Temporal Progression of Lesions in Guinea Pigs Infected With Lassa Virus.

Lassa virus (LASV) infection causes an acute, multisystemic viral hemorrhagic fever that annually infects an estimated 100 000 to 300 000 persons in West Africa. This pathogenesis study evaluated the temporal progression of disease in guinea pigs following aerosol and subcutaneous inoculation of the Josiah strain of LASV as well as the usefulness of Strain 13 guinea pigs as an animal model for Lassa fever. After experimental infection, guinea pigs ( Cavia porcellus; n = 67) were serially sampled to evaluate the temporal progression of infection, gross and histologic lesions, and serum chemistry and hematologic changes. Guinea pigs developed viremia on day 5 to 6 postexposure (PE), with clinical signs appearing by day 7 to 8 PE. Complete blood counts revealed lymphopenia and thrombocytopenia. Gross pathologic findings included skin lesions and congested lungs. Histologic lesions consisted of cortical lymphoid depletion by day 6 to 7 PE with lymphohistiocytic interstitial pneumonia at 7 to 8 days PE. Scattered hepatocellular degeneration and cell death were also noted in the liver and, to a lesser extent, in other tissues including the haired skin, lung, heart, adrenal gland, lymph nodes, thymus, and spleen. The first cell types to demonstrate staining for viral antigen were fibroblastic reticular cells and macrophages/dendritic cells in the lymph nodes on day 5 to 6 PE. This study demonstrates similarities between Lassa viral disease in human infections and experimental guinea pig infection. These shared pathologic characteristics support the utility of guinea pigs as an additional animal model for vaccine and therapeutic development under the Food and Drug Administration's Animal Rule.

Pathology of experimental aerosol Zaire ebolavirus infection in rhesus macaques.

There is limited knowledge of the pathogenesis of human ebolavirus infections and no reported human cases acquired by the aerosol route. There is a threat of ebolavirus as an aerosolized biological weapon, and this study evaluated the pathogenesis of aerosol infection in 18 rhesus macaques. Important and unique findings include early infection of the respiratory lymphoid tissues, early fibrin deposition in the splenic white pulp, and perivasculitis and vasculitis in superficial dermal blood vessels of haired skin with rash. Initial infection occurred in the respiratory lymphoid tissues, fibroblastic reticular cells, dendritic cells, alveolar macrophages, and blood monocytes. Virus spread to regional lymph nodes, where significant viral replication occurred. Virus secondarily infected many additional blood monocytes and spread from the respiratory tissues to multiple organs, including the liver and spleen. Viremia, increased temperature, lymphocytopenia, neutrophilia, thrombocytopenia, and increased alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transpeptidase, total bilirubin, serum urea nitrogen, creatinine, and hypoalbuminemia were measurable mid to late infection. Infection progressed rapidly with whole-body destruction of lymphoid tissues, hepatic necrosis, vasculitis, hemorrhage, and extravascular fibrin accumulation. Hypothermia and thrombocytopenia were noted in late stages with the development of disseminated intravascular coagulation and shock. This study provides unprecedented insight into pathogenesis of human aerosol Zaire ebolavirus infection and suggests development of a medical countermeasure to aerosol infection will be a great challenge due to massive early infection of respiratory lymphoid tissues. Rhesus macaques may be used as a model of aerosol infection that will allow the development of lifesaving medical countermeasures under the Food and Drug Administration's animal rule.

Thyroid adenocarcinoma in a bald eagle (Haliaeetus leukocephalus).

Thyroid adenocarcinoma was diagnosed in an adult bald eagle (Haliaeetus leukocephalus) with clinical signs of weakness manifested by inability to fly. Physical examination at the time of admission revealed dried blood in the pharynx and glottis and the presence of pharyngeal trichomonads. Radiographs revealed a large soft tissue mass in the area of the left coracoid and clavicular bones. One month following successful treatment for trichomoniasis, the bird suffered an acute episode of tracheal hemorrhage and died. Necropsy revealed a large mass within the interclavicular air sac. The histologic features were consistent with thyroid adenocarcinoma. This is the first report of thyroid neoplasia in a member of the order Falconiformes.

Lesions of neonatally induced toxoplasmosis in cats.

Five pregnant queens were inoculated orally with Toxoplasma gondii tissue cysts. Twenty-two live and three dead kittens were born 16 to 31 days after inoculation. Four kittens were eaten by queens and, thus, were not available for histologic examination. Twenty-one kittens that died or were euthanatized on day 2 (two kittens), 4 (one kitten), 5 (five kittens), 6 (five kittens), 7 (one kitten), 8 (four kittens), 16 (two kittens), and 29 (one kitten) after birth were studied histologically. T gondii was detected by bioassay and was seen in histologic sections of tissues from all 21 kittens. The histologic lesions associated with neonatal toxoplasmosis were widely disseminated infiltrates of macrophages and neutrophils often accompanied by necrosis; lymphocytes and plasma cells were occasionally present. The most consistent lesions were proliferative interstitial pneumonia (21/21); necrotizing hepatitis (20/21); myocarditis (21/21); skeletal myositis (21/21); glossal myositis (19/19); nonsuppurative encephalitis affecting the cerebrum (18/18), brain stem (15/15), and spinal cord (9/9); uveitis (19/19); necrotizing adrenal adenitis (18/18); and interstitial nephritis (16/21). Placental lesions (2/2) consisted of grossly visible areas of necrosis and mineralization.

Aerosolized staphylococcal enterotoxin B-induced pulmonary lesions in rhesus monkeys (Macaca mulatta).

The pathology of aerosolized staphylococcal enterotoxin B (SEB) was studied in the nonhuman primate. Six juvenile rhesus monkeys that received multiple lethal inhaled doses of SEB developed diarrhea and vomiting within 24 hr followed by depression, dyspnea, and shock. Three of 6 animals died by 52 hr. The most striking gross lesion in all 6 monkeys was diffuse severe pulmonary edema. Histologically, edema fluid was present within the peribronchiolar, peribronchial, and perivascular interstitium, alveolar septa, and alveoli. The adventitia of pulmonary vessels was infiltrated by lymphocytes, macrophages, and fewer neutrophils. Numerous large lymphocytes with occasional mitotic figures were within pulmonary vessels, often occluding alveolar capillaries. These cells were strongly immunoreactive with monoclonal antibodies against CD3, establishing them as T cells. Ultrastructurally, endothelial cell junctions were intact, and endothelial cells and type I pneumocytes contained numerous pinocytotic vesicles. Alveolar septal interstitial spaces were expanded by edema. The mechanism of these SEB-induced pulmonary lesions was not determined. We hypothesize that cytokine production by activated T cells may have caused vascular permeability changes leading to widespread pulmonary edema and shock.