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.

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.

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.

The incidence of Chlamydia pneumoniae lower respiratory tract infections among university students in northern California.

Chlamydia pneumoniae has recently been identified as a cause of lower respiratory tract infections. From March 1987 to March 1988, 259 university students-151 students with lower respiratory tract infections and 108 controls-from the University of California, Berkeley, were studied to determine the incidence and pattern of C pneumoniae lower respiratory tract infections. Serologic evidence of a recent C pneumoniae infection was found in less than 2%, and the organism was not isolated from any of the subjects. Despite the paucity of evidence of a recent infection, 47.5% of this university population showed serologic evidence of a previous C pneumoniae infection. The lower incidence of C pneumoniae infection in our population, when compared with previous reports, suggests that there may be geographic and temporal differences or fluctuations among populations.

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.

Antigenic variants of Colorado tick fever virus.

Twenty strains of Colorado tick fever (CTF) virus, isolated from ticks, mammals and humans, and two antigenic relatives of CTF virus were compared in cross-neutralization tests. Viruses were tested using single-inoculation sera prepared in hamsters. Antigenic variation, as measured by differences detected in the neutralization test, was noted among the virus isolates identified as strains of CTF virus. The virus strains isolated from humans appeared to vary the most in serological reactions. The two antigenic relatives of CTF virus are clearly distinct from strains of CTF and are different from each other. Antigenic relationships between these two viruses were established using two sets of single-inoculation antisera and both complement fixation and neutralization tests. Six distinct antigenic variants of CTF virus isolated from humans and the virus strain from ticks (75V1906) that showed the least antigenic variation, were tested against 49 coded serum pairs from clinically diagnosed cases of CTF. Significant differences were noted in the number of convalescent-phase sera that reacted with each virus strain and in the number of seroconversions observed with each test virus strain. Convalescent phase sera that reacted with multiple virus strains often varied significantly in antibody titre from one virus strain to another. This indicates that, in some instances, antibody was probably produced in response to infection by different antigenic variants of CTF virus.

An overview of Colorado tick fever.

Certain features of Colorado tick fever (CTF) virus and the disease it causes may be relevant to studies on bluetongue virus (BTV), or other orbiviruses. Rapid and easy detection of viral antigen in infected tissues and peripheral blood cells by immunofluorescence staining facilitate diagnosis of the disease. The prolonged (3-4 months) viremia is due to persistent intracellular infection, particularly of erythrocytes, in which the virus is protected from antibody or other host defense mechanisms. This results in more efficient maintenance of the virus cycle in nature, but might lead to adverse effects in the human host. Clues to understanding chronic viral infections or viral immunosuppression might be gained by further research on CTF and other orbiviruses.

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.

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.

Historical perspectives on California encephalitis virus in California.

CEV is primarily associated with Ae. melanimon as its maintenance host and vector in California. A few species of lagomorphs and rodents will develop a transient viremia when infected. Infection of domestic mammals and man is frequent but rarely results in a clinical disease. Extensive field and laboratory studies lead to the conclusion that CEV probably is a mosquito virus that is partially adapted to a narrow range of vertebrate hosts but is not reliant on vertebrates for its continuous existence. JCV has many similarities to CEV in California in that it is dependent on one mosquito, Cu. inornata, as its vector and, as far as is known, the same group of mammalian species as for CEV serve as hosts for JCV.

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.

Multiple-antigen slide test for detection of immunoglobulin M antibodies in newborn and infant sera by immunofluorescence.

A microimmunofluorescence test was evaluated for use in measuring immunoglobulin M (IgM) antibodies in infant sera to five of the agents implicated in congenital and neonatal disease. Pen point dots of Toxoplasma gondii, cytomegalovirus, rubella virus, herpes simplex virus, and chlamydial cell culture antigens were applied to each circle of eight-circle printed slides. These multiple-antigen slides greatly facilitated the screening of 607 sera from infants and 117 sera from mothers for the presence of IgM antibody to these agents. Forty sera could be examined microscopically in approximately 30 min. All sera reacting with one or more antigens were tested for rheumatoid factor by the latex method, absorbed with glutaraldehyde-cross-linked human IgG, and retested for the presence of IgM antibody. IgM antibody to cytomegalovirus was demonstrated in sera from four newborns, but IgM antibody to rubella virus could not be detected until 21 days after birth, although rubella virus was isolated from sera from five younger infants. This may indicate that rubella IgM levels in many congenitally infected newborns are too low to be measured by the immunofluorescence method. Five percent of the sera from infants in this study possessed demonstrable IgM antibody to one of the antigens.

Direct immunofluorescence staining for detection of herpes simplex and varicella-zoster virus antigens in vesicular lesions and certain tissue specimens.

Direct immunofluorescence (IF) staining was compared with virus isolation for detection of herpes simplex viruses (HSV) and varicella-zoster virus (VZV) directly in clinical materials. These included 199 vesicular lesion specimens and 280 tissue specimens. Correspondence between IF and isolation results was 88% in testing for HSV in lesion specimens and 98% in testing for HSV in various tissue (mostly brain) specimens. Overall, IF was positive for 82% of the specimens in which HSV was demonstrated, and virus was isolated from 89% of the HSV-positive specimens. IF was markedly more sensitive than isolation for demonstrating VZV in lesion and tissue specimens, detecting all of the specimens positive for VZV, whereas isolation detected only 23%. IF detected VZV antigen in a number of lesion specimens taken late after onset, past the time when they would be expected to yield infectious virus. Specificity of positive IF reactions for HSV or VZV in the absence of virus isolation was supported by the facts that (i) staining was obtained with only a single, presumably homologous, immune conjugate, (ii) clinical symptoms were compatible with infection with the virus for which positive IF findings were obtained, and (iii) positive electron microscopy findings for herpesviruses or positive serological results for VZV were also obtained in some instances. Factors to be considered in achieving specificity of IF staining for these human herpesviruses are discussed.

Diagnosis of rabies by immunofluorescence in trypsin-treated histologic sections.

After trypsin digestion of 4% formaldehyde (10% formalin)-fixed, paraffin-embedded brain sections, immunofluorescence identification of rabies antigen was successful in three human rabies cases and in experimentally infected mice. The method allows better interpretation of the anatomic localization of rabies antigen and will be helpful in studies of the pathogenesis of rabies. It will also be diagnostically useful where fresh or fresh-frozen brain tissue is not available, although it should not be considered as a replacement for standard immunofluorescence and mouse inoculation techniques for rabies diagnosis.

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.