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Experimental infection of cattle of different ages with infectious bovine rhinotracheitis virus (Strichen strain)
J. COMP.
PATH.
1983.
20.5
93.
VOL.
EXPERIMENTAL DIFFERENT RHINOTRACHEITIS
AGES
INFECTION OF CATTLE OF WITH INFECTIOUS BOVINE VIRUS (STRICHEN STRAIN) BY
P. M.
MSOLLA, of Glasgow
Lniwrsi,.ify
A. WISEMAN, Veterinary
E. M. ALLAN
School, Bearsden Road, Bearsden,
and I. E. Glnsgou~ GGI
SELMAN
IQH,
1.K.
INTRODUCTION
During the last few years, the nature of infectious bovine rhinotracheitis (IBR) in Britain has changed from a mild, economically unimportant, sporadic disease to a severe disorder prevalent in most areas of the country (Allan, Pirie, Msolla, Selman and Wiseman, 1980; Wiseman, Msolla, Selman, Allan and Pirie, 1980). The incidence of disease has been highest in fattening, beef cattle although the disorder has been confirmed in adult cattle and also young calves. In view of the dramatic change in the nature of IBR, the pathogenicity of a recent virus isolate was studied in different ages of cattle to determine the relationship between age and susceptibility to infection. MATERIALS
AND
METHODS
Experimental Animals Four groups of cattle were infected: they were 4 P-week-old (Group A) and 6 5-week-old Ayrshire bull calves (Group B), 4 6-month-old (Group C) and 3 18-monthold Friesian bullocks (Group D). Two animals of the same age were used as controls for each of the groups and they were housed separately from the infected animals. All the cattle had been purchased from a local dealer when about l-week-old, and had been reared at the Veterinary School.
Method of Infection One millilitre “Strichen” strain Imray, 1978) at lated into each culture into each
of a tissue culture suspension (titre=lO’.’ TCID,, per ml) of the of IBR virus (Wiseman, Msolla, Selman, Allan, Cornwell, Pirie and the third passage in secondary calf kidney cell cultures, was inocunostril. The control animals were given 1 ml of uninfected tissue nostril.
Clinical Examination The animals were examined twice daily after infection (p.i.) and then once daily.
for 7 days before infection
and for 14 days
Serology Serum from every animal was examined for neutralizing (SN) antibodies to IBR virus 1 week before infection and every day from day 6 to day 15 p.i. by the technique described previously (Msolla, Wiseman and Selman, 198 1) . OOZl-9975/83/020205+06
$03.00/O
@ 1983
Academic
Press
Inc.
(London)
Limitrd
206
P.
M.
MSOLLAet
al.
Microbiology Nasal and ocular swabs were taken on 2 occasions during the week before infection and from day 4 to day 15 p.i. At necropsy, samples of tissue for virus isolation were collected from the nasal conchae, nasopharynx, trachea, lung parenchyma and small bronchi. Virus isolation was carried out in tube-cultures of secondary calf kidney and calf testes cells as described previously (Wiseman et al., 1978). Samples were considered to be negative if a cytopathic effect had not developed by the fifth day of the third passage. Samples of lung were also examined for the presence of bacteria and mycoplasms by methods described previously (Pirie and Allan, 1975).
Pathotogy Animals in Groups A, B and C were killed humanely and exsanguinated at the following times p.i. : day 4-A3, B5, B6; day 5-Bl, B3; day 6-Cl, C4; day 33B2, B4. The control calves were also killed 4 to 6 days after Groups A, B and C had been infected. The samples of tissue for light microscopy taken from the respiratory
tract and other organs were processedby methods described previously (Wiseman et al., 1978). RESULTS
Clinical Findings The first signs of illness were slight dullness and a serous o&o-nasal discharge which were observed on day 1 p.i. in Groups A and B, on day 2 in Group C and on day 3 in Group D. Pyrexia ( ,39*4X) and conjunctivitis had developed by the next day when the animals were duller and had a reduced appetite. At the same time they began to drool saliva, there was a sudden increase in the frequency of coughing and small, raised, white plaques were seen on the nasal mucous membranes. By day 3 (Group A) and day 4 (Groups B, C, D) p.i., every animal had developed the characteristic signs of severe IBR: dullness, anorexia, pyrexia (up to 41*4”C), profuse seromucoid ocular and nasal discharge, conjunctivitis, diphtheritic plaques on nasal mucosa, drooling saliva, hyperpnoea, tachypnoea (respiration rate=30 to 50 per min) and regular coughing. Petechial haemorrhages were observed on the nasal mucosa of 4 bullocks (Cl, C3, C4, DZ). Small, white granular lesions developed on the conjunctivae of 2 individuals (B3, C2) but marked conjunctival oedema was not seen. Eight animals from Group A (‘2 calves), Group B (4 calves) and Group C (2 bullocks) died ( 1 animal) or were killed (7 animals) from day 3 to day 6 p.i. The 2 remaining calves in Group A began to drink again on day 5 p.i. but they remained dull and subsequently developed a purulent ocular and nasal discharge. Their clinical condition had not improved noticeably by day 9 and, because they were still pyrexic (39.7 ; 40*8”C), they were given 500 mg oxytetracycline (Terramycin : Pfizer, England) intravenously for 3 days. This produced a rapid clinical response and within 1 week they had fully recovered. The surviving calves in Groups B and C were still slightly dull on day 6 p.i. but they had begun to eat again and were not pyrexic. By 12 to 14 days p.i., the only abnormal signs were mild conjunctivitis, dried ocular discharge, OCcasional coughing and congested nasal mucous membranes with healing plaques. The 2 remaining calves in Group B, were killed 33 days p.i. because they had developed chronic pneumonia.
AGE
AND
IBR
207
INEECTION
The animals in Group D began to eat again on day 5 and their demeanour, appetite and rectal temperatures were all normal the following day, although they were still drooling saliva slightly. On day 10 p.i., the only abnormal findings were reddening of the nasal mucosa and a slight serous oculo-nasal discharge. The control animals did not develop any clinical signs suggestive of IBR virus infection. SerologicaE Findings Serum neutralizing antibodies were detected initially in the animals in Group D, 2 on day 7 p.i. and 1 on day 10 p.i.; the remaining 6 animals in Groups A, B and C were first found to be positive on day 12 p.i. Antibodies were not detected in any of the control animals. Pathological Findings The macroscopic and microscopic appearance of the respiratory tracts of the 8 calves examined from 3 to 6 days p.i. were similar and, although they varied in degree, the Iesions in the younger calves were more severe and more widespread than those in the older animals. The major details of the pathological findings have been summarized and are presented in Table 1. One of the 2-weekold calves (Al) died 3 days p.i., having had diarrhoea for 6 days but, nevertheless, typical lesions of severe IBR were present in the respiratory tract. TABLE THE
MAJOR
Site Nasal
conchae
Lungs nodes
1
CHANGES 3-6 DAYS AFTER INFECTION OF STRAIN OF INFECTIOUS BOVINE RHINOTRAcHEITlS
Macroscopic
Larynxpharynxtrachea
Lymph
PATHOLOGICAL
CATTLE VlRUS
WITH
THE
“STRICHEN"
Microscopic
Congestion, oedema, rhinitis. Neutrophilic Congestion, oedema, yellow-white muco-pus. infiltration of epithelium Many, small, diphtheritic lesions. Several granular areas Congestion, oedema, epithelial hyperplasia and Congestion, oedema, extensive necrosis. Subepithelial lymphocytic petechial haemorrhages. Few, small, diphtheritic aggregates. Submucosal glands dilated and surrounded by plasma cells and lymphocytes lesions Exudative pneumonia. Cuffing-type lesions. Consolidation of anterior lobes Bronchitis Retropharyngeal-enlarged, haemorrhagic, oedematous, Bronchial and mediastinal-normal
Macroscopically, there was congestion and oedema with an inflammatory exudate present in the upper respiratory tract and also in the major bronchi of calf A3. Microscopically, the main changes were rhinitis, a severe pharyngitis with many large subepithelial lymphocytic aggregates, epithelial hyperplasia with necrosis and the accumulation of cellular debris and mucus in the lumen. The submucosal glands appeared active and were surrounded by plasma cells
208
I’.
M.
MSOLLA
f?t al.
and lymphocytes which occasionally obliterated the tubule or duct. In the 2 animals (B2, B4) examined 33 days p.i., the nasal conchae were congested and there was a moderately severe pharyngitis, laryngitis and tracheitis, with small petechial haemorrhages in the nasopharynx and a severe exudative pneumonia with marked bronchitis. None of the control calves had lesions in the nasal conchae, nasopharynx and trachea, although all had several foci of cuffing pneumonia. Viral inclusion bodies were not identified in any of the sections examined. Microbiological
Findings
Infectious bovine rhinotracheitis virus was not isolated from any of the calves before infection nor from any of the control animals afterwards. However, in every infected individual, virus was recovered daily from nasal swabs until either 12 or 13 days p.i. and from ocular swabs until from 6 to 10 days p.i. (mean =8*6 days). The virus was recovered from every site in the respiratory tract in calf A3 and in every site, apart from the lungs, in the 6 other animals killed 4 to 6 days pi. In addition, virus was recovered on one occasion from the brain (Cl) and the kidney (C4). Although virus was not recovered from either of the calves (B2, B4) killed after 33 days, Corynebacterium pyogenes and Mycophsma disfar were isolated from the lungs of calves B2 and B4, respectively. The virus was not isolated from any of the control calves. DISCUSSION
Every animal challenged intra-nasally with the “Strichen” strain of IBR virus developed a disease similar to but less severe than that observed in the field (Allan et al., 1980; Wiseman et al., 1980). The clinical signs developed earlier and were more severe and more persistent in the young calves than in the 6 and 18 month old bullocks. Both surviving 2-week-old calves developed a purulent nasal discharge and their clinical condition had not improved by day 9 p.i. when antibiotic therapy was instituted. Within a week, they appeared to have made a complete clinical recovery. On the other hand, the 4 5-week-old calves, which were affected to a similar degree, were not treated and two developed a severe chronic pneumonia. It is significant that the latter 2 animals were the only ones from which recognized pulmonary pathogens (C. pyogenes, M. dispar) were isolated at necropsy, although focal lesions of exudative pneumonia were present in every calf. The fact that recognized pulmonary pathogens were not present in significant numbers probably contributed to the relative mildness of the experimental disease compared with that in the field in which secondary infection appears to play a major role in determining the severity of the disorder. On the other hand, pneumonic lesions almost certainly had been present before challenge with the virus since “cuffing-type” lesions were identified in the control calves and in a proportion of the infected animals. There was no detectable difference in the frequency or duration of IBR virus
AGE
AND
I-BA
‘EN.FECTION
209
isolation between the different age groups. Virus was present for a longer period in the nasal epithelium than on the conjunctivae and this would explain the greater efficiency of virus isolation from nasal compared to ocular swabs in field incidents (Wiseman et al., 1980). Although IBR virus was isolated from the nasal conchae, nasopharynx and trachea of every calf killed 4 to 6 days p.i., it was recovered only once from the lungs and that was from the youngest animal examined. Despite the isolation of virus from the brain and kidney, each on one occasion, lesions were not present in either organ. Every animal exposed to the virus had developed SN antibodies within 12 days. In previous investigations, in contrast, SN antibodies were not detected in all experimentally infected animals (Abinanti and Plumer, 1961; Hughes, Olander and Wada, 1964). The most likely explanation is that the technique used in this study was more sensitive than that used by these earlier workers. The clinical, pathological and virological findings in this study are in broad agreement with the results of others who have studied experimentally produced IBR in New Zealand (Webster and Manktelow, 1959), North America (Abinanti and Plumer, 1961; Hughes et nl., 1964) and England (Markson and Darbyshire, 1966). Webster and Manktelow (1959) reported that there was a difference in age susceptibility to IBR virus infection but they used multiple routes of virus inoculation. In our investigation, young calves developed a more severe disease than older animals when challenged via the intranasal route alone. This variation in susceptibility to IBR virus infection may have been due to an age-related difference in cell mediated immune capacity, which, it has been suggested, is mainly responsible for recovery from bovine herpesvirus 1 infection (Rouse and Babiuk, 1978). SUMMARY
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. ACKNOWLEDGMENTS
The authors wish to thank ProfessorsW. I. M. McIntyre and W. F. H. Jarrett for their advice and encouragement, and Mrs B. Gillies for typing the manuscript. This work was partially financed by a grant from the Agricultural Research Council. REFERENCES
Abinanti, F. R., and Plumer, G. J. (1961). The isolation of infectious bovine rhinotracheitis virus from cattle affected with conjunctivitis-observations on the experimental infection, American Journal of Veterinary Research, 22, 13-I 7. Allan, E. M., Pirie, H. M., Msolla, P. M., Selman, I. E., and Wiseman, A. ( 1980).
210
P.
The pathological
M.
MSOLLAetd
features of severe cases of infectious
bovine rhinotracheitis.
Veterinary Record, 107, 441-445.
Hughes, J. P., Olander, H. J., and Wada, E. M. (1964). Keratoconjunctivitis associated with infectious bovine rhinotracheitis. Journal of the American Veterinary Medical Association, 145, 32-39. Markson, L. M., and Darbyshire, J. H. (1966). The reaction of calves to experimental infection with the Oxford strain of infectious bovine rhinotracheitis virus. British
Veterinary Journal,
122, 522-529.
Msolla, P. M., Wiseman, A., and Selman, I. E. (1981). The prevalence of serum neutralizing antibodies to infectious bovine rhinotracheitis virus in Scotland. Journal of Hygiene, Cambridge, Ss, 209-215. Pirie, H. M., and Allan, E. M. (1975). Mycoplasmas and cuffing pneumonia in a group of calves. Veterinary Record, 97, 345-349. Rouse, B. T., and Babiuk, L. A. (1978). Mechanisms of recovery from herpesvirus infections-a review. Canadian Journal of Comparative Medicine, 42,414-427. Webster, R. G., and Manktelow, B. W. (1959). Some observations on infectious bovine rhinotracheitis in New Zealand. New Zealand Veterinary Journal, 7, 143-148. Wiseman, A., Msolla, P. M., Selman, I. E., Allan, E. M., Cornwell, H. J. C., Pirie, H. M., and Imray, W. S. (1978). A n acute severe outbreak of infectious bovine rhinotracheitis: clinical, epidemiological, microbiological and pathological aspects. Veterinary Record, 103, 391-397. Wiseman, A., Msolla, P. M., Selman, I. E., Allan, E. M., and Pirie, H. M. (1980). Clinical and epidemiological features of 15 incidents of severe infectious bovine rhinotracheitis. Veterinary Record, 107, 436-441. [Received for publication,
February 18th, 19821
PATH.
1983.
20.5
93.
VOL.
EXPERIMENTAL DIFFERENT RHINOTRACHEITIS
AGES
INFECTION OF CATTLE OF WITH INFECTIOUS BOVINE VIRUS (STRICHEN STRAIN) BY
P. M.
MSOLLA, of Glasgow
Lniwrsi,.ify
A. WISEMAN, Veterinary
E. M. ALLAN
School, Bearsden Road, Bearsden,
and I. E. Glnsgou~ GGI
SELMAN
IQH,
1.K.
INTRODUCTION
During the last few years, the nature of infectious bovine rhinotracheitis (IBR) in Britain has changed from a mild, economically unimportant, sporadic disease to a severe disorder prevalent in most areas of the country (Allan, Pirie, Msolla, Selman and Wiseman, 1980; Wiseman, Msolla, Selman, Allan and Pirie, 1980). The incidence of disease has been highest in fattening, beef cattle although the disorder has been confirmed in adult cattle and also young calves. In view of the dramatic change in the nature of IBR, the pathogenicity of a recent virus isolate was studied in different ages of cattle to determine the relationship between age and susceptibility to infection. MATERIALS
AND
METHODS
Experimental Animals Four groups of cattle were infected: they were 4 P-week-old (Group A) and 6 5-week-old Ayrshire bull calves (Group B), 4 6-month-old (Group C) and 3 18-monthold Friesian bullocks (Group D). Two animals of the same age were used as controls for each of the groups and they were housed separately from the infected animals. All the cattle had been purchased from a local dealer when about l-week-old, and had been reared at the Veterinary School.
Method of Infection One millilitre “Strichen” strain Imray, 1978) at lated into each culture into each
of a tissue culture suspension (titre=lO’.’ TCID,, per ml) of the of IBR virus (Wiseman, Msolla, Selman, Allan, Cornwell, Pirie and the third passage in secondary calf kidney cell cultures, was inocunostril. The control animals were given 1 ml of uninfected tissue nostril.
Clinical Examination The animals were examined twice daily after infection (p.i.) and then once daily.
for 7 days before infection
and for 14 days
Serology Serum from every animal was examined for neutralizing (SN) antibodies to IBR virus 1 week before infection and every day from day 6 to day 15 p.i. by the technique described previously (Msolla, Wiseman and Selman, 198 1) . OOZl-9975/83/020205+06
$03.00/O
@ 1983
Academic
Press
Inc.
(London)
Limitrd
206
P.
M.
MSOLLAet
al.
Microbiology Nasal and ocular swabs were taken on 2 occasions during the week before infection and from day 4 to day 15 p.i. At necropsy, samples of tissue for virus isolation were collected from the nasal conchae, nasopharynx, trachea, lung parenchyma and small bronchi. Virus isolation was carried out in tube-cultures of secondary calf kidney and calf testes cells as described previously (Wiseman et al., 1978). Samples were considered to be negative if a cytopathic effect had not developed by the fifth day of the third passage. Samples of lung were also examined for the presence of bacteria and mycoplasms by methods described previously (Pirie and Allan, 1975).
Pathotogy Animals in Groups A, B and C were killed humanely and exsanguinated at the following times p.i. : day 4-A3, B5, B6; day 5-Bl, B3; day 6-Cl, C4; day 33B2, B4. The control calves were also killed 4 to 6 days after Groups A, B and C had been infected. The samples of tissue for light microscopy taken from the respiratory
tract and other organs were processedby methods described previously (Wiseman et al., 1978). RESULTS
Clinical Findings The first signs of illness were slight dullness and a serous o&o-nasal discharge which were observed on day 1 p.i. in Groups A and B, on day 2 in Group C and on day 3 in Group D. Pyrexia ( ,39*4X) and conjunctivitis had developed by the next day when the animals were duller and had a reduced appetite. At the same time they began to drool saliva, there was a sudden increase in the frequency of coughing and small, raised, white plaques were seen on the nasal mucous membranes. By day 3 (Group A) and day 4 (Groups B, C, D) p.i., every animal had developed the characteristic signs of severe IBR: dullness, anorexia, pyrexia (up to 41*4”C), profuse seromucoid ocular and nasal discharge, conjunctivitis, diphtheritic plaques on nasal mucosa, drooling saliva, hyperpnoea, tachypnoea (respiration rate=30 to 50 per min) and regular coughing. Petechial haemorrhages were observed on the nasal mucosa of 4 bullocks (Cl, C3, C4, DZ). Small, white granular lesions developed on the conjunctivae of 2 individuals (B3, C2) but marked conjunctival oedema was not seen. Eight animals from Group A (‘2 calves), Group B (4 calves) and Group C (2 bullocks) died ( 1 animal) or were killed (7 animals) from day 3 to day 6 p.i. The 2 remaining calves in Group A began to drink again on day 5 p.i. but they remained dull and subsequently developed a purulent ocular and nasal discharge. Their clinical condition had not improved noticeably by day 9 and, because they were still pyrexic (39.7 ; 40*8”C), they were given 500 mg oxytetracycline (Terramycin : Pfizer, England) intravenously for 3 days. This produced a rapid clinical response and within 1 week they had fully recovered. The surviving calves in Groups B and C were still slightly dull on day 6 p.i. but they had begun to eat again and were not pyrexic. By 12 to 14 days p.i., the only abnormal signs were mild conjunctivitis, dried ocular discharge, OCcasional coughing and congested nasal mucous membranes with healing plaques. The 2 remaining calves in Group B, were killed 33 days p.i. because they had developed chronic pneumonia.
AGE
AND
IBR
207
INEECTION
The animals in Group D began to eat again on day 5 and their demeanour, appetite and rectal temperatures were all normal the following day, although they were still drooling saliva slightly. On day 10 p.i., the only abnormal findings were reddening of the nasal mucosa and a slight serous oculo-nasal discharge. The control animals did not develop any clinical signs suggestive of IBR virus infection. SerologicaE Findings Serum neutralizing antibodies were detected initially in the animals in Group D, 2 on day 7 p.i. and 1 on day 10 p.i.; the remaining 6 animals in Groups A, B and C were first found to be positive on day 12 p.i. Antibodies were not detected in any of the control animals. Pathological Findings The macroscopic and microscopic appearance of the respiratory tracts of the 8 calves examined from 3 to 6 days p.i. were similar and, although they varied in degree, the Iesions in the younger calves were more severe and more widespread than those in the older animals. The major details of the pathological findings have been summarized and are presented in Table 1. One of the 2-weekold calves (Al) died 3 days p.i., having had diarrhoea for 6 days but, nevertheless, typical lesions of severe IBR were present in the respiratory tract. TABLE THE
MAJOR
Site Nasal
conchae
Lungs nodes
1
CHANGES 3-6 DAYS AFTER INFECTION OF STRAIN OF INFECTIOUS BOVINE RHINOTRAcHEITlS
Macroscopic
Larynxpharynxtrachea
Lymph
PATHOLOGICAL
CATTLE VlRUS
WITH
THE
“STRICHEN"
Microscopic
Congestion, oedema, rhinitis. Neutrophilic Congestion, oedema, yellow-white muco-pus. infiltration of epithelium Many, small, diphtheritic lesions. Several granular areas Congestion, oedema, epithelial hyperplasia and Congestion, oedema, extensive necrosis. Subepithelial lymphocytic petechial haemorrhages. Few, small, diphtheritic aggregates. Submucosal glands dilated and surrounded by plasma cells and lymphocytes lesions Exudative pneumonia. Cuffing-type lesions. Consolidation of anterior lobes Bronchitis Retropharyngeal-enlarged, haemorrhagic, oedematous, Bronchial and mediastinal-normal
Macroscopically, there was congestion and oedema with an inflammatory exudate present in the upper respiratory tract and also in the major bronchi of calf A3. Microscopically, the main changes were rhinitis, a severe pharyngitis with many large subepithelial lymphocytic aggregates, epithelial hyperplasia with necrosis and the accumulation of cellular debris and mucus in the lumen. The submucosal glands appeared active and were surrounded by plasma cells
208
I’.
M.
MSOLLA
f?t al.
and lymphocytes which occasionally obliterated the tubule or duct. In the 2 animals (B2, B4) examined 33 days p.i., the nasal conchae were congested and there was a moderately severe pharyngitis, laryngitis and tracheitis, with small petechial haemorrhages in the nasopharynx and a severe exudative pneumonia with marked bronchitis. None of the control calves had lesions in the nasal conchae, nasopharynx and trachea, although all had several foci of cuffing pneumonia. Viral inclusion bodies were not identified in any of the sections examined. Microbiological
Findings
Infectious bovine rhinotracheitis virus was not isolated from any of the calves before infection nor from any of the control animals afterwards. However, in every infected individual, virus was recovered daily from nasal swabs until either 12 or 13 days p.i. and from ocular swabs until from 6 to 10 days p.i. (mean =8*6 days). The virus was recovered from every site in the respiratory tract in calf A3 and in every site, apart from the lungs, in the 6 other animals killed 4 to 6 days pi. In addition, virus was recovered on one occasion from the brain (Cl) and the kidney (C4). Although virus was not recovered from either of the calves (B2, B4) killed after 33 days, Corynebacterium pyogenes and Mycophsma disfar were isolated from the lungs of calves B2 and B4, respectively. The virus was not isolated from any of the control calves. DISCUSSION
Every animal challenged intra-nasally with the “Strichen” strain of IBR virus developed a disease similar to but less severe than that observed in the field (Allan et al., 1980; Wiseman et al., 1980). The clinical signs developed earlier and were more severe and more persistent in the young calves than in the 6 and 18 month old bullocks. Both surviving 2-week-old calves developed a purulent nasal discharge and their clinical condition had not improved by day 9 p.i. when antibiotic therapy was instituted. Within a week, they appeared to have made a complete clinical recovery. On the other hand, the 4 5-week-old calves, which were affected to a similar degree, were not treated and two developed a severe chronic pneumonia. It is significant that the latter 2 animals were the only ones from which recognized pulmonary pathogens (C. pyogenes, M. dispar) were isolated at necropsy, although focal lesions of exudative pneumonia were present in every calf. The fact that recognized pulmonary pathogens were not present in significant numbers probably contributed to the relative mildness of the experimental disease compared with that in the field in which secondary infection appears to play a major role in determining the severity of the disorder. On the other hand, pneumonic lesions almost certainly had been present before challenge with the virus since “cuffing-type” lesions were identified in the control calves and in a proportion of the infected animals. There was no detectable difference in the frequency or duration of IBR virus
AGE
AND
I-BA
‘EN.FECTION
209
isolation between the different age groups. Virus was present for a longer period in the nasal epithelium than on the conjunctivae and this would explain the greater efficiency of virus isolation from nasal compared to ocular swabs in field incidents (Wiseman et al., 1980). Although IBR virus was isolated from the nasal conchae, nasopharynx and trachea of every calf killed 4 to 6 days p.i., it was recovered only once from the lungs and that was from the youngest animal examined. Despite the isolation of virus from the brain and kidney, each on one occasion, lesions were not present in either organ. Every animal exposed to the virus had developed SN antibodies within 12 days. In previous investigations, in contrast, SN antibodies were not detected in all experimentally infected animals (Abinanti and Plumer, 1961; Hughes, Olander and Wada, 1964). The most likely explanation is that the technique used in this study was more sensitive than that used by these earlier workers. The clinical, pathological and virological findings in this study are in broad agreement with the results of others who have studied experimentally produced IBR in New Zealand (Webster and Manktelow, 1959), North America (Abinanti and Plumer, 1961; Hughes et nl., 1964) and England (Markson and Darbyshire, 1966). Webster and Manktelow (1959) reported that there was a difference in age susceptibility to IBR virus infection but they used multiple routes of virus inoculation. In our investigation, young calves developed a more severe disease than older animals when challenged via the intranasal route alone. This variation in susceptibility to IBR virus infection may have been due to an age-related difference in cell mediated immune capacity, which, it has been suggested, is mainly responsible for recovery from bovine herpesvirus 1 infection (Rouse and Babiuk, 1978). SUMMARY
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. ACKNOWLEDGMENTS
The authors wish to thank ProfessorsW. I. M. McIntyre and W. F. H. Jarrett for their advice and encouragement, and Mrs B. Gillies for typing the manuscript. This work was partially financed by a grant from the Agricultural Research Council. REFERENCES
Abinanti, F. R., and Plumer, G. J. (1961). The isolation of infectious bovine rhinotracheitis virus from cattle affected with conjunctivitis-observations on the experimental infection, American Journal of Veterinary Research, 22, 13-I 7. Allan, E. M., Pirie, H. M., Msolla, P. M., Selman, I. E., and Wiseman, A. ( 1980).
210
P.
The pathological
M.
MSOLLAetd
features of severe cases of infectious
bovine rhinotracheitis.
Veterinary Record, 107, 441-445.
Hughes, J. P., Olander, H. J., and Wada, E. M. (1964). Keratoconjunctivitis associated with infectious bovine rhinotracheitis. Journal of the American Veterinary Medical Association, 145, 32-39. Markson, L. M., and Darbyshire, J. H. (1966). The reaction of calves to experimental infection with the Oxford strain of infectious bovine rhinotracheitis virus. British
Veterinary Journal,
122, 522-529.
Msolla, P. M., Wiseman, A., and Selman, I. E. (1981). The prevalence of serum neutralizing antibodies to infectious bovine rhinotracheitis virus in Scotland. Journal of Hygiene, Cambridge, Ss, 209-215. Pirie, H. M., and Allan, E. M. (1975). Mycoplasmas and cuffing pneumonia in a group of calves. Veterinary Record, 97, 345-349. Rouse, B. T., and Babiuk, L. A. (1978). Mechanisms of recovery from herpesvirus infections-a review. Canadian Journal of Comparative Medicine, 42,414-427. Webster, R. G., and Manktelow, B. W. (1959). Some observations on infectious bovine rhinotracheitis in New Zealand. New Zealand Veterinary Journal, 7, 143-148. Wiseman, A., Msolla, P. M., Selman, I. E., Allan, E. M., Cornwell, H. J. C., Pirie, H. M., and Imray, W. S. (1978). A n acute severe outbreak of infectious bovine rhinotracheitis: clinical, epidemiological, microbiological and pathological aspects. Veterinary Record, 103, 391-397. Wiseman, A., Msolla, P. M., Selman, I. E., Allan, E. M., and Pirie, H. M. (1980). Clinical and epidemiological features of 15 incidents of severe infectious bovine rhinotracheitis. Veterinary Record, 107, 436-441. [Received for publication,
February 18th, 19821