Abstract. The Ehrlichia phagocytophila-group also includes E. equi and the human granulocytic ehrlichiosis (HGE) agent that are probably a single species. Disease is mild to severe illness in ruminants, horses, and humans, but the comparative pathology and ehrlichial distribution in tissues is poorly described. We compared pathology and ehrlichial distribution in humans with HGE, horses with E. equi infection, and a sheep with E. phagocytophila infection. Frequent findings included splenic lymphoid depletion, small macrophage aggregates and apoptoses in liver, and paracortical hyperplasia in lymph nodes. Bone marrow was normocellular or hypercellular. Only the spleen was frequently infected; other organs with infected cells included lung, liver, heart, and kidney, but lesions were present in lung and liver only. Most infected cells were neutrophils. Ehrlichia phagocytophila-group infections are associated with moderate tissue damage. While the pathogenesis of granulocytic ehrlichiosis is not clear, pathologic studies suggest that the process is initiated by ehrlichia-infected cells but may result from host-mediated injury and immunosuppression.Ehrlichioses are rickettsial infections that occur in animals and humans and are caused by microorganisms of the genus Ehrlichia. The genus Ehrlichia belongs to the family Rickettsiaceae and consists of small obligatory intracellular bacteria that average 0.5-1.5 m in length, which proliferate in vacuoles in the cytoplasm of leukocytes and other cells of bone marrow or mesodermal origin. 1 The Ehrlichia phagocytophila-group includes E. phagocytophila, E. equi, and the human granulocytic ehrlichia. The prototype for the E. phagocytophila genogroup (a cluster of closely related bacteria based upon gene sequences) is E. phagocytophila, a European pathogen of ruminant neutrophils that causes tick-borne fever in sheep, goats, and cattle. 2 Ehrlichia equi is an agent of both equine and canine granulocytic ehrlichiosis.3,4 Homology of the 16S ribosomal DNA of these organisms, as well as that of the newly identified agent of human granulocytic ehrlichiosis (HGE), is more than 99.8%.5-8 These species are phylogenetically and antigenically very similar. 5,9 In addition, the HGE agent produces a disease in the horse similar from that caused by E. equi 10 and infection of horses with the agent of HGE confers resistance to E. equi challenge. 11 The causative agent of tick-borne fever was first discovered in Scotland in 1932; 12 however, the disease has probably been recorded in sheep for more than 200 years in Norway. 13 The disease is characterized by fever, leukopenia, marked neutropenia, and thrombocytopenia. 14 Equine granulocytic ehrlichiosis has been a recognized disease of horses in California since the 1960s.15 Clinical manifestations include fever, lethargy, anorexia, distal limb edema, petechiation, icterus, ataxia, reluctance to move, and thrombocytopenia. 16 Human granulocytic ehrlichiosis is a recently described disease characterized by fever, headache, myalgia, chills, va...

This report describes the clinical laboratory findings in golden hamsters experimentally infected with yellow fever (YF) virus. An accompanying paper describes the pathologic findings. Following intraperitoneal inoculation of a virulent strain of YF virus, hamsters developed a high-titered viremia (up to 109/mL) lasting 5--6 days and abnormal liver function tests. YF hemagglutination-inhibiting antibodies appeared 4 or 5 days after infection, often while viremia was still present. The mortality rate in YF-infected hamsters was variable, depending on the virus strain and the age of the animals. Clinical and pathologic changes in the infected hamsters were very similar to those described in experimentally infected macaques and in fatal human cases of YF, which indicates that the golden hamster may be an excellent alternative animal model, in place of nonhuman primates, for research on the pathogenesis and treatment of YF and other viscerotropic flavivirus diseases.

Human granulocytic ehrlichiosis (HGE) results in fever, pancytopenia, and mild liver injury. We used a mouse model to examine immunity in the pathogenesis of HGE. HGE agent-infected C3H/HeJ mice were necropsied over 21 days. Histologic, immunohistologic, and serologic analyses, blood culture, tissue and blood polymerase chain reaction (PCR), cell counts, serum chemistries, and plasma cytokine ELISAs were performed. No clinical signs were detected. Ehrlichiae were identified in neutrophils in hematopoietic tissues maximally on day 7. Interleukin (IL)-10 levels were high throughout, whereas interferon (IFN)-gamma levels peaked on days 7 and 10 and dropped thereafter. Hepatic lymphohistiocytic aggregates with apoptoses were maximal at day 14. HGE-agent infection of mice induces pathologic changes similar to those in infected humans, despite differences in cytokine profile. The IFN-gamma peak prior to maximal pathologic change, when ehrlichiae are absent in tissues, suggests a role for host immunity in the pathogenesis of HGE.

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Abstract. To identify potential zoonotic reservoirs of pathogenic leptospires in the Peruvian Amazon basin, wild mammals were trapped from July 1997 to December 1998 near the city of Iquitos. After extraction of nucleic acids from animal kidneys, DNA of pathogenic leptospires was identified by polymerase chain reaction (PCR) assays using one of two primer sets, one amplifying a region of the 23S rRNA gene, and the other amplifying a gene fragment specific for Leptospira spp (G1/G2 primers). Overall, 29% (40 of 136) of the mammals tested showed evidence of renal infection by Leptospira spp., including 20% (13 of 64) of the rodents, 39% (20 of 51) of the marsupials, and 35% (7 of 20) of the chiropterans (bats). Marsupials and chiropterans were implicated as more significant reservoir hosts of leptospires pathogenic to humans than previously recognized.