Vector competence of Aedes vexans (Diptera: Culicidae) for West Nile virus and potential as an enzootic vector.

Vector competence of Aedes vexans (Meigen) and Culex pipiens pipiens L. (Diptera: Culicidae) for West Nile virus (family Flaviviridae, genus Flavivirus, WNV) was compared. Infection rates of both species were similar 14 d after feeding on chickens, with WNV titers ranging from 10(4.2) to 10(8.7) plaque-forming units (PFU)/ml. Median infectious doses and 95% confidence intervals (CI) were 10(6.0(5.8, 63)) and 10(5.7(5.4, 5.9)) PFU for Ae. vexans and Cx. p. pipiens, respectively. WNV transmission was not observed in Ae. vexans that fed on chickens with WNV titers < 10(5.0) PFU/ml, in contrast to a mean (95% CI) transmission rate of 7(2,18)% for Cx. p. pipiens. Mean WNV transmission rates for Ae. vexans and Cx. p. pipiens were 13(7,21)% and 10(5,19)%, respectively, after feeding on chickens with WNV titers of 10(5.3 +/- 0.1) and 10(5.7 +/- 0.1) PFU/ml, and 31(25,37)% and 41(30,53)% after feeding on chickens with WNV titers > or = 10(6.1 +/- 0.1) PFU/ml. Time postinfection (p.i.) significantly influenced WNV transmission by Ae. vexans as indicated by a nearly 10-fold increase in transmission rate between days 7 and 14 p.i. Mean WNV load expectorated with saliva ofAe. vexans was 10(2.4(2.1, 2.7)) PFU, and it was not significantly affected by the titer of chickens on which they originally fed or time p.i. These data indicate that vector competence of the primarily mammalophilic Ae. vexans, which also feeds on birds, approaches that of Cx. p. pipiens for WNV. Because peridomestic mammals, such as cottontail rabbits, squirrels, and chipmunks, develop WNV titers infective for Ae. vexans, this species may play a significant role in WNV enzootic cycles.

The potential of Aedes triseriatus (Diptera: Culicidae) as an enzootic vector of West Nile virus.

The susceptibility of Aedes triseriatus (Say) (Diptera: Culicidae) to low levels of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) was determined and compared with that of Culex pipiens L. to assess the likelihood of its participation in an enzootic cycle involving mammals. Ae. triseriatus and Cx. pipiens were exposed to WNV by feeding on baby chickens with WNV serum titers ranging from 10(4.1 +/- 0.1) to 10(8.6 +/- 0.1) plaque-forming units (PFU)/ml and from 10(4.1 +/- 0.1) to 10(7.0) PFU/ml, respectively. Infection rates and 95% confidence intervals (CIs) of 8% (4, 14) and 25% (15, 38) occurred in Ae. triseriatus and Cx. pipiens after feeding on chickens with WNV titers of 10(4.1 +/- 0.1) PFU/ml and increased to 65% (49, 79) and 100% (72, 100) in Ae. triseriatus and Cx. pipiens after feeding on chickens with titers of 10(7.1 +/- 0.1) PFU/ml. The mean infection rate of Ae. triseriatus ranged from 97% (84, 100) to 100% (79, 100) after feeding on chickens with WNV titers of > or = 10(8.2) PFU/ml. The infectious dose (ID)50 values for Ae. triseriatus and Cx. pipiens were 10(6.5) (6.4, 6.7) and 10(4.9) (4.6, 5.1) PFU/ml, respectively. The combined estimated transmission rate of Ae. triseriatus at 14 and 18 d after feeding on chickens with a mean WNV titer of 10(8.6 +/- 0.1) PFU/ml was 55%. Although Ae. triseriatus is significantly less susceptible to WNV than Cx. pipiens, the susceptibility of Ae. triseriatus to WNV titers < 10(5.0) PFU/ml and its ability to transmit WNV suggest that Ae. triseriatus has the potential to be an enzootic vector among mammalian populations.

The effect of a killed porcine reproductive and respiratory syndrome virus (PRRSV) vaccine treatment on virus shedding in previously PRRSV infected pigs.

Two experiments were conducted to investigate if virus shedding could be reduced following a killed porcine reproductive and respiratory syndrome virus (PRRSV) vaccination (KV) of PRRSV infected pigs. In experiment 1, PRRSV infected pigs were vaccinated with KV on days 14 and 28 following infection. Viremia and serum neutralizing (SN) antibody were compared to infected pigs with no KV. The second experiment was conducted in an identical manner. In addition to viremia and SN antibody, virus in oropharyngeal scrapings and interferon gamma (IFN-gamma) producing cells were monitored. Magnitude and duration of viremia were not different between KV vaccinated and non-vaccinated groups. No virus was detected in oropharyngeal scraping from any pig, nor was there a difference in the detection of viral RNA. In both experiments, however, increases in SN titer and number of IFN-gamma producing cells were observed. The SN titer was significantly higher in KV vaccinated groups than in non-vaccinated group on days 42 and 42-56 following infection in experiments 1 and 2, respectively. The number of IFN-gamma producing cells was slightly higher in KV vaccinated groups than in non-vaccinated group on days 42 and 63. These observations suggest that KV had no effect on virus shedding. However, previously infected pigs responded immunologically to KV, as demonstrated by increases in SN antibody titers and IFN-gamma producing cells.

Evaluation of the efficacy of lambda-cyhalothrin applied by three spray application methods for emergency control of Aedes aegypti in Costa Rica.

An extended duration formulation of lambda-cyhalothrin (Icon CS) applied as either an ultra-low volume (ULV) or thermal fog spray from a new hand-held sprayer (Twin-Fog) or as a low-volume spray (LV) from a backpack mist blower against Aedes aegypti was evaluated in Costa Rica. Spray applications were made at the front door for 1 min or to each room for 15 sec for the ULV and LV, and thermal fog applications were made to houses in separate blocks for each treatment. The efficacy and duration of effectiveness of the spray was determined from sentinel caged mosquito mortality and mosquito collections from within houses using hand-held, battery-powered aspirators. Sentinel caged mosquito mortality in both open and sequestered locations was 97-100% for the ULV and thermal fog spray treatments, with control mortality less than 2%. Both ULV applications (front door and each room) provided 3 wk of significant control (P < 0.05) based on adult Ae. aegypti house collections.

Identification of neutralizing and nonneutralizing epitopes in the porcine reproductive and respiratory syndrome virus GP5 ectodomain.

After infection of swine with porcine reproductive and respiratory syndrome virus (PRRSV), there is a rapid rise of PRRSV-specific nonneutralizing antibodies (NNA), while neutralizing antibodies (NA) are detectable not sooner than 3 weeks later. To characterize neutralizing epitopes, we selected phages from a 12-mer phage display library using anti-PRRSV neutralizing monoclonal antibody (MAb) ISU25-C1. In addition, phages carrying peptides recognized by swine antibodies with high seroneutralizing titer were isolated after subtracting from the library those clones binding to swine anti-PRRSV serum with no neutralizing activity. Two epitopes located in the ectodomain of PRRSV GP5 were identified. One of these epitopes, which we named epitope B, was recognized both by neutralizing MAb ISU25-C1 and swine neutralizing serum (NS) but not by swine nonneutralizing serum (NNS), indicating that it is a neutralizing epitope. Epitope B is sequential, conserved among isolates, and not immunodominant. Antibodies directed against it are detected in serum late after infection. In contrast, the other epitope, which we named epitope A, is hypervariable and immunodominant. Antibodies against it appear early after infection with PRRSV. This epitope is recognized by swine NNA but is not recognized by either neutralizing MAb ISU25-C1 or swine NA, indicating that it is not involved in PRRSV neutralization. During infection with PRRSV, epitope A may act as a decoy, eliciting most of the antibodies directed to GP5 and delaying the induction of NA against epitope B for at least 3 weeks. These results are relevant to the design of vaccines against PRRSV.

Detection of dengue virus neutralizing antibodies in bats from Costa Rica and Ecuador.

Neutralizing antibodies for dengue virus serotypes 1 and 2 and serotypes 2 and 3 were detected in 1998 in 12 of 53 (22.6%) and 3 of 10 (30.0%) bats sampled in Costa Rica and Ecuador, respectively. Dengue is a consistent health problem in the two Costa Rican communities in which bats were sampled. The high percentage of bats with neutralizing antibodies to dengue virus in these two Costa Rican communities suggests that bats may become infected with dengue virus. This appears to be the case in Costa Rica and Ecuador.

Categorization of North American porcine reproductive and respiratory syndrome viruses: epitopic profiles of the N, M, GP5 and GP3 proteins and susceptibility to neutralization.

Eleven epitopes were identified by murine monoclonal antibodies (MAbs) that represented the N, M, GP5 and GP3 proteins of the North American (NA) porcine reproductive and respiratory syndrome (PRRS) virus, KY 35 (NVSL 46907). Three discontinuous epitopes of the N and M proteins were designated EpORF7-Fd through Hd and EpORF6-Ad through Cd. Five continuous epitopes of the GP5 and GP3 proteins were designated EpORF5-A through C and EpORF3-A and B. The MAbs representing EpORF5-C and EpORF6-A and B had neutralizing activity. The MAbs representing the above epitopes, except EpORF7-Gd and Hd, expanded the virus marker system described in a previous study in which a panel of 69 NA viruses and the Lelystad virus were categorized into 5 antigenic groups, I15 through V15 based on the presence or absence of 5 continuous epitopes of the N protein. Antigenic groups I15 and II15, which represented 84.7 and 11.6% of all viruses tested, were categorized further into 9 and 4 subgroups, respectively. The remaining NA viruses and the Lelystad virus were distributed among 4 groups, one of which was represented by 2 subgroups. Significant (P<0.05) differences in sensitivity to neutralization of 28 viruses representing 6 antigenic groups by the 3 neutralizing MAbs suggested that sensitivity to neutralization may also be of value in categorizing PRRS viruses.

Longevity and spontaneous flight activity of Culex tarsalis (Diptera: Culicidae) infected with western equine encephalomyelitis virus.

The longevity of an Iowa strain of Culex tarsalis Coquillett fed blood meals containing 2 concentrations of western equine encephalomyelitis virus from Iowa (WEE-7738) was compared with that of Cx. tarsalis fed blood without virus. Females exposed to 4.7-5.0 log TCID50 per mosquito of WEE-7738 did not live as long as mosquitoes exposed to 2.7-3.0 log TCID50 per mosquito or controls. Only 1% of mosquitoes fed blood containing the higher virus concentration survived to day 18 after exposure. However, 13% of mosquitoes fed blood with the lower virus titer and 19.5% of the controls were still alive on day 18 after exposure. Flight activity scores of Cx. tarsalis infected with 4.7-5.0 log TCID50 per mosquito of WEE-7738 were 27.5% lower, and there were 26.1% fewer spontaneous flights than noninfected controls from days 6-11 after infection. After day 8 after infection, infected Cx. tarsalis had 37.1% lower activity scores and 40.0% fewer spontaneous flights than noninfected controls. Virus infection did not affect how long a mosquito flew in a 24-h period (the daily flying time) or the duration of individual flights. The spontaneous flight activity pattern (circadian rhythm) of infected mosquitoes was identical to those of controls. Both infected and noninfected mosquitoes began spontaneous flight activity at 2000-2100 hours (CST) and were active throughout the entire dark phase of the 24-h cycle. Although mosquitoes were active throughout the night, there was a burst or peak of activity between 2200 and 2300 hours when the complete dark cycle began. These results indicate that the adverse effect of WEE infection on longevity and spontaneous flight activity of Cx. tarsalis may decrease vectorial capacity of Cx. tarsalis for WEE.

Vector competence of Culex tarsalis (Diptera: Culicidae) from Iowa for a sympatric strain of western equine encephalomyelitis (WEE-7738) virus.

Experiments were designed to evaluate the vector competence of Culex tarsalis Coquillet from an area (Sioux City) where Cx. tarsalis is most abundant in Iowa for western equine encephalomyelitis virus (WEE-7738). WEE-7738 was isolated from Aedes trivittatus (Coquillet) collected in Ames, IA, in 1977. Infection rate, dissemination rate, multiplication efficiency, and transmission rate were determined for this virus in the SC strain of Cx. tarsalis. SC strain of Cx. tarsalis was as susceptible to WEE-7738 as Californian strains of Cx. tarsalis were to BFS1703 strain of WEE; OID50 of SC Cx. tarsalis was 2.63 log TCID50 per mosquito and OID50 of Californian strains of Cx. tarsalis were 2.0-4.1 log PFU per mosquito. However, transmission of WEE-7738 (4.2%) by the SC strain of Cx. tarsalis was lower than those (10-60%) reported in other studies.

Antigenic and genetic variations of the 15 kD nucleocapsid protein of porcine reproductive and respiratory syndrome virus isolates.

The antigenic variability of the 15 kD nucleocapsid protein of porcine reproductive and respiratory syndrome (PRRS) virus was characterized with a panel of 24 monoclonal antibodies (MAbs) raised against the American PRRS virus isolate ISU-P. Five continuous epitopes designated EpORF7-A through E were revealed by the reactivity pattern of these MAbs with 67 American field isolates, two modified-live vaccine viruses, and the European Lelystad virus as determined by the indirect immnofluorescence assay and Western immunoblotting and confirmed by additivity and blocking enzyme-linked immunosorbent assays. The reactivity pattern of isolates in the IFA permitted their subdivision into 4 American antigenic groups which represented 84.1, 11.6, 2.9 and 1.4% of viruses tested. The antigenic variation among isolates was correlated to single, group specific nucleotide substitutions and mediated by a combination of at least 4 of the 5 epitopes. EpORF7-A was conserved in all American isolates and the Lelystad virus which constituted a separate antigenic group. Consequently, monoclonal antibodies specific for EpORF7-A may prove useful as the antigenic basis for a universal diagnostic test for the PRRS virus. EpORF7-C, D and E were only present in the American isolates tested.

Use of polymerase chain reaction to simultaneously detect and type bovine viral diarrhoea viruses isolated from clinical specimens.

The techniques of indirect immunofluorescence (IF), immuno-peroxidase (IP) staining and the one-step reverse transcriptase polymerase chain reaction (RT-PCR) were compared for detection of 102 isolates of bovine viral diarrhoea virus (BVDV) in infected cell cultures. The BVDV was obtained from bovine clinical specimens, including sera, buffy coats and tissues, submitted from farms located in the States of Iowa and Wisconsin, United States of America. The IF technique detected 88/102 (86.3%) of the viral isolates, whereas IP staining detected an additional 4 isolates (92/102; 90%). The one-step RT-PCR using primers derived from the 5' untranslated region of the BVDV genome detected 102/102 (100%) of the BVDV isolates. A second-round PCR utilising another pair of PCR primers from the 5' untranslated region, allowed rapid genotyping of BVDV. The procedure used showed that the PCR assay based on the 5' untranslated region of the virus genome is the most sensitive indicator for BVDV detection in cell culture, and is also of considerable epidemiological importance since it allowed rapid genotyping of BVDV isolated from clinical specimens. In addition to detection and genotyping of BVDV isolated from clinical specimens, the RT-PCR procedure can be used for routine screening of locally produced and imported biologicals for BVDV contamination. However, the procedure requires further refinement to enable direct application on the clinical specimen.

Impact of dengue virus infection on feeding behavior of Aedes aegypti.

In addition to heavily infecting the salivary glands of Aedes aegypti (L.) mosquitoes, dengue viruses produce a significant infection of the nervous system, involving the brain, Johnston's organ, compound eye, and thoracic and abdominal ganglion. To determine if dengue infection affects feeding behavior of Ae. aegypti we measured feeding times, counted the number of feeding delays or interruptions, and by in situ immunocytochemistry techniques determined the spatial and temporal distribution of dengue infections in females parenterally infected with dengue 3 virus. The mean of the total time required for feeding by infected mosquitoes was significantly longer than the time required by uninfected mosquitoes. Similarly, the mean of the time spent probing was significantly longer in infected mosquitoes than in uninfected mosquitoes when day after inoculation was considered. Significant increases in the length of feeding activity in infected mosquitoes corresponded to virus infection in organs that are known to control or influence activities associated with blood feeding. Sequential infections of the salivary glands (five days postinoculation [PI]), brain and compound eye (eight days PI), and Johnston's organ and midgut and abdominal ganglion (11 days PI) of most mosquitoes were observed. The increased time required by infected Ae. aegypti mosquitoes to acquire a blood meal may contribute to the efficiency of Ae. aegypti as a vector of dengue virus. Longer feeding periods are more likely to be interrupted by the host, which increases the chance that an infected mosquito will probe or feed on additional hosts.

Porcine reproductive and respiratory syndrome virus: routes of excretion.

This study was conducted to delineate potential sites of exit and duration of shedding of porcine reproductive and respiratory syndrome virus (PRRSV). Two experiments of 6 pigs each were conducted. Pigs were farrowed in isolation, weaned at 7 days of age, and housed in individual HEPA filtered isolation chambers. In each experiment, 3 pigs served as controls and 3 were inoculated intranasally with PRRSV (ATCC VR-2402) at 3 weeks of age. In a first experiment, on days 7, 14, 21, 28, 35, and 42 post-inoculation (p.i.), pigs were anesthetized and intubated. The following samples were collected: serum, saliva, conjunctival swabs, urine by cystocentesis, and feces. Upon recovery from anesthesia, the endotracheal tube was removed, rinsed, and the rinse retained. In the second experiment, the sampling schedule was expanded and serum, saliva, and oropharyngeal samples were collected from day 55 to day 124 p.i. at 14 day intervals. Virus was isolated in porcine alveolar macrophages up to day 14 from urine, day 21 from serum, day 35 from endotracheal tube rinse, day 42 from saliva, and day 84 from oropharyngeal samples. No virus was recovered from conjunctival swabs, fecal samples, or negative control samples. This is the first report of isolation of PRRSV from saliva. Virus-contaminated saliva, especially when considered in the context of social dominance behavior among pigs, may plan an important role in PRRSV transmission. These results support previous reports of persistent infection with PRRSV with prolonged recovery of virus from tonsils of swine.

Porcine reproductive and respiratory syndrome virus: a persistent infection.

Persistent infection with porcine reproductive and respiratory syndrome virus (PRRSV) was shown in experimentally infected pigs by isolation of virus from oropharyngeal samples for up to 157 days after challenge. Four 4 week old, conventional, PRRSV antibody-negative pigs were intranasally inoculated with PRRSV (ATCC VR-2402). Serum samples were collected every 2 to 3 days until day 42 post inoculation (PI), then approximately every 14 days until day 213 PI. Fecal samples were collected at the time of serum collection through day 35 PI. Oropharyngeal samples were collected at the time of serum collection from 56 to 213 days PI by scraping the oropharyngeal area with a sterile spoon, especially targeting the palatine tonsil. Turbinate, tonsil, lung, parotid salivary gland, spleen, lymph nodes and serum were collected postmortem on day 220 PI. Virus isolation (VI) on porcine alveolar macrophage cultures was attempted on all serum, fecal and oropharyngeal samples, as well as tissues collected postmortem. Postmortem tonsil tissues and selected fecal samples were also assayed for the presence of PRRSV RNA by the polymerase chain reaction (PCR). Serum antibody titers were determined by IFA, ELISA and SVN. Virus was isolated from all serum samples collected on days 2 to 11 PI and intermittently for up to 23 days in two pigs. No PRRSV was isolated from fecal samples, but 3 of 24 samples were PCR positive, suggesting the presence of inactivated virus. Oropharyngeal samples from each pig were VI positive 1 or more times between 56 and 157 days PI. Oropharyngeal samples from 3 of 4 pigs were VI positive on days 56, 70 and 84 PI. Virus was isolated from one pig on day 157 PI, 134 days after the last isolation of virus from serum from this animal. Virus was isolated from oropharyngeal samples for several weeks after the maximum serum antibody response, as measured by IFA, ELISA and SVN tests. All tissues collected postmortem were VI negative and postmortem tonsil samples were also negative by PCR. An important element in the transmission of PRRSV is the duration of virus shedding. The results of this study provided direct evidence of persistent PRRSV infection and explain field observations of long-term herd infection and transmission via purchase of clinically normal, but PRRSV infected, animals. Effective prevention and control strategies will need to be developed in the context of these results.

Field isolates of porcine reproductive and respiratory syndrome virus (PRRSV) vary in their susceptibility to antibody dependent enhancement (ADE) of infection.

Seventeen porcine reproductive and respiratory syndrome virus (PRRSV) field isolates, including isolate ISU-P, were evaluated for their susceptibility to antibody dependent enhancement (ADE) of infection mediated by antibodies raised against PRRSV isolate ISU-P. Progeny virus yields of ISU-P and 4 of 16 field isolates in porcine alveolar macrophages (PAM) were reduced following treatment with a concentration of antibody that neutralized ISU-P (p < 0.01). In contrast, the yields of 12 of 17 field isolates were enhanced (p < 0.01). Treatment of all isolates with a 10-fold lower concentration of this antibody significantly (p < 0.01) increased virus yields of all isolates in PAM. However, the degree of enhancement varied among the isolates when compared to the enhancement of the yield of ISU-P. While no differences in enhancement were observed among ISU-P and 9 field isolates, yield enhancement of 6 and 1 isolates were less than and more than the yield enhancement of ISU-P, respectively (p < 0.05). The degree of enhancement mediated by a high concentration of antibody raised against ISU-P was inversely proportional to the ability of the antibody to neutralize the isolates (r = 0.92). In contrast, no direct correlation (r = 0.32) was observed between the degree of enhancement mediated by a low concentration of antibody and the ability of the antibody to neutralize the isolates. These data suggest that the variability in the susceptibility of PRRSV isolates to ADE arise from quantitative and/or qualitative differences in the antigenic determinants associated with virus neutralization and/or ADE. The antigenic diversity and the wide range in the susceptibility to ADE that exists among field isolates indicate that ADE should be taken into consideration in the development of effective immunization strategies for PRRS.

Survival of Ixodes scapularis (Acari: Ixodidae) exposed to cold.

The cold hardiness of Ixodes scapularis Say unengorged larvae, engorged larvae, unengorged nymphs, engorged nymphs, and unengorged adults was evaluated. Ticks were exposed to cold for 2 or 8 h at a range of temperatures. Likelihood ratio tests and LT50 estimates were used to evaluate cold hardiness. Likelihood ratio tests indicated that stage and engorgement effects were significant with the exception of the stage effect between engorged larvae and engorged nymphs. LT50 estimates indicated that unengorged nymphs were the most cold-hardy, followed by engorged nymphs, unengorged adults, and both unengorged and engorged larvae. Sex of adult ticks had no statistically significant effect on cold hardiness. Unengorged larvae and unengorged nymphs were tested for evidence of a cold-hardening response. No larvae or nymphs exposed to a cold pretreatment and subsequent cold treatment displayed rapid cold-hardening.

Antibody-dependent enhancement (ADE) of porcine reproductive and respiratory syndrome virus (PRRSV) infection in pigs.

Infection of porcine alveolar macrophages by the porcine reproductive and respiratory syndrome virus (PRRSV) was significantly enhanced in vitro by antibody raised against the PRRSV isolate ISU-P (p < 0.01). Increased yields and infection rates were highly correlated (r = 0.95) and the ratio of yield to infection rate was greater than 1.4, suggesting that more than one mechanism was responsible for enhanced infection. Antibody-dependent enhancement (ADE) of infection was also demonstrated in vivo using a completely randomized block design (n = 16). The mean level and duration of viremia were greater (p < 0.05) in pigs injected with subneutralizing amounts of PRRSV-specific IgG prior to virus challenge than in control pigs injected with normal IgG. In contrast, virus replication was significantly (p < 0.01) inhibited in pigs with neutralizing antibody titers of 4 log2. The period of time that subneutralizing levels of antibody can persist and contribute to ADE of PRRSV infection was estimated in 4 pigs injected with PRRSV-specific IgG to yield an initial neutralizing antibody titer of 3.8 log2. Neutralizing activity declined to undetectable levels by day 37 postinjection (PI). ADE activity was first detected in undiluted sera on day 20 PI and persisted through day 62 PI. Western immunoblot analysis of sera collected between days 37 and 62 PI detected antibodies specific for the 15-kDa nucleocapsid and 26-kDa glycosylated envelope proteins. These results strongly suggest that ADE has the potential to contribute to the pathogenesis of PRRSV infection and is mediated by antibody specific for the 26-kDa envelope protein.

Characterization of the humoral immune response to porcine reproductive and respiratory syndrome (PRRS) virus infection.

The development of the humoral immune response against porcine reproductive and respiratory syndrome (PRRS) virus was monitored by an indirect fluorescent antibody (IFA) test, immunoperoxidase monolayer assay (IPMA), enzyme-linked immunosorbent assay (ELISA), and serum virus neutralization (SVN) test over a 105-day period in 8 pigs experimentally infected with ATCC strain VR-2402. Specific antibodies against PRRS virus were first detected by the IFA test, IPMA, ELISA, and the SVN test 9-11, 5-9, 9-13, and 9-28 days postinoculation (PI), respectively, and reached their maximum values by 4-5, 5-6, 4-6, and 10-11 weeks PI, respectively, thereafter. After reaching maximum value, all assays showed a decline in antibody levels. Assuming a constant rate of antibody decay, it was estimated by regression analysis that the ELISA, IFA, IPMA, and SVN antibody titers would approach the lower limits of detection by approximately days 137, 158, 324, and 356 PI, respectively. In this study, the immunoperoxidase monolayer assay appeared to offer slightly better performance relative to the IFA test, ELISA, and SVN test in terms of earlier detection and slower rate of decline in antibody titers. Western immunoblot analysis revealed that antibody specific for the 15-kD viral protein was present in all pigs by 7 days PI and persisted throughout the 105-day observation period. Initial detection of antibodies to the 19-, 23-, and 26-kD proteins varied among pigs, ranging from 9 to 35 days PI. Thereafter, the antibody responses to these 3 viral proteins of PRRS virus continued to be detected throughout the 105-day study period.(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary survey of pseudorabies virus prevalence in swine herds of Thailand and comparison of the relative efficacy of gI indirect and blocking ELISAS.

A survey of 15 swine herds ranging in size from approximately 200 to 2,000 head in central Thailand was conducted to determine the prevalence of pseudorabies (PR) in the region and to determine the infection rate within herds. All swine in the survey had been routinely vaccinated with gI deletion mutant modified live virus PR vaccines. Sera from individual pigs were tested for PR virus specific antibodies with both the gI blocking ELISA and the gI indirect ELISA. Fourteen (93.3%) of the herds were found to be infected with wild type PR virus. The infection rate within these 14 herds was more than 20% in 10 (71.0%) herds and ranged from 2.1 to 15.6% in the remaining 4 herds. The per cent agreement between the gI indirect and blocking assays was 99.3% for all field sera tested. This high level of agreement between the epitope specific gI blocking ELISA and the multiple epitope specific indirect gI ELISA indicates that both tests can be used with equal efficacy and that it is unlikely that field strains that could go undetected by the gI blocking ELISA exist in central Thailand.