Isolation of western equine encephalitis virus from an opossum.

The first isolation of an arbovirus (western equine encephalo-myelitis virus) from an opossum in the United States is reported.

Rabies virus in nasal mucosa of naturally infected bats.

Rabies virus was demonstrated in the olfactory mucosa of naturally infected bats by staining with fluorescent antibody and by isolation of the virus from the nasal tissues. The olfactory mucosa is a potential portal of entry and exit for airborne rabies virus in bat caves.

Fatal pulmonary psittacosis and aspergillosis. Case report of dual infection.

A 59-year-old man in previously good health had acute, progressive bronchopneumonia and died after a three-week course of illness, despite treatment with various antibiotics. Serologic, microbiologic, and histologic findings indicated infection with both Chlamydia psittaci and Aspergillus fumigatus. Disseminated, invasive aspergillosis sometimes is a complication of chronic respiratory disease, malignancy, or other deficiency of host defenses, but to our knowledge, this is the first report of psittacosis as a coincidental, probably predisposing disease.

Recovery from encephalomyelitis caused by Herpesvirus simiae. Report of a case.

A 29-year-old monkey handler developed an acute encephalomyelitis with neuromuscular dysfunction that progressed to respiratory arrest on the 18th day of illness. Thereafter, with supportive care, the patient's condition improved steadily. The titer of neutralizing antibodies to H simiae rose from 1:4 (eighth day of illness) to 1:512 (47th day of illness). Apparently the fifth known survivor of H simiae (herpesvirus B) encephalomyelitis, this patient is also remarkable because of virtually complete recovery, apparently the second documented instance of a good outcome.

Correlation of Culex tarsalis population indices with the incidence of St. Louis encephalitis and western equine encephalomyelitis in California.

Mosquito population indices from California for the period 1953-1973 were analyzed to determine their association with activity of St. Louis encephalitis (SLE) and western equine encephalomyelitis (WEE) viruses. Culex tarsalis female populations, as measured by New Jersey light trap indices (LTI), correlated positively with the incidence rates of encephalitis in humans, and were a reliable means of forecasting the years of highest incidence. The critical level of C. tarsalis in urban areas below which no human cases of SLE and WEE were detected was an LTI of 0.1. Critical urban levels of C. tarsalis associated with significant human SLE or WEE incidence ranged between LTIs of 6.4 (for rural mosquito abatement districts [MADs] with large resident human populations). Peaks in annual incidence of SLE and WEE in humans occurred during years when seasonal average C. tarsalis female populations in urban areas reached a LTI of 21. Peaks in weekly incidence of SLE and WEE were associated, respectively, with weekly LTIs of 21 and 81 in urban traps. Isolation rates of SLE virus from mosquito pools and transmission of the virus to enzootic hosts were highest when urban LTIs were between 10 and 19.9 and between 5 and 9.9, respectively. The WEE viral isolations and enzootic transmission rates were highest when LTIs in urban areas were 1-4.9.

Survey for evidence of Colorado tick fever virus outside of the known endemic area in California.

A virus very similar or identical to Colorado tick fever (CTF) virus was recovered from the blood clot of one of 104 black-tailed jack rabbits (Lepus californicus) examined during a survey for various zoonotic agents in mammals and ticks from the University of California, Hopland Field Station, Mendocino County, California, 1974--79. This is the first reported isolation of a CTF-like virus from L. californicus, and only the second time such a virus has been found in northwestern California. Mendocino County is located far outside the known distributional ranges of the most common mammalian hosts of CTF virus and of Dermacentor andersoni, the only proven tick vector for man. The viral isolate is very similar to a CTF-like virus previously recovered from the blood and spleen of a western gray squirrel (Sciurus griseus) from San Luis Obispo County, an area also outside of the previously-known CTF area. Virus was not isolated from 14 additional species of mammals (354 specimens) or from eight species of ticks (4,487 individuals), but CTF-neutralizing antibodies were detected in 28 of 771 (3.6%) sera from seven of 15 mammalian species including significant titers (greater than or equal to 1:8) in two species and one subspecies not previously reported as natural hosts, i.e., brush mouse (Peromyscus boylii), pinyon mouse (P. truei), and Columbian black-tailed deer (Odocoileus hemionus columbianus). CTF indirect immunofluorescent antibodies also were detected in 26 of 129 (20.2%) sera belonging to four of five mammalian species tested. Neutralizing antibodies were found in sera of deer from other localities in Mendocino County, from a deer mouse from Napa County, and from a brush rabbit from Monterey County as well. These findings suggest that a virus identical or similar to CTF virus is widespread in northwestern-westcentral California, and that surveillance for human cases of CTF or a similar disease should be extended to cover this region.

Landscape ecology of arboviruses in southern California: temporal and spatial patterns of vector and virus activity in Coachella Valley, 1990-1992.

Consistent temporal and spatial patterns in the activity of Culex tarsalis Coquillett and western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses were delineated that were useful in developing a stratified surveillance program. Vernal increases in Cx. tarsalis abundance typically were associated with flooding of saline marshes along the north shore of the Salton Sea and were followed 6-8 wk later by the onset of WEE and SLE virus activity. Viruses then spread to managed marsh (duck club) and agricultural habitats in the Whitewater Channel flood plain and, depending upon the intensity of amplification, to agricultural and residential areas in the more elevated northwestern portion of the valley. Mean annual Cx. tarsalis abundance was correlated inversely with elevation and distance from the Salton Sea. Abundance was greatest at managed marsh habitats. Although spatially correlated with vector abundance among sites, virus transmission rates to sentinel chickens were asynchronous temporally with vector abundance. Seroconversion rates were related to flock location but not flock size (10 versus 20 chickens). Human cases were not detected during the study period, despite elevated transmission rates of both WEE and SLE viruses to sentinel chickens positioned in peridomestic habitats.

Ecological observations on the 1989 outbreak of St. Louis encephalitis virus in the southern San Joaquin Valley of California.

Temporal and spatial patterns of St. Louis encephalitis (SLE) virus transmission were compared at permanent study areas in the southern San Joaquin Valley during years with low (1988 and 1990) and elevated (1989) viral activity. During 1989 and 1990, virus appeared first at sentinel chicken flocks exhibiting low to moderate seroconversion rates at the end of the previous season. This finding, and the early season seroconversion of sentinel chickens at a marsh habitat on 5 March and 2 April 1990, circumstantially indicated that SLE virus may have overwintered on the valley during the winters of 1988-1989 and 1989-1990. The mechanism of overwintering was not elucidated further, because virus could not be isolated from overwintering adult mosquitoes or from immatures collected during the spring. An outbreak of 26 confirmed SLE cases occurred in 1989 during a drought year (rainfall 50% of normal) and followed a spring with elevated temperatures (1.7-3.4 degrees C above normal) and Culex tarsalis Coquillett abundance. Cx. tarsalis was the primary vector, being most abundant during the virus amplification period in early summer and most frequently infected (70 SLE virus positive pools/329 tested). SLE virus also was detected in Culex quinquefasciatus Say (14/65) and Cx. stigmatosoma Dyar (1/4); however, both species were distributed focally and increased in abundance only after widespread seroconversions had occurred in sentinel chickens. Increased virus activity during 1989 was not accompanied by marked changes in vector susceptibility or in SLE virus infectivity for mosquitoes. Decreased virus activity in the Bakersfield area during 1990 could not be attributed to immunity in passeriform birds, because a small seroprevalence survey indicated that few adult birds had antibodies to SLE virus.

Serological survey for rabies antibodies in raptors from California.

Fifty-three newly captive birds of prey were tested serologically for neutralizing antibodies against rabies virus, using a fluorescent focus inhibition test. No significant antibody titers were detected with this sensitive and specific technique in any of these birds. This study supports the contention that free-ranging birds of prey are of limited importance in the epidemiology of rabies.

Tularemia in a mule deer.

A case of tularemia was confirmed in a 51-year-old man who acquired the disease from a mule deer, Odocoileus hemionus. Francisella tularensis was isolated from bone marrow of the deer carcass.

Use of monoclonal antibodies to confirm vaccine-induced rabies in ten dogs, two cats, and one fox.

A panel of 8 monoclonal antibodies to rabies glycoprotein antigen was used to characterize the modified-live virus vaccines marketed in the United States during the last 10 years. Thirteen of 14 rabies virus isolates from 11 dogs, 2 cats, and 1 fox suspected of developing vaccine-induced rabies were shown to have reactivity patterns that were identical to the vaccine administered. Reactivity patterns for 20 rabies isolates from human beings, wild animals, or domestic animals with no history of recent vaccination with modified-live virus rabies vaccine were different from those obtained for vaccines.

Rabies vaccine virus infection in three dogs.

Ascending paralysis developed in 3 dogs, 12 to 14 days following inoculation with a modified live virus, chicken embryo origin, low egg passage, Flury strain rabies vaccine. The paralysis began in the inoculated limb but rapidly involved both hindlimbs. Partial paresis of the forelimbs was seen several days following the hindlimb paralysis in all 3 dogs, and in 1 of these dogs the infection ascended rapidly to the brain as well. Two of the dogs recovered within 1 and 2 months, respectively, but the 3rd dog died within 5 days of the onset of paralytic signs. The fatal case was complicated by naturally acquired coincidental distemper. Serologic studies in 2 dogs and virus isolation from the 3rd dog indicated that rabies virus was the cause of the paralysis in 2 of the dogs and contributed to the disease syndrome in the 3rd dog. Virus could not be isolated from the saliva of CSF of the 2 surviving dogs. The virus isolated in the fatal case appeared to have some of the characteristics of the vaccine virus, as determined by its behavior in mice, cell culture, and embryonating chicken eggs and by its failure to produce Negri bodies in the brain of the infected dog.

Main Drain virus as a cause of equine encephalomyelitis.

Main Drain virus, which is thought to be transmitted normally among rabbits and various rodents by its natural vector, Culicoides variipennis, was isolated repeatedly from brain tissue of a sick horse from Sacramento County, California, and was implicated as the causative agent. Signs of illness were incoordination and ataxia, stiff neck, head pressing, inability to swallow, fever, and tachycardia.

Viremia and serological responses in adult chickens infected with western equine encephalomyelitis and St. Louis encephalitis viruses.

Adult hens, similar to those used for arbovirus surveillance, were experimentally infected with western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses to describe the viremia response, to compare serological testing methods, and to evaluate a new method of collecting whole blood onto filter paper strips from lancet pricks of the chicken comb. Young (19 weeks), but not old (38 weeks), hens developed a low-titer, transient viremia for a 1-day period. Immunoglobulin G (IgG) was detected by days 10 and 14 after infection with WEE and SLE viruses, respectively, by indirect fluorescent antibody tests, hemagglutination inhibition tests, and plaque reduction neutralization tests on sera and in direct enzyme immunoassays (EIA) on both sera and eluates from filter paper samples. Immunoglobulin M (IgM) was first detected in sera 2 and 3 days before IgG, respectively, but IgM could not be detected reliably in eluates from dried blood. Sera and dried blood samples collected from naturally infected sentinel chickens gave comparable results when tested by an EIA for IgG.