West Nile virus transmission and ecology in birds

The ecology of the strain of West Nile virus (WNV) introduced into the United States in 1999 has similarities to the native flavivirus, St. Louis encephalitis (SLE) virus, but has unique features not observed with SLE virus or with WNV in the old world. The primary route of transmission for most of the arboviruses in North America is by mosquito, and infected native birds usually do not suffer morbidity or mortality. An exception to this pattern is eastern equine encephalitis virus, which has an alternate direct route of transmission among nonnative birds, and some mortality of native bird species occurs. The strain of WNV circulating in the northeastern United States is unique in that it causes significant mortality in exotic and native bird species, especially in the American crow (Corvus brachyrhynchos). Because of the lack of information on the susceptibility and pathogenesis of WNV for this species, experimental studies were conducted at the USGS National Wildlife Health Center. In two separate studies, crows were inoculated with a 1999 New York strain of WNV, and all experimentally infected crows died. In one of the studies, control crows in regular contact with experimentally inoculated crows in the same room but not inoculated with WNV succumbed to infection. The direct transmission between crows was most likely by the oral route. Inoculated crows were viremic before death, and high titers of virus were isolated from a variety of tissues. The significance of the experimental direct transmission among captive crows is unknown.

Pathology of fatal West Nile virus infections in native and exotic birds during the 1999 outbreak in New York City, New York

West Nile fever caused fatal disease in humans, horses, and birds in the northeastern United States during 1999. We studied birds from two wildlife facilities in New York City, New York, that died or were euthanatized and were suspected to have West Nile virus infections. Using standard histologic and ultrastructural methods, virus isolation, immunohistochemistry, in situ hybridization and reverse-transcriptase polymerase chain reaction, we identified West Nile virus as the cause of clinical disease, severe pathologic changes, and death in 27 birds representing eight orders and 14 species. Virus was detected in 23/26 brains (88%), 24/ 25 hearts (96%), 15/18 spleens (83%), 14/20 livers (70%), 20/20 kidneys (100%), 10/13 adrenals (77%), 13/ 14 intestines (93%), 10/12 pancreata (83%), 5/12 lungs (42%), and 4/8 ovaries (50%) by one or more methods. Cellular targets included neurons and glial cells in the brain, spinal cord, and peripheral ganglia; myocardial fibers; macrophages and blood monocytes; renal tubular epithelium; adrenal cortical cells; pancreatic acinar cells and islet cells; intestinal crypt epithelium; oocytes; and fibroblasts and smooth muscle cells. Purkinje cells were especially targeted, except in crows and magpies. Gross hemorrhage of the brain, splenomegaly, meningoencephalitis, and myocarditis were the most prominent lesions. Immunohistochemistry was an efficient and reliable method for identifying infected cases, but the polyclonal antibody cross-reacted with St. Louis encephalitis virus and other flaviviruses. In contrast, the in situ hybridization probe pWNV-E (WN-USAMRIID99) reacted only with West Nile virus. These methods should aid diagnosticians faced with the emergence of West Nile virus in the United States.

Coraco-clavicular joint: normal variant in humans. A radiographic demonstration in the human and non-human primate

The coraco-clavicular joint is a true synovial joint that may become painful in some patients after trauma. Among the descriptions of this entity is the assertion that the coraco-clavicular joint is routinely seen in gorillas and gibbons. We undertook to assess the incidence of this variant among gorillas, gibbons, and other non-human primates. All available radiographs of large primates performed at the International Wildlife Conservation Park/Bronx Zoo (IWCP) over the past 10 years were reviewed by a musculoskeletal radiologist (human radiology). All radiographs were taken during the normal clinical care of the non-human primate population of the IWCP and are a part of each animal's clinical record. Eighty-one non-human primate radiographs were suitable for study as they contained the region of interest. The 81 radiographic examinations included 14 different species of non-human primates. The coraco-clavicular joint was seen in 4 out of 9 silver-leaf langur, 2 out of 8 lowland gorilla, and in 1 out of 6 white-handed gibbon. In all non-human primate cases where the coraco-clavicular joint occurred, it was bilateral. In 1 out of 8 mandrill, there were very wide distal clavicular ends that articulated both with the coracoid and with the acromion. The coraco-clavicular joint differs from an ossified coraco-clavicular ligament. The radiographic appearance is characteristic and is found in both humans and some non-human primate species. It may rarely become painful following trauma. When symptomatic in humans, resection of this anomalous articulation is curative.