Maternal antibodies against equine influenza virus in foals and their interference with vaccination.

Foals that were born to mares vaccinated twice a year against influenza had moderate to high haemagglutination-inhibition antibody titers at 24 hours after birth. The foals were vaccinated at six and ten weeks of age, and again at three to five months after birth. Four months after the third vaccination no antibodies against A/H7N7 and A/H3N8 influenza viruses were detected in these foals. Thus, maternal antibodies probably prevented the development of antibodies against equine influenza virus after vaccination. Foals born to the same mares one year later were monitored to determine the rate of decline of maternal antibodies against influenza viruses. Antibody titers of the foals shortly after birth were similar to those of the mares at foaling. The antibodies persisted for three to six months, and their biological half-life was estimated to be approximately 38 days. Two vaccinations of foals against influenza after the maternal antibodies had virtually disappeared resulted in an antibody response in most, but still not all, foals. These findings suggest that foals should not be vaccinated against influenza until maternal antibodies have disappeared.     

Interference of maternal antibodies with the immune response of foals after vaccination against equine influenza.

The purpose of the study was twofold. First, using two groups of 22 foals each, we investigated the extent to which maternal antibodies interfere with the humoral response against equine influenza. The foals were born to mares that had been vaccinated twice yearly against influenza since 1982. Foals of group I were vaccinated three times at early ages (12, 16, and 32 weeks of age), and foals of group II were likewise vaccinated but a later ages (24, 28, and 44 weeks of age). After the first and second vaccinations, neither group showed an increase in antibodies that inhibit haemagglutination. Group II foals, however, had a significantly stronger antibody response against nucleoprotein after the second vaccination than the foals of group I. After the third vaccination, group II foals had a significantly stronger and longer lasting antibody response against haemagglutinin than the foals of group I. However, the antibody response to nucleoprotein was comparable in both groups. Second, the foals of group II were studied to determine the persistence of maternal antibodies directed against a common nucleoprotein and the haemagglutinin of two strains of equine influenza A virus. Biological half-lives of 39, 32, and 33 days were calculated for maternal antibodies directed against haemagglutinin of strains H7N7 Prague and H3N8 Miami, and against the nucleoprotein respectively. Maternal antibody titres at the time of vaccination were closely related to the degree of interference with the immune response. Because even small amounts of maternal antibodies interfered with the efficacy of vaccination, we conclude that foals born to mares vaccinated more than once yearly against influenza virus should not be vaccinated before 24 weeks of age.     

West Nile Virus Antibody Titers and Total Immunoglobulin G Concentrations in Foals from Mares Vaccinated in Late Gestation

This study was conducted to determine whether prepartum vaccination of mares would enhance passive transfer of West Nile virus (WNV)-specific antibodies and to characterize the pattern of decline for maternally derived WNV antibodies in foals. Seventeen light horse mares were allocated to WNV or control treatments. At 30 days before expected foaling, mares were vaccinated for encephalomyelitis, tetanus, herpesvirus, and influenza. At this time, WNV mares were vaccinated with a killed WNV vaccine. Blood samples were taken from mares 30 days before expected foaling, from mares and foals within 24 hours of foaling (0 days), and from foals at 7, 30, 60, 90, 120, 150, and 180 days of age as well as 30 days after an initial (PV1) and subsequent (PV2) WNV vaccination. Serum was analyzed for titer to WNV and total immunoglobulin G (IgG). Although WNV titer did not change over time in control mares, an increase (P < .05) was observed in WNV titer for WNV mares vaccinated 30 days before expected foaling. Foals of WNV dams had greater (P < .05) WNV titers than foals of control dams. Mean WNV titers of all foals increased from 0 to 7 days and declined through 180 days of age. Total IgG of foals increased from days 0 to 7, declined from days 30 to 120, and increased from days 150 through PV2. These results suggest that vaccination of mares for WNV in late gestation has a beneficial effect on foal WNV titer.     

Passive transfer of maternal immunoglobulin isotype antibodies against tetanus and influenza and their effect on the response of foals to vaccination.

Influenza and tetanus-specific antibodies of the IgG sub-isotypes are posively transferred to foals via colostrum and inhibit their response to inactivated influenza vaccines and tetanus toxoid. High titres of influenza antibodies of IgGa and IgGb subisotypes and tetanus antibodies of the IgGa, IgGb and IgG(T) subisotypes were detected in postsucking serum samples collected from foals born to mares that had received booster doses of multicomponent vaccines during the last 2 months of gestation. Thereafter, titres declined in an exponential manner but were still detectable in all foals at age 26 weeks, regardless of whether they had been vaccinated prior to age 26 weeks. Mean +/- s.e. half-life of decline of influenza IgGa antibodies (27.0 +/- 2.3 days) was significantly shorter than that of influenza IgGb antibodies (39.1 +/- 2.7 days; P<0.005). Tetanus IgGa and IgGb antibodies declined with half-lives of 28.8 +/- 3.0 and 34.8 +/- 5.1 days, respectively. Titres of tetanus IgG(T) antibodies were substantially higher than those of influenza IgG(T) antibodies in postsucking samples and remained so through age 26 weeks, declining with a half-life of approximately 35 days. Postsucking titres of tetanus and influenza antibodies of the IgA isotype were low and declined rapidly to undetectable levels. Yearlings showed significant increases in titre of influenza IgGa, IgGb and IgG(T) subisotype antibodies but no increase in influenza IgA antibodies in response to 2 doses of multicomponent vaccines containing tetanus toxoid and inactivated influenza A-1 and A-2 antigens. Yearlings also showed strong tetanus IgGa, IgGb and IgG(T) subisotype responses to one dose of vaccine and a substantial further rise in titre in response to administration of a second dose 3 weeks later, but failed to show an increase in titre of tetanus IgA antibodies. The influenza and tetanus IgGa, IgGb and IgG(T) subisotype responses of 6-month-old foals to vaccination followed the same pattern as those shown by yearlings but titres were generally lower. In contrast, 3-month-old foals failed to show increases in titre of either influenza or tetanus IgG subisotypes in response to 2 doses of vaccine and generally needed 1-3 additional booster doses of vaccine to achieve titres similar to those achieved by yearlings after 2 doses. Based on the finding that maternal antibodies exert a significant inhibitory effect on the response of foals to tetanus toxoid and inactivated influenza antigens, it is recommended that primary immunisation of foals born to vaccinated mares should not commence before age 6 months.     

Duration of immunity induced by an adjuvanted and inactivated equine influenza, tetanus and equine herpesvirus 1 and 4 combination vaccine

An adjuvanted vaccine containing inactivated equine influenza, herpesvirus antigens, and tetanus toxoid was administered to young seronegative foals of 8 months of age by deep intramuscular injection in the neck (Group A). The first two vaccinations were given 4 weeks apart. The third was administered 6 months later. Another group of foals (Group B) was vaccinated according to the same scheme at the same time with monovalent equine herpes virus (EHV) vaccine (EHV1.4) vaccine. Antibody responses to the equine influenza (single radial haemolysis; SRH) and tetanus (ToBi ELISA) components of the vaccines were examined from first vaccination until 1 year after the third vaccination. The influenza components of the combination vaccine induced high antibody titres at two weeks after the second vaccination whereafter titres declined until the time of the third vaccination. After the third vaccination, the titres rose rapidly again to remain high for at least 1 year. Antibody titres against tetanus peaked only after the third vaccination but remained high enough to offer protective immunity for at least 1 year. Foals vaccinated with monovalent EHV1.4 remained seronegative for influenza and tetanus throughout the study. Four and a half months after the third vaccination of groups A and B, a third group of animals was vaccinated twice with monovalent EHV1.4 vaccine 4 weeks apart (Group C). Two weeks after the administration of the second dose in the later group, all groups (A, B, C and an unvaccinated control group D) were challenged with EHV-4. Vaccinated foals (Group A, B, C) showed a clear reduction of clinical symptoms and virus excretion after EHV-4 challenge compared with the unvaccinated control foals. No difference could be demonstrated among the vaccinated groups, suggesting that the combination vaccine protects as well as the monovalent vaccine. In EHV1.4-vaccinated foals both antigenic fractions induced clear protection up to 6 months after vaccination (9). It can therefore be anticipated that the efficacy of the combination vaccine against EHV-1 challenge is similar to the efficacy against EHV-1 induced by EHV1.4 vaccination.     

Passive transfer of naturally acquired specific immunity against West Nile Virus to foals in a semi-feral pony herd

Horses naturally exposed to West Nile Virus (WNV) or vaccinated against WNV develop humoral immunity thought to be protective against development of clinical disease in exposed or infected animals. No reports evaluate the efficacy of passive transfer of naturally acquired specific WNV humoral immunity from dam to foal. The purpose of this study was to investigate passive transfer of naturally acquired immunity to WNV to foals born in a herd of semi-feral ponies, not vaccinated against WNV, in an endemic area, with many dams having seroconverted because of natural exposure. Microwell serum neutralization titers against WNV were determined in all mares and foals. Serum IgG concentration was determined in foals by serial radial immunodiffusion. Differences in IgG concentration between seropositive and seronegative foals were examined by means of the Mann-Whitney U-test. Linear regression was used to evaluate the association between mare and foal titers. Seventeen mare-foal pairs were studied; 1 foal had inadequate IgG concentration. IgG concentration was not different between seronegative and seropositive foals (P = .24). Mare and foal titers were significantly correlated in foals with adequate passive transfer of immunity (Spearman's rho = .84; P < .001); >90% of the foal's titer was explained by the mare's titer (R2 = 0.91; P < .001). Passive transfer of specific immunity to WNV is present in pony foals with adequate passive transfer of immunity born to seroconverted mares.     

Serological responses and clinical outcome after vaccination of mares and foals with equine herpesvirus type 1 and 4 (EHV-1 and EHV-4) vaccines

Equine herpesvirus type 1 and type 4 (EHV-1 and EHV-4) cause infections of horses worldwide. While both EHV-1 and EHV-4 cause respiratory disease, abortion and myeloencephalopathy are observed after infection with EHV-1 in the vast majority of cases. Disease control is achieved by hygiene measures that include immunization with either inactivated or modified live virus (MLV) vaccine preparations. We here compared the efficacy of commercially available vaccines, an EHV-1/EHV-4 inactivated combination and an MLV vaccine, with respect to induction of humoral responses and protection of clinical disease (abortion) in pregnant mares and foals on a large stud with a total of approximately 3500 horses. The MLV vaccine was administered twice during pregnancy (months 5 and 8 of gestation) to 383 mares (49.4%), while the inactivated vaccine was administered three times (months 5, 7, and 9) to 392 mares (50.6%). From the vaccinated mares, 192 (MLV) and 150 (inactivated) were randomly selected for serological analyses. There was no significant difference between the groups with respect to magnitude or duration of the humoral responses as assessed by serum neutralization assays (median range from 1:42 to 1:130) and probing for EHV-1-specific IgG isotypes, although neutralizing responses were higher in animals vaccinated with the MLV preparation at all time points sampled. The total number of abortions in the study population was 55/775 (7.1%), 9 of which were attributed to EHV-1. Seven of the abortions were in the inactivated and two in the MLV vaccine group (p=0.16). When foals of vaccinated mares were followed up, a dramatic drop of serum neutralizing titers (median below 1:8) was observed in all groups, indicating that the half-life of maternally derived antibody is less than 4 weeks.     

Is there a benefit from an early booster vaccination in the control of equine influenza?

Conventional equine influenza vaccination schedules consist of a primary course of two vaccinations given 4-6 weeks apart followed by a third vaccination (booster) given approximately 5 months later. In between the primary course and the third vaccination, horses are generally considered not to be adequately protected against influenza. This study aimed to investigate whether Thoroughbred foals would benefit from a vaccination schedule in which the third vaccination was given earlier than in conventional vaccination schedules. The vaccines used were an inactivated whole virus equine influenza vaccine and an inactivated whole virus combination vaccine containing equine influenza and equine herpesvirus antigens. Four groups of foals were vaccinated with the two vaccines according to a conventional and an accelerated vaccination schedule in which the third vaccination was given 14 weeks after the first administration. In both groups, the fourth vaccination was given at the normally recommended interval of 26 weeks after the third vaccination for the combination vaccine and 52 weeks after the third vaccination with the influenza only vaccine. The horses were 4-11 months of age and seronegative for influenza. Immunological responses after vaccination were monitored for several months using the single radial haemolysis test. The results indicated that 28 weeks after the first vaccination, antibody levels in horses vaccinated according to the accelerated schedule were not significantly higher than in horses vaccinated according to the conventional schedule. In addition, the total level of antibody production (area under the curve) was not significantly different at that point although antibody titres were slightly higher (but not significantly so) between 16-30 weeks in the accelerated schedule. Between the third and fourth doses, horses vaccinated according to the accelerated schedule had antibodies against influenza below the level required for clinical protection for 39 and 18 weeks for the influenza only and the combination vaccine, respectively, whereas those vaccinated according to the conventional schedule had antibody titres below the level for clinical protection for 9-15 weeks in the corresponding period for both vaccines. Horses vaccinated according to the accelerated schedule with the combination vaccine had lower antibody titres after the fourth vaccination than those vaccinated according to the conventional schedule after the third vaccination, although antibody titres prior to vaccination were similar. For the influenza only vaccine, titres after the accelerated fourth administration were not different to those after the conventional third vaccination. There was no benefit from early booster vaccinations with the vaccines used in this study, so for these vaccines the conventional schedule provided better protection than the selected accelerated alternative. This may contrast with some other vaccine formulations, although a direct comparison using similar protocols has not been made.     

Effect of maternal antibodies on induction and persistence of vaccine-induced immune responses against bovine viral diarrhea virus type II in young calves

OBJECTIVE: To determine the effect of maternally derived antibodies on induction of protective immune responses against bovine viral diarrhea virus (BVDV) type II in young calves vaccinated with a modified-live bovine viral diarrhea virus (BVDV) type I vaccine. DESIGN: Blinded controlled challenge study. ANIMALS: 24 neonatal Holstein and Holstein-cross calves that were deprived of maternal colostrum and fed pooled colostrum that contained a high concentration of (n = 6) or no (18) antibodies to BVDV. PROCEDURE: At 10 to 14 days of age, 6 seropositive and 6 seronegative calves were given a combination vaccine containing modified-live BVDV type I. All calves were kept in isolation for 4.5 months. Six calves of the remaining 12 untreated calves were vaccinated with the same combination vaccine at approximately 4 months of age. Three weeks later, all calves were challenged intranasally with a virulent BVDV type II. RESULTS: Seronegative unvaccinated calves and seropositive calves that were vaccinated at 2 weeks of age developed severe disease, and 4 calves in each of these groups required euthanasia. Seronegative calves that were vaccinated at 2 weeks or 4 months of age developed only mild or no clinical signs of disease. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that a single dose of a modified-live BVDV type-I vaccine given at 10 to 14 days of age can protect susceptible young calves from virulent BVDV type II infection for at least 4 months, but high concentrations of BVDV-specific maternally derived antibodies can block the induction of the response.     

Serum antibody response to canine parvovirus, canine adenovirus-1, and canine distemper virus in dogs with known status of immunization: study of dogs in Sweden

Serum antibody titers to canine parvovirus (CPV), canine adenovirus-1 (CAV-1), and canine distemper virus (CDV) were measured in dogs with known immunization status. The dogs represented 3 groups: nonvaccinated dogs less than 12 months old; vaccinated dogs less than 12 months old; and adult dogs greater than 12 months old. For practical reasons, the population from which the specimens were obtained could be considered as free from natural infection with CAV-1 and CDV. In nonvaccinated dogs less than 12 months old, antibodies against all 3 viruses were measured at the time the dogs were given their first vaccination. Altogether, 50.7% of the dogs had titer greater than or equal to 1:10 to CPV, and 26.1 and 46.2% had titer greater than or equal to 1:8 to CAV-1 and CDV, respectively. The concentration of maternal antibody seemed to be of major importance for failure of immunization with use of inactivated CPV vaccine, but not with CAV-1 and CDV vaccination. In dogs less than 12 months old and vaccinated against CPV infection with inactivated virus, only 11.5% had titer greater than or equal to 1:80. In dogs vaccinated against infectious canine hepatitis and canine distemper, 63.2 and 78.3%, respectively, had titer greater than or equal to 1:16. In adult dogs greater than 2 months old and vaccinated against CPV infection, less than 50% had titer greater than or equal to 1:80, regardless of time after vaccination. There was no significant difference in titer between vaccinated and nonvaccinated dogs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of antibodies against Sarcocystis neurona in cerebrospinal fluid from clinically normal neonatal foals

OBJECTIVE: To determine whether antibodies against Sarcocystis neurona could be detected in CSF from clinically normal neonatal (2 to 7 days old) and young (2 to 3 months old) foals. DESIGN: Prospective study. ANIMALS: 15 clinically normal neonatal Thoroughbred foals. PROCEDURE: Serum and CSF samples were obtained from foals at 2 to 7 days of age and tested for antibodies against S. neurona by means of western blotting. Serum samples from the mares were also tested for antibodies against S. neurona. Additional CSF and blood samples were obtained from 5 foals between 13 and 41 days after birth and between 62 and 90 days after birth. RESULTS: Antibodies against S. neurona were detected in serum from 13 mares and their foals; antibodies against S. neurona were detected in CSF from 12 of these 13 foals. Degree of immunoreactivity in serum and CSF decreased over time, and antibodies against S. neurona were no longer detected in CSF from 2 foals 83 and 84 days after birth. However, antibodies could still be detected in CSF from the other 3 foals between 62 and 90 days after birth. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that antibodies against S. neurona can be detected in CSF from clinically normal neonatal (2 to 7 days old) foals born to seropositive mares. This suggests that western blotting of CSF cannot be reliably used to diagnose equine protozoal myeloencephalitis in foals < 3 months of age born to seropositive mares.     

Interpretation of the detection of Sarcocystis neurona antibodies in the serum of young horses

Horses that are exposed to Sarcocystis neurona, a causative agent of equine protozoal myeloencephalitis, produce antibodies that are detectable in serum by western blot (WB). A positive test is indicative of exposure to the organism. Positive tests in young horses can be complicated by the presence of maternal antibodies. Passive transfer of maternal antibodies to S. neurona from seropositive mares to their foals was evaluated. Foals were sampled at birth (presuckle), at 24h of age (postsuckle), and at monthly intervals. All foals sampled before suckling were seronegative. Thirty-three foals from 33 seropositive mares became seropositive with colostrum ingestion at 24h of age, confirming that passive transfer of S. neurona maternal antibodies occurs. Thirty-one of the 33 foals became seronegative by 9 months of age, with a mean seronegative conversion time of 4.2 months. These results indicate that evaluation of exposure to S. neurona by WB analysis of serum may be misleading in young horses.     

A follow up study on antibodies against Lawsonia intracellularis in mares and foals from two breeding farms in Germany

Equine proliferative enteropathy (EPE) caused by Lawsonia (L.) intracellularis is an emerging disease in foals, particularly in North America. Since a case report in Germany exists, the objective of this study was to examine the incidence of L. intracellularis-antibodies in healthy horses from two German breeding farms. In group 1, serum samples from 24 (year 1) and 16 (year 2) Haflinger mares and their foals were taken. In group 2, over a period of five months, serum samples of six warmblood mares and foals were collected monthly from birth until the foals became seronegative. Serum samples were tested using an ELISA system. Results are expressed as Percentage of Inhibiton (PI). All adult mares (100%) of both groups were seropositive at each point in time (PI-value > 30). In group 1,7/24 foals (29.2%) in year 1 and 4/16 foals (25%) in year 2 had antibodies.The seropositive foals from year 2 had the same dams as the seropositive foals from year 1. In group 2 five of six foals were seropositive after birth. Antibodies decreased from March to July in mares and foals. In July, all five foals tested negative for the first time between the ages of 82 and 141 days (median 115 days). PI-values of mares were significantly correlated with PI-values of their foals. Higher PI-values were seen in younger foals and early in spring. Loss of antibodies in foals at the age of three to five months could be a risk factor for infection and appearance of EPE.     

EHV-1 and EHV-4 infection in vaccinated mares and their foals

A silent cycle of equine herpesvirus 1 infection was described following epidemiological studies of unvaccinated mares and foals on a Hunter Valley stud farm. Following the introduction of routine vaccination with an inactivated whole virus equine herpesvirus 1 (EHV-1) and equine herpesvirus 4 (EHV-4) vaccine in 1997, a subsequent study identified excretion of EHV-1 and EHV-4 in nasal swab samples tested by PCR from vaccinated mares and their unweaned, unvaccinated foals. The current sero-epidemiological investigation of vaccinated mares and their young foals found serological evidence of EHV-1 and EHV-4 infection in mares and foals in the first 5 weeks of life. The results further support that EHV-1 and EHV-4 circulate in vaccinated populations of mares and their unweaned foals and confirms the continuation of the cycle of EHV-1 and EHV-4 infection.     

Safety of a temperature-sensitive vaccine strain of bovine viral diarrhea virus in pregnant cows

Safety tests were conducted in 78 pregnant cows vaccinated with a commercial preparation of a temperature-sensitive vaccine strain of bovine viral diarrhea (BVD) virus. After vaccination, seroconversion was detected in 33 (97%) of 34 cattle that did not have antibodies against BVD virus. Overall, 43 (91%) of 47 cows with prevaccination titers less than or equal to 4 seroconverted. During the test period, cows did not become naturally infected with BVD virus, and BVD-associated reactions to the vaccine were not observed in vaccinated cows. Calves born to vaccinated cows did not have clinical signs of fetal BVD. Precolostral blood samples collected from the progeny of cows that were seronegative at vaccination were free of antibody against BVD virus. Bovine viral diarrhea virus was not isolated from the cattle evaluated in the present study.     

Vaccination of pregnant ponies against equine rhinopneumonitis

Bovine herpesvirus 1247 (one dose) was given subcutaneously to five pregnant pony mares between 227 and 319 days of their gestations. There were no adverse clinical reactions, and the virus was not recovered from nasal swabs collected during a 2-week period after vaccination. Four ponies foaled full-term, live, healthy foals. The foal of the fifth mare (No. 1) was found dead, but on the basis of the pathologic and virologic examinations, the virus was not considered to be the cause of the death. At 3 weeks after vaccination, the pregnant pony mares had a 13- to 250-fold increase in serum antibody titer to equine herpesvirus-1. A virulent-virus challenge exposure of all pony mares at 208 days after vaccination resulted in antibody titers greater than those just before this exposure. Virus was recovered from nasal swabs from vaccinated mares only on postexposure day 1, whereas the one control (nonvaccinated) pony shed virus for at least 3 days after challenge exposure. The immunogenic and the nonabortifacient characteristics of the herpesvirus 1247 in pregnant pony mares indicate that it may be useful to vaccinate horses against equine herpesvirus-1.     

The influence of age and maternal antibodies on the postvaccinal response against swine influenza viruses in pigs

The influence of age and maternal immunity on the development and duration of postvaccinal humoral response against swine influenza viruses (SIV) were investigated under experimental conditions. Piglets born to immune and non-immune sows were vaccinated twice with bivalent inactivated vaccine. Vaccination was done according to 5 different schedules: 1+4, 1+8, 4+8, 8+10 or 8+12 weeks of age. Antibodies to the haemagglutinin type 1 and 3 were determined using the haemagglutination inhibition (HI) test. Maternally derived antibodies (MDA) against H1N1 and H3N2 in the serum of unvaccinated piglets born to immune sows were above the positive level until about 13-14 and 9-10 weeks of life, respectively. No serological responses were seen in any of the groups after the first vaccination. After the second dose of vaccine production of antibodies was observed even before the complete disappearance of maternal antibodies. MDA, however, were associated with reduced antibody response. In MDA-negative piglets, an active humoral postvaccinal response was developed in all vaccinated pigs. The age at which the vaccine was given was associated with the differences in the magnitude of antibody response to SIV. In general those pigs that were vaccinated for the first time at the age of 1 week, developed lower maximum titres after the second vaccination, and become seronegative earlier than pigs that were vaccinated for the first time at 4 or 8 weeks of age.     

Detection of EHV-1 and EHV-4 DNA in unweaned Thoroughbred foals from vaccinated mares on a large stud farm

REASONS FOR PERFORMING STUDY: A silent cycle of equine herpesvirus 1 infection has been described following epidemiological studies in unvaccinated mares and foals. In 1997, an inactivated whole virus EHV-1 and EHV-4 vaccine was released commercially in Australia and used on many stud farms. However, it was not known what effect vaccination might have on the cycle of infection of EHV-1. OBJECTIVE: To investigate whether EHV-1 and EHV-4 could be detected in young foals from vaccinated mares. METHODS: Nasal and blood samples were tested by PCR and ELISA after collection from 237 unvaccinated, unweaned foals and vaccinated and nonvaccinated mares during the breeding season of 2000. RESULTS: EHV-1 and EHV-4 DNA was detected in nasal swab samples from foals as young as age 11 days. CONCLUSIONS: These results confirm that EHV-1 and EHV-4 circulate in vaccinated populations of mares and their unweaned, unvaccinated foals. POTENTIAL RELEVANCE: The evidence that the cycle of EHV-1 and EHV-4 infection is continuing and that very young foals are becoming infected should assist stud farms in their management of the threat posed by these viruses.     

Immune response of the llama (Lama glama) to tetanus toxoid vaccination

An ELISA was developed to measure serum concentrations of tetanus toxoid-specific immunoglobulins. The titers obtained with this assay were compatible with those obtained by the standard mouse toxin-neutralization test. Serum samples from 123 llamas were analyzed for ELISA titers to tetanus toxoid. Of the 82 vaccinated adults, 75 (91%) had titers greater than or equal to 1:50. The vaccination status and titers of weanlings and juveniles (3 to 12 months old) varied; of the 21 vaccinated, 17 (81%) had titers greater than or equal to 1:50 and 7 of 9 (78%) unvaccinated llamas had titers less than 1:50. The ELISA titers of unvaccinated llamas less than 8 weeks old (crias) were matched with the maternal titers. All crias with titers less than 1:50 had dams with titers greater than or equal to 1:50.     

Serological responses of mares and weanlings following vaccination with an inactivated whole virus equine herpesvirus 1 and equine herpesvirus 4 vaccine

Equine herpesvirus 1 (EHV-1) is a major cause of respiratory disease and abortion in horses worldwide. Although some vaccines have been shown experimentally to reduce disease, there are few reports of the responses to vaccination in the field. This study measured antibody responses to vaccination of 159 mares (aged 4-17 years) and 101 foals (aged 3-6 months) on a large stud farm with a killed whole virus EHV-1/4 vaccine used as per the manufacturer's recommendations. Using an EHV glycoprotein D (gD)-specific ELISA and a type-specific glycoprotein G (gG) ELISA, respectively 13.8 and 28.9% of mares, and 42.6 and 46.6% of foals were classed as responding to vaccination. Additionally, 16.4 and 17.6% of mares were classified as persistently seropositive mares. Using both assays, responder mares and foals had lower week 0 mean ELISA absorbances than non-responder mares and foals. Responder mares were ten times more likely to have responder foals, and non-responder mares were six times more likely to have non-responder foals than other mares using the gG ELISA. Mares aged 7 years or less and foals aged 4 months or more were more likely to respond to vaccination than animals in other age groups. There was no association between response of mares and the number of previous vaccinations received and persistently seropositive mares did not respond to vaccination. This study documents the responses of mares and foals to vaccination in a large scale commercial environment in 2000, and suggests that knowledge of antibody status may allow a more selective vaccination strategy, representing considerable savings to industry.