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.     

Studies of passive immunity in foals to equine viral arteritis

The capacity of colostral samples collected from mares immune to equine viral arteritis to neutralize arteritis virus was two or more times greater than that present in the dams' sera. This activity in the mammary secretions was very low or undetectable after 1 week. The capacity of sera from eight of the nine foals born to immune mares to neutralize arteritis virus was high at 1 week of age. All of the titres had declined to extinction after 2–6 months. Arteritis virus neutralization was not detected in serum collected from foals prior to nursing or in samples from non-immune mares and their foals.Foals from immune mares developed mild signs or no signs of disease when inoculated nasally with virulent arteritis virus at 6 days of age.Seven- to nine-day-old foals from non-immune mares responded to vaccinationas they had appreciable serum-virus neutralizing antibody titres 6 months after vaccination and did not develop signs of disease when inoculated nasally with virulent virus. Foals of the same ages from immune mares did not respond to the vaccine since antibody could not be detected 6 months after vaccination and they either died or experienced clinically severe disease when inoculated nasally with virulent arteritis virus.     

Serological evidence for Japanese encephalitis and West Nile viruses in domestic animals of Nepal

A regional survey was conducted in Nepal for antibody to Japanese encephalitis virus (JEV) in domestic animals. Sera from pigs, and limited numbers of ducks and horses were collected from 16 districts in 2002-2003 and subjected to three serological tests. Of 270 porcine sera tested by C-ELISA, 55% were found positive for the presence of antibodies against Japanese encephalitis virus. Additional testing for IgM antibody to JEV revealed less than 2% of C-ELISA positive sera had evidence of recent JEV infection. Plaque reduction neutralisation tests (PRNT) using JEV, Murray Valley encephalitis (MVEV) and Kunjin (KUNV) viruses implicated JEV as the flavivirus associated with the observed antibody response in most sero-positive pigs. However, eight porcine sera with predominant neutralising antibody for KUNV (an Australasian subtype of West Nile Virus) provided evidence for the circulation of West Nile virus in Nepal.     

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.     

First evidence of Kunjin strain of West Nile virus associated with saltwater crocodile (Crocodylus porosus) skin lesions

Recently, the Kunjin strain of West Nile virus (WNV_KUN) has been detected using qRT‐PCR in belly skin lesions of farmed juvenile saltwater crocodiles. This follows an established association between similar lesions and West Nile virus in American alligators. The lesions present as cutaneous lymphohistiocytic aggregates in the dermal layers of both species. While these lesion do not create an obvious defect on the live crocodile, upon tanning the lesion area collapses and does not uptake the dye evenly, thus reducing its aesthetic appeal. As a result, skins are being rejected jeopardising the economic viability of the Australian crocodile industry. Over 50 skin lesions have since been confirmed as WNV_KUN‐positive and preliminary evidence of lesion restructuring is presented. Horizontal transmission of WNV_KUN by mosquitoes is well‐established but other transmission routes, such as ingestion and cloacal shedding, need further evaluation. An infection trial is currently underway to ensure WNV_KUN is the causative agent of these skin lesions.     

Foal IgG and opsonizing anti-Rhodococcus equi antibodies after immunization of pregnant mares with a protective VapA candidate vaccine

The aim of this study was to evaluate serum IgG antibody levels and opsonizing activity in foals from pregnant mares immunized with either proteins from an R. equi strain containing virulence-associated protein A (VapA), an immunodominant surface-expressed lipoprotein encoded by a virulence plasmid crucial for virulence in foals, or a whole killed virulent R. equi preparation. Forty-eight pregnant mares were distributed into three groups, i.e. 24 immunized with R. equi VapA protein antigen associated with a water-based nanoparticle adjuvant (Montanide IMS 3012), 8 immunized with whole killed R. equi, and 16 non-immunized as control. Serum IgG and opsonizing capacity were evaluated during pregnancy in mares, and up to day 45 post-delivery in foals in which R. equi infections were recorded in the first 6 months of life. Pregnant mares immunized with virulent R. equi proteins developed higher serum IgG and opsonic activity which were transferred to the foals than either in the whole R. equi immunized or the control group. Four foals developed pneumonia in the control group while none in immunized groups. Results support further evaluation of VapA protein antigen associated with a water-based nanoparticle adjuvant as a candidate vaccine for immunization of pregnant mares resulting in passive antibody-mediated protection of foals.     

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.     

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.     

Pathogenicity of equine herpesvirus 1 subtype 2 for foals and adult pony mares

Three pony mares and 4 pony foals were inoculated with a subtype 2 strain of equine herpesvirus 1. Foals had periods of fever 12 h and 2.5 days after inoculation and leukopenia, involving both neutrophils and lymphocytes, followed by leukocytosis. Mares had transient fever and leukopenia 24 hours after inoculation that were less severe than in foals. An increase in circulating virus-neutralizing antibody was seen in 2 of 3 inoculated mares, but not in foals. Attempts to isolate virus from blood were unsuccessful. These studies show that equine herpesvirus 1 subtype 2 is a mild pathogen for ponies and infection may result in inapparent clinical disease.     

Bursin as an adjuvant is a potent enhancer of immune response in mice immunized with the JEV subunit vaccine

Adjuvants play an important role in the formulation of effective and appropriate vaccines. A series of synthetic bursin and bursin-like peptides was heterologously expressed in Escherichia coli. The use of bursin as an adjuvant enhanced the specific immune responses of mice immunized with a recombinant Japanese encephalitis virus E-binding domain (JEV E-BD) fusion protein. The effect was determined in the form of protective anti-JEV E titers, antibodies (IgG1 and IgG2a), spleen cell lymphocyte proliferation, the levels of interferon-gamma and interleukin-4 cytokines, and the T-lymphocyte sub-type composition. The IgG2a titer and interferon-gamma level suggested that the E-BD protein potentiates the Th1 immune response. These responses were changed when the immunogen was combined with one of the synthetic peptides as adjuvant. JEV-neutralization assay results show that the presence of bursin significantly enhance the JEV-neutralizing titer. We conclude that bursin as an adjuvant is a potent enhancer of immune response in mice immunized with the JEV subunit vaccine, and represents a promising adjuvant for vaccination.     

Equine neonatal isoerythrolysis: evidence for prevention by maternal antibodies to the Ca blood group antigen

Foals with the Ca blood group antigen on their RBC were given colostrum with anti-Ca antibodies (6 foals) or colostrum without anti-Ca antibodies (6 foals). The PCV were determined at birth and 2, 4, and 6 days after birth for the foals in each group. Significant differences were not observed for the PCV between the 2 groups, indicating that foals were not adversely affected by ingesting colostrum with the anti-Ca antibody. Standardbred mares without the Aa blood group antigen were evaluated to determine whether production of anti-Ca antibodies influenced production of anti-Aa antibodies. Of 266 mares without the Aa antigen, 3 of 61 (5%) mares without the Ca blood group antigen produced anti-Aa antibodies and 43 of 205 (21%) with the Ca blood group antigen produced anti-Aa antibodies. These 2 groups of mares were significantly (P = 0.006) different; Ca-negative mares were less likely to produce antibodies to Aa than were mares with the Ca blood group antigen. This observation was consistent with a hypothesis of antibody-mediated immunosuppression of immune response to the Aa blood group antigen by antibodies to the Ca blood group antigen, ie, when a mare is exposed to her foal's RBC and already has antibodies to the Ca blood group antigen on the foal's RBC, then she is less likely to initiate an immune response to the Aa blood group antigen also on the foal's RBC.     

Detection and effects on platelet function of anti-platelet antibody in mule foals with experimentally induced neonatal alloimmune thrombocytopenia

Horse mares carrying mule foals were immunized during the last trimester of pregnancy with whole acid-citrate-dextrose-anticoagulated donkey blood to experimentally induce neonatal alloimmune thrombocytopenia. Thrombocytopenia occurred in the neonatal mule foals born to immunized horse mares within 24 hours after ingestion of their dams' colostrum. Mule foals born to mares not immunized with donkey blood did not develop thrombocytopenia. These findings suggest that antibodies may have been directed against a donkey platelet antigen present in the mule foals but not present in their dams. The objectives of this study were to determine whether anti-platelet antibody could be detected in mule foals with experimentally induced neonatal alloimmune thrombocytopenia, to identify any platelet proteins recognized by serum antibody in these foals, and to determine if platelet function was altered by sera from these mule foals. An indirect enzyme-linked immunosorbent assay demonstrated significantly higher absorption at 1:200 of platelet-bindable immunoglobulin G in serum from thrombocytopenic mule foals, compared with nonthrombocytopenic mule foals. Sera from thrombocytopenic and nonthrombocytopenic mule foals produced similar binding patterns in western immunoblots with donkey platelet proteins separated on sodium dodecyl sulfate polyacrylamide gels. Maximal platelet aggregation and relative slope of aggregation in response to collagen were significantly inhibited after incubation with sera from thrombocytopenic mule foals. These results suggest that mule foals with induced alloimmune thrombocytopenia have serum antibodies that bind to platelets and may compete with collagen binding sites to impair platelet aggregation.     

乙型脑炎重组伪狂犬病病毒TK-/gG-/NS+1的安全性及免疫性

用含有日本乙型脑炎病毒 (SA14 - 14 - 2株 )非结构蛋白 NS1基因的重组伪狂犬病病毒 TK- / g G- / NS 1 免疫BAL B/ c小鼠和断奶仔猪。结果表明 ,该重组病毒对 BAL B/ c小鼠和断奶仔猪是安全的 ,免疫的 BAL B/ c小鼠能抵抗伪狂犬病病毒 (PRV )强毒 (Ea株 )的致死性攻击 ,免疫的断奶仔猪能产生乙型脑炎病毒 (JEV)特异性抗体和 JEV特异性 CTL 活性。     

Antibodies to Berne virus in horses and other animals

After inoculation into 2 foals, Berne virus induced neutralizing antibody, but did not cause clinical symptoms. In a horizontal study of seropositive mares and their offspring, a decline of maternal antibodies and a sudden synchronous seroconversion in all foals were observed, again without clinical symptoms. The virus is widespread in the Swiss horse population and has been so during the last decade; rises in antibody titers were noted in 9% of paired sera sampled at random. Positive reactions were also obtained in serum neutralization tests and ELISA using small numbers of horse sera from Germany, France and the U.S.A. The results of neutralization tests and ELISA were correlated in 83% of random samples tested; 13% were neutralization-positive and ELISA-negative and in 4% the inverse was observed. Neutralizing activity was found in the sera of other ungulates (cattle, goat, sheep and pig), laboratory rabbits and 2 species of wild mice (Clethrionomys glareolus and Apodemus sylvaticus). Inconclusive results were obtained with feline and human sera; those from dogs and foxes (Vulpes vulpes) were consistently negative. The probable occurrence of antigenic variants in Berne-type viruses is discussed.     

Maternal dexamethasone treatment in late gestation induces precocious fetal maturation and delivery in healthy Thoroughbred mares

Reasons for performing study: The foal requires an active hypothalamo‐pituitary‐adrenal (HPA) axis for organ maturation and post natal survival. Prenatal administration of synthetic glucocorticoids may provide an effective method for inducing fetal maturation safely in the mare. Objectives: To determine whether dexamethasone administered to late pregnant mares: 1) will induce fetal maturation and precocious delivery; 2) is safe to use and 3) to identify endocrine responses in the mare and foal. Methods: Pregnant Thoroughbred mares received either 100 mg dexamethasone i.m. (treated n = 5) or 50 ml saline i.m. (control n = 5) at 315, 316 and 317 days of gestation. Plasma progestagens, cortisol and prostaglandin F_2α metabolite (PGFM) concentrations were measured before and after treatment. The foals were weighed, the crown‐rump length (CRL) measured and an adrenal stimulation test performed on Day 1. Results: Dexamethasone significantly (P<0.01) reduced gestation length in treated mares without apparent adverse effects. Plasma progestagens increased (P<0.05), and cortisol and PGFM (P<0.05) decreased, following dexamethasone treatment compared with control mares. Foals were clinically mature but those from dexamethasone treated mares had reduced (P<0.05) CRL, but not bodyweights, compared with controls. Their cortisol concentrations increased following exogenous adrenocorticotrophic hormone stimulation but 2 foals from dexamethasone treated mares showed evidence of adrenal suppression. Conclusions: Dexamethasone stimulates precocious fetal maturation and delivery in healthy late pregnant mares. However, fetal HPA activity may be suppressed. Potential relevance: Dexamethasone treatment could be used to improve foal viability in mares at risk of preterm delivery. The endocrine effects of such a therapy must be evaluated before clinical intervention with glucocorticoids can be recommended.     

Immune potency of lyophilized, killed vaccine for equine viral arteritis and its protection against abortion in pregnant mares

Immune potency test was conducted in horses by inoculating a killed vaccine for equine viral arteritis (EVA) which had been freeze-dried and contained aluminum hydroxide adjuvant. Serum neutralizing (SN) antibody to equine arteritis virus (EAV) was detected at maximal titers of 1:80 to 1:640, 1 to 2 weeks after 2-dose vaccination of 6 female horses. However, 6 pregnant mares inoculated with the vaccine which had been kept in storage for 1 year at 4°C produced much higher titers ranging from 1:320 to 1:1280. A maximal mean titer of 1:199.5 occurred in the 1st and 2nd week after 2-dose inoculation with the nonpreserved vaccine, whereas a maximal mean titer of 1:794.3 occurred in the 2nd week using the preserved vaccine. The horses showed no systemic or local adverse reactions clinically or hematologically after vaccination. Four of the 6 vaccinated pregnant mares were exposed to the Bucyrus strain of EAV but resisted challenge exposure, while 3 nonvaccinated control pregnant mares revealed acute EVA causing abortion and death. Isolation of EAV was positive from the body tissues of the aborted and dead fetuses and their dams, but was negative from the vaccinated mares. No significant rise of SN antibody titers was detected in the vaccinated mares following challenge exposure, suggesting that the vaccine can protect against EAV infection in pregnant mares and prevent abortion or death.     

Studies on the immunogenicity of Streptococcus equi vaccines in foals.

The ability of either formalin-treated or heat-inactivated whole Streptococcus equi cell vaccines or partially purified M-protein of S. equi to give rise to protective antibody levels was studied in Standardbred foals by serological means. Two commercial preparations, i.e. a beta-propiolactone killed whole S. equi cell bacterin and a cell-free extract of S. equi cells were included in the study. The mean passive hemagglutination antibody titers (10 X log2) in sera of foals given either four doses of formalin-treated whole cell vaccine or an initial dose of formalin-treated followed by three doses of heat-inactivated vaccine with or without levamisole were significantly higher two weeks after the final dose. These passive hemagglutination antibody titers were higher in foals given formalin-treated whole cell vaccine (6.7 +/- 1.5) than given commercial bacterin (4.5 +/- 2.1). The passive hemagglutination antibody titers in all the groups decreased at 12 to 16 weeks after fourth dose of the vaccine. Foals given a commercial cell-free extract did not show a significant increase in passive hemagglutination antibody titers even up to four weeks after third dose. A group of six pony foals immunized with partially-purified M protein showed mean passive hemagglutination antibody titers lower than those observed in foals given whole cell vaccines. In a challenge experiment with S. equi, two of six foals vaccinated with partially-purified M-protein and all three controls developed clinical disease. The passive hemagglutination antibody of vaccinated foals increased after challenge, while at 28 days postchallenge the passive hemagglutination antibody titers of vaccinates and recovered controls were similar.     

Lactation and reproductive performance of mares fed added dietary fat during late gestation and early lactation

Eighteen pregnant mares were randomly allotted to one of two treatment groups. The control group was fed a conventional concentrate and the fat group was fed a concentrate containing 5% feed-grade rendered fat. Both concentrates had the same nutrient:calorie ratio and were fed in amounts required to maintain zero change in percent body fat of the mares. During the study, which began 60 d prior to expected foaling date and ended 60 d postpartum, mares were monitored for feed intake, body weight, rump fat thickness, ration digestibility, plasma glucose and lipid concentrations, milk composition and reproductive efficiency. Birth weight, growth rate, and plasma glucose and lipid concentrations were also measured in foals. Mares fed fat consumed less concentrate (P<.09 during the last 60 d of gestation but consumed similar amounts of concentrate over 60 d of lactation. Protein and ether extract digestion was higher (P<.05 and P<.09, respectively) in the mares fed fat during the postpartum period. Dietary treatment had no influence on plasma glucose or lipid concentrations of the mares or plasma glucose concentrations of their foals, but foals whose dams were fed fat had higher plasma lipid concentrations at birth (P<.01), d 10 and d 30 (P<.05). Percent fat was higher in milk samples from mares fed fat at d 10 (P<.09, 1.23 vs .99%) and d 60 (P<.01, .72 vs .43%) of lactation. Reproductive performance was not significantly different between treatment groups, however there was a trend for a shorter postpartum interval and fewer cycles per pregnancy in the mares fed added fat. Foals from both groups were of similar size and weight at birth and had similar weight gains over 60 d, however, foals nursing mares fed fat tended to gain more weight in the first week of life (1.85 vs 1.56 kg/d) and have more rump fat at d 60 (.53 vs .44 cm) than foals nursing control mares.     

Sero-survey on Aino, Akabane, Chuzan, bovine ephemeral fever and Japanese encephalitis virus of cattle and swine in Korea

Vector-borne arboviruses produce mild to severe symptoms in domestic animals. Bovine ephemeral fever (BEF), Akabane, Aino, and Chuzan virus have been primarily attributed to reproductive disorders or febrile diseases in cattle, and Japanese encephalitis virus (JEV) is mainly associated with reproductive failures in swine. We investigated antibody titers from domestic swine against four bovine arboviruses (BEF, Akabane, Aino, and Chuzan virus) and from cattle against JEV in Korea. While the positive rates for Akabane and BEF were 37.4% and 15.7%, the positive incidence of Chuzan and Aino were relatively low, with positive rates of 3.04% and 0.4%, respectively, based on a virus neutralization assay. Antibody titers against more than one virus were also frequently detected in domestic swine. The incidence of JEV was 51.3% among domestic cattle. In addition, one positive case was detected in the thoracic fluids from 35 aborted calves, based on the hemagglutination inhibition test. Our results indicate that swine are susceptible hosts of bovine arboviruses without showing clinical symptoms in a natural environment. Moreover, we confirmed that JEV could be associated with reproductive failure in pregnant cattle, as were other vector-borne bovine arboviruses assessed in this study.