-old New Zealand red male rabbits, Oryctolagus cuniculi. SPF (Pasteurella free)
History: Received from vendor. Quarantined for 5 days to determine health status and for acclimation to laboratory post-shipping. (Weather was cold and snowy.) First case of exophthalmos noted 1 month after shipment as unilateral exophthalmos with mild mucosuppurative discharge. Animals were not used on protocol. No signs of lethargy until 2 days prior to euthanasia.
Gross Pathology: Planned necropsy due to ocular lesion. Animals were destined for use in superficial ophthalmic toxicology testing.
Laboratory Results: Staphylococcus was isolated from all four rabbits (Staphylococcus capitis from one and Staphylococcus aurieuloris from three cases).
Contributor's Diagnosis and Comments:
This was an interesting case of staphylococcosis in four rabbits. All had retrobulbar abscess formation of the left eye with ocular discharge, and at death each had either unilateral or bilateral fibrinosuppurative and necrotizing bronchopneumonia. In one rabbit, the inflammation (abscesses) extended into the lower jaw. We isolated Staphylococcus from all four cases. (Staphylococcus capitis from one and Staphyloccus aurieloris from three cases). At the same time as these cases, two of our laboratory animal technicians developed severe conjunctivitis while caring for these rabbits. Little objective data is available concerning the incidence of staphylococcosis in rabbits; however, it is generally conceded to be quite common. Likewise, the disease appears to be common among wild rabbits including jack rabbits and cotton-tails. Staphylococcus aureus is most often isolated from affected rabbits. The septicemic form is most common in young rabbits or rabbits stressed from various causes. Rabbits may be infected by S. aureus with little or no clinical signs. The organism may reside in the nasal sinus or lungs and may be spread by direct contact or by aerosol. Once infected, a rabbit is likely to develop clinical disease when its resistance is sufficiently decreased. Infection of skin wounds is a common route of infection and results in suppurative inflammation of the skin and subcutaneous abscesses. Septicemia may also result from skin infection. The clinical signs depend on the site and duration of infection. There may, of course, be no clinical disease related to infection; however, swelling, redness, and induration of the skin, subcutaneous tissue, and/or mammary glands may occur in acute and subacute infection. In chronic infections, abscesses develop in the subcutaneous tissue and mammary glands, and these appear as firm or fluctuant swellings. In cases of acute septicemia, there may be fever, anorexia, depression, and death. Suppurative inflammation of the skin and subcutaneous tissue is typically seen with staphylococcosis. The inflammation usually becomes chronic, and thick-walled abscesses containing thick, white, suppurative exudate develop. Septicemia may result in peracute death with only a few nonspecific lesions; however, if the rabbit survives this phase, abscesses may develop in many internal organs. The heart, kidneys, lung, liver, spleen, epididymis, testes, and joints may be affected. Osteitis and osteomyelitis similar to that seen in actinomycosis has been described.
AFIP Diagnosis: Lung: Bronchopneumonia, necrosuppurative, subacute, diffuse, severe, with type II pneumocyte hyperplasia, pleuritis and colonies of cocci, New Zealand red rabbit (Oryctolagus cuniculi), lagamorph.
Conference Note: The conference participants agreed with the contributor's diagnosis. A Gram stain presented during the conference demonstrated numerous gram-positive cocci occurring primarily in clusters. The microscopic lesions in this section are typical of staphylococcal pneumonia.
Staphylococcus aureus is a pyogenic, nonmotile, gram-positive coccus that tends to form grape-like clusters. S. aureus and other pathogenic staphylococci possess a multitude of virulence factors including surface proteins involved in adherence to host cells, secreted enzymes that degrade host proteins, and secreted toxins that damage host cells. Additionally, staphylococci have surface receptors for fibrinogen, fibronectin and vitronectin which allow the bacterium to bind to host endothelial cells and a surface receptor for laminin which allow the bacterium to bind extracellular matrix proteins and invade host tissues. Important secreted enzymes include hyaluronidase, which depolymerizes hyaluronic acid, staphylokinase, which activates serum proteases to induce fibrinolysis, and coagulase, which clots plasma directly and promotes the encapsulation of foci of infection. S. aureus produces multiple hemolytic exotoxins including toxin, which is directly cytolytic by forming transmembrane pores; toxin, a sphingomyelinase; and toxin, which is a detergent-like peptide.
Contributor: Comparative Pathology Branch, Comparative Medicine Division, U.S. Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, MD 21010-5425.
International Veterinary Pathology Slide Bank: None.
Signalment: 12-week-old Hyline laying pullets.
History: Sudden increase in mortality.
Gross Pathology: Birds are in good general body condition. The tracheal mucosa is hemorrhagic and the lumen contains fibrinonecrotic exudate.
Laboratory Results: Avian herpesvirus was isolated from the trachea by tissue culture and CAM egg inoculation. Infectious laryngotracheitis (ILT) was confirmed by PCR. Moderate mixed miscellaneous bacteria were recovered from the tracheal exudate.
Contributor's Diagnosis and Comments: Tracheitis, severe, acute, generalized, necrotizing. Etiology: Avian herpes virus (infectious laryngotracheitis virus).
Infectious laryngotracheitis in gallinaceous birds is caused by avian herpesvirus- 1. Disease is characterized by acute onset of dyspnea, coughing and head shaking with expectoration of hemorrhagic exudate.¹ Increased mortality rates are usually attributable to occlusion of bronchial airways with caseous exudate. Mortality rates can vary with virus strain pathogenicity and partial protection by vaccination. Vaccinated and recovered birds can become carriers with lifetime intermittent shedding of the virus.²
Commercial vaccines are available in endemic areas. There is no treatment available although early (re)vaccination of the flock in the face of an outbreak may protect unaffected birds.²
The characteristic lesion of ILT is hemorrhagic tracheitis. Histologically, there is a severe necrotizing tracheitis associated with epithelial necrosis and sloughing, infiltration of the submucosa with mixed inflammatory cells and the presence of large basophilic intranuclear inclusion bodies within single epithelial cells, or in syncytia.²
AFIP Diagnosis: Trachea and larynx: Laryngotracheitis, necrotizing, subacute, diffuse, severe, with syncytial cells and eosinophilic intranuclear inclusion bodies, Hyline chicken, avian, etiology consistent with avian herpesvirus (infectious laryngotracheitis virus).
Conference Note: This is a classic case of infectious laryngotracheitis. We included larynx in our morphologic diagnosis because several of the slides contained a small section of larynx. Also, pseudomembranes were variably present among the sections.
Infectious laryngotracheitis virus is an avian alpha-herpesvirus with a narrow host spectrum; it primarily affects domestic poultry over 8 weeks of age. Several gallinaceous birds, including pheasants and peafowl, also are susceptible. Canaries may be infected as well.
Unlike other herpesviruses, natural transmission is exclusively
aerogenic. The virus has an affinity for the respiratory epithelium
and viremia does not develop. The virus is occasionally recovered
from the esophagus and intestine. Other important diseases caused
by avian alpha-herpesviruses include Marek's disease, which affects
gallinaceous birds; Amazon tracheitis, which affects the genus
Amazona and Bourke's parrots; and duck plaque (duck viral enteritis),
which affects ducks, geese, and swans.
Contributor: Animal Health Centre, British Columbia Ministry of Agriculture, Fisheries, and Food, 1767 Angus Campbell Road, Abbotsford, British Columbia V2S- 4N8.
International Veterinary Pathology Slide Bank:
Laser disc frame #23509.
Signalment: Sandhill crane (Grus canadensis), male, 2-months-old.
History: This crane was part of a collection at a zoological park. He was found recumbent and died before treatment could be administered.
Gross Pathology: The spleen was enlarged and mottled. Multiple, widely disseminated white nodules (0.5mm in diameter) were present in liver, cardiac muscle, and pancreas.
Laboratory Results: None.
Contributor's Diagnosis and Comments: Severe, diffuse, granulomatous hepatitis, with intracellular coccidian meronts.
Disease Diagnosis: Disseminated visceral coccidiosis.
Cause: Eimeria gruis and/or Eimeria reichenowi.
Histology: In the liver there is a prominent infiltrate of mononuclear cells surrounding portal triads, portal veins and sublobular veins. The infiltrate extends into surrounding sinusoids and consists of numerous parasitized monocytes (presumed to be macrophages), with fewer lymphocytes and plasma cells. The monocytes contain basophilic cytoplasmic meronts and merozoites. In the central areas of intense infiltration, there are foci of necrosis characterized by karyolysis and pyknosis. In other organs (lung, ventriculus, spleen and heart), parasitized monocytes and multiple granulomas also are present. Intravascular monocytes and/or lymphocytes containing meronts are particularly prominent in the blood capillaries of the lung. Sexual stages (macrogametes and microgametes) are present along with numerous meronts in the small intestinal epithelial cells.
E. gruis and E. reichenowi have been reported in wild and captive whooping cranes and sandhill cranes as the cause of visceral coccidiosis. The more severe infections have been in young captive cranes. Surveys in sandhill cranes indicate a high prevalence of infection in the wild. The presence of oocysts in the trachea and bronchi of experimentally infected cranes demonstrates that these species of Eimeria are capable of completing their life cycle in the digestive and respiratory tracts.
AFIP Diagnosis: Liver: Hepatitis, histiocytic and lymphoplasmacytic, random, moderate, with extensive hepatocellular loss, and intrahistiocytic protozoa, sandhill crane (Grus canadensis), avian.
Conference Note: The coccidians Eimeria gruis and Eimeria reichenowi are common parasites of sandhill and whooping cranes in North America. Although Eimeria sp. infections are generally diseases of the intestinal tract, a few species can develop at extraintestinal sites. Disseminated visceral coccidiosis was first recognized as a disease entity at the Patuxent Wildlife Research Center in Laurel, Maryland. Granulomatous inflammation may be observed in many tissues and results in bronchopneumonia, hepatitis, myocarditis, splenitis, and enteritis. The disseminated visceral infection by these protozoans has resulted in the deaths of a number of whooping and sandhill cranes less than two weeks of age. Mature cranes seem to be less susceptible to infection and are able to tolerate the coccidian parasite. Histologically, granulomatous nodules contain numerous parasitized mononuclear cells with both merogonic and gametogenic stages of eimerian coccidia. In one study, many of the granulomatous foci were noted within the adventitia of blood vessels, suggesting hematogenous dissemination of the infection.
Contributor: College of Veterinary Medicine, Department of Pathology, University of Georgia, Athens, GA 30602.
International Veterinary Pathology Slide Bank: None.
Case IV - L32 (AFIP 2558780)
Signalment: 3-week-old pigeon.
History: A pigeon from a small backyard flock was found with a mass over the head at slaughter. The bird's general condition was good.
Gross Pathology: There was a 30x30x4 mm, flattened mass covering the top of the head. It was moderately well demarcated and had a rough surface scarcely covered with atrophic feathers. On cut section the tumor was homogeneously white and firm. It extended to the cranium bone and did not penetrate the meninges.
Laboratory Results: None.
Contributor's Diagnosis and Comments: Skin: Schwannoma, malignant.
The tumor was poorly demarcated, non-encapsulated and had an infiltrating type of growth. It extended from a largely ulcerated skin surface down to and invading the cranium bone. Segmentally the bone was effaced by the tumor reaching the dura matter. The tumor was predominantly composed of anastomosing areas of loosely arranged short fascicles bathed in a moderately abundant clear extracellular matrix. Alternating with these areas were less abundant condensations forming whirling arrangements around preexisting nerves, vessels and entrapped feather follicles.
Neoplastic cells were very frequently associated in 5-15 cell units characterized by distinct palisading of their nuclei at the periphery of aggregates of parallel eosinophilic fibers (Verocay bodies). Cellular morphology was heterogeneous. Most neoplastic cells were small spindle cells with an irregularly oval to fusiform nucleus, a stippled to reticular chromatin pattern, and 2-5 small nucleoli. The tumor contained a moderate number of scatter large neoplastic cells with abundant and finely granular eosinophilic cytoplasm and a round open-faced nucleus showing sometimes a large nucleolus. Some of these cells were hypereosinophilic with a hyperchromatic nucleus (degenerate). The mitotic index was very low (approximately 1 mitotic figure per 10 fields examined at X400). Neoplastic cells were negative for rabbit anti-cow S-100.
The tumor contained a small number of heterophils infiltrating the matrix and marginated in blood vessels, perivascular aggregates of mononuclear cells and a few pigment-laden macrophages. The surface was largely covered by a serocellular crust.
There is a very scant literature on peripheral nerve sheath tumors in birds. They include neurofibroma, neurofibrosarcoma, neurilemmoma or schwannoma and ganglioneuroma. This case is remarkable for the degree of differentiation, the malignant type of growth and the age of the animal. Palisading, a striking feature of this tumor, is uncommon in avian nerve sheath tumors. The term schwannoma was preferred owing to the predominance of schwann cell type in the tumor. Malignancy was judged from infiltrative growth and invasiveness.
AFIP Diagnosis: Feathered skin, top of head: Ganglioneuroma, pigeon, avian.
Conference Note: Although careful consideration was given to the contributor's diagnosis of malignant schwannoma, the diagnosis of ganglioneuroma is favored. As mentioned by the contributor, there are moderate numbers of scattered, large, neoplastic cells with abundant finely granular eosinophilic cytoplasm, round open-faced nuclei and sometimes large single nucleoli. These cells stained well with cresyl violet and are interpreted to be neurons. Ganglioneuromas are benign neuroectodermal tumors that contain both Schwann cells, which predominate, and neurons.
Contributor: Laboratoires PFIZER, Centre de Recherche, BP 159, 37401, AMBOISE CEDEX, FRANCE.
International Veterinary Pathology Slide Bank: None.
Captain, VC, USA
Registry of Veterinary Pathology*
Department of Veterinary Pathology
Armed Forces Institute of Pathology
(202)782-2615; DSN: 662-2615
* The American Veterinary Medical Association and the American College of Veterinary Pathologists are co-sponsors of the Registry of Veterinary Pathology. The C.L. Davis Foundation also provides substantial support for the Registry.