Bovine herpesvirus 1: molecular and antigenic characteristics of variant viruses isolated from calves with neurological disease

This report presents data showing that several virus isolates recovered in Argentina, mainly from calves with non-purulent meningo-encephalitis, represent a hitherto unrecognized antigenic variant of BHV-1. The following experimental approaches have been adopted to demonstrate both the unique features among and the relatedness with BHV-1 of these isolates: i) crossed serum neutralization test with rabbit immune sera, ii) analysis by SDS-polyacrylamide gel electrophoresis of radio-labeled virus induced polypeptides and glycoproteins, iii) discriminating reactivity of a panel of monoclonal antibodies which recognize known virus types, and iv) restriction endonuclease analysis of viral DNA. Another strain of BHV-1, which exhibits a specific neuropathogenic potential [Hall et al., Austral. Vet. J. 42, 229-237 (1966)] shares all major features with the viral strains originating from Argentina. Our results imply that antigenic variants of BHV-1 exist and that they can be accurately and easily identified and differentiated by the available methods.

Logical description of bovine herpesvirus type 1 latent infection

Description of the interactions between bovine herpesvirus type 1 (BHV-1) and cattle was performed by the method known as kinetic logic. This logical formalization uses variables with two possible values, 1 and 0, which tell whether an element is present or not at a significant level. To each variable is associated a function which tells if the element is being produced at a significant rate. The temporal relation between a variable and its associated function is given by specific time delays. The BHV-1 infection system is described by a set of five logical equations which tell in what conditions each function is on or off. The five functions are: V, development of viral multiplication; R, development of reactivation of the latent virus; A, development of an immune response; G, establishment of the viral genome; M, development of a memory of a first immune response. Several examples are detailed in a dynamic analysis, in connection with known experimental data.

Short repeats cause heterogeneity at genomic terminus of bovine herpesvirus 1

Analysis of the genomes of different bovine herpesvirus 1 strains revealed a UL terminal HindIII fragment differing in size (from 2.4 to 2.8 kilobases). This fragment polymorphism occurred in the DNA of a wild-type isolate, in highly passaged, apathogenic tissue culture derivatives, and in plaque-purified substrains. This heterogeneity was due to variations in the copy number of a 14-base-pair tandem repeat comprising the base sequence 5'-GCTCCTCCTCCCTC-3', which also exists, with some differences, in other short reiteration sequences of herpes simplex virus type 1, Epstein-Barr virus, and related human cellular DNA. Furthermore, the tandem repeat array was located in close proximity to the left end of the viral genome and may functionally be involved in viral replication.

Ovarian lesions induced in heifers by intravenous inoculation with modified-live infectious bovine rhinotracheitis virus on the day after breeding

Four commercially available vaccine strains of modified-live infectious bovine rhinotracheitis virus were passaged once in embryonic bovine kidney cells. Heifers were inoculated IV on the day after breeding with 5.0 ml of nondiluted cell culture fluid of each of the 4 strains. Virus was reisolated from nasal swabs and blood collected during the week after inoculation. The heifers were killed 9 to 14 days after inoculation. Mild-to-marked inflammatory and necrotic lesions were seen in the corpora lutea and ovaries of the heifers. The lesions were similar to, and almost as severe as, those resulting from the inoculation of virulent strains of infectious bovine rhinotracheitis virus. Adrenal lesions were also found in all heifers examined. Virus was reisolated from the ovaries of only 4 of the 8 heifers. However, virus was confirmed in the ovaries of all 8 heifers, using immunofluorescent or ultrastructural studies. Heifers with severe luteal damage had abnormally low plasma progesterone concentrations.

Reaction of goats to infection with infectious bovine rhinotracheitis virus

Intranasal exposure of goats to infectious bovine rhinotracheitis virus resulted in mild respiratory disease and virus reisolation from nasal secretions. No disease was produced in goats exposed to the same virus by the genital or ocular routes. There was serological evidence of contact transmission of infection from infected goats to cattle. Virus recrudescence was not detected in goats treated with dexamethasone two months after virus inoculation.

Thymidine kinase-negative bovine herpesvirus type 1 mutant is stable and highly attenuated in calves

Calves were vaccinated intranasally (IN) or intravenously (IV) with a thymidine kinase-negative (tk-) BHV-1 mutant. Vaccinated calves developed neutralizing antibodies but did not show clinical signs of infectious bovine rhinotracheitis (IBR). Vaccination also prevented clinical signs of IBR disease following IN challenge exposure of the calves to parental Los Angeles (LA) and USDA Cooper strains of tk+ BHV-1. Nasal swabs were collected for 10 days after the vaccination and the challenge exposures to monitor BHV-1 multiplication. At both 91 and 121 days post vaccination (PV), calves were also stressed for 5 days with dexamethasone (DEX) to induce reactivation of BHV-1 and nasal swabs were obtained. tk- BHV-1 multiplied in the nasal mucosa of IN vaccinated calves and was also recovered after DEX treatment. Likewise, tk- BHV-1 was isolated from the buffy coat fraction of IV vaccinated calves, but not from nasal swabs. tk- BHV-1 vaccination reduced the multiplication of tk+ BHV-1 in the nasal mucosa, but did not completely prevent development of a persistent infection by the challenge virus. The phenotypes of viruses isolated from the nasal swabs and buffy coats were analyzed by enzyme assays of extracts from virus-infected cells and by plaque autoradiography. These assays showed that tk- BHV-1 can persist for at least 3 months in vaccinated calves and may also be transmitted from vaccinated to control calves without reverting in vivo to tk+. The results demonstrate that the tk- BHV mutant is attenuated and efficacious as a vaccine.

In utero infection of swine fetuses with infectious bovine rhinotracheitis virus (bovine herpesvirus-1)

The pathogenesis of infectious bovine rhinotracheitis (IBR) virus (bovine herpesvirus-1) was studied in porcine fetuses after in utero inoculation. Laparotomies were performed on 8 seronegative pregnant sows at 34 to 86 days of gestation, and all fetuses in 1 uterine horn of each sow were exposed to IBR virus via inoculation into the amniotic sacs. Fetuses in the other horn served as controls. Clinical signs of infection were not observed in the sows, except for 2 sows that aborted at postinoculation days (PID) 11 and 15. Fetuses of the remaining 6 sows were collected at slaughter on PID 15 to 28. Fetuses were examined for gross abnormalities, presence of IBR virus in tissues, and the formation of neutralizing antibodies to IBR virus. Of 33 inoculated fetuses from 6 sows, 10 were mummified, 11 were hemorrhagic and/or edematous, and 12 were alive. Necrotic lesions were observed on the skin and in the liver of dead and live fetuses. Virus was recovered from 29 of 33 inoculated fetuses. Infectious bovine rhinotracheitis virus was isolated from fetal skin, liver, lungs, kidney, spleen, stomach contents, brain, amniotic fluid, and placenta. Virus was isolated from 4 of 11 fetuses recovered from 1 aborting sow. Antibodies to IBR virus were not detected in sera from the sows. However, antibodies were detected in 6 of 15 fetuses inoculated at 63 to 86 days of gestation and collected at slaughter at 86 to 112 days of gestation. The youngest fetus with detectable IBR antibody was estimated to be 74 days of gestation by measuring crown-rump length of the fetus.

The possible role of stress in the induction of pneumonic pasteurellosis

Five groups of range bred calves (four calves per group) were used to investigate the effect of stress on susceptibility to aerosol exposures with bovine herpesvirus-1 or Pasteurella haemolytica. Twelve calves were weaned, transported, processed at a commercial feedlot and transported to isolation facilities three days later. An aerosol challenge of either 10 colony forming units of P. haemolytica or 10 plaque forming units of bovine herpesvirus-1 virus was given to two groups of calves and the third group was not challenged. The fourth group was transported directly to the isolation facilities after weaning and aerosol challenged with P. haemolytica. The fifth group remained at the farm after weaning and was not challenged. All transported animals had elevated plasma cortisol levels which remained above normal for at least three days postchallenge. The blastogenic response of all calves was depressed after leaving the farm and remained depressed throughout the experiment. The suppression correlated well with elevated serum cortisol levels. Calves processed through the feedlot encountered bovine herpesvirus-1 because eight out of 12 animals seroconverted to this antigen. Most calves seroconverted to P. haemolytica whether they were experimentally challenged or not. Where the unchallenged calves encountered P. haemolytica is unknown. Calves challenged with bovine herpesvirus-1 but not with P. haemolytica, had significant clinical signs of pneumonia and two animals died due to bovine herpesvirus-1 infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of bovine herpes virus-type 1 isolates by restriction endonuclease fingerprinting

In an effort to determine whether distinct types of bovine herpesvirus 1 are responsible for causing specific syndromes, the polypeptides and DNA of 93 BHV 1 isolates from the province of Alberta as well as vaccine strains and numerous other Canadian, U.S. and European isolates were analyzed by PAGE and restriction endonuclease fingerprinting, respectively. The polypeptide patterns showed only slight variations: only six isolates contained polypeptides that varied from the norm in their molecular weight, or were absent. Although on the basis of endonuclease patterns the isolates could be categorized into three "strains" and nine "sub-strains", we were unable to associate any of the strains with specific clinical signs. This suggests that the type of disease caused may be determined more by the route of infection and animal management practices than by the inherent properties of certain types of BHV 1. Most of the Albertan isolates were of one BHV 1 type and sub-type.

Challenge exposure of cattle vaccinated with a chemically altered strain of Pasteurella haemolytica

Calves vaccinated with a chemically altered strain of Pasteurella haemolytica and their nonvaccinated controls were challenge exposed intranasally with the Cooper strain of infectious bovine rhinotracheitis virus. Five days later, the calves were challenge exposed intratracheally with the P haemolytica type A1. Calves that had been vaccinated with large, medium, or small doses of the chemically altered vaccinal strain of P haemolytica had various degrees of resistance to the experimental challenge exposure. Nonvaccinated animals developed severe respiratory tract disease and pneumonia after challenge exposure.

Viral-bacterial pneumonia in calves: duration of the interaction between bovine herpesvirus 1 and Pasteurella haemolytica

Sixteen six to eight month old beef calves were exposed individually to a five minute aerosol of bovine herpesvirus 1, isolate 108. Aerosol exposure to Pasteurella haemolytica (biotype A, serotype 1) was administered individually for five minutes at either four, ten, 20 or 30 days after the virus. Fibrinous pneumonia and pleuritis occurred in all four groups but were most extensive and severe in those exposed to the virus and bacterium four days apart (the positive controls). Fibrinous pneumonia was associated with persistence of bovine herpesvirus 1 in the respiratory tract despite resolution of virus-induced necrotic lesions of the respiratory mucosa. The results presented here suggest that, although the severity of viral-bacterial synergism may be influenced by virus-induced morphological changes, the continued presence of viral antigens after the resolution of respiratory mucosal lesions may continue to exert some effect on host defenses and disease processes.

A comparison of the virulence of three strains of infectious bovine rhinotracheitis virus

The virulence of three strains of infectious bovine rhinotracheitis (IBR) virus was compared in six-month-old Ayrshire-cross calves. The strains were an isolate from a recent severe outbreak of IBR in Scotland (Strichen strain), the prototype British strain (Oxford strain) and a North American isolate (Colorado strain). The Colorado and Strichen strains produced the characteristic clinical signs and pathological lesions of severe IBR three to four days post infection (p.i.). The Strichen strain was slightly more virulent, possibly as a result of its having been passaged fewer times in tissue culture. In contrast, the Oxford strain produced a mild clinical response with minimal pathological lesions. Virus was recovered from nasal swabs for a longer-period from the calves infected with the Strichen strain (up to 13 days p.i.) and Colorado strain (up to 12 days p.i.) than from the animals infected with the Oxford strain (up to 10 days p.i.). These findings support the suggestion that the recent epidemic of severe IBR in Britain had resulted from the importation of a "new" strain of virus.

Experimental infection of cattle of different ages with infectious bovine rhinotracheitis virus (Strichen strain)

The clinical signs and pathological lesions which developed in various ages of cattle experimentally infected intranasally with the "Strichen" strain of IBR virus were similar to, but generally milder than, those of the field disease. The clinical signs were most severe 4 days after infection and had almost wholly regressed after 12 days. Serum neutralizing antibodies were detected in every animal. Virus was isolated from nasal and ocular swabs for up to 13 days and 10 days, respectively, after infection. The clinical signs and the pathological lesions were more severe in the younger animals.

A review of infectious bovine rhinotracheitis, shipping fever pneumonia and viral-bacterial synergism in respiratory disease of cattle

Unanswered questions on the etiology and prevention of shipping fever pneumonia have allowed this disease to remain one of the most costly to the North American cattle industry. Research in this area has indirected that while Pasteurella haemolytica and, to a lesser extent, P. multocida are involved in most cases, they seem to require additional factors to help initiate the disease process. Bovine herpes virus 1 has been shown experimentally to be one such factor. This review examines in some detail the topics of infectious bovine rhinotracheitis, shipping fever, and viral-bacterial interactions in the production of respiratory disease in various species. It deals with history, definitions, etiologies, clinical signs and lesions, and considers exposure levels, transmission and various pathogenetic mechanisms that are postulated or known to occur.

Experimental infection of wildebeest with the herpesvirus of infectious bovine rhinotracheitis/infectious pustular vulvovaginitis

Intravaginal inoculation of a wildebeest (Connochaetes taurinus) with a wildebeest strain of the infectious bovine rhinotracheitis/infectious pustular vulvovaginitis herpesvirus induced only mild vulvovaginitis. The same virus did not produce any disease in another wildebeest exposed intranasally. A wildebeest bull which was inoculated by preputial instillation developed mild posthitis. The virus was reisolated only from the sites of inoculation. A carrier state was initiated in a wildebeest inoculated only once, intravaginally. The presence of this virus in the various secretions is a potential source for venereal transmission.

Experimental infection of eastern cottontail rabbits Sylvilagus floridanus) with infectious bovine rhinotracheitis virus

Experimental infection of eastern cottontail rabbits (Sylvilagus floridanus) with infectious bovine rhinotracheitis virus caused acute keratoconjunctivitis and a fatal systemic infection. The clinical syndrome was characterized initially by blepharospasm and ocular discharge. The rabbits were markedly depressed on post-exposure day (PED) 5 and were dead or moribund on PED 6. The virus was readily recovered from liver and adrenal gland tissue on PED 6 and from conjunctival swabs on PED 1 to 6. Histopathologic studies revealed a few necrotic foci in the liver and multiple focal to diffuse necrosis of the adrenal glands. Viral isolation and immunofluorescence tests were used to demonstrate a direct association between infectious bovine rhinotracheitis viral antigens and the lesions.

Experimental infection of rabbits with the virus of infectious bovine rhinotracheitis

Adult and newborn rabbits were infected with the LA strain of infectious bovine rhinotracheitis virus. Adult rabbits developed only mild, self-limiting conjunctivitis, but had microscopic inflammatory foci in the liver and adrenal glands. Newborn rabbits developed a severe, sometimes fatal, generalized infection with focal and diffuse necrosis of the liver and adrenal glands.

Sensitivity of infectious bovine rhinotracheitis virus to ether

The sensitivity of 12 field isolates of infectious boviine rhinotracheitis (IBR) virus and four commercial modified-live infectious bovine rhinotracheitis virus vaccine strains was determined after exposure to 20% ethyl ether (anesthetic) for 16 h at 4 c. The infectivity of five field strains was reduced by varying degrees, whereas seven were found to be resistant. Three vaccine strains were moderately sensitive, and one strain was resistant. Four of the sensitive field strains were isolated from the conjunctiva and the other was isolated from the surface of the epiglottis of natural infective cattle. Strains of virus isolated from fetal tissue and nasal cavity were resistant. All viruses were readily inactivated by chloroform treatment.

Studies on the effects of infectious bovine rhinotracheitis virus on reproduction in heifers

Natural venereal infection of heifers with IBR virus resulted in vulvovaginal lesions in 9 of 12 heifers at 3 weeks after introducttion to bulls, and virus was isolated from 5 of the 9 affected animals. The infection was not associated with any effect on conception. Experimental nasal and conjunctival infection of 18 heifers pregnant for 3, 5 or 7 months with a genital strain of IBR virus caused mild rhinitis or conjunctivitis in all inoculated animals and virus was recovered from 14 animals at 8 days after inoculation. No effects on pregnancy were recorded.