[show abstract][hide abstract] ABSTRACT: Porcine circovirus-2 (PCV-2) is considered the major etiological agent of post-weaning multisystemic wasting syndrome (PMWS) in pigs. The clinical manifestations of the disease are correlated with moderate to high amounts of PCV-2 DNA in biological samples of affected pigs. A threshold of 107 DNA copies/ml is suggested as the trigger factor for symptoms. A comparative study was conducted to determine which quantitative method would be more suitable to estimate the PCV-2 DNA load. Two polymerase chain reaction (PCR) assays were developed: a competitive PCR (cPCR) and a SYBR Green–based real-time PCR. The assays were compared for their capacity to detect PCV-2 in DNA samples extracted from liver, lung, spleen, mesenteric lymph nodes, and kidney of PMWS-affected (n = 23) or non–PMWS-affected pigs (n = 9). Both assays could successfully quantify PCV-2 DNA in all tissue samples and were able to detect significant differences between the numbers of PCV-2 DNA copies found in tissues of PMWS-affected and non–PMWS-affected pigs (≥102.5). The highest mean viral loads were detected by the SYBR Green real-time PCR, up to 107.0±1.5 copies/100 ng of total DNA sample, while the cPCR detected up to 104.8±1.5. A mean difference of 101.8 was found between the amounts of PCV-2 DNA detected, using the SYBR Green real-time PCR and the cPCR, suggesting that the viral load threshold for PMWS should be determined for each particular assay.
Journal of veterinary diagnostic investigation. 01/2011; 23:1160-1167.
[show abstract][hide abstract] ABSTRACT: The serum neutralization (SN) test is often taken as “gold standard” to measure neutralizing antibodies to bovine herpesviruses. However, in view of the further subdivisions of bovine herpesviruses in types/subtypes, defining which virus to use at challeng in SN testing may be difficult. In view of that, this study was carried out to re-evaluate (SN) sensitivity with different types/subtypes of bovine herpesviruses types 1 (BoHV-1) and 5 (BoHV-5) as challenge viruses. Bovine sera (n=810) were collected from two distinct geographic regions and tested by SN with three type 1 viruses (BoHV-1.1 strains “Los Angeles” and “EVI123/98”; BoHV-1.2a strain “SV265/96”) and three type 5 viruses (BoHV-5a strain “EVI88/95”; BoHV-5b strain “A663” and BoHV-5c “ISO97/95”). SN was performed with a 1 hour incubation of the serum-virus mixtures at 37oC against 100 TCID50 of each of the viruses. SN sensitivity varied greatly depending on the challenge virus used in the test. The highest sensitivity (327 positive/810 total sera tested; 40.37%) was attained when the positive results to the six viruses were added together. No association could be found between any a particular type or subtype of virus and the sensitivity of the test. When positive results to each single strain were considered, SN sensitivity varied from 41.7% to 81.7%, depending on the virus and the geographic region of origin of the sera. Variation was detected even when challenge viruses belonged to the same subtype, where disagreement between positive results reached 41 %. These results indicate that SN tests against single viruses, as performed here, may display a remarkably low sensitivity; performing SN tests against a number of different viruses may increase considerably SN sensitivity. Furthermore, the choice of virus used for challenge is critical in SN tests. In addition, sera from different geographic regions may give rise to disagreeing results with different strains of BoHV-1 and BoHV-5. This might be particularly relevant for control programs and in international trade, were maximum sensitivity should be targeted.
[show abstract][hide abstract] ABSTRACT: This study was carried out to estimate the prevalence of antibodies to bovine herpesviruses types 1(BoHV-1) and 5 (BoHV-5) in the state of Rio Grande do Sul (RS),
Brazil, by testing serum samples against different BoHV-1 and BoHV-5 strains. The sera examined were obtained from a larger sample designed to estimate the prevalence of bovine brucellosis within the state. All sera were collected from cows 24 months or older, not vaccinated to bovine herpesviruses, from both dairy and beef herds. The number of samples to be tested was calculated based on an estimated prevalence of infection of 33%, with an average standard deviation of ≤1% and a 95% limit of agreement. Sera from 2.200 cattle from 390 farms distributed in 158 counties were tested by serum neutralization (SN) tests in search for antibodies to the following strains: BoHV-1.1 (strains EVI123/98 and Los Angeles), BoHV-5a (strain EVI88/95) and BoHV-5b (strain A663). The overall seroprevalence to BoHV-1 and BoHV-5 in the sampled herds was 29.2% (642/2.200); seropositive animals were detected in 225 (57.7%) of the sampled farms. Prevalence estimates varied according to the virus used for challenge in SN tests. The highest prevalence and sensitivity were attained when positive SN results against the four different strains were added together. The use of only one virus for challenge in SN tests would lead to a loss in sensitivity from 20.4% to 34.6% when compared to the combined SN-positive results. These findings provide evidence that antibodies to BoHV-1 and BoHV-5 are largely spread in dairy and beef herds in RS, although prevalence in distinct geographic regions is quite variable. The results were strongly affected by the virus strains used for challenge in SN testing. This must be taken into account when performing serologic tests to detect BoHV-1 and BoHV-5 antibodies. As SN test is not capable of discriminating between antibody responses to BoHV-1 and BoHV-5, typespecific prevalence remains unknown.
[show abstract][hide abstract] ABSTRACT: The results of 23 years of rabies diagnosis carried out at the Veterinary Research
Institute Desidério Finamor, in the state of Rio Grande do Sul, RS, Brazil, are reported.
From 1985 to 2007, a total of 23.460 specimens were examined, corresponding to 95% of the total number of samples submitted to rabies laboratory diagnosis notified within the state. Diagnostic methods included standard techniques such as the fluorescent antibody test (FAT) and mouse inoculation test (MIT). No cases of human rabies occurred in the period. Rabies virus (RV) was detected in 739 specimens (3.1%), from which 656 (88.7%) were from cattle. The virus was also identified in specimens from 23 dogs (3.1%), 21 horses (2.9%), 29 bats (4.0%), 4 cats (0.5%), 3 sheep (0.4%), 2 pigs (0.27%) and a wild animal of undetermined species (0.13%). The last case of rabies associated with a canine variant was diagnosed in 1988. Two cases of rabies associated with bat variant viruses were reported, in a domestic cat (2001) and in a dog (2007). In cattle, a marked tendency to a decrease in the number of cases was detected in the examined period. In contrast, an increase in the number of cases in haematophagous as well as in non haematophagous bats is noticed. However, as the number of bat specimens submitted for diagnosis has increased, this finding most likely reflects a higher degree of awareness on the possible role for bats in the rabies transmission cycle, rather than any particular changes on the virus or its hosts.