[An epizootiologic study of an outbreak of equine influenza in the Czech Republic in the fall of 1995]. / Epizootologická studie vzplanutí chripky koní v Ceské republice na podzim roku 1995.

A mild outbreak of acute respiratory infection was reported in racing horses in the fall of 1995. Four studs were investigated for the sources and routes of infection. In five horses from two herds, virus isolates were obtained which, in preliminary typing experiments, were identified as the influenza A/equi 2 virus. The presence of this illness in all the examined herds was confirmed by a rise in specific antibody titres. The affected animals included both older vaccinated horses and young horses not yet vaccinated. Epidemiological studies suggested that the spread of infection occurred in situations where infected and non-infected horses were together, most frequently at races. Newly infected horses brought the infection back to their studs where further animals became infected. Some of them, still being in the incubation period without any clinical signs, may have taken part in another race and passed the infection onto healthy animals from other studs. Since the races usually took place in 7-day intervals, the epidemiological chain remained continuous. The causes of the outbreak of infection in vaccinated horses are analysed. The length of post-vaccination immunity, the antigenic composition of vaccines and their completion with new strains of the influenza virus are discussed.

Development of a disease control programme based on the use of an inactivated vaccine against infectious bovine rhinotracheitis.

Studies to investigate the efficacy of an inactivated vaccine against infectious bovine rhinotracheitis (IBR) suggest that this vaccine can prevent the in utero infection of calves from experimentally infected dams. In an experimental herd the inactivated vaccine induced a humoral immune response in both seropositive and seronegative cattle and, after subsequent intratracheal infection with IBR (BHV-1) virus, prevented development of symptoms in the cows and protected their fetuses against infection. The calves were all healthy and were born at term. The non-vaccinated, seronegative cows responded to the experimental infection with mild respiratory disease and abortion of 4 out of 10 fetuses. All organs from the aborted fetuses were found to have IBR virus. Through the use of this vaccine, the nucleus of a seronegative, virus-free breeding herd can be established. Thus, valuable genetic material can be preserved and the eradication of IBR becomes a realistic prospect. From our initially strictly controlled experiments producing 234 healthy calves, our programme was expanded into farm practice where 1001 calves were reared free from IBR virus.

[Detection of herpesvirus serum antibodies in red deer (Cervus elaphus) imported into the Czech Republic]. / Prukaz protilátek proti herpesvirum v sérech jelena evropského (Cervus elaphus) importovaného do Ceské republiky.

Antibodies reacting in the virus-neutralisation test with bovine herpesvirus (BHV-1), the causative agent of infectious bovine rhinotracheitis (IBR), were demonstrated in a herd of red deer (Cervus elaphus) imported into the Czech Republic. Sera from the same collection were later tested against a homologous virus, termed herpesvirus cervidae 1 (HVC-1), isolated from red deer in Scotland. Out of 165 imported animals, antibodies to BHV-1 were found in 68% and to HVC-1 in 71% of the animals. Titres of antibodies to the two viruses ranged from 1 : 2 to 1 : 4 or were occasionally greater. As documented by several experimental studies carried out abroad, the HVC-1 virus, though antigenically closely related to BHV-1 virus, is not pathogenic to cattle under natural conditions. Antibodies which reacted with both BHV-1 and HVC-1 were also demonstrated in 3 out of 7 roebucks randomly shot in this territory.

The efficacy of an inactivated IBR vaccine in the prevention of intra-uterine infection and its use in a disease-control programme.

The effects of administration of an established, inactivated IBR vaccine were studied in 30 cows from two herds (one seropositive and one seronegative). All acquired immunity which, after subsequent intratracheal infection with IBR virus, prevented development of symptoms in the cows and protected their foetuses against viral infection in utero. The calves were all healthy and were born at normal term. Ten non-vaccinated cows from the seronegative herd responded to the experimental infection with mild respiratory disease and abortion of four out of 10 foetuses. Organs from the aborted foetuses were found to have IBR virus. In a breeding herd, without clinical signs of disease but with 40% of cows tested as seropositive, a 2-year disease-control programme was initiated. A total of 234 newborn calves were examined and it was shown that immunization of their dams with an inactivated vaccine conferred full in utero protection against IBR-virus infection. When such calves are reared in isolation they can be used as the nucleus for a seronegative breeding herd.

Comparative between-laboratory trials of the liquid-phase blocking sandwich ELISA for the detection of antibodies to foot-and-mouth disease virus.

Fifty bovine serum samples were tested for the presence or amounts of antibodies to foot-and-mouth disease (FMD) virus serotypes A, O and C by the liquid-phase blocking sandwich ELISA (lpb-ELISA) using reagents prepared by the World Reference Laboratory for Foot-and-Mouth Disease (WRL) in Pirbright, U.K. Twenty of the sera had been collected before extensive vaccination with a commercial inactivated trivalent FMD vaccine was ceased and the remaining thirty originated from animals which had not been vaccinated for more than one year. After the test had been completed, the samples were sent to another two laboratories to be examined by the same assay. Results obtained in the laboratories were compared to assess the degree of agreement in serological tests for FMD in cattle. Antibodies to at least one of the three FMD virus (FMDV) serotypes were demonstrated in 70% of the serum samples. Antibodies to the antigens A5, O1 and C1 were present in 58%, 66% and 58% of the sera, respectively. The overall between-laboratory agreement of the results of the lpb-ELISA for the detection of antibodies against all three serotypes was 96%. Discrepancies in terms of type specificity did not exceed 10%. Most discrepancies were recorded in sera with low antibody titres or optical densities (OD) around the cut-off point. An increase of concentration of C1 antigen in reaction mixture reduced the sensitivity of ELISA and results of screening tests became negative in sera with antibody titres of 1: 90 and lower.(ABSTRACT TRUNCATED AT 250 WORDS)

[The effect of short-term isolation of vaccinated chicks on the incidence of Marek's disease]. / Vliv krátkodobé izolace vakcinovaných kurat na výskyt Markovy choroby.

In chickens immunized by normal and tenfold doses of MARVAK vaccine (100 and 1,000 PFU) we investigated protective effects against the natural contact infection of chickens that were exposed to the infection immediately after vaccination, or at the intervals of 48 and 72 hours, and 7 and 14 days. Studying the elimination of Marek's disease virus by feather follicles, the health condition of chickens, tumor frequency and mortality rate we demonstrated that neither of these doses could protect the chickens from the disease if they were exposed to contact infection just after vaccination. An expressive protective effect was observed in chickens isolated for 7-14 days and there was not recorded any difference in the protection against the disease after the doses of 100 and 1,000 PFU. The main and feasible measure against MD is to prevent an early infection of newborn chickens by improving the zoohygienic conditions.

[Isolation and identification of the infectious pancreatic necrosis virus in trout]. / Izolace a identifikace viru infekcní nekrózy pankreatu pstruhu.

The first isolation and identification of the infectious pancreatic necrosis virus in trout in Czechoslovakia is described. The RTG-2, PG and CHSE cell lines were used for isolation and the identification was made by the methods of electron microscopy, cross virus-neutralizing test, and immunofluorescence. As demonstrated, all the isolates in the Czechoslovak territory are serologically identical and are closely related (or perhaps congruent) with the Sp reference strain which has the highest frequency in Europe. The described methodical procedure is also applicable to the diagnostics of other virus diseases of fish.

Experimental infection of sheep with Bhanja virus.

Seven juvenile sheep were infected subcutaneously (s.c.) or intracerebrally (i.c.) with Bhanja virus. Distinct symptoms of CNS affection (ataxia, pareses) were observed only in the case of i.c. application of a massive dose (10(-7) to 10(9) SMicLD50) of the Bg 336/336 strain. A short-term and low viremia (one to four days p.i.) was ascertained after i.c. infection with a dose of 10(4.7) to 10(9.2) SMicLD50 of the same strain. On the other hand, the high titres of neutralization antibodies were detected even after inoculation of small doses of the virus (e.g. 50 SMicLD50). Unlike the symptomatic response, the immune response of sheep to Bhanja virus is high.