Detection of foot-and-mouth disease virus infection in vaccinated cattle

The aim of this study was to evaluate the value of commercially available kits for the detection of foot-and-mouth disease (FMD) virus infection in vaccinated cattle. The cattle were vaccinated with a commercial aqueous FMD vaccine type A24 and subsequently challenged 28 days post vaccination with homologous FMD virus. Seven of eight animals were protected from clinical disease and all became carriers. They were bled sequentially for up to 130 days post infection and samples of sera were tested with three ELISA kits: CHEKIT FMD-3ABC, Ceditest FMDV-NS and SVANOIR FMDV 3ABC-Ab ELISA. The Ceditest kit appears to be relatively higher sensitive than the others. When examined with this ELISA, all cattle developed of FMDV nonstructural proteins (NSPs) antibodies and remained positive throughout the period of the experiment. The response of antibodies against 3ABC antigen delayed in two cattle challenged with FMDV A24 virus. One of the cattle reacted negatively in Svanoir ELISA kit and sera from two animals were found negative in CHEKIT ELISA. It can be concluded that all tested kits can be a promising tool for FMD control and eradication campaigns in situation where emergency vaccination was applied.     

Detection of carriers of foot-and-mouth disease virus among vaccinated cattle

To investigate and optimise detection of carriers, we vaccinated 15 calves with an inactivated vaccine based on foot-and-mouth disease virus (FMDV) A Turkey strain and challenged them and two further non-vaccinated calves with the homologous virus four weeks later. To determine transmission to a sensitive animal, we put a sentinel calf among the infected cattle from 60 days post-infection until the end of the experiment at 609 days post-infection. Samples were tested for the presence of FMDV, viral genome, specific IgA antibodies, antibodies against FMDV non-structural (NS) proteins or neutralising antibodies. Virus and viral genome was intermittently isolated from probang samples and the number of isolations decreased over time. During the first 100 days significantly more samples were positive by RT-PCR than by virus isolation (VI), whereas, late after infection more samples were positive by virus isolation. All the inoculated cattle developed high titres of neutralising antibodies that remained high during the entire experiment. An IgA antibody response was intermittently detected in the oropharyngeal fluid of 14 of the 17 calves, while all of them developed detectable levels of antibodies to NS proteins of FMDV in serum, which declined slowly beyond 34 days post-infection. Nevertheless, at 609 days after inoculation, 10 cattle (60%) were still positive by NS ELISA. Of the 17 cattle in our experiment, 16 became carriers. Despite frequent reallocation between a different pair of infected cattle no transmission to the sentinel calf occurred. It remained negative in all assays during the entire experiment. The results of this experiment show that the NS ELISA is currently the most sensitive method to detect carriers in a vaccinated cattle population.     

Transmission of foot-and-mouth disease by vaccinated cattle following natural challenge

Cattle vaccinated with a conventional monovalent type O1 foot-and-mouth disease (FMD) vaccine were challenged between four and 21 days after vaccination by short-term exposure to homologous airborne virus produced by pigs. Transmission was then assessed by housing susceptible cattle with the vaccinated animals and testing and observing all the animals for signs of infection and clinical disease. All 18 cattle vaccinated three weeks before challenge resisted clinical disease and although four contracted subclinical infection, there was no transmission to susceptible cattle in contact. One of the two groups of cattle vaccinated two weeks previously transmitted subclinical infection, but not disease, to susceptible animals housed with them from day 0 after challenge. Subclinical infection was manifested by a transient viraemia which was not followed by a detectable circulating antibody response. Shorter periods (seven or four days) from vaccination to challenge resulted in transmission of disease from clinically normal vaccinated to in-contact animals in one of two experiments. The severe challenge presented by the diseased in-contact animals than overwhelmed the immunity of the vaccinated animals. The results indicate that during emergency vaccination programmes it is advisable to vaccinate all FMD-susceptible animals within the vaccination zone and that at the outer boundary of the zone vaccinated animals should be kept separated from unvaccinated animals for at least three weeks.     

Testing the protective effectiveness of avirulent vaccines against trichophytosis in cattle

The protective action of live avirulent vaccine against bovine trichophytosis, produced by the Bioveta National Corporation at Ivanovice na Hané, was very good and fully comparable with the earlier vaccine produced from the virulent live culture of Trichophyton verrucosum. Experimental challenge with a massive dose of a virulent strain of T. verrucosum produced only minor surface dermal changes in the calves vaccinated with these vaccines, but these changes spontaneously disappeared in a short time. In the control non-vaccinated calves, large and deep lesions were induced by the challenge, spreading to the neighbouring tissues. Compared with both live biopreparations, the protective effect of inactivated vaccine prepared by the irradiation of virulent vaccine with Co60 was much lower.     

Stimulation by heterotypic antigens of foot-and-mouth disease virus antibodies in vaccinated cattle

Immunisation of cattle with foot-and-mouth disease virus failed to raise a level of antibody that provides protection against heterotypic challenge. Further the 12S substructure, produced from the 146S particle, was ineffective in providing protection against challenge by homotypic virus. These findings suggest considerable antigenic differences in the virus serotypes and between the virus and its substructure. Inoculation of homologous 12S and heterologous 1246S and 12S antigens into vaccinated cattle, however, revealed antigenic relationship between different serotypes, and between serotypes and their substructures.     

Investigation of an outbreak of foot-and-mouth disease in vaccinated dairy cattle in Thailand

SUMMARY An outbreak of foot-and-mouth disease that spread between two related vaccinated dairy herds was investigated. Although the cattle were of similar vaccination status, in one herd there was high morbidity, whereas in the other there was considerably lower morbidity. The relationship between the vaccine virus and the outbreak virus was expressed as an r value determined by the two-dimensional neutralisation test. Bovine serum homologous to the vaccine virus indicated a close antigenic relationship between the vaccine virus and the outbreak virus (r = 0.61). The source of the outbreak virus was not determined. The investigation suggested a requirement for close contact between stock for foot-and-mouth disease to spread in a tropical environment, in contrast to the capacity of the disease to spread considerable distances by aerosol transmission in temperate climates.     

Protection of cattle and swine against foot-and-mouth disease, using biosynthetic peptide vaccines

A single dose of foot-and-mouth disease (FMD) virus protein 1 (VP1) peptide, expressed in Escherichia coli as a fusion protein with 190 amino acids (AA) of the LE' protein of the tryptophan operon of E coli, elicited an immune response in steers sufficient to withstand the challenge of exposure to animals with acute FMD. The 58-micrograms dose of viral peptide, composed of a segment of the VP1 from the A12 strain (A12) of FMD virus (FMDV; A12-32dimer) in a tandem repeat configuration of AA137 through 168 and emulsified with oil adjuvant, elicited a serologic response in cattle equivalent to that obtained using conventional whole virus vaccines. Two groups of swine were vaccinated, 1 with the A12-32dimer as used in cattle and 1 with AA131 through 157 from VP1 of the A24 strain (A24) of FMDV (A24-peptide), expressed in the same system as A12-32dimer, but as a single copy per molecule. In swine, the 58-micrograms dose of the A12-32dimer repeated at 28 days was an effective immunogen; all swine were protected against A12 and, in addition, the vaccine protected 50% of the swine against A24. The 29-micrograms dose of A24-peptide, administered according to the same schedule, elicited protection against A24 in 50% of the vaccinates and, in addition, protected 25% of those vaccinates against A12. The serologic response elicited by A12-32dimer against A24 virus was considerably greater than the response elicited by A24-peptide against A12 virus. The evidence of multiple immunogenic epitopes between AA131 and AA168 was evaluated.     

Presence of antibodies to non-structural proteins of foot-and-mouth disease virus in repeatedly vaccinated cattle

For the purpose of removing infected animals by detecting humoral immune responses to non-structural proteins of the foot-and-mouth disease (FMD) virus, antibodies induced by contaminated residual non-structural proteins contained in less pure FMD vaccine can be problematic for serological screening. The aim of the present study was to measure the possible presence of antibodies against these non-structural proteins in repeatedly vaccinated calves and beef cattle. Five imported FMD vaccines were examined using two commercial ELISA kits, UBI FMDV NS EIA and Ceditest FMDV-NS, for serological testing. After five doses of vaccination, the serum of one calf tested positive, and two vaccines induced a significant increase in anti-3ABC antibodies in calves. This finding demonstrated that a positive reaction to non-structural proteins due to impurities in the FMD vaccine was detectable using commercial tests. A low percentage of field sera sampled from beef cattle in Kinmen also tested positive, but the key factor resulting in the positive reactions could not be positively identified based on our data.     

The airborne dispersal of foot-and-mouth disease virus from vaccinated and recovered pigs, cattle and sheep after exposure to infection.

Foot-and-mouth disease virus was detected during two periods in the air of looseboxes which housed susceptible, vaccinated or recovered pigs, cattle or sheep exposed to infection. The first was 30 min to 22 h after exposure and occurred in all animals. The second was two to seven days after exposure and occurred with those susceptible and vaccinated animals which developed clinical lesions, and with vaccinated and recovered pigs and sheep, which did not develop clinical lesions. Vaccination of animals before exposure resulted in less or no virus being detected. The virus during the first period was attributed to virus trapped on the animal during exposure, and the virus during the second period to limited multiplication in the respiratory tract. Control of movement for two weeks after contact with infection is suggested as a means of preventing spread of foot-and-mouth disease in areas that contain vaccinated animals.     

A Bayesian evaluation of six diagnostic tests for foot-and-mouth disease for vaccinated and non-vaccinated cattle

The sensitivity and specificity of six ELISA tests for foot-and-mouth disease (FMD) to discriminate between sero-converted (for non-structural FMD virus proteins) and non-sero-converted cattle were evaluated for vaccinated and unvaccinated cattle. Since none of the tests could be considered as a proper reference test and for about half of the tested sera the true status (sero-converted or not for non-structural proteins, i.e. presence of antibodies) of the animals was unknown, a Bayesian analysis employing a latent class model was used that did not rely on the use of a reference test or gold standard. Prior information about prevalence for subsets of the data and specificity of the tests was incorporated into the analysis. The specificity of the six tests for vaccinated and non-vaccinated cattle ranged from 96 to 99%. For vaccinated cattle, one test stood out with an estimated sensitivity of 94% (95% CI from 89.8 to 98.1%). Second best for vaccinated cattle were two tests with estimated sensitivities of 85% (95% CI from 78.9 to 89.7%) and 92% (95% CI from 86.2 to 95.6%). For non-vaccinated cattle, the sensitivities of these three tests were around 97%. The remaining three tests showed lower estimated sensitivity for vaccinated cattle, ranging from 57 to 79%.     

The effectiveness of foot-and-mouth disease vaccines in Switzerland. II. Stability problems

One of the vaccines that were used in 1988 to immunize the Swiss national cattle population against foot-and mouth disease (FMD) was apparently not stable. Data, provided by the manufacturer, indicated a high initial antigenic content for serotype O. Protection experiments at the end of the vaccination campaign, however, indicated a substantial loss of serotype O antigen in the vaccine. Serological data, obtained during the campaign indicated that only 12% of the primovaccinated animals and 63% of previously vaccinated animals received an amount of FMD viral antigen sufficient to induce protective immunity. The primovaccinated animals were revaccinated in fall 1988 with a new batch provided by the same manufacturer. The new vaccine induced high titers of neutralizing antibodies in primo- and an anamnestic response in revaccinated cattle.