INFECTIOUS BOVINE RHINOTRACHEITIS

INTRODUCTION• Infectious bovine rhinotracheitis was first described in

1955 as a new respiratory disease of feedlot cattle in western USA. Isolation of the virus was accomplished soon thereafter. It was soon recognized in dairy cattle and later associated with infectious pustular vulvovaginitis (IPV) & abortion.

HISTORY• There were 525 cattle in a cow-calf and feedlot

operation, of which 150 were feeders and the remainder the breeding herd. Several fences prevented direct contact between the breeding herd and the feedlot cattle. Most of the animals in the feedlot originated from the calf crop, but approximately 30% were purchased. All breeding herd additions were home raised heifers and were vaccinated against clostridial diseases and brucellosis routinely at four to five months of age.

• The three-yearold cattle were vaccinated for IBR as calves in 1970. However, the two affected heifers may not have received Brucella strain 19 and IBR vaccinations, as they did not have vaccination tags in their ears. The breeding herd was maintained under range conditions and no unusual health problems had occurred. Only one or two abortions had occurred over the last five years and pneumonia had been limited to the feedlot.

• Nutritional myopathy had been a continuing problem in newborn calves and animals were routinely treated and supplemented with selenium and vitamin E. A few heifers and cows confined for close observation in a calving paddock adjacent to the feedlot were in contact with two sows and their litters which had free access to the paddock. The owner reported they sometimes molested the cattle by nibbling at their hindquarters while they were lying down.

DISTRIBUTION• The IBR virus is widely distributed. The virus has been

isolated or anti-body detected from cattle in all parts of the world. In addition to cattle, goat, swine and water-buffalo, the virus has been reported in a variety of wild ruminants throughout the world.

ETIOLOGY• The etiologic agent, “BOVID HERPESVIRUS-1” or

“BOVINE HERPESVIRUS-1” is a member of genus “Herpesvirus” of the family “Herperviridae”. Sometime called the IBR-IPV virus, it has all properties of herpesviruses and grows rapidly in a wide variety of cell cultures producing distinctive cytopathologic changes which are readily neutralized by a specific anti-sera. It is a comparatively easy agent to isolate and identify.

• Most IBR & IPV are similar immunologically although the wide variety of clinical manifestations suggests the biotypes with affinity for various tissues may occur. Slight strain difference can detected by immunologic methods.

EPIDEMIOLOGY• Because of the ease of transmission and capacity for

perpetuation, IBR is regarded as virtually ubiquitous among cattle populations.

• The incubation period varies from 2-6 days depending on the dose, route of incubation and the criteria for indicating the onset of disease.

• The infection is easily transmitted because large quantities of IBR virus are exteriorized in respiratory, ocular and reproductive secretions of infected cattle. The virus is perpetuated in population by direct contact between infected cattle and by occasional reactivation of latent infections, resulting in a renewed shedding of the virus.

• Feedlot cattle seem to have higher attack rates, more severe disease and fatality rates than range cattle or diary cattle. These differences probably result from shipment, aggregation, social acclimatization, exposure to multiple pathogens and other stresses.

CLINICAL FINDINDGS• A three-year old heifer became weak in the hind legs and knuckled at

the fetlocks. Incoordination became more pronounced over 48 hours until the animal was unable to stand, her hind legs becoming rigid. The animal remained recumbent for five days and was then euthanized.

• One week later a second three-year old heifer began a similar clinical syndrome and within 24 hours she was unable to rise. The owner treated her with 500 ml of a calcium preparation subcutaneously, two injections of penicillin-dihydrostreptomycin, and one injection of a selenium preparation. The animal was referred to the Provincial Veterinary Laboratory by a practitioner for post mortem examination.

• Flaccid paralysis of the hind quarters was the principal clinical sign with motor paralysis of the hind limbs and tail and partial sensory paralysis distal to the stifle joints. The forelimbs were unaffected. When the animal was unloaded she immediately and voraciously attacked her left side and flank area by biting the skin. A pronounced lesion had already been made by this action and hair and skin had been excoriated.

CONTROL• It can be best controlled by vaccinations.