The role of goats as reservoir hosts for bovine herpes virus 1 under field conditions

Bovine herpesvirus 1 (BoHV1) is the cause of economically significant viral infections in cattle. Respiratory symptoms associated with the infection are known as Infectious Bovine Rhinotracheitis (IBR). Sheep and goats are less sensitive to the infection although their role in inter-species viral transmission under field conditions is subject to controversy. The objective of this study was to investigate seroprevalence of BoHV1 infections in cattle, sheep, and goats raised together for at least a year. Blood serum samples were taken from 226 cattle, 1.053 sheep, and 277 goats from 17 small- to medium-scale farms. BoHV1-specific antibody presence and titers were determined using virus neutralization test. In total, 73 of the 226 cattle (32.3%) were seropositive. The infection was detected in 13 of the 17 farms. Infection rates ranged from 5.8 to 88.8%. Only one of the 1053 sheep (0.09%) was seropositive. However, 58 of the 277 (20.9%) goats were seropositive. Goat samples taken from 8 of the 17 farms were seropositive with infection rates ranging from 17 to 38.9%. Statistical analysis showed a significant correlation in infection rates between cattle and goats but not sheep. These results suggest that goats may be more sensitive to the BHV1 infection than sheep and the role of goats as possible reservoirs for BoHV1 in the control and eradication of BHV1 in cattle should be considered in future studies.

Pathogens at the livestock-wildlife interface in Western Alberta: does transmission route matter?

In southwestern Alberta, interactions between beef cattle and free-ranging elk (Cervus elaphus) may provide opportunities for pathogen transmission. To assess the importance of the transmission route on the potential for interspecies transmission, we conducted a cross-sectional study on four endemic livestock pathogens with three different transmission routes: Bovine Viral Diarrhea Virus and Bovine Herpesvirus 1 (predominantly direct transmission), Mycobacterium avium subsp. paratuberculosis (MAP) (indirect fecal-oral transmission), Neospora caninum (indirect transmission with definitive host). We assessed the occurrence of these pathogens in 28 cow-calf operations exposed or non-exposed to elk, and in 10 elk herds exposed or not to cattle. We characterized the effect of species commingling as a risk factor of pathogen exposure and documented the perceived risk of pathogen transmission at this wildlife-livestock interface in the rural community. Herpesviruses found in elk were elk-specific gamma-herpesviruses unrelated to cattle viruses. Pestivirus exposure in elk could not be ascertained to be of livestock origin. Evidence of MAP circulation was found in both elk and cattle, but there was no statistical effect of the species commingling. Finally, N. caninum was more frequently detected in elk exposed to cattle and this association was still significant after adjustment for herd and sampling year clustering, and individual elk age and sex. Only indirectly transmitted pathogens co-occurred in cattle and elk, indicating the potential importance of the transmission route in assessing the risk of pathogen transmission in multi-species grazing systems.

Spatial hierarchical variances and age covariances for seroprevalence to Leptospira interrogans serovar hardjo, BoHV-1 and BVDV for cattle in the State of Paraíba, Brazil

We estimated spatial hierarchal variances and age-group covariances for seroprevalence to Leptospira interrogans serovar hardjo (LeptoH), bovine viral-diarrhea virus (BVDV) and bovine herpesvirus type 1 (BoHV-1) among 2343 cattle from 72 properties sampled in the State of Paraíba, Brazil in 2000. From each property, eight animals in each of the four age categories were evaluated. The age categories studied were: pre-weaned (0-6 months), young (7-18 months), replacement (19-30 months) and mature (>30 months). Overall seroprevalence to LeptoH was 16.0% and showed clustering at all levels of the spatial hierarchy and had a high posterior probability of being negatively correlated between replacement and mature groups within herds. Seroprevalence to BoHV-1 was 46.6% and demonstrated very little clustering among levels of the spatial hierarchy and was positively correlated between young and replacement groups within herds. Seroprevalence to BVD was 22.2% and was strongly clustered within herds and was positively correlated between young and replacement age groups within herds.

Quantification of the transmission of bovine herpesvirus 1 among red deer (Cervus elaphus) under experimental conditions

Bovine herpesvirus 1 (BHV1) is endemically present in a cattle population that lives in a nature reserve in the Netherlands. Red deer (Cervus elaphus), living in the same nature reserve, can come into contact with the BHV1-infected cattle and could then become infected with BHV1. For the eradication of BHV1 in cattle, it is, therefore, important to know whether red deer alone can play a role in the transmission of BHV1. For that reason, we quantified the transmission of BHV1 among farmed red deer under experimental conditions. Two groups of ten animals were formed. In each group, five of these animals were inoculated with BHV1 and the other five served as contact animals. Three inoculated animals in each transmission experiment became infected and none of the contact animals became infected. The one-sided 95% confidence interval for R [0.0-0.94] showed that limited transmission might occur among red deer. Based on these results, we would expect only minor outbreaks of BHV1 to occur in red deer populations. We concluded that BHV1 will probably not survive longer than a few decades (several times the mean deer lifetime) in red deer populations. Consequently, it is not necessary for the eradication of BHV1 in cattle to eradicate BHV1 in red deer populations as well.

Airborne transmission of BHV1, BRSV, and BVDV among cattle is possible under experimental conditions

To control the diseases caused by bovine herpesvirus 1 (BHV1), bovine respiratory syncytial virus (BRSV), and bovine virus diarrhoea virus (BVDV), it is crucial to know their modes of transmission. The purpose of this study was to determine whether these viruses can be transmitted by air to a substantial extent. Calves were housed in two separate isolation stables in which a unidirectional airflow was maintained through a tube in the wall. In one stable, three of the five calves were experimentally infected with BHV1 and later with BRSV. In the BVDV experiment, two calves persistently infected with BVDV (PI-calves) instead of experimentally infected calves, were used as the source of the virus. In all the calves infections were monitored using virus and antibody detection. Results showed that all the three viruses were transmitted by air. BHV1 spread to sentinel calves in the adjacent stable within three days, and BRSV within nine days, and BVDV spread to sentinel calves probably within one week. Although airborne transmission is possibly not the main route of transmission, these findings will have consequences for disease prevention and regulations in control programmes.

[Introduction of BHV1 on dairy farms. Risk assessment by cattle farmers and veterinarians]

A study is being carried out at Wageningen Agricultural University together with, among others, the Animal Health Service to determine the possibilities and economic consequences of a more closed farming system for (Dutch) dairy farms. Three identical workshops, held in the evening, were organized as part of the study. The opinion of farmers and their veterinarians on the importance of risk factors for the introduction of diseases on a farm was determined, using Bovine Herpes Virus type 1 (BHV1) as an example. In total, 27 farmers and 13 veterinarians participated in the workshops and completed a computerized questionnaire that was based on Adapted Conjoint Analysis (ACA). The results of the farmers and veterinarians were compared. Both farmers and veterinarians seemed well aware of the risk of direct animal contacts for introduction of BHV1. Farmers thought visitors to be of more risk than veterinarians. By making use of information obtained from the ACA workshops, it will be possible to improve the advice given to different groups in the dairy sector.

Risk of infection with bovine herpes virus 1 (BHV1): a review

Bovine Herpes Virus 1 (BHV1) consists of three subtypes, which probably differ in their epizootiological characteristics. BHV1 subtypes 1 and 2a are mainly associated with the respiratory form of the disease (IBR), subtype 2b with IPV/IBP, and subtype 3 with encephalitis. BHV1 subtype 1 is excreted in high titres in nasal secretions and spreads more effectively than the other subtypes. Cattle are the only significant source of viral spread. Although other species may become infected, they probably do not contribute to the spread of BHV1. Airborne transmission or spread of the virus by humans is believed to be of minor importance.

An in vivo study of a glycoprotein gIII-negative bovine herpesvirus 1 (BHV-1) mutant expressing beta-galactosidase: evaluation of the role of gIII in virus infectivity and its use as a vector for mucosal immunization

We constructed a recombinant BHV-1 in which the glycoprotein gIII gene was replaced by the Escherichia coli lacZ gene. The resultant virus mimics the simple gIII deletion mutant in its growth characteristics in cell culture; however, it expresses beta-galactosidase in virus-infected cells. Further characterization of its virulence and the immune responses elicited by it was conducted in cattle. The mutant virus retained the ability to establish an infection when administered intranasally. Infected animals were also capable of transmitting virus to sentinel penmates. However, the mutant virus showed a reduced replication efficiency in the respiratory tract of cattle, as manifested by significantly lower virus shedding and a shorter duration of shedding when compared to wild-type (wt) BHV-1 infections. The mutant virus induced an efficient anti-BHV-1 antibody response and convalescent cattle were fully protected from subsequent wt virus challenge. In addition, cattle infected with the lacZ-expressing virus developed antibodies to beta-galactosidase. Our results demonstrate that the presence of gIII is not a prerequisite for BHV-1 infection; however, gIII does play an important role in maintaining virus replication efficacy in its natural host. With respect to developing BHV-1 as a vaccine vector, our results indicate that deletion of the gIII gene, which partially attenuates the virus and serves as a vaccine virus marker, does not compromise immunogenicity to BHV-1. Most importantly, this vector is effective in delivering foreign antigens to mucosal surfaces of the respiratory tract.

BHV1 infections: relevance and spread in Europe

Infections caused by BHV1 are very common in Europe, but the disease pattern is quite different: the diseases of the genital tract are most common, those of the respiratory tract vary in intensity and prevalence. Digestive disorders connected with BHV1 are in general only observed in calves and mainly in Belgium. Virus strains causing abortion or encephalitis are only present in a few countries. The same is true for BHV1 induced mastitis. Dermatitis and lesions in the interdigital space seem to be a rare event. BHV1 infections are frequently complicated by bacterial secondary infections, but there is evidence that BHV1 infections can occur simultaneously with bovine virus diarrhoea (BVD) and/or parainfluenza-3 (PI 3) virus. The biggest problem associated with BHV1 infection is the ability of the agent to become latent following a primary infection. The genome of the virus probably remains during the life of the animal in the ganglia of the region where the primary infection occurred. No vaccination can overcome this latent stage. By prophylactic vaccination it is possible to prevent an outbreak of clinical disease but it is impossible to prevent infection followed by the establishment of latency. Eradication programmes in Austria, Denmark and Switzerland have removed most of the seropositive cattle from the bovine populations. Currently a sanitary programme is also being conducted in Germany.

Experimental transmission of bovine viral diseases by insemination with contaminated semen or during embryo transfer

Three experimental approaches were used to study transmission of blue tongue (BT), infectious bovine rhinotracheitis (IBR) and bovine virus diarrhoea (BVD) viruses. These were insemination with contaminated semen, experimental infection of embryo donor cows, or transfer of embryos experimentally exposed to virus in vitro to normal recipients. Parameters assessed included number and quality of embryos produced, virus detection (isolation and electron microscopy), serology and histopathology. All superovulated sesceptible cows inseminated with semen containing blue tongue virus (BTV) (n = 2) or infectious bovine rhinotracheitis virus (IBRV) (n = 2) became infected. One cow inseminated with semen containing BTV produced seven virus-free seven-day-old embryos; the second cow failed to produce any embryos. One of two cows inseminated with semen containing IBRV produced two underdeveloped, virus-free embryos while no embryos were produced by the second cow. One of two cows inseminated with semen containing bovine viral diarrhoea virus (BVDV) became infected. Two poorly developed, virus-free seven-day-old embryos were recovered from one of these cows. Superovulated susceptible cows inoculated either intramuscularly with BTV (n = 3) or intranasally with IBR virus (n = 2) became infected. Virus was isolated from some tissues of two BTV-infected cows, neither of which produced embryos. A third BTV-infected cow produced two virus-free embryos collected at necropsy five days after inoculation. One of two cows experimentally infected with IBR virus, produced three embryos but virus was not detected either by electron microscopy (1 embryo) or in cell culture by cytopathic alterations (1 embryo).(ABSTRACT TRUNCATED AT 400 WORDS)

Diseases of wapiti utilizing cattle range in southwestern Alberta

Specimens from 28 wapiti (Cervus elaphus canadensis) were collected by hunters in southwestern Alberta in 1984. Various tests were performed to detect infections and conditions that could affect cattle sharing the range or cause disease in wapiti. Serum antibodies were present against leptospiral serovars autumnalis (25%), bratislava (4%), and icterohaemorrhagiae (8%), and the viruses of bovine virus diarrhea (52%), infectious bovine rhinotracheitis (45%), and parainfluenza type 3 (13%). No serological evidence of bovine respiratory syncytial virus, Brucella, Anaplasma, bluetongue virus, or epizootic hemorrhagic disease virus was found, nor were any lesions of vesicular diseases, necrotic stomatitis or nutritional myopathy evident. Focal interstitial nephritis and sarcocystosis were diagnosed histologically in 40% and 75%, respectively, of the wapiti tested. The prevalence of giant liver flukes (Fascioloides magna) was 50% and of lungworms (Dictyocaulus viviparus) 32%. Leptospiral serology on cattle in the area did not indicate that wapiti or cattle were a serious source of infection to each other. The giant liver fluke was the parasite most likely to be amplified by wapiti for cattle. Within the limits of this study, the results indicated that wapiti in the Waterton area do not pose a disease threat to the cattle with which they range, but periodic observational studies in these wapiti would be a useful means of early detection of any changes in the interspecies relationship.

Diagnosis and prophylaxis of infectious bovine rhinotracheitis: the role of virus latency

Efficient methods of diagnosis and prophylaxis of infectious bovine rhinotracheitis must consider the concept of latency of the etiological agent, infectious bovine rhinotracheitis virus (Bovine herpesvirus 1; BHV 1). The identification of BHV 1 in nasal mucus samples or a rise in specific antibodies have to be cautiously interpreted, because they can signify either a primary infection or a reexcretion of the virus after reactivation. The isolated virus can also either be a vaccine or a virulent strain. Another aspect of BHV 1 infection diagnosis is the detection of latent carriers, which are able to transmit the virus to uninfected animals; delayed hypersensitivity test seems to be a good candidate. The classical methods of prophylaxis protect the animal against the disease, but they should also impede the reexcretion of virulent strains by latent carriers. Since, in several countries, attenuated viruses are used as vaccines, a special emphasis has to be laid on the persistence of these vaccine viruses in a latent form in the bovine population.

Observations on the epidemiology of the herpesvirus of infectous bovine rhinotracheitis/infectious pustular vulvovaginitis in wildebeest

Spontaneous vulvovaginitis erupted in wildebeest (Connochaetes taurinus) after betamethasone inoculation. Infectious bovine rhinotracheitis/infectious pustular vulvovaginitis (IBR/IPV) is probably a venereal disease because virgin wildebeest did not develop vulvovaginitis after betamethasone injections, nor was the virus transmitted to these virgin wildebeest and steers which were in pen contact with the affected animals. A domestic bovine heifer developed mild IPV and became a virus carrier, when exposed to the wildebeest IPV virus by vaginal instillation.

Effect of temperature, relative humidity and medium on the aerosol stability of infectious bovine rhinotracheitis virus

Aerosols of infectious bovine rhinotracheitis virus were generated with a Devilbiss 40 nebulizer from Eagle's minimum essential medium, nasal secretion from a noninfected calf and nasal secretion from a calf artificially infected with infectious bovine rhinotracheitis virus and aged in a rotating drum at temperatures of 6 degrees C or 32 degrees C and relative humidities of 30% or 90%. The aerosols were sampled at seven minutes after start of spraying, one hour, two hours and three hours with an all glass impinger (AGI-30) and titrated for infectivity in cell cultures. Physical decay was determined by a rhodamine B tracer technique. During spraying (seven minutes from start of spraying), the virus was usually more stable in aerosols of nasal secretion from a noninfected calf and at 90% relative humidity. In nasal secretion from a noninfected calf the virus survived best at 90% relative humidity when the temperature was 6 degrees C and best at 30% relative humidity when the temperature was 32 degrees C. During aging, biological decay was greater at the higher temperature, and at 6 degrees C, the highest decay rates occurred at 30% relative humidity in Eagle's minimum essential medium and at 90% relative humidity in nasal secretion from a noninfected calf. The stability of infectious bovine rhinotracheitis virus infected nasal secretion was not widely different from that in noninfected nasal secretion, although under certain conditions greater survival occurred in the noninfected secretion.

Persistence of infection with infectious bovine rhinotracheitis virus in Danish cattle herds

The later course of IBR virus infections in 11 dairy herds in endemic areas and in an imported beef herd is described. In 2 herds the infection was limited to those animals which developed a genital infection after insemination with semen from an infected AI centre. In two other herds where genital infection was observed clinically a spreading occurred, probably because of carelessness in clinical examinations, although the possibility of an additional spreading by the respiratory route had to be considered, too. In one herd signs of a respiratory disorder were noticed and assumed to have been caused directly by IBR virus. In the other 7 herds a spreading by the respiratory route was evidenced serologically. In some of these herds there were no indications of spreading after the extensive initial spreading, while in others there were single cases of infection later on, in particular in one small herd where the ventilation was inadequate.