Penicillin-induced hemolytic anemia and acute hepatic failure following treatment of tetanus in a horse

Acute, severe hemolytic anemia occurred in a horse being treated for tetanus with intravenous penicillin and tetanus antitoxin. During treatment, the horse developed a positive direct antiglobulin test and a high titer (maximum 1:1024) of IgG anti-penicillin antibody. The horse recovered from the tetanus and penicillin induced hemolytic anemia, but later developed acute hepatic failure, probably resulting from the administration of equine origin tetanus antitoxin.     

The effect of age on serum antibody titers after rabies and influenza vaccination in healthy horses

BACKGROUND: The proportion of geriatric horses within the equine population has increased in the past decade, but there is limited information on the immune function of these animals. HYPOTHESIS: Aged horses will have a lesser increase in serum antibody response to vaccination. ANIMALS: Thirty-four aged healthy horses (> or = 20 years) and 29 younger adult horses (4-12 years) of various breeds. METHODS: All horses were vaccinated with vaccines of killed rabies and influenza virus. Horses in each age group were allocated to receive either rabies or influenza booster vaccine 4 weeks after the initial vaccination. Serum samples were taken at 0, 4, 8, and 24 weeks. Rabies serum neutralization titers and equine influenza virus specific antibody sub-isotypes (IgGa, IgGb, IgG(T), and IgA) as well as single radial hemolysis (SRH) titers were determined. RESULTS: Rabies antibody titers were similar in the 2 age groups at all sampling times. Aged horses had higher IgGa and IgGb influenza antibody titers before vaccination than younger horses but similar titers after vaccination (P= .004 and P= .0027, respectively). Younger horses had significantly greater increases in titer than aged horses at all sampling times for IgGa (P= .001) and at 8 and 24 weeks for IgGb (P= .041 and .01, respectively). There was no detectable serum IgG(T) at any time point. A significant booster vaccine effect was seen for both antirabies and anti-influenza titers. Anti-influenza titer before vaccination also had a significant effect on subsequent antibody response. CONCLUSIONS AND CLINICAL IMPORTANCE: Healthy aged horses generated a primary immune response to a killed rabies vaccine similar to that of younger adult horses. Aged horses had a significantly reduced anamnestic response to influenza vaccine.     

A longitudinal study of rotavirus antibody titers in swine in a closed specific pathogen-free herd.

In a newly established closed specific pathogen-free (SPF) swine herd, gilt/sow suckling and weaned pig rotavirus specific antibody titers were followed for three lactations by enzyme-linked immunosorbent assay (ELISA) to gain insight into the dynamics of herd antibody titers to group A rotavirus. Among gilts/sows, serum antirotavirus IgG titers increased during each lactation with a subsequent drop in titer between farrowings. Serum antirotavirus IgM titers declined during each lactation and with subsequent parity. Serum antirotavirus IgA titers remained constant during lactations and among parities. In colostrum and milk, antirotavirus IgA antibody was abundant. Differences in titer were not noticed between gilts and second litter sows but third litter sows had significantly higher titers than the first two groups. Antirotavirus IgG was high in colostrum but nearly nonexistent in milk. This titer did not vary significantly within or among parities. There was a linear regression in the titers of baby pig serum antirotavirus IgG from the post colostral sample through to seven weeks old, after which titer began to increase. No difference in baby pig serum antirotavirus IgG was noted among the three litters. Serum antirotavirus IgA and IgM were undetectable in baby pig sera after 2-3 weeks of age. Coproantibody to rotavirus was sporadically present in pig feces for 2-3 weeks after birth with highest titers in the IgA fraction. We conclude that although it is probable that age resistance of pigs to rotavirus diarrhea occurs, humoral immunity as measured by ELISA rotavirus antibody titers may not be intimately involved in virus clearance since in our studies baby pigs passively received large amounts of antibody but still excreted pathogenic virus. The finding of increasing levels of serum antirotavirus IgG in gilt/sow serum suggest that exposure to antigen of dams occur without significant increases in antirotavirus IgG titers in either colostrum, milk, or baby pig serum.     

Induction of immune response and protection from equine viral arteritis (EVA) by formalin inactivated-virus vaccine for EVA in horses

Thirty-nine horses included 3 pregnant mares were examined by inoculating with formalin inactivated-virus vaccine for EVA. Antibody response of horses after one dose vaccination was somewhat poor and 50% effective inoculum dose of the vaccine should be included 10(8.4) pfu of virus before inactivation. After 2 doses given at an interval of 4 weeks, the horses developed such high titer of SN antibody as up to 1:5,120. The SN titer declined rather rapidly, but supplemental administration of the vaccine at an interval of more than 2 months elicited a prompt antibody response and SN titers persisted as 1:80 to 1:320 at 6 months after the administration. Therefore, supplemental administration of the vaccine as booster every 6 months or 1 year would be capable of maintaining high titer of SN antibody. The inactivated-virus vaccine prevented horses from clinical disease of EVA and protected pregnant mares from abortion by challenge exposure with virulent virus. Fifty percent protective dose in SN titer of 1:43 was confirmed by clinical signs and viremia.     

Rapid and specific serodiagnosis of western equine encephalitis virus infection in horses

Paired sera from 28 nonvaccinated horses with serologically confirmed western equine encephalitis (WEE) virus infections were evaluated for immunoglobulin (Ig)M and IgG directed against WEE virus, by use of enzyme immunoassay. Twenty-one of the horses developed greater than or equal to 4-fold increases or decreases in serum IgM titers in paired serum samples, confirming the diagnosis of WEE in these horses. Of the remaining 7 horses, 1 had stable IgM titers, 1 had a 2-fold increase in IgM titer between paired sera, 2 had 2-fold decreases in IgM titer, and for 3 horses adequate volumes were not available for both sera of the pair. Twenty-nine of 56 blood samples collected from these 28 horses had been collected within the first 3 days after clinical disease was recognized; all 28 horses and 48 of 53 available serum samples had IgM antibody to WEE virus. Immunoglobulin M also was detected in sera of 27 of 45 other nonvaccinated horses that had illnesses clinically compatible with WEE. Sera with IgM did not have cross-reacting IgM against eastern equine encephalitis virus. Therefore, the sensitivity, specificity, and lack of persistence of IgM was useful in the rapid diagnosis of WEE virus infections in horses.     

Isotype-specific antibodies in horses and dogs with immune-mediated hemolytic anemia

Classes of antibody bound to erythrocytes were determined using direct immunofluorescence (DIF) flow cytometry in 3 horses and 12 dogs with immune-mediated hemolytic anemia (IMHA). Background levels of antibody binding were determined in samples from 12 horses and 12 dogs that were free of clinical disease. The range of nonspecific binding of a fluorescein isothiocyanate (FITC)-conjugated goat anti-equine immunoglobulin G (IgG) was 19.9–36.7%, but was eliminated by the use of the F(ab)₂ fragment of FITC-conjugated goat anti-equine IgG. Background binding by other class-specific antibodies to equine and canine erythrocytes was negligible. The DIF results were compared to the direct antiglobulin (Coombs) test in 5 horses and 20 dogs with anemia. The former assay was more sensitive in dogs with IMHA than was the Coombs' test (100% versus 58%). In contrast, the Coombs' test had better specificity than the DIF assay (100% versus 87.5%, respectively). Using clinical parameters or response to therapy as the comparison, the positive and negative predictive values for the DIF test were 92% and 100% compared to the values of the Coombs' test of 100% and 62%. The DIF assay detected low levels of cells bound with antibody (<30%) in 5 dogs that were Coombs' test-negative. For both species, performance of the DIF test was independent of the prozone effect. Five dogs with IMHA had IgG and IgM on erythrocytes, 5 had IgG, and 2 had IgM. Three horses had surface-bound IgG, including a horse with suspected penicillin-induced IMHA, a foal with neonatal isoerythrolysis, and a foal with clostridial septicemia. The DIF method was valuable in monitoring the response to therapy in the foal with neonatal isoerythrolysis.     

Serosurvey of horses with evidence of equine monocytic ehrlichiosis

In August 1986, an extensive serosurvey for prevalence of IgG and IgM antibodies against Ehrlichia risticii, the causative agent of equine monocytic ehrlichiosis (EME), was performed at 2 Ohio racetracks, River Downs (RD) and Beulah Park (BP). Of 840 horses at RD and 574 at BP, 13 and 20%, respectively, were IgG antibody-positive (by indirect fluorescent antibody test results), with antibody titer ranging from 1:20 to 1:10,240. The titer observed at highest frequency at both racetracks was 1:80. A higher proportion of horses was ill at RD (operating during the summer months) than at BP (winter track). Of ill horses, 41% (24/58) at RD and 58% (11/19) at BP were seropositive. At RD, 70% (589/840) of all horses and 95% (102/107) of IgG seropositive horses had been stabled only at RD during the month prior to testing. Analysis of these sera by use of an ELISA to detect IgM antibody against E risticii antigen indicated that at RD, 42% (57/137) of the seropositive horses were IgM seropositive. At BP, 17% (20/120) of seropositive horses were IgM seropositive. The larger number of IgM seropositive horses at RD indicates that more horses were recently infected at RD than at BP (P = 0.0001). Therefore, at least half the seropositive horses at RD seemed to have acquired the infection at RD. These serosurvey data also indicate that at BP and RD, 78% (85/109) and 91% (111/122) of IgG seropositive horses, respectively, had subclinical infection. At less than or equal to 1:40 titer, there was no difference in seropositive rates between healthy and ill horses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Isolation of Ross River virus from mosquitoes and from horses with signs of musculo-skeletal disease

OBJECTIVE: To report clinical and clinicopathological findings in horses naturally infected with Ross River virus (RRV) and identify likely mosquito arbovirus vector species. PROCEDURES: Veterinarians submitted serum samples from 750 horses because they suspected Ross River virus (RRV) infection. The samples were tested for the presence of IgM and IgG antibody to RRV and for the presence of virus. Mosquitoes were trapped, differentiated to species level and tested for the presence of RRV by virus isolation. RESULTS: RRV was isolated from six species of mosquitoes (Ochlerotatus camptorhyncus, Culex globocoxitus, Cx. australicus, Cx. annulirostris, Cx. quinquefasciatus, Anopheles annulipes) and from 13 horses with clinical signs of musculo-skeletal disease. Antibody to RRV was detected in 420 of the 750 serum samples; 307 contained IgG only; 76 contained both IgM and IgG and 37 contained only IgM antibody to RRV. Virus was isolated from horses with IgM antibody only. CONCLUSIONS: RRV can be isolated from infected horses during the short time period when there is an overlap of clinical signs, positive IgM serology and viraemia. Early spring infections of horses may occur if RRV infected mosquito vectors are present. RRV has not been shown to cause clinical disease in horses. This is the first report of isolation of RRV from Oc. camptorhyncus in the Murray region and indicates a potential for infection of humans and animals in autumn as well as in spring.     

Cross-neutralizing and subclass characteristics of antibody from horses with equine infectious anemia virus

Antibody responses in horses with equine infectious anemia virus (EIAV) were examined to determine their cross-neutralizing capacity. Antibodies induced by infection with any of six biologically cloned variants of EIAV cross-neutralized multiple variants from the group. Anti-EIAV antibody was found in both the IgG and IgG(T) subclasses in plasmas with virus-neutralizing activity and the majority of antiviral antibody was of the IgG(T) subclass. Depletion of IgG(T) did not increase the neutralization indexes of either neutralizing or non-neutralizing plasma samples.     

IgG antibody subclass response against equine herpesvirus type 4 in horses

In this study, IgG subclass responses against equine herpesvirus type 4 (EHV-4) were examined by enzyme-linked immunosorbent assay (ELISA) using a type-specific region of EHV-4 glycoprotein G (gG). ELISA using sera collected from horses experimentally infected with EHV-4 revealed that IgGa and IgGb antibodies were detected at high level, but IgGc and IgG(T) antibody responses were detected at low level or were undetectable. The IgGa antibody response reached its peak on day 10 post-infection, and then dropped. The IgGb antibody response reached its maximum level on day 12 post-infection, and then the level was sustained during at least 28 days after infection. Forty healthy racehorses that had already been infected with EHV-4 possessed antibody against EHV-4. Although IgGa antibodies specific for EHV-4 were not detected in any horses, IgGb antibodies were detected and the levels correlated with total IgG antibodies against EHV-4 gG. The results suggest that EHV-4-specific IgGa and IgGb antibodies are induced in EHV-4-infected horses, and that IgGb antibody, but not IgGa, is long lasting.     

The diagnostic significance of the direct antiglobulin test (DAT) in anemic dogs

The direct antiglobulin test (DAT) was positivein 134 (36.1%) of 371 anemic dogs with internal diseases. Four principal types of reaction were recognized: IgG alone in 15 (11.2%), IgG + C' in 41 (30.6%), C' alone in 74 (55.2%) and IgM + C' in 2 (1.5%). Rarely, IgM and/or IgA reactions occurred in association with strong IgG + C' reactions. In 2 (1.5%) DAT-positive dogs the type of reaction was not clear. One or more symptoms of hemolysis, such as hemoglobinemia, indirect type hyperbilirubinemia, increased red cell osmotic fragility, and increased fecal urobilinogen excretion, were demonstrated in 84 DAT-positive dogs. These consisted of 10 of 15 dogs with IgG type DAT, 36 of 41 dogs with IgG + C' type DAT, 36 of 74 dogs with C' type DAT and 2 of 2 dogs with IgM + C' type DAT. Most dogs with IgG + C' type reactions had severe hemolysis, whereas "primary" or "associated" diseases were recognized in only 26 of 56 cases. IgG type incomplete warm antibody, reacting with pooled donor cells, was demonstrated in red cell eluates in each of 3 dogs with IgG type DAT and in 6 of 7 dogs with IgG + C' type reactions. This indicates that dogs with IgG or IgG + C' reactions usually have autoimmune hemolytic anemia. In dogs with C' type DAT, indications of hemolysis were frequently minimal or absent. Symptoms almost always indicated some "primary" disorder. Diagnoses mainly included infections, inflammatory and neoplastic (especially myelo- and lymphoproliferative)diseases. In only 7 (9.5%) of 74 dogs with C' type DAT no diagnosis other than (transient peracute) hemolytic anemia was made. The results of tests for antibodies in the serum and red cell eluates were always negative in dogs with C' type DAT. In one dog with hemolytic anemia and C' + IgM type DAT, there was a high titer of IgM cold agglutinins in the serum and in heat eluates. It is concluded that a positive DAT with anti-IgG antiserum is a strong indication of autoimmune hemolytic anemia but that a reaction of the C' alone type is a rather common phenomenon in canine internal diseases which is seldom associated with serious hemolysis.     

Antibody index and specific antibody quotient in horses after intragastric administration of Sarcocystis neurona sporocysts

OBJECTIVE: To investigate the use of a specific antibody index (AI) that relates Sarcocystis neurona-specific IgG quotient (Q(SN)) to total IgG quotient (Q(IgG)) for the detection of the anti-S neurona antibody fraction of CNS origin in CSF samples obtained from horses after intragastric administration of S neurona sporocysts. ANIMALS: 18 adult horses. PROCEDURES: 14 horses underwent intragastric inoculation (day 0) with S neurona sporocysts, and 4 horses remained unchallenged; blood and CSF samples were collected on days - 1 and 84. For purposes of another study, some challenged horses received intermittent administration of ponazuril (20 mg/kg, PO). Sarcocystis neurona-specific IgG concentrations in CSF (SN(CSF)) and plasma (SN(plasma)) were measured via a direct ELISA involving merozoite lysate antigen and reported as ELISA units (EUs; arbitrary units based on a nominal titer for undiluted immune plasma of 100,000 EUs/mL). Total IgG concentrations in CSF (IgG(CSF)) and plasma (IgG(plasma)) were quantified via a sandwich ELISA and a radial immunodiffusion assay, respectively; Q(SN), Q(IgG), and AI were calculated. RESULTS: Following sporocyst challenge, mean +/- SEM SN(CSF) and SN(plasma) increased significantly (from 8.8 +/- 1.0 EUs/mL to 270.0 +/- 112.7 EUs/mL and from 1,737 +/- 245 EUs/mL to 43,169 +/- 13,770 EUs/mL, respectively). Challenge did not affect total IgG concentration, Q(SN), Q(IgG), or AI. CONCLUSIONS AND CLINICAL RELEVANCE: S neurona-specific IgG detected in CSF samples from sporocyst-challenged horses appeared to be extraneural in origin; thus, this experimental challenge may not reliably result in CNS infection. Calculation of a specific AI may have application to the diagnosis of S neurona-associated myeloencephalitis in horses.     

Effects of blood contamination of cerebrospinal fluid on results of indirect fluorescent antibody tests for detection of antibodies against Sarcocystis neurona and Neospora hughesi.

The purpose of this study was to determine the effect of blood contamination of cerebrospinal fluid (CSF) on the results of indirect fluorescent antibody tests (IFATs) for Sarcocystis neurona and Neospora hughesi. The in vitro study used antibody-negative CSF collected from non-neurologic horses immediately after euthanasia and blood samples from 40 healthy horses that had a range of IFAT antibody titers against S. neurona and N. hughesi. Serial dilutions of whole blood were made in seronegative CSF to generate blood-contaminated CSF with red blood cell (RBC) concentrations ranging from 10 to 100,000 RBCs/microl. The blood-contaminated CSF samples were then tested for antibodies against both pathogens using IFAT. Blood contamination of CSF had no detectable effect on IFAT results for S. neurona or N. hughesi at any serologic titer when the RBC concentration in CSF was <10,000 RBCs/microl. At concentrations of 10,000-100,000 RBCs/microl of CSF, positive CSF results (IFAT titer >or=5) for S. neurona and N. hughesi were detected only when the corresponding serum titers were >or=160 and >or=80, respectively. The IFAT performed on CSF is reliable for testing horses for equine protozoal myeloencephalitis caused by S. neurona or N. hughesi, even when blood contamination causes the RBC concentration in CSF to be up to 10,000 RBCs/microl.     

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.     

Neutralizing antibodies against vesicular stomatitis viruses (serotypes New Jersey and Indiana) in horses in Costa Rica.

Serum samples were collected from domestic horses in 4 different regions of Costa Rica to detect antibodies against vesicular stomatitis viruses, serotypes New Jersey (VSV-NJ) and Indiana (VSV-IN). A total of 214 samples were tested by the virus neutralization test. The sampling regions were identified as low North Pacific dry area (1), low Middle Atlantic humid area (2), low South Pacific humid area (3), and the highlands (4). In region 1, 97.1% of horses were positive for VSV-NJ and 16.5% were positive for VSV-IN. The mean antibody titer and its standard deviation after logarithmic transformation were 5.86 +/- 0.9 for VSV-NJ and 3.55 +/- 1.66 for VSV-IN for region 1. In region 2, 40.7% of horses were positive for VSV-NJ and 32.2% were positive for VSV-IN. The mean antibody titer in region 2 was 4.33 +/- 1.82 for VSV-NJ and 3.47 +/- 1.73 for VSV-IN. In region 3, 20.79% of horses were positive for VSV-NJ and 27.6% were positive for VSV-IN. The mean antibody titer in region 3 was 4.39 +/- 1.89 for VSV-NJ and 3.47 +/- 1.82 for VSV-IN. In region 4, 91.3% of horses were positive for VSV-NJ and 73.9% were positive for VSV-IN. The mean antibody titer in region 4 was 5.77 +/- 1.10 for VSV-NJ and 4.85 +/- 1.63 for VSV-IN. This is the first published report of the detection of virus-neutralizing antibodies against VSV-NJ and VSV-IN in horses in Costa Rica.     

Red maple (Acer rubrum) leaf toxicosis in horses: a retrospective study of 32 cases

BACKGROUND: Ingestion of wilted red maple leaves by horses can result in severe hemolytic anemia and methemoglobinemia. Little is known about what factors influence the outcome of red maple leaf toxicosis in horses. HYPOTHESIS: Our hypothesis was that physical examination findings, clinicopathologic variables or therapeutic modalities may predict outcome in horses with red maple leaf toxicity. ANIMALS: Horses with red maple leaf toxicosis presented to referral hospitals in the southeast region of the United States. METHODS: A multi-institutional retrospective study was designed to identify factors that predict mortality in horses with red maple toxicosis. RESULTS: Thirty-two horses with red maple toxicosis were identified, 19 of which died. Twenty-nine horses presented with anemia and 24 had clinicopathologic evidence of systemic inflammation. Renal insufficiency was identified in 12/30 (41%) horses. Laminitis (9/28) and colic (13/30) also were identified in horses with red maple toxicosis, but development of these 2 conditions did not have a negative effect on short-term survival. Horses with red maple toxicosis that survived to discharge were likely to have developed pyrexia during hospitalization (P = .030). Horses that were treated with a corticosteroid had a significantly increased likelihood of death (P = .045). There was no significant relationship between initial serum hemoglobin concentration, methemoglobin concentration, or percentage methemoglobin and mortality in this horse series. CONCLUSIONS AND CLINICAL IMPORTANCE: This study suggests that information obtained on initial examination cannot be used to accurately predict survival in horses with red maple toxicosis, but horses that receive corticosteroids are unlikely to survive.     

Serum Amyloid A (SAA) Concentration after Vaccination in Horses and Mules

Serum amyloid A (SAA) is a sensitive acute-phase response (APR) marker in equids. Prominent APRs with elevations of SAA concentrations ([SAA]) have been reported after vaccination. The authors hypothesized that vaccination with an inactivated EHV-1/-4 vaccine would cause increase in [SAA] and antibody responses and that higher [SAA] would be positively correlated with the antibody titer in both equids. Twelve Haflinger horses and 12 mules were included in this longitudinal prospective study. All horses and mules were vaccinated with a commercially available EHV-1/-4 vaccine. Blood was sampled before and after vaccination to measure [SAA] and virus-neutralizing response (VN-T). In horses and mules, significantly higher [SAA] were measured on days 1, 3, and 5 after EHV-1/-4 vaccination; [SAA] on day 1 after vaccination were only measured in animals that developed fever, where mean [SAA] were significantly higher in horses than in mules (horses: 1,365.75 ± 87.64 mg/L, mules: 615.5 ± 153.444 mg/L) (P > .05). Four horses and 2 mules developed fever after vaccination, lasting for ≤24 hours. Increased antibody responses (VN-T) on days 7 and 14 after vaccination were observed in all animals, whereas mules showed higher overall antibody responses. Nevertheless, [SAA] did not correlate with the intensity of the antibody responses (VN-T) stimulated by the vaccine (P < .05). EHV-1/-4 vaccination caused a prominent APR, higher in horses than in mules, but [SAA] did not correlate with antibody responses. Measuring [SAA] after vaccination could help identify severe APRs that may require longer resting intervals before training or competition.     

Antibody coefficients for the diagnosis of equine protozoal myeloencephalitis

Background: Diagnosis of equine protozoal myeloencephalitis (EPM) remains a challenge for equine practitioners. Current utilized methods have inadequate sensitivity and specificity, because of a high number of false positive results. Hypothesis/Objective: Evaluation of antibody indices to Sarcocystis neurona should provide high sensitivity and specificity for diagnosis of EPM. Animals: Archived samples from 29 clinical patients. Methods: Archived serum and cerebrospinal fluid (CSF) samples from clinical patients with either EPM (14) or cervical vertebral compressive myelopathy (CVM) (15) were examined and tested for anti‐S. neurona antibodies by the SnSAG2 ELISA. The results were used to calculate the antibody index (AI) and C‐value. Sensitivity and specificity were calculated, and the AI, C‐value, immunoglobulin G (IgG) concentrations, and anti‐S. neurona titers compared. In addition, negative CSF was spiked in varying concentrations with blood from a horse with a high anti‐S. neurona titer, and the tests repeated. Results: Results demonstrated that the IgG concentration, anti‐S. neurona titer, AI, and C‐value were significantly higher (P < .05) in horses with EPM than in those with CVM. Sensitivity and specificity of the AI was 71 and 100%, respectively, and that of the C‐value was 86 and 100%, respectively. In addition, the AI and C‐value from the samples spiked with S. neurona positive blood remained below 1 (eg, negative) in CSF with a red blood cell (RBC) count up to 10⁵ RBC/μL. Conclusions/Clinical Importance: Results of the study demonstrate the value of calculating the AI and C‐value in the diagnosis of EPM in horses. In addition, the test is robust in the presence of blood contamination.     

Serodiagnosis of western equine encephalitis virus infections: relationships of antibody titer and test to observed onset of clinical illness

Sera from horses and human beings with clinically diagnosed western equine encephalitis (WEE) virus infections were tested for hemagglutination-inhibition (HI), complement-fixation (CF), and neutralizing (N) antibody to WEE virus. These tests confirmed infection in 43.8% (HI), 56.3% (CF), and 80.4% (N) of horses and 54.5% (HI), 59.1% (CF), and 77.3% (N) of human beings. Use of the N test as an adjunct to the HI and CF tests increased the likelihood of serologic confirmation to 91.7%. In both horses and human beings, N antibody increased steeply at the end of the 1st week after onset. The results suggested that the presence of a high HI, CF, and/or N antibody titer in a single serum obtained from horses during the acute phase of illness caused by WEE virus can be used as presumptive evidence for infection with this virus.     

Antibody responses of horses to equine influenza viruses during a postepizootic period in Japan.

The antibody responses to equine influenza viruses were investigated during a postepizootic period of the disease. Serum samples were collected from a total of 128 horses on three occasions during the years 1967-77. No significant increase of hemagglutination-inhibition antibody titers to subtypes 1 and 2 of equine influenza virus were detected in any of the sera tested. The maternal hemagglutination-inhibition antibody titers of foals decreased over a four month interval. A marked increase of the titers was recognized in only the equine influenza virus vaccinated horses. These findings suggest that equine influenza virus was not prevalent in the horse populations during the observation period. In such conditions, the dissemination of equine influenza viruses in the horses is discussed in relation to introduction of the disease from abroad. We also examined whether the doctrine of original antigenic sin, an immunological phenomenon recognized in human influenza, was applicable for equine influenza. However, no marked increase of hemagglutination-inhibition antibody titer to the primary infecting subtype in the 44 horses was observed after administration of the heterologous subtype vaccine.