29
Ldboralory Animals (978) 12, 29-32
A serological survey of accredited breeding colonies in the United Kingdom for common rodent viruses P. CARTHEW & A. VERSTRAETE Medical
Research
Council Laboratory
Animals
Centre,
Summary This paper reports the results of a general survey, the first in the United Kingdom, carried out on accredited breeding col'o'niesof mice, rats and guinea-pigs over a period of a year. While the results show the potential usefulness of a viral accreditation grading scheme, they also show that contamination of breeding colonies with inapparent viral infections is widespread. This situation can only be improved by the continuous monitoring of animal stocks for rodent viruses, with the aim of improving the standard of animals available for research and for pharmacological, toxicological and routine diagnostic procedures. Since 1950 the Laboratory Animals Centre at Carshalton has operated an accreditation scheme (LAC, 1974), the purpose of the grading being to provide laboratory animals with a defined microbiological flora, which are safe for breeders to supply to schools (Category *) and also of a high enough standard to reduce complications in research use. The viruses proscribed at present are ectromelia for mice, myxomatosis for rabbits, and lymphocytic choriomeningitis (LCM) for all rodent species as it is an important human pathogen. The success of
the scheme in the case of these viruses is best demon-
strated by the fact that these diseases are now unknown in accredited breeding colonies in the UK. In the USA (Parker, Tennant, Ward & Rowe, ]965) and on the continent of Europe (Jakoik & Skoda, 1972), studies have been made to establish in greater detail the viral status of colonies of laboratory animals, and the necessity for these investigations is easily understood against the background of problems when considering the difficulties caused by epizootics of viruses such as Sendai and mouse hepatitis virus (Sebesteny & Hill, ]974), both of which can be lethal to mice. In the present paper we report the results of a general serological survey carried out over the year 1975-6 of accredited breeding colonies in the UK of mice, rats, and guinea-pigs, for antibody titres to the common rodent viruses. As well as recording the incidence of virus antibody titres in the colonies examined, an attempt has been made (with some success) to correlate the presence or absence of infection to the category of grading under the accreditation grading scheme (LAC, ]974).
Woodmansterne
Road, Carshalton,
Surrey,
SM5 4EF
Some difficulties which may be encountered by cross infection with viruses such as Sendai and Reovirus 3 (Reo 3) are pointed out, as well as the possibility of 'reservoirs' of inapparently-infected species in some colonies being responsible for outbreaks of disease in susceptible species kept in the same animal house. Materials and methods Animals
Mice, rats and guinea-pigs were supplied by breeders as necessitated under the Rules of Accreditation (LAC, ]974). Guinea-pig and rat sera were taken individually by bleeding animals from the heart. Mice sera were collected by bleeding from the heart, and were kept either individually or pooled. Some colonies were examined twice in the year, each examination being treated as a separate result. No significant serological changes in an individual colony were detected in this way. Blood cells
Red blood cells were collected in Alsevers solution on the day of use and washed 3 times in haemag-
glutination buffer prior to use. Vaccinia positive
fowl cells, and Sykes tinted fowl cells (for Sendai, HAl), were obtained from Salisbury Laboratories, ]7 Stratford Road, Salisbury, Wiltshire. Antigens
The antigens used in serological testing were either prepared in our laboratory or purchased from Microbiological Associates (Dynatch Laboratories Ltd, Daux Road, Billingshurst, Sussex). Laboratory Animals Centre prepared antigens Vaccinia virus. The vaccinia virus used for the
haemagglutination inhibition test (HAl) for ectromelia was prepared from a seed stock provided by the Central Public Health Laboratory at Colindale. Virus was propagated on the chorioallantoic membranes (CAMs) of 10 day old fertile SPF hens' eggs supplied by Wickham Laboratories, Winchester Road, Wickham, Hants. After 72 h at 37°C the CAMs were removed, ground up and centrifuged at 2000g. The resulting supernatant was used as a vaccinia virus haemagglutination (HA titre 256).
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
Carthew
30
Sendai virus. A seed stock of Sendai virus was obtained from the Central Public Health Laboratory at Colindale and propagated in the allantoic cavity of to day old fertile SPF hens' eggs described above. After 48 h at 37°C the allantoic fluid was removed, centrifuged and used as a source of Sendai virus haemagglutination (HA titre 2000 with Sykes tinted fowl cells). Reovirus 3 (Reo 3). A seed stock of Reovirus 3 was obtained from Dr E. J. Bell of Ruchill Hospital, Glasgow and grown in BHK 2\ cells. After 6 days when the cell sheets showed 100% cytopathic effect the tissue culture fluid was harvested and assayed for haemagglutination using a type-tested human 0 red blood cell. The resulting fluid showed a haemagglutinating titre of 32 units. Pneumonia virus of mice (PVM). Pneumonia virus of mice was obtained from the American Type Culture Collection, Rockville, Maryland, and propagated in BHK 2\ cells. After \4 days the tissue culture fluid was harvested and assayed for haemagglutination using mouse red blood cells. The haemagglutination titre of this material was 256 units. Purchased antigens Other common rodent virus antigens were purchased from Microbiological Associates (Dynatch Laboratories Ltd) and comprised Theiler's mouse encephalitis (GDYII), newborn mouse pneumonitis (K vir.us), minute virus of mice (MYM), polyoma virus, Kilham rat virus (KR V), Toolan virus (H I), mouse adenovirus (MA) and mouse hepatitis virus (M HY-polyvalent antigen). Lymphocytic choriomeningitis virus was provided by the Central Public Health Laboratory, Colindale.
Serological testing The details of the serological tests using both haemagglutination-inhibition and complementfixation tests were taken from Parket et al. (1965) and by more detailed personal communication from J. C. Parker of Microbiological Associates, Bethesda. For the haemagglutination test for Sendai virus, sera were diluted I in 5 and incubated with an equal volume of 6 % fowl red blood cells (Sykes tinted fowl cells) overnight at 4°C to adsorb nonspecific agglutinins; the samples were then spun at 1000g for 5 min and the supernatant used directly in the test using 4 units of Sendai virus haemagglutinin (Needham, 1976). For the haemagglutination test for ectromelia virus, sera were heat-inactivated at 56°C for 30 min, double diluted, and incubated at room temperature for 1 h with 4 units of vaccinia virus haemagglutinin, prior to the addition of ,1% vaccinia positive fowl cells: results were read by.' the 'teardrop' method (Rohde & Karesek, 1970). LCM tests were also carried out by the foot-pad
& Verstraete
injection method of Skinner & Knight (1971) for the detection of persistent tolerantly infected animals.
Treatment of sera and standard reference-positive sera All sera used in the HAl test were heat inactivated at 56°C for 30 min prior to use (except for the Sendai test-see above). Vaccinia virus antisera was obtained from the Central Public Health Laboratory, Colindale. All other reference-positive sera for individual viruses were obtained from Microbiological Associates (Dynatch Laboratorits Ltd). For the complement-fixation tests, sera were routinely treated with 25 % vol/vol guinea-pig complement at 37°C for I h and then heat-inactivated at 56°C for 30 min, to remove anticomplementary activity.
Significance of serological tUres (Parker et aI, 1966) For HAl, test titres of » I in 10 for K virus and PVM were considered positive, while» 1 in 20 for GDYlI, Reo 3, KRY, HI and MYM (after RDE treatment) were considered positive. Polyoma titres of» I in 40 were considered positive. For CF tests titres » 1 in 5 were taken as positive.
Results The examination of accredited breeders' sera for common rodent virus antibody titres showed quite clearly that there was no evidence of virus infection with LCM in any species, nor of ectromelia in mice (Table I). It was also pleasing to note that mouse adenovirus (MA) and polyoma were not found in mouse colonies, while minute virus of mice (MYM) and Reo 3 were absent in rat colonies. However for all other viruses examined, serological evidence of previ'ous infection was found. This is summarised jn Table I. Table l. Serological incidence of common rodent virus infections in the 3 major laboratory species, on the basis of percentage positive sera and percentage examined colonies found to be positive (in parentheses)
Virus
Rodentspecies mouse rat
Ectromelia 0 PYM 30(50) GOVIl 33(58) Reo 3 26(44) K 10(25) KRY NNI HI NNI MYM 31(55) Polyoma 0 MHY 20(32) Sendai 4(2) LCM 0 MA 0 NNI Not a recorded natural NO Not determined.
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
guinea-pig
NNI NNI 48(60) 32(50) NO NO 0 53(77) NNI NNI 53(76) NNI 16(30) 48(85) 0 NNI NNI NNI NNI NNI 20(25) 7(16) 0 0 NNI NNI infection of this species.
UK rodent
31
virus survey
Table 2. Relationship of the incidence of virus antibody to the grading of mice Category Virus % positive positive sera colonies colonies examined 25 PVM 2/3 16 MHV 1/3 MVM 29 2/2 GD VII 62 2/2 •• 8 K 1/6 Reo 3 43 4/7 25 PVM 3/7 25 MHV 2/8 MVM 50 6/7 GD VII 50 1/3 25 K 3/6 Reo 3 28 3/7 19 PVM 3{7 MHV 36 4/7 14 MVM 1/4 14 GD VII 1{3 •••• 16 Reo 3 1/2 66 PVM 2/3 15 1{5 MVM 4 Sendai 1/5 33 GD VII 3/4
•
.;.
The incidence of serologically positive titres and infected colonies is shown in Table I for mice, rats and guinea-pigs. Tables 2, 3 and 4 show the correlation of % positive sera and incidence of positive colonies for the different grades of mice, rats and guinea-pigs examined under the accreditation scheme.
Table 3. Relationship of the incidence of virus antibody to the grading of rats Category Virus % positive positive sera colonies colonies examined
••
••• ••••
KRV
Sendai PVM HI KRV Sendai PVM HI KRV HI
50
25 90 50
44 20 48 5 9 20
5/5
3/7
2/2 1{2 9/12 8{16 6{9
2{9 2{4
1/2
Discussion The absence of serological evidence of LCM and ectromelia is understandable, as both these viruses have been included in the accreditation scheme and screened for on a routine basis for a number of years. In mouse colonies, the overall picture is fairly grim; 6 commonly occurring viral infections are
Table 4. Relationship of the incidence of virus antibody to the grading of guinea-pigs Category Virus % positive positive sera colonies colonies examined •• 60 HI 5/5 Reo 3 50 4/5 PVM 80 4/4 Sendai 6 2/10 ••• HI 66 6/6 Reo 3 66 5/6 PVM 15 1/5 Sendai 4 2/11 12 •••• Reo 3 1/2
revealed. However, Sendai is not really as widespread as is commonly supposed, and only I colony was found to have been infected; unfortunately that was a Category···· colony. Apart from the absence of MHV and K virus in Category· •• • colonies, the general incidence of other murine viruses is roughly the same as in ., •• and ••• colonies. However, most breeders would consider the exclusion of MHV alone in a Category·"· colony a worthwhile achievement. In rats, the viral disease picture is more encouraging. Although KR V is present in all categories of rat colonies, Category···· colonies were found to be free of Sendai and PVM. This is especially encouraging when it is noted that the incidence of Sendai and PVM is high in lower-grade colonies. Thus, it would seem that in rat colonies barrier mainenance is particularly successful in keeping virus infections out and raising the standards of breeding animals. In guinea-pigs, a similar situation is found. Although the incidence of Reo 3 titres is uniformly high in all colonies, the absence of Sendai, HI and PVM from Category •• ** animals is very
encouraging, as is the absence of Sendai from most other Categories. An interesting point which arises from this serological survey is the absence of certain diseases in specie~ susceptible to the infection. For example Sendai, whilst occurring in only a single mouse colony, is certainly widespread in rat and, to a lesser extent, guinea-pig colonies. The presence of 'carrier states' for diseases is well known, and the housing together of different species may be the basis of a viral 'reservoir' which can lead to sudden enzootics of disease in a previously healthy species. This danger should obviously be borne in mind in designing an animal house, as well as in animal houses where the danger from reservoir species is apparent through serological evidence gained from routine screening for rodent viruses. While barrier maintenance is undoubtedly of use in reducing the
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
Carthew & Verstraete
32
incidence of viral infection in laboratory rodents, only regular serological screening will succeed in revealing the true disease status of any animal colony. This is exemplified by LCM and ectromelia. The importance of defining the disease status of laboratory animals can be best understood when it is considered that the persistent tolerant infection of mice with Reo 3 can lead to the contamination of transplantable tumours (Collins & Parker, 1972), with consequent damage to the scientific results obtained from such animals (see ASEP, 1971) and from the point of view of an overt disease outbreak of Reo 3 in a mouse colony. Where a particular virus has been identified in a breeding colony there is at present no really effective method of eradicating the infection by using
drug treatment. Until this becomes possible caesarian rederivation, which is widely used to eliminate viral infections, will have to continue with its attendant high cost and disruption of breeding and research programmes. Acknowledgements
The authors would like to thank Dr J. Parker of Microbiological Associates, Bethesda; USA for his kind advice and for furnishing the detailed methods used in the HAl tests which were developed in his laboratory, and Mr J. Needham of the Clinical Research Centre, Harrow for furnishing the details of the .serological test for Sendai virus, developed in his laboratory.
References
ASEP (1971). Symposium
on diseases of laboratory animals complicating biomedical research. American Journal of Pathology 64, 624-769.
Collins, M. 1. & Parker, 1. C. (1972). Murine virus contaminants of leukemia viruses and transplantable tumours. Journal of the National Cancer Institute 49, 1139-1]43. Jakoik, J. & Skoda, R. (1972).Studies on the occurrence of latent virus infections in some European conventional, SPF and germfree mouse colonies. Zeitschrift fUr Versuchstierkunde 14, 281-289. LAC·(l974). The Accreditation and Recognition Schemes
for suppliers of laboratory animals. Laboratory Animals Centre Manual Series I, 2nd ed. Needham, J. R. (]976). Control of animal health in a modern experimental unit: laboratory and microbiological investigations. Thesis for Fellowship of the
Institute of Medical Laboratory Sciences, pp. 48-58.
Parker, J. C, Tennant, R. W., Ward, T. G. & Rowe, W. P. (1965). Virus studies with germfree mice. 1. Preparation of serological diagnostic reagents and survey of germfree and monocontaminated mice for indigenous murine viruses.Journal of the National Cancer Institute 34,37] -380. Rohde, W. & Karesek, E. (1970). Zur Seriodiagnostick der Ectromelie 'bie Versuchsmliusen. Archiv fUr Experimentelle Veteriniirmedizin B 24, 655-660. Sebesteny, A. & Hill, A. C. (1974). Hepatitis and brain lesions due to mouse hepatitis virus accompanied by wasting in nude mice. Laboratory Animals 8, 317-326. Skinner, H. H. & Knight, E. H. (1971). Monitoring mouse stocks for lymphocytic choriomeningitis virus -a human pathogen. Laboratory Animals 5, 73-87.
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
Ldboralory Animals (978) 12, 29-32
A serological survey of accredited breeding colonies in the United Kingdom for common rodent viruses P. CARTHEW & A. VERSTRAETE Medical
Research
Council Laboratory
Animals
Centre,
Summary This paper reports the results of a general survey, the first in the United Kingdom, carried out on accredited breeding col'o'niesof mice, rats and guinea-pigs over a period of a year. While the results show the potential usefulness of a viral accreditation grading scheme, they also show that contamination of breeding colonies with inapparent viral infections is widespread. This situation can only be improved by the continuous monitoring of animal stocks for rodent viruses, with the aim of improving the standard of animals available for research and for pharmacological, toxicological and routine diagnostic procedures. Since 1950 the Laboratory Animals Centre at Carshalton has operated an accreditation scheme (LAC, 1974), the purpose of the grading being to provide laboratory animals with a defined microbiological flora, which are safe for breeders to supply to schools (Category *) and also of a high enough standard to reduce complications in research use. The viruses proscribed at present are ectromelia for mice, myxomatosis for rabbits, and lymphocytic choriomeningitis (LCM) for all rodent species as it is an important human pathogen. The success of
the scheme in the case of these viruses is best demon-
strated by the fact that these diseases are now unknown in accredited breeding colonies in the UK. In the USA (Parker, Tennant, Ward & Rowe, ]965) and on the continent of Europe (Jakoik & Skoda, 1972), studies have been made to establish in greater detail the viral status of colonies of laboratory animals, and the necessity for these investigations is easily understood against the background of problems when considering the difficulties caused by epizootics of viruses such as Sendai and mouse hepatitis virus (Sebesteny & Hill, ]974), both of which can be lethal to mice. In the present paper we report the results of a general serological survey carried out over the year 1975-6 of accredited breeding colonies in the UK of mice, rats, and guinea-pigs, for antibody titres to the common rodent viruses. As well as recording the incidence of virus antibody titres in the colonies examined, an attempt has been made (with some success) to correlate the presence or absence of infection to the category of grading under the accreditation grading scheme (LAC, ]974).
Woodmansterne
Road, Carshalton,
Surrey,
SM5 4EF
Some difficulties which may be encountered by cross infection with viruses such as Sendai and Reovirus 3 (Reo 3) are pointed out, as well as the possibility of 'reservoirs' of inapparently-infected species in some colonies being responsible for outbreaks of disease in susceptible species kept in the same animal house. Materials and methods Animals
Mice, rats and guinea-pigs were supplied by breeders as necessitated under the Rules of Accreditation (LAC, ]974). Guinea-pig and rat sera were taken individually by bleeding animals from the heart. Mice sera were collected by bleeding from the heart, and were kept either individually or pooled. Some colonies were examined twice in the year, each examination being treated as a separate result. No significant serological changes in an individual colony were detected in this way. Blood cells
Red blood cells were collected in Alsevers solution on the day of use and washed 3 times in haemag-
glutination buffer prior to use. Vaccinia positive
fowl cells, and Sykes tinted fowl cells (for Sendai, HAl), were obtained from Salisbury Laboratories, ]7 Stratford Road, Salisbury, Wiltshire. Antigens
The antigens used in serological testing were either prepared in our laboratory or purchased from Microbiological Associates (Dynatch Laboratories Ltd, Daux Road, Billingshurst, Sussex). Laboratory Animals Centre prepared antigens Vaccinia virus. The vaccinia virus used for the
haemagglutination inhibition test (HAl) for ectromelia was prepared from a seed stock provided by the Central Public Health Laboratory at Colindale. Virus was propagated on the chorioallantoic membranes (CAMs) of 10 day old fertile SPF hens' eggs supplied by Wickham Laboratories, Winchester Road, Wickham, Hants. After 72 h at 37°C the CAMs were removed, ground up and centrifuged at 2000g. The resulting supernatant was used as a vaccinia virus haemagglutination (HA titre 256).
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
Carthew
30
Sendai virus. A seed stock of Sendai virus was obtained from the Central Public Health Laboratory at Colindale and propagated in the allantoic cavity of to day old fertile SPF hens' eggs described above. After 48 h at 37°C the allantoic fluid was removed, centrifuged and used as a source of Sendai virus haemagglutination (HA titre 2000 with Sykes tinted fowl cells). Reovirus 3 (Reo 3). A seed stock of Reovirus 3 was obtained from Dr E. J. Bell of Ruchill Hospital, Glasgow and grown in BHK 2\ cells. After 6 days when the cell sheets showed 100% cytopathic effect the tissue culture fluid was harvested and assayed for haemagglutination using a type-tested human 0 red blood cell. The resulting fluid showed a haemagglutinating titre of 32 units. Pneumonia virus of mice (PVM). Pneumonia virus of mice was obtained from the American Type Culture Collection, Rockville, Maryland, and propagated in BHK 2\ cells. After \4 days the tissue culture fluid was harvested and assayed for haemagglutination using mouse red blood cells. The haemagglutination titre of this material was 256 units. Purchased antigens Other common rodent virus antigens were purchased from Microbiological Associates (Dynatch Laboratories Ltd) and comprised Theiler's mouse encephalitis (GDYII), newborn mouse pneumonitis (K vir.us), minute virus of mice (MYM), polyoma virus, Kilham rat virus (KR V), Toolan virus (H I), mouse adenovirus (MA) and mouse hepatitis virus (M HY-polyvalent antigen). Lymphocytic choriomeningitis virus was provided by the Central Public Health Laboratory, Colindale.
Serological testing The details of the serological tests using both haemagglutination-inhibition and complementfixation tests were taken from Parket et al. (1965) and by more detailed personal communication from J. C. Parker of Microbiological Associates, Bethesda. For the haemagglutination test for Sendai virus, sera were diluted I in 5 and incubated with an equal volume of 6 % fowl red blood cells (Sykes tinted fowl cells) overnight at 4°C to adsorb nonspecific agglutinins; the samples were then spun at 1000g for 5 min and the supernatant used directly in the test using 4 units of Sendai virus haemagglutinin (Needham, 1976). For the haemagglutination test for ectromelia virus, sera were heat-inactivated at 56°C for 30 min, double diluted, and incubated at room temperature for 1 h with 4 units of vaccinia virus haemagglutinin, prior to the addition of ,1% vaccinia positive fowl cells: results were read by.' the 'teardrop' method (Rohde & Karesek, 1970). LCM tests were also carried out by the foot-pad
& Verstraete
injection method of Skinner & Knight (1971) for the detection of persistent tolerantly infected animals.
Treatment of sera and standard reference-positive sera All sera used in the HAl test were heat inactivated at 56°C for 30 min prior to use (except for the Sendai test-see above). Vaccinia virus antisera was obtained from the Central Public Health Laboratory, Colindale. All other reference-positive sera for individual viruses were obtained from Microbiological Associates (Dynatch Laboratorits Ltd). For the complement-fixation tests, sera were routinely treated with 25 % vol/vol guinea-pig complement at 37°C for I h and then heat-inactivated at 56°C for 30 min, to remove anticomplementary activity.
Significance of serological tUres (Parker et aI, 1966) For HAl, test titres of » I in 10 for K virus and PVM were considered positive, while» 1 in 20 for GDYlI, Reo 3, KRY, HI and MYM (after RDE treatment) were considered positive. Polyoma titres of» I in 40 were considered positive. For CF tests titres » 1 in 5 were taken as positive.
Results The examination of accredited breeders' sera for common rodent virus antibody titres showed quite clearly that there was no evidence of virus infection with LCM in any species, nor of ectromelia in mice (Table I). It was also pleasing to note that mouse adenovirus (MA) and polyoma were not found in mouse colonies, while minute virus of mice (MYM) and Reo 3 were absent in rat colonies. However for all other viruses examined, serological evidence of previ'ous infection was found. This is summarised jn Table I. Table l. Serological incidence of common rodent virus infections in the 3 major laboratory species, on the basis of percentage positive sera and percentage examined colonies found to be positive (in parentheses)
Virus
Rodentspecies mouse rat
Ectromelia 0 PYM 30(50) GOVIl 33(58) Reo 3 26(44) K 10(25) KRY NNI HI NNI MYM 31(55) Polyoma 0 MHY 20(32) Sendai 4(2) LCM 0 MA 0 NNI Not a recorded natural NO Not determined.
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
guinea-pig
NNI NNI 48(60) 32(50) NO NO 0 53(77) NNI NNI 53(76) NNI 16(30) 48(85) 0 NNI NNI NNI NNI NNI 20(25) 7(16) 0 0 NNI NNI infection of this species.
UK rodent
31
virus survey
Table 2. Relationship of the incidence of virus antibody to the grading of mice Category Virus % positive positive sera colonies colonies examined 25 PVM 2/3 16 MHV 1/3 MVM 29 2/2 GD VII 62 2/2 •• 8 K 1/6 Reo 3 43 4/7 25 PVM 3/7 25 MHV 2/8 MVM 50 6/7 GD VII 50 1/3 25 K 3/6 Reo 3 28 3/7 19 PVM 3{7 MHV 36 4/7 14 MVM 1/4 14 GD VII 1{3 •••• 16 Reo 3 1/2 66 PVM 2/3 15 1{5 MVM 4 Sendai 1/5 33 GD VII 3/4
•
.;.
The incidence of serologically positive titres and infected colonies is shown in Table I for mice, rats and guinea-pigs. Tables 2, 3 and 4 show the correlation of % positive sera and incidence of positive colonies for the different grades of mice, rats and guinea-pigs examined under the accreditation scheme.
Table 3. Relationship of the incidence of virus antibody to the grading of rats Category Virus % positive positive sera colonies colonies examined
••
••• ••••
KRV
Sendai PVM HI KRV Sendai PVM HI KRV HI
50
25 90 50
44 20 48 5 9 20
5/5
3/7
2/2 1{2 9/12 8{16 6{9
2{9 2{4
1/2
Discussion The absence of serological evidence of LCM and ectromelia is understandable, as both these viruses have been included in the accreditation scheme and screened for on a routine basis for a number of years. In mouse colonies, the overall picture is fairly grim; 6 commonly occurring viral infections are
Table 4. Relationship of the incidence of virus antibody to the grading of guinea-pigs Category Virus % positive positive sera colonies colonies examined •• 60 HI 5/5 Reo 3 50 4/5 PVM 80 4/4 Sendai 6 2/10 ••• HI 66 6/6 Reo 3 66 5/6 PVM 15 1/5 Sendai 4 2/11 12 •••• Reo 3 1/2
revealed. However, Sendai is not really as widespread as is commonly supposed, and only I colony was found to have been infected; unfortunately that was a Category···· colony. Apart from the absence of MHV and K virus in Category· •• • colonies, the general incidence of other murine viruses is roughly the same as in ., •• and ••• colonies. However, most breeders would consider the exclusion of MHV alone in a Category·"· colony a worthwhile achievement. In rats, the viral disease picture is more encouraging. Although KR V is present in all categories of rat colonies, Category···· colonies were found to be free of Sendai and PVM. This is especially encouraging when it is noted that the incidence of Sendai and PVM is high in lower-grade colonies. Thus, it would seem that in rat colonies barrier mainenance is particularly successful in keeping virus infections out and raising the standards of breeding animals. In guinea-pigs, a similar situation is found. Although the incidence of Reo 3 titres is uniformly high in all colonies, the absence of Sendai, HI and PVM from Category •• ** animals is very
encouraging, as is the absence of Sendai from most other Categories. An interesting point which arises from this serological survey is the absence of certain diseases in specie~ susceptible to the infection. For example Sendai, whilst occurring in only a single mouse colony, is certainly widespread in rat and, to a lesser extent, guinea-pig colonies. The presence of 'carrier states' for diseases is well known, and the housing together of different species may be the basis of a viral 'reservoir' which can lead to sudden enzootics of disease in a previously healthy species. This danger should obviously be borne in mind in designing an animal house, as well as in animal houses where the danger from reservoir species is apparent through serological evidence gained from routine screening for rodent viruses. While barrier maintenance is undoubtedly of use in reducing the
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
Carthew & Verstraete
32
incidence of viral infection in laboratory rodents, only regular serological screening will succeed in revealing the true disease status of any animal colony. This is exemplified by LCM and ectromelia. The importance of defining the disease status of laboratory animals can be best understood when it is considered that the persistent tolerant infection of mice with Reo 3 can lead to the contamination of transplantable tumours (Collins & Parker, 1972), with consequent damage to the scientific results obtained from such animals (see ASEP, 1971) and from the point of view of an overt disease outbreak of Reo 3 in a mouse colony. Where a particular virus has been identified in a breeding colony there is at present no really effective method of eradicating the infection by using
drug treatment. Until this becomes possible caesarian rederivation, which is widely used to eliminate viral infections, will have to continue with its attendant high cost and disruption of breeding and research programmes. Acknowledgements
The authors would like to thank Dr J. Parker of Microbiological Associates, Bethesda; USA for his kind advice and for furnishing the detailed methods used in the HAl tests which were developed in his laboratory, and Mr J. Needham of the Clinical Research Centre, Harrow for furnishing the details of the .serological test for Sendai virus, developed in his laboratory.
References
ASEP (1971). Symposium
on diseases of laboratory animals complicating biomedical research. American Journal of Pathology 64, 624-769.
Collins, M. 1. & Parker, 1. C. (1972). Murine virus contaminants of leukemia viruses and transplantable tumours. Journal of the National Cancer Institute 49, 1139-1]43. Jakoik, J. & Skoda, R. (1972).Studies on the occurrence of latent virus infections in some European conventional, SPF and germfree mouse colonies. Zeitschrift fUr Versuchstierkunde 14, 281-289. LAC·(l974). The Accreditation and Recognition Schemes
for suppliers of laboratory animals. Laboratory Animals Centre Manual Series I, 2nd ed. Needham, J. R. (]976). Control of animal health in a modern experimental unit: laboratory and microbiological investigations. Thesis for Fellowship of the
Institute of Medical Laboratory Sciences, pp. 48-58.
Parker, J. C, Tennant, R. W., Ward, T. G. & Rowe, W. P. (1965). Virus studies with germfree mice. 1. Preparation of serological diagnostic reagents and survey of germfree and monocontaminated mice for indigenous murine viruses.Journal of the National Cancer Institute 34,37] -380. Rohde, W. & Karesek, E. (1970). Zur Seriodiagnostick der Ectromelie 'bie Versuchsmliusen. Archiv fUr Experimentelle Veteriniirmedizin B 24, 655-660. Sebesteny, A. & Hill, A. C. (1974). Hepatitis and brain lesions due to mouse hepatitis virus accompanied by wasting in nude mice. Laboratory Animals 8, 317-326. Skinner, H. H. & Knight, E. H. (1971). Monitoring mouse stocks for lymphocytic choriomeningitis virus -a human pathogen. Laboratory Animals 5, 73-87.
Downloaded from lan.sagepub.com at MICHIGAN STATE UNIV on March 6, 2015
