Joe Brownlie

Epidemiological patterns of foot-and-mouth disease worldwide.

Foot-and-Mouth Disease (FMD) is a clinical syndrome in animals due to FMD virus that exists in seven serotypes, whereby recovery from one sero-type does not confer immunity against the other six. So when considering intervention strategies in endemic settings, it is important to take account of the characteristics of the different serotypes in different ecological systems. FMD serotypes are not uniformly distributed in the regions of the world where the disease still occurs. For example, the cumulative incidence of FMD serotypes show that six of the seven serotypes of FMD (O, A, C, SAT-1, SAT-2, SAT-3) have occurred in Africa, while Asia contends with four sero-types (O, A, C, Asia-1), and South America with only three (O, A, C). Periodically there have been incursions of Types SAT-1 and SAT-2 from Africa into the Middle East. This paper describes the global dynamics for the seven sero-types and attempts to define FMD epidemiological clusters in the different regions of the world. These have been described on a continent by continent basis. The review has reaffirmed that the movement of infected animals is the most important factor in the spread of FMD within the endemically infected regions. It also shows that the eco-system based approach for defining the epidemiological patterns of FMD in endemic, which was originally described in South America, can apply readily to other parts of the world. It is proposed that any coordinated regional or global strategy for FMD control should be based on a sound epidemiological assessment of the incidence and distribution of FMD, identifying risk sources as either primary or secondary endemic eco-systems.

Detection of a group 2 coronavirus in dogs with canine infectious respiratory disease.

Abstract An investigation into the causes of canine infectious respiratory disease was carried out in a large rehoming kennel. Tissue samples taken from the respiratory tract of diseased dogs were tested for the presence of coronaviruses using RT–PCR with conserved primers for the polymerase gene. Sequence analysis of four positive samples showed the presence of a coronavirus with high similarity to both bovine and human coronavirus (strain OC43) in their polymerase and spike genes, whereas there was a low similarity to comparable genes in the enteric canine coronavirus. This canine respiratory coronavirus (CRCV) was detected by RT–PCR in 32/119 tracheal and 20/119 lung samples, with the highest prevalence being detected in dogs with mild clinical symptoms. Serological analysis showed that the presence of antibodies against CRCV on the day of entry into the kennel decreased the risk of developing respiratory disease.

Comparison by the neutralisation assay of pairs of non-cytopathogenic and cytopathogenic strains of bovine virus diarrhoea virus isolated from cases of mucosal disease.

Neutralising antibody to non-cytopathogenic and cytopathogenic strains of bovine virus diarrhoea virus (BVDV) was assayed in a microtitre test in which cultures of calf testis cells were stained by the immunoperoxidase method to detect viral replication. Fourteen BVDV strains were compared in cross neutralisation tests with antisera prepared in gnotobiotic calves. Ten of the strains comprised five pairs of non-cytopathogenic and cytopathogenic BVDV. Each pair was isolated from an animal with mucosal disease. All five animals were from five separate outbreaks of the disease. Each pair of strains from the same outbreak was found to be antigenically indistinguishable. In contrast, when the coefficient of antigenic similarity was calculated 11 of 45 comparisons between the pairs and 46 of 91 comparisons between all 14 viruses gave R values that distinguished strains. The observations suggest that an antigenic spectrum within a single related group exists for BVDV strains, rather than distinct serotypes. The findings are also consistent with the suggestion that cytopathogenic strains from natural outbreaks of mucosal disease arise by mutation from non-cytopathogenic virus.

Variation in the intracellular polypeptide profiles from different isolates of bovine virus diarrhoea virus

SummaryVariation of the intracellular polypeptides induced in calf testis cells by 5 cloned isolates of bovine virus diarrhoea virus (BVDV) was examined. Three of the isolates were cytopathic (NADL, C 2415 and Pe 515 c) and two were non-cytopathic (C 1226 and Pe 515 nc) in these cells. The isolates Pe 515 c and Pe 515 nc were both isolated from an animal with clinical signs of mucosal disease. In cells infected with NADL, 8 virus specific proteins (vp 1 to vp 8) with molecular weights ranging from 120,000 (vp 1) to 23,000 (vp 8) were detected. Isolates C 2415 and Pe 515 c gave a similar array of polypeptides to NADL, but the 3 cytopathic isolates could be distinguished by the variation in the molecular weights of some of the proteins. The non-cytopathic isolates could also be distinguished from each other by this type of molecular variation; however, one feature that characterised these strains, when compared to the cytopathic isolates, was the absence of vp 2. Comparison of the polypeptides induced by Pe 515 c and Pe 515 nc showed that apart from the lack of vp 2 in the Pe 515 nc virus profile, the molecular weights of the other viral proteins were similar. This supports serological evidence that for mucosal disease to occur the pair of cytopathic and non-cytopathic viruses must be closely related. Four of the polypeptides induced by Pe 515 c were shown to be glycoproteins.

Protection against respiratory infection with bovine virus diarrhoea virus by passively acquired antibody.

Susceptibility to infection with bovine virus diarrhoea virus (BVDV) was compared for calves with varying amounts of specific antibody in their sera passively acquired from the ingestion of colostrum. Challenge consisted of intranasal exposure to a strain of BVDV isolated from an outbreak of respiratory disease. Resistance to infection, as judged by nasopharyngeal shedding of virus, was directly related to the titre of neutralizing antibodies in sera. Besides protecting against infection of the upper respiratory tract, passive antibody, which was mainly IgG1, also protected against viraemia and, to a lesser extent, leukopenia. In the presence of colostral antibody, neutralizing and IgG1 antibody responses were apparently inhibited, but a specific IgG2 response occurred.

Longitudinal Study of Viruses Associated with Canine Infectious Respiratory Disease

ABSTRACT In this investigation a population of dogs at a rehoming center was monitored over a period of 2 years. Despite regular vaccination of incoming dogs against distemper, canine adenovirus type 2 (CAV-2), and canine parainfluenza virus (CPIV), respiratory disease was endemic. Tissue samples from the respiratory tract as well as paired serum samples were collected for analysis. The development of PCR assays for the detection of CPIV, canine adenovirus types 1 and 2, and canine herpesvirus (CHV) is described. Surprisingly, canine adenovirus was not detected in samples from this population, whereas 19.4% of tracheal and 10.4% of lung samples were positive for CPIV and 12.8% of tracheal and 9.6% of lung samples were positive for CHV. As reported previously, a novel canine respiratory coronavirus (CRCoV) was detected in this population (K. Erles, C. Toomey, H. W. Brooks, and J. Brownlie, Virology 310:216-223, 2003). Infections with CRCoV occurred mostly during the first week of a dogs stay at the kennel, whereas CPIV and CHV were detected at later time points. Furthermore, the evaluation of an enzyme-linked immunosorbent assay for detection of antibodies to CPIV and an immunofluorescence assay for detection of antibodies to CHV is described. This study shows that CPIV is present at kennels despite vaccination. In addition, other agents such as CHV and CRCoV may play a role in the pathogenesis of canine respiratory disease, whereas CAV-2 and canine distemper virus were not present in this population, indicating that their prevalence in the United Kingdom is low due to widespread vaccination of dogs.

The association of Streptococcus equi subsp. zooepidemicus with canine infectious respiratory disease.

Abstract Canine infectious respiratory disease (CIRD) is a multi-factorial infection that affects many kennelled dogs despite the wide use of vaccination. Current vaccines aim to protect against viral agents and a single bacterial agent, Bordetella bronchiseptica. We sought to examine the role of streptococcal species in CIRD. The isolation and identification of streptococci in the lower respiratory tract of clinically healthy dogs and those with CIRD were used to correlate the presence of specific streptococcal species with respiratory disease. In this study we report that the presence of S. equi subsp. zooepidemicus is associated with increasing severity of disease in a population of kennelled dogs with endemic CIRD.

Immunity to bovine virus diarrhoea virus in calves: the role of different T-cell subpopulations analysed by specific depletion in vivo with monoclonal antibodies

Gnotobiotic calves were injected intravenously with murine monoclonal antibodies (mAb) directed against the BoCD4, BoCD8 or BoWC1 antigens that define the three major T-lymphocyte subpopulations in cattle. This produced a transient, specific depletion of each cell type in the circulation. Calves were then infected intranasally with a non-cytopathogenic biotype of bovine virus diarrhoea virus and the effect of the specific depletion with the mAb on viraemia and shedding of virus from the nasopharynx determined. Depletion of the cells expressing the BoCD4 antigen resulted in an extension of the duration of viraemia and an increase in the titre of virus in blood. No effect on nasopharyngeal shedding was noted. Depletion of either of the other two T-cell subsets that expressed the BoCD8 antigen or the BoWC1 antigen present on the gamma/delta T-cells had no demonstrable effect. These findings are interpreted as showing that the BoCD4+ cells play a pivotal role in controlling a primary infection with this virus but MHC class I restricted BoCD8+ T-cells are not a major effector mechanism. The BoCD4+ cells may be acting directly or be mediators of T-cell help.

An enzyme-linked immunosorbent assay (Elisa) for the detection of antibodies to bovine viral diarrhoea virus (BVDV) in cattle sera

A microtitre ELISA has been established for the quantitation of antibodies to bovine viral diarrhoea virus (BVDV). Single dilutions of sera were assayed and units of antibody were calculated from a standard curve. In order to detect the maximum number of responding animals both IgG1 and IgG2 antibody should be assayed, although detection of IgG1 alone was nearly as effective. The ELISA was as sensitive as the virus neutralization test for detection of antibody; comparison of an ELISA that detected IgG1 plus IgG2 antibody to BVDV with the virus neutralization test gave a correlation coefficient (r) of 0.89 (P less than 0.001 for 95 compared sera). Although similar amounts of IgG1 and IgG2 antibodies were present in sera from both experimentally- and naturally-infected cattle, antibody to BVDV in colostrum and in the sera from young calves was predominantly IgG1. The number of adult cows with antibody was 40 out of 41 while 36 of 44 calves reared in a beef unit were found to have produced antibody by the time they were 31.5 weeks old, an indication of the high prevalence of BVDV in the cattle population.

DNA vaccination against bovine viral diarrhoea virus induces humoral and cellular responses in cattle with evidence for protection against viral challenge.

The immune response induced by a DNA construct expressing the E2 envelope glycoprotein of bovine viral diarrhoea virus (BVDV) was studied in cattle. Four groups of five calves, were immunised by intradermal injection with a total of 1mg of plasmid DNA on each of two occasions, with a 3-week dose interval. Group 1 received non-coding plasmid DNA only (control), group 2 received the E2 coding plasmid (0.5mg) plus non-coding plasmid DNA (0.5mg) and groups 3 and 4 received the E2 coding plasmid plus plasmid encoding either bovine interleukin 2 (IL-2) or granulocyte macrophage colony stimulating factor (GM-CSF) respectively. Two weeks after the final immunisation, all calves were challenged by intranasal inoculation with 5 x 10(6) TCID(50) of homologous virus. On the day of challenge, neutralising antibodies were detectable in 13 of 15 vaccinated calves (one animal in each of groups 3 and 4 remained seronegative at this point). Thereafter, a strong anamnestic serological response was evident in all vaccinated animals. Furthermore, T-cell proliferation following in vitro re-stimulation with BVDV antigen was significantly elevated in the cytokine adjuvanted groups. This enhancement of BVDV specific immune responses in vaccinated animals was reflected in the clinical responses observed post-challenge. In particular, reduced febrile responses provided evidence of a disease sparing effect of vaccination. Significantly, whilst a transient viraemia was detected in all control animals following challenge, no virus was isolated from the leucocytes from 8 out of the 15 vaccinated animals. In groups 2 and 4, three animals remained virus free, although virus was isolated from two animals in each group at a single time point, while in group 3, three out of five animals had detectable viraemia. In summary, the administration of a DNA vaccine encoding only the E2 glycoprotein of BVDV induced a disease sparing effect in vaccinated calves following challenge and protected more than half of the vaccinated animals from detectable viraemia.