Transmission of vesicular stomatitis virus from infected to noninfected black flies co-feeding on nonviremic deer mice.

Vesicular stomatitis is an economically important arboviral disease of livestock. Viremia is absent in infected mammalian hosts, and the mechanism by which insects become infected with the causative agents, vesicular stomatitis viruses, remains unknown. Because infected and noninfected insects potentially feed on the same host in nature, infected and noninfected black flies were allowed to feed on the same host. Viremia was not detected in the host after infection by a black fly bite, but because noninfected black flies acquired the virus while co-feeding on the same host with infected black flies, it is concluded that a viremic host is not necessary for an insect to be infected with the virus. Thus co-feeding is a mechanism of infection for an insect-transmitted virus.

Laboratory vector competence of black flies (Diptera:Simuliidae) for the Indiana serotype of vesicular stomatitis virus.

In previous experiments we have demonstrated that colonized and wild black flies are competent laboratory vectors of different Mexican and Western USA isolates of vesicular stomatitis virus, serotype New Jersey (VSV-NJ). We have recently demonstrated biological VSV-NJ transmission by black flies using animal models. In the study described here, we tested the vector competence of colonized and wild black flies for the vesicular stomatitis virus, serotype Indiana (VSV-IN). A 1998 equine isolate was used. After a 10 day incubation period, saliva from experimentally infected Simulium vittatum and S. notatum was individually collected and tested for the presence of infectious virus. Virus was detected in the saliva of both species following oral infection, indicating that they are competent laboratory vectors of VSV-IN. In addition, the results suggest that the black fly gut may exert evolutionary pressures on the virus.

Bite transmission of vesicular stomatitis virus (New Jersey serotype) to laboratory mice by Simulium vittatum (Diptera: Simuliidae).

Laboratory-reared female black flies (Simulium vittatum Zetterstedt) were infected experimentally with a 1997 vesicular stomatitis virus New Jersey serotype isolate and allowed to feed on susceptible laboratory mice. All mice exposed to black fly bite seroconverted by day 21 after infection, an indication of virus transmission. In addition, viral RNA was detected in the spleen of several mice. These findings are consistent with the hypothesis that black flies are involved in VSV-NJ transmission during epizootics in the western USA and represent the 1st confirmed example of biological transmission of an arbovirus by a member of the Simuliidae using an animal model.

Vector competence of select black fly species for vesicular stomatitis virus (New Jersey serotype).

Black flies collected from southern Arizona were evaluated for their vector competence to the Oaxaca and Camp Verde isolates of vesicular stomatitis virus (New Jersey serotype) (VSV-NJ). The Camp Verde isolate is the index isolate of the 1982-1983 VSV-NJ epizootic that infected humans and livestock in 14 western states. Previous experiments have shown that colonized Simulium vittatum females are competent laboratory vectors of both virus isolates. However, under controlled laboratory conditions, Simulium bivittatum and S. longithallum were found to be incompetent vectors of both virus isolates. After oral infections, the Oaxaca isolate replicated in 35% and 38% of S. bivittatum and S. longithallum, respectively, but did not disseminate to the salivary glands. Thus, virus was not detected in the saliva of either black fly species with either VSV-NJ isolate, indicating the presence of a midgut barrier. Simulium notatum was found to be a competent laboratory vector of both virus isolates. Infectious virions were detected in the saliva of 23% and 26% of S. notatum infected orally with the Oaxaca and Camp Verde VSV-NJ isolates, respectively. This study suggests that the black fly identified as S. bivittatum was probably not involved in virus dissemination during the 1982-1983 epizootic in the western United States. Because the geographic distribution of S. notatum is not known, its involvement in that epizootic remains obscure.

Biological transmission of vesicular stomatitis virus (New Jersey) by Simulium vittatum (Diptera: Simuliidae).

Simulium vittatum females were shown to be competent vectors for the New Jersey serotype (VSNJ) of vesicular stomatitis virus (Camp Verde strain). Seventy percent of females infected intrathoracically transmitted infectious virions in their saliva after a 10-d incubation period. When infected with virus per os, 63% of the flies tested were positive at day 10, and 45% of flies infected in this manner also secreted virus in their saliva by day 9 or 10 after infection. When ingested by S. vittatum females, VSNJ virus readily replicated and increased from a mean baseline titer of 1.2 x 10(4) pfu per fly to 3 x 10(4) pfu per fly on day 10. An eclipse phase was demonstrated between approximately 18 and 48 h postinfection. This experimental evidence supports the hypothesis that black flies play a major role in the epizootic transmission of VSNJ. This is also the first confirmed example of biological transmission of an arbovirus by a member of the Simuliidae.

Canine distemper virus infection and encephalitis in javelinas (collared peccaries).

Canine distemper virus has been isolated in dog lymphocyte cultures from the brains of three javelinas that became moribund with signs of encephalitis. Canine distemper viral antigen was demonstrated predominantly in neurons and morbillivirus-like structures were seen by electron microscopy in brains of diseased animals. Serological studies suggest that CDV infection may be common in javelinas.

Antigenic relatedness of pigeon herpes encephalomyelitis virus to other avian herpesviruses.

Pigeon herpes encephalomyelitis virus (PHEV) was compared with seven avian herpesviruses for antigenic relatedness using monospecific antisera and the indirect fluorescent-antibody (IFA), agar-gel-immunodiffusion, and serum-neutralization tests. No antigenic relationship was detected between PHEV and Marek's disease virus, turkey herpesvirus, infectious laryngotracheitis virus, and duck enteritis virus. A common precipitating antigen was detected between the PHEV and pigeon herpesvirus (PHV), owl herpesvirus (OHV), and falcon herpesvirus (FHV). These four viruses also cross-reacted in the IFA test. Weak neutralizing activity was detected only between PHV antiserum and PHEV. These results suggest that the PHEV should be classified as a herpesvirus related to, but distinct from, the PHV-OHV-FHV group of viruses with which it shares common antigens.

Differentiation of vaccine strains and field isolates of pseudorabies (Aujeszky's disease) virus: trypsin sensitivity and mouse virulence markers.

Five cloned virulent North American field isolates and 2 European vaccine strains of pseudorabies (PR) viruses were compared by their sensitivity to trypsin and their virulence for mice. Marked differences in trypsin sensitivity were detected between and among virulent and vaccine PR viruses. These differences were distinct enough to characterize a virus as either sensitive or resistant to trypsin. This test also differentiated 2 virulent viruses which were previously shown to be indistinguishable on the basis of their sensitivity to thermal inactivation. Mouse virulence was evaluated by comparing the mean times-to-death of mice infected with individual viruses. Three distinct levels of virulence were observed. The two vaccine viruses were differentiated from each other and from virulent virus. Mice infected with the vaccine viruses required 23 to 118 hours longer to die than mice which were infected with virulent virus. A significant difference of 5.6 hours (P less than .005) was also detected between mice infected with 2 different field viruses. When viruses were described according to their marker profiles, 5 of 6 possible combinations were revealed. The 2 vaccine viruses could be described by separate profiles and virulent viruses could be described by 1 of 3 profiles.

Differentiation of vaccine strains and field isolates of pseudorabies (Aujeszky's disease) virus: thermal sensitivity and rabbit virulence markers.

Eleven cloned North American pseudorabies virus (PRV) strains and the European vaccine strains K and BUK were characterized by their thermal sensitivity and rabbit virulence markers. Heat sensitivity of the strains and isolates ranged from the highly heat resistant strain K, to the extremely heat labile strain BUK and isolate Be. The inactivation curves of each virus were transformed to the logarithmic scale and their standardized slopes and predicted virus survival values at 30 minutes were plotted against each other. The result was a distribution of points that represented a thermal sensitivity spectrum (TSS). Virus strains were subsequently categorized into 1 of 3 groups according to their position in the TSS. Viruses were also categorized into three groups according to their ability to clinically infect rabbits, their ability to produce pruritus and the time required to kill. When individual strains were described according to their marker profiles, 5 of 9 possible marker combinations were revealed. The 2 vaccine strains were each described by separate profiles. Virulent field isolates were characterized by 1 of 3 different profiles.

Epizootiologic aspects of viscerotropic velogenic Newcastle disease in six pet bird species.

Pet birds of 6 species were exposed to a psittacine isolate to viscerotropic velogenic Newcastle disease (VVND) virus to evaluate the impact of VVND in those species. Species examined were the budgerigar, yellow-headed Amazon parrot, canary, halfmoon conure, lesser hill mynah, and blackheaded nun. Five of the 6 species were highly susceptible to infection with VVND virus. Canaries were relatively refractory to infection with the virus. Contact birds of the same species developed infections almost as rapidly as did the birds directly exposed to nebulized VVND virus. Mortality was most marked for the conures. Less than half of the parrots exposed to nebulized virus died of VVND. Of the directly exposed budgerigars, mynahs, and nuns, 16% to 22% died during an observation period of postexposure days 0 through 28.

Interactions between viscerotropic velogenic Newcastle diseases virus and pet birds of six species. I. Clinical and serologic responses, and viral excretion.

Clinical and serologic responses to a psittacine isolate of viscerotropic velogenic Newcastle disease virus (VVNDV) were evaluated in pet birds of six species: budgerigar, yellow-headed Amazon parrot, halfmoon conure, lesser hill mynah, black-headed nun, canary. The clinical response was most marked in the budgerigars, parrots, and conures, and only minimal in the nuns. Between post-exposure days (PED) 3 and 5 some birds developed ruffled plumage, conjunctivitis, and central nervous system dysfunction: ataxia, wing tremors, paralysis of the extremities, and tremors of the head accompanied by nodding and jerking. Mortality by PED 203 was 55% (29/52) in the halfmoon conures, 22% (23/105) in budgerigars, 29% (12/42) in parrots, and 21% (15/71) in nuns. The only clinical signs in canaries and mynahs were progressive death losses, respectively 25% (33/132) and 21% (10/48). The visceral lesions common in chickens with VVNDV were not observed in these six species. Canaries rapidly eliminated Newcastle disease virus (NDV), whereas it was detected for protracted periods in the oral and cloacal secretions of the other five species (for more than a year in parrots). Serologic evaluation by the hemagglutination-inhibition and neutralization tests also indicated prolonged NDV infections in 5 of the 6 species. The seroconversion rate observed in canaries was minimal (13%).

Interactions between viscerotropic velogenic Newcastle disease virus and pet birds of six species. II. Viral evolution through bird passage.

Following in vivo studies in pet birds of 6 species, 279 Newcastle disease virus (NDV) reisolates were selected for characterization by the embryonated-chicken-egg mean-death-time, plaque-assay, hemagglutination-elution, and hemagglutinin-thermostability techniques. Initially, the 279 isolates were screened by the mean-death-time and plaque-assay techniques, and 5 sequential isolates were chosen for each of 3 budgerigars and 2 parrots for characterization by the other 2 in vitro assays to determine whether the Colorado Psittacine Isolate of viscerotropic velogenic (VV) NDV (COPI-VVNDV) had evolved during passage through pet birds. Nineteen isolates were then selected for chicken back-passage studies. Fifteen of the 19 isolates were chosen for potential avirulence for 8-week-old domestic chickens. The 4 remaining isolates produced large red plaques when assayed and were therefore used as virulent virus controls likely to be VVNDV. Subsequent in vitro characterization of selected back-passage chicken NDV isolates demonstrated little change in the 4 parameters originally evaluated for the pet-bird isolates used for the back-passage studies. Although the psittacine isolate slowly evolved to relatively avirulent strains of NDV by passage in pet birds, reversion did not occur during the chicken back-passage studies.

Rapid diagnosis of Venezuelan equine encephalomyelitis by fluorescence microscopy.

Goat Venezuelan equine encephalomyelitis (VEE) antiserum and normal serum were conjugated and evaluated for staining sensitivity and specificity. Cross-staining with either eastern or western equine encephalomyelitis virus-infected cells did not occur. The baby hamster kidney (BHK-21) cell line when combined with highly specific VEE conjugate detected 100 medium suckling mouse intracerebral lethal doses (suckling mouse LD-50/IC) of the 1B subtype of VEE virus per milliliter of equine tissue suspension. Conjugated goat antiserum was assayed for sensitivity for detection of VEE virus-infected equine serums and tissue suspensions. The BHK-21 cell line was superior to either primary duck embryo fibroblast (DEF) cells or African green monkey kidney (Vero) cells for propagating the GJ9-1BJ subtype of VEE virus.

Inclusion body disease (herpesvirus infection) of falcons (IBDF).

Inclusion body disease of falcons (IBDF) is caused by a herpesvirus. The clinical course is short, 24 to 72 hours in duration, and is characterized by mild to severe depression and weakness often accompanied by anorexia. The disease is invariably fatal. The virus has a marked affinity for the reticuloendothelial system and hepatocytes,producing focal to diffuse necrosis of infected tissues accompanied by the formation of intranuclear inclusion bodies. The virus is pathogenic for American kestrels (Falco sparverius) and great horned owls (Bubo virginianus) in which typical lesions of IBDF are reproduced. The lesions of IBDF are similar to those produced by some herpesvirus infections in other avian species.

Differentiation of strains of infectious bovine rhinotracheitis virus by neutralization kinetics with late 19S rabbit antibodies.

Two vaccine, two respiratory (infectious bovine rhinotracheitis [IBR]), and two genital (infectious pustular vulvovaginitis [IPV]) strains of infectious bovine rhinotracheitis virus were compared by neutralization kinetics using late 19S antibody (AB). The two vaccine strains were indistinguishable from one another, but were neutralized far more rapidly than the other four strains when either anti-IBR or anti-IPV 19S AB was used. The two IPV strains were indistinguishable from one another, but were neutralized significantly more rapidly than the two IBR strains when anti-IBR 19S AB was used. The 2 IBR strains were neutralized at a similar rate with the latter globulin preparation. Almost identical results were obtained with anti-IPV 19S AB, except that one IPV strain was neutralized at a rate similar to the IBR strains. However, when early and late rabbit 7S AB were used, IBR strains could not be distinguished from IPV strains by neutralization kinetics. Preliminary experiments indicated that both early and late 19S rabbit antibodies neutralized the homologous strain more rapidly than the heterologous strain, but the difference was more noticeable with late 19S AB. It was also determined that neutralization of IBR-IPV virus by specific early and late 19S rabbit AB and early 7S rabbit AB was markedly enhanced by guinea pig complement. Neutralization of this virus by late 7S AB, however, was only slightly enhanced by complement. These results suggest that vaccine strains of IBR-IPV virus may be distinguished by neutralization kinetics with late 19S rabbit AB, and that genital and respiratory strains may possibly also be distinguishable with some 19S AB preparations.

Lead poisoning in chickens and the effect of lead on interferon and antibody production.

The effect of aqueous lead acetate given per os to chickens for 35 consecutive days and the effect of lead on interferon and antibody production was investigated. Chickens were found to tolerate levels of lead as high as 160 mg/kg/day without exhibiting clinical signs or hematological changes in spite of very high levels of lead in the blood (6.2 ppm). It is apparent from these findings that chickens are more resistant to lead poisoning than humans, horses, dogs and wild fowl such as ducks. Subclinical lead doses did not affect interferon induction in response to statolon and Newcastle Disease virus (NDV)-B(1). Interferon concentrations and duration in serum were markedly decreased in chickens which received lead at the 320 mg/kg level. Long time lead exposure had no marked effect on antibody production to NDV in chickens. No consistent correlation was observed between blood lead concentration and antibody titer. The results of these studies indicate that long term subclinical lead intake suppresses neither interferon nor antibody production in chickens.