A field study of persistence of antibodies in California horses vaccinated against western, eastern, and Venezuelan equine encephalomyelitis.

As a result of the continuing threat of Venezuelan equine encephalomyelitis (VEE), a study was made to determine if revaccination against VEE (TC-83 vaccine) was feasible and if revaccination could be incorporated into other routine vaccination practices. Of the horses given annual vaccination with bivalent western equine encephalomyelitis (WEE) and eastern equine encephalomyelitis (EEE) vaccine, 57% retained detectable serum-neutralizing (SN) antiboyd titers for VEE 18 months after the initial VEE vaccination was given. Of horses with no record of WEE-EEE vacinnation, 100% retained detectable VEE SN antibody titers over the same period. The VEE geometric mean titer was 25 times greater for horses not previously vaccinated against WEE-EEE than for horses given annual WEE-EEE vaccination at the time of VEE vaccination. In horses vaccinated against VEE 18 months previously, the geometric mean titer increased from 4 to 70 at 48 days after the intitial WEE-EEE vaccination. This increase indicated that similar antigenic factors for VEE are possibly present in bivalent WEE-EEE vaccine. In horses previously vaccinated against WEE-EEE and VEE, the best SN antibody response to VEE revaccination occurred when VEE vaccine was given simultaneously with the bivalent WEE-EEE vaccine. Of 150 serum samples tested by both the SN and the hemagglutination-inhibiton tests, agreement between positive reactions at greater than or equal to 1:10 was 70% for VEE, 81% for EEE, and 87% for WEE.     

Response to and efficacy of vaccination against eastern equine encephalomyelitis virus in emus

OBJECTIVE: To evaluate humoral immune responses of emus vaccinated with commercially available equine polyvalent or experimental monovalent eastern equine encephalomyelitis (EEE) virus and western equine encephalomyelitis (WEE) virus vaccines and to determine whether vaccinated emus were protected against challenge with EEE virus. DESIGN: Cohort study. ANIMALS: 25 emus. PROCEDURE: Birds were randomly assigned to groups (n = 5/group) and vaccinated with 1 of 2 commercially available polyvalent equine vaccines, a monovalent EEE virus vaccine, or a monovalent WEE virus vaccine or were not vaccinated. Neutralizing antibody responses against EEE and WEE viruses were examined at regular intervals for up to 9 months. All emus vaccinated with the equine vaccines and 2 unvaccinated control birds were challenged with EEE virus. An additional unvaccinated bird was housed with the control birds to assess the possibility of contact transmission. RESULTS: All 4 vaccines induced detectable neutralizing antibody titers, and all birds vaccinated with the equine vaccines were fully protected against an otherwise lethal dose of EEE virus. Unvaccinated challenged birds developed viremia (> 10(9) plaque-forming units/ml of blood) and shed virus in feces, oral secretions, and regurgitated material. The unvaccinated pen-mate became infected in the absence of mosquito vectors, presumably as a result of direct virus transmission between birds. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that emus infected with EEE virus develop a high-titer viremia and suggest that they may serve as important virus reservoirs. Infected emus shed EEE virus in secretions and excretions, making them a direct hazard to pen-mates and attending humans. Commercially available polyvalent equine vaccines protect emus against EEE virus infection.     

Immune responses to commercial equine vaccines against equine herpesvirus-1, equine influenza virus, eastern equine encephalomyelitis, and tetanus

Horses are commonly vaccinated to protect against pathogens which are responsible for diseases which are endemic within the general horse population, such as equine influenza virus (EIV) and equine herpesvirus-1 (EHV-1), and against a variety of diseases which are less common but which lead to greater morbidity and mortality, such as eastern equine encephalomyelitis virus (EEE) and tetanus. This study consisted of two trials which investigated the antigenicity of commercially available vaccines licensed in the USA to protect against EIV, EHV-1 respiratory disease, EHV-1 abortion, EEE and tetanus in horses. Trial I was conducted to compare serological responses to vaccines produced by three manufacturers against EIV, EHV-1 (respiratory disease), EEE, and tetanus given as multivalent preparations or as multiple vaccine courses. Trial II compared vaccines from two manufacturers licensed to protect against EHV-1 abortion, and measured EHV-1-specific interferon-gamma (IFN-gamma) mRNA production in addition to serological evidence of antigenicity. In Trial I significant differences were found between the antigenicity of different commercial vaccines that should be considered in product selection. It was difficult to identify vaccines that generate significant immune responses to respiratory viruses. The most dramatic differences in vaccine performance occurred in the case of the tetanus antigen. In Trial II both vaccines generated significant antibody responses and showed evidence of EHV-1-specific IFN-gamma mRNA responses. Overall there were wide variations in vaccine response, and the vaccines with the best responses were not produced by a single manufacturer. Differences in vaccine performance may have resulted from differences in antigen load and adjuvant formulation.     

Serologic responses of pregnant thoroughbred mares to vaccination with an inactivated equine herpesvirus 1 vaccine

The immunogenic potency and safety of a chemically inactivated equine herpesvirus 1 vaccine with added adjuvant was evaluated by testing serum-neutralizing and complement-fixation antibody responses of pregnant Thoroughbred mares. The vaccinated population comprised 321 pregnant mares on 7 farms; 3 in Normandy, France; 1 in Kildare, Ireland; and 3 in central Kentucky. The pattern of antibody response to vaccination was found qualitatively and quantitatively similar to that of pregnant mares previously vaccinated and determined by challenge exposure to be immune to abortigenic infection under experimentally controlled conditions. The safety of the vaccine was demonstrated by the occurrence of only 2 local untoward reactions to the administration of 941 IM injections.     

Immunological response of chickens to eastern equine encephalomyelitis virus

The dominant immunoglobulin against eastern equine encephalomyelitis (EEE) virus and its duration and the longevity of the EEE virus haemagglutination inhibition (HI) antibodies were determined in sentinel and 125 immunised and hyperimmunised domestic chickens by enzyme-linked immunosorbent assay and the HI test respectively. The chickens ranged in age from 10 weeks to 18 months, were of varied pedigrees and from different countries. Results show that the HI antibody (IgG) is short-lived. It peaks and disappears within 30 days. The secondary response is dominated by the IgM immunoglobulin which is relatively long-lasting. These results are contrary to classical expectations and were observed in all the chickens studied. If these observations are found to be characteristic of birds generally, the present standard method of EEE virus seroepidemiological surveillance must be modified to be effective.     

Serologic and clinical responses of premunized, vaccinated, and previously infected cattle to challenge exposure by two different Anaplasma marginale isolates

Two Anaplasma marginale isolates, one originating in Florida (FAM) and the other from Virginia (VAM), were compared immunologically by cross-challenge exposure of 14 Anaplasma carrier cattle, 8 previously infected cattle, and 6 splenectomized carrier calves. In addition, 28 cattle vaccinated with a commercially available adjuvant killed vaccine and 22 nonvaccinated cattle were challenge exposed with either FAM or VAM. A detectable clinical response was not produced by either FAM or VAM challenge exposure in carrier and previously infected cattle; however, evidence of A marginale growth as characterized by low percentages of parasitemia and increased serum complement-fixation titers was seen in carrier cattle given a heterologous challenge organism and in previously infected cattle inoculated with either homologous or heterologous organisms. Among splenectomized calves, there was virtually no cross protection to the heterologous challenge exposure, whereas a homologous challenge failed to elicit any detectable response. Vaccinated cattle were resistant to VAM exposure, but the clinical response to FAM exposure was severe with a 47% mortality. Most of these cattle displayed typical acute anaplasmosis that was only marginally less severe than that encountered in nonvaccinated cattle.     

Immunologic responses to West Nile virus in vaccinated and clinically affected horses

OBJECTIVE: To compare neutralizing antibody response between horses vaccinated against West Nile virus (WNV) and horses that survived naturally occurring infection. DESIGN: Cross-sectional observational study. ANIMALS: 187 horses vaccinated with a killed WNV vaccine and 37 horses with confirmed clinical WNV infection. PROCEDURE: Serum was collected from vaccinated horses prior to and 4 to 6 weeks after completion of an initial vaccination series (2 doses) and 5 to 7 months later. Serum was collected from affected horses 4 to 6 weeks after laboratory diagnosis of infection and 5 to 7 months after the first sample was obtained. The IgM capture ELISA, plaque reduction neutralization test (PRNT), and microtiter virus neutralization test were used. RESULTS: All affected horses had PRNT titers > or = 1:100 at 4 to 6 weeks after onset of disease, and 90% (18/20) maintained this titer for 5 to 7 months. After the second vaccination, 67% of vaccinated horses had PRNT titers > or = 1:100 and 14% had titers < 1:10. Five to 7 months later, 33% (28/84) of vaccinated horses had PRNT titers > or = 1:100, whereas 29% (24/84) had titers < 1:10. Vaccinated and clinically affected horses' end point titers had decreased by 5 to 7 months after vaccination. CONCLUSIONS AND CLINICAL RELEVANCE: A portion of horses vaccinated against WNV may respond poorly. Vaccination every 6 months may be indicated in certain horses and in areas of high vector activity. Other preventative methods such as mosquito control are warranted to prevent WNV infection in horses.     

Occurrence and distribution of western equine encephalomyelitis in Florida.

Research and surveillance programs relating to the occurrence and distribution of western equine encephalomyelitis virus in Florida, conducted between 1955 and 1976, suggest that the virus is (1) an endemic arbordae, (2) transmitted in a continuous cycle throughout the year by Culiseta melanura mosquitoes, and (3) restricted to fresh water swamps and waterways in central, north, and northwest Florida.     

Detection of eastern equine encephalomyelitis virus antigen in equine brain tissue by enzyme-linked immunosorbent assay

Sensitivity and specificity of an antigen-capture ELISA vs virus isolation in cell culture were evaluated for the detection of eastern equine encephalomyelitis (EEE) virus in the brain tissue of naturally infected equids. Brain specimens from 16 equids with neurologic disease were examined by ELISA and by inoculation onto baby hamster kidney cell cultures. Of 10 brain samples from which virus was isolated in the cell culture bioassay, all were correctly identified as containing EEE virus antigen by ELISA. None of the remaining 6 specimens, without detectable infectious EEE virus, contained detectable antigen. Sensitivity and specificity of the ELISA were 100% with no false-positive or false-negative results. The antigen-capture ELISA was a rapid, sensitive, specific, and simple alternative to a traditional bioassay for the detection of EEE virus.