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Prevalence of brucellosis infection in cattle in the Mexican states of Neuvo Leon, Tamaulipas and Coahuila as determined by the ELISA
Preventive Veterinary Medicine, 3 (1985) 445--448
445
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
P R E V A L E N C E O F B R U C E L L O S I S I N F E C T I O N IN C A T T L E I N T H E MEXICAN STATES OF NUEVO LEON, TAMAULIPAS AND COAHUILA AS D E T E R M I N E D B Y T H E E L I S A
R.F. TECLAW', F. HECK',G.G. WAGNER', S. ROMO'and Z. GARCLA3
' D e p a r t m e n t o f Veterinary Microbiology and Parasitology, Texas A & M University, College Station, T X 77843 :U.S.A.) 2 Facultad de Medicina Veterinaria, Universidad A u t o n o m a de Nuevo Leon, Monterrey (Mexico) 3 Centro Nacional de Parasitologia Animal, Jiutepec, Morelos (Mexico)
(Accepted for publication 2 July 1985)
ABSTRACT
Teclaw, R.F., Heck, F., Wagner, G.G., Romo, S. and Garcia, Z., 1985. Prevalence of brucellosis infection in cattle in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila as determined by the ELISA. Prey. Vet. Med., 3: 445--448. Serum samples from 2070 cattle from 40 ranches in northeastern Mexico were tested for antibody activity to Brucella abortus using the enzyme-linked immunosorbent assay (ELISA). The overall prevalence rate in the 40 herds was 2.4% and there was at least one positive animal in 14 herds (35%). The herd prevalence rates ranged from 0 to 13.8% with the average for positive herds of 6.5%. The average proportion positive for the five dairy herds was 7.3%.
INTRODUCTION Brucellosis has b e e n the s u b j e c t o f n u m e r o u s scientific r e p o r t s and a l m o s t e v e r y c o u n t r y has s o m e f o r m o f g o v e r n m e n t - s p o n s o r e d c o n t r o l p r o g r a m . T h e U n i t e d S t a t e s has h a d an active brucellosis e r a d i c a t i o n p r o g r a m since 1 9 3 4 ( N a t i o n a l R e s e a r c h Council, 1977). T e x a s r a n k s high a m o n g t h e states w i t h brucellosis p r o b l e m s , w i t h a p p r o x i m a t e l y 2 1 8 5 h e r d s u n d e r q u a r a n t i n e ( T e x a s A n i m a l H e a l t h C o m m i s s i o n , 1983). M o s t o f t h e i n f e c t e d h e r d s in T e x a s o c c u r in t h e e a s t e r n p a r t o f t h e state, b u t a significant n u m b e r o f i n f e c t e d cattle are l o c a t e d in e x t r e m e s o u t h Texas. In 1 9 8 3 , f o r e x a m p l e , in 21 c o u n t i e s in s o u t h T e x a s l o c a t e d w i t h i n a p p r o x i m a t e l y 150 k m o f t h e M e x i c a n b o r d e r , 151 o f a p p r o x i m a t e l y 1 0 9 0 0 h e r d s (1.4%) w e r e u n d e r q u a r a n t i n e f o r brucellosis. T h e r e is a c o n s i d e r a b l e traffic o f a n i m a l s bet w e e n t h e U n i t e d States a n d Mexico, and m a n y M e x i c a n cattle e n d u p in T e x a s . Since t h e p r e v a l e n c e o f b o v i n e brucellosis in t h e area o f M e x i c o
0167-5877/85]$03.30
© 1985 Elsevier Science Publishers B.V.
446
adjacent to south Texas is not well defined, the importance of the importation and/or straying of cattle into Texas cannot be assessed. Serum samples from northeastern Mexico had already been collected for an epidemiologic survey for hemotropic diseases (Teclaw et al., 1985). The purpose of this paper is to report the results of a serologic survey using the enzyme-linked immunosorbent assay (ELISA) for Brucella antibody activity in cattle in northeastern Mexico. M A T E R I A L S AND METHODS
The collection and processing of samples has been described (Teclaw et al., 1985). Sex was recorded for 40.6% of the animals, and of these 81.4% were females. Age was recorded for 32.7% of the animals; 90.1% were i>2 years of age. The age and sex distribution in the remaining animals was similar. Thus, the majority of the animals sampled were adult females. Testing of sera using ELISA and interpretation of results were as previously described (Byrd et al., 1979; Heck et al., 1980). Field sera and positive and negative controls were diluted 1 : 20 for test purposes. Sera with positive or suspicious ELISA reactions were reported as positive. The results for each ranch tested were reported as proportion positive. RESULTS
A total of 2070 serum samples from 14 herds on 40 ranches in northeastern Mexico were tested for antibody activity to Brucella abortus using the ELISA. Sera from 50 of these animals were positive, giving an overall prevalence rate of 2.4% and a herd infection rate of 35%. The proportion positive ranged from 0 to 13.8%, and the herd average for positive herds was 6.5%. The average proportion positive for the five dairy herds was 7.3%. The locations of each ranch and the numbers tested and numbers positive are shown in Fig. 1. Most of the infected herds appear to be clustered to the north and east of the city of Monterrey, Nuevo Leon. DISCUSSION
The proportion of herds with antibody activity to Brucella abortus in northeastern Mexico is higher than in the adjacent area of south Texas, 35% vs 1.6% (Texas Animal Health Commission, 1983). Both areas are ecologically and climatically similar. The low number of infected animals in the infected herds indicates that, as detected by ELISA and under the conditions found in northeastern Mexico, brucellosis is not highly contagious within herds. The stocking density in this area of Mexico is on the average lower than in south Texas, and since stocking densities are directly correlated with exposure potential (Nicoletti, 1980), a higher prevalence rate would be
447 expected in Texas. Also, Kellar et al. (1979) found that dairy herds infected with B. abortus were more likely to have frequent additions than non-infected herds. Since Mexican herds tend to be more stable in terms of additions than the Texas herds, a higher herd infection rate would again be expected in Texas. An obvious explanation for the differences in herd infection rates in south Texas and northeastern Mexico is the success of the brucellosis eradication program in Texas, and although the data support that conclusion they do not prove it: other explanations can be made for the difference. The herds sampled in the Mexican study were not selected at random but were included because the owners had contact with university veterinarians and were willing to cooperate. Such owners tended to be more progressive than average and thus more likely to have improved pastures with higher stocking densities and to make more frequent purchases of replacements for genetic improvement. Thus a bias in the survey methods may have
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PREVALENCE
I Reynosa
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Fig. 1. Ranch location, approximate herd prevalence rate o f antibody activity and reactors per animal tested for B. abortus. " D " = Dairy.
448
resulted in an inflated level of infected herds. On the other hand, the Texas data are based on almost 100% of the herds in the area and thus are less likely to have sampling biases. One of the reasons for testing the Mexican sera for antibody activity to Brucella was to assess the threat of the importation (legal and illegal) or straying of Mexican cattle into the United States. Based on the data from 40 herds in northeastern Mexico, it can be stated that entry of cattle from this area into the United States should be accompanied by careful testing, isolation and retesting to avoid the introduction of Brucella. ACKNOWLEDGEMENTS
This report is based upon work supported by the U.S. Department of Agriculture under Agreement No. USDA/OICD/MX-TX-116 and the Texas Agricultural Experiment Station Project No. TAES-H-6261. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture. We wish to thank Dr. Benjamin A. Jara Guillen, Director General of Animal Health for the Secretary of Agriculture, Mexico, for permission to publish this paper and Roberta Pugh for technical assistance.
REFERENCES Byrd, J.W., Heck, F.C. and Hidalgo, R.J., 1979. Evaluation of the enzyme-linked immunosorbent assay for detecting Brucella abortus antibodies. Am. J. Vet. Res., 40: 896--898. Heck, F.C., Williams, J.D. and Pruett, J., 1980. Interpretation of spectrophotometric absorbance values to define results of enzyme-linked immunosorbent assays. J. Clin. Microbiol., 11 : 398--401. Kellar, J., Marra, R. and Martin, W., 1979. Brucellosis in Ontario: a case control study. Can. J. Comp. Med., 40: 119--128. National Research Council, 1977. Brucellosis research; an evaluation. Subcommittee on Brucellosis, Committee on Animal Health, Board on Agriculture and Renewable Resources, Commission on Natural Resources, Washington, DC. Nicoletti, P., 1980. The epidemiology of bovine brucellosis. Adv. Vet. Sci. Comp. Med., 24: 69--98. Teclaw, R.F., Romo, S., Garcia, Z., Castaneda, M. and Wagner, GG., 1985. A seroepidemiologic study of bovine babesiosis in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila. Prey. Vet. Med., 3: 403--415. Texas Animal Health Commission, 1983. Quarterly Report, Texas Bovine Brucellosis Program, May 31, 1983. Austin, TX.
445
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
P R E V A L E N C E O F B R U C E L L O S I S I N F E C T I O N IN C A T T L E I N T H E MEXICAN STATES OF NUEVO LEON, TAMAULIPAS AND COAHUILA AS D E T E R M I N E D B Y T H E E L I S A
R.F. TECLAW', F. HECK',G.G. WAGNER', S. ROMO'and Z. GARCLA3
' D e p a r t m e n t o f Veterinary Microbiology and Parasitology, Texas A & M University, College Station, T X 77843 :U.S.A.) 2 Facultad de Medicina Veterinaria, Universidad A u t o n o m a de Nuevo Leon, Monterrey (Mexico) 3 Centro Nacional de Parasitologia Animal, Jiutepec, Morelos (Mexico)
(Accepted for publication 2 July 1985)
ABSTRACT
Teclaw, R.F., Heck, F., Wagner, G.G., Romo, S. and Garcia, Z., 1985. Prevalence of brucellosis infection in cattle in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila as determined by the ELISA. Prey. Vet. Med., 3: 445--448. Serum samples from 2070 cattle from 40 ranches in northeastern Mexico were tested for antibody activity to Brucella abortus using the enzyme-linked immunosorbent assay (ELISA). The overall prevalence rate in the 40 herds was 2.4% and there was at least one positive animal in 14 herds (35%). The herd prevalence rates ranged from 0 to 13.8% with the average for positive herds of 6.5%. The average proportion positive for the five dairy herds was 7.3%.
INTRODUCTION Brucellosis has b e e n the s u b j e c t o f n u m e r o u s scientific r e p o r t s and a l m o s t e v e r y c o u n t r y has s o m e f o r m o f g o v e r n m e n t - s p o n s o r e d c o n t r o l p r o g r a m . T h e U n i t e d S t a t e s has h a d an active brucellosis e r a d i c a t i o n p r o g r a m since 1 9 3 4 ( N a t i o n a l R e s e a r c h Council, 1977). T e x a s r a n k s high a m o n g t h e states w i t h brucellosis p r o b l e m s , w i t h a p p r o x i m a t e l y 2 1 8 5 h e r d s u n d e r q u a r a n t i n e ( T e x a s A n i m a l H e a l t h C o m m i s s i o n , 1983). M o s t o f t h e i n f e c t e d h e r d s in T e x a s o c c u r in t h e e a s t e r n p a r t o f t h e state, b u t a significant n u m b e r o f i n f e c t e d cattle are l o c a t e d in e x t r e m e s o u t h Texas. In 1 9 8 3 , f o r e x a m p l e , in 21 c o u n t i e s in s o u t h T e x a s l o c a t e d w i t h i n a p p r o x i m a t e l y 150 k m o f t h e M e x i c a n b o r d e r , 151 o f a p p r o x i m a t e l y 1 0 9 0 0 h e r d s (1.4%) w e r e u n d e r q u a r a n t i n e f o r brucellosis. T h e r e is a c o n s i d e r a b l e traffic o f a n i m a l s bet w e e n t h e U n i t e d States a n d Mexico, and m a n y M e x i c a n cattle e n d u p in T e x a s . Since t h e p r e v a l e n c e o f b o v i n e brucellosis in t h e area o f M e x i c o
0167-5877/85]$03.30
© 1985 Elsevier Science Publishers B.V.
446
adjacent to south Texas is not well defined, the importance of the importation and/or straying of cattle into Texas cannot be assessed. Serum samples from northeastern Mexico had already been collected for an epidemiologic survey for hemotropic diseases (Teclaw et al., 1985). The purpose of this paper is to report the results of a serologic survey using the enzyme-linked immunosorbent assay (ELISA) for Brucella antibody activity in cattle in northeastern Mexico. M A T E R I A L S AND METHODS
The collection and processing of samples has been described (Teclaw et al., 1985). Sex was recorded for 40.6% of the animals, and of these 81.4% were females. Age was recorded for 32.7% of the animals; 90.1% were i>2 years of age. The age and sex distribution in the remaining animals was similar. Thus, the majority of the animals sampled were adult females. Testing of sera using ELISA and interpretation of results were as previously described (Byrd et al., 1979; Heck et al., 1980). Field sera and positive and negative controls were diluted 1 : 20 for test purposes. Sera with positive or suspicious ELISA reactions were reported as positive. The results for each ranch tested were reported as proportion positive. RESULTS
A total of 2070 serum samples from 14 herds on 40 ranches in northeastern Mexico were tested for antibody activity to Brucella abortus using the ELISA. Sera from 50 of these animals were positive, giving an overall prevalence rate of 2.4% and a herd infection rate of 35%. The proportion positive ranged from 0 to 13.8%, and the herd average for positive herds was 6.5%. The average proportion positive for the five dairy herds was 7.3%. The locations of each ranch and the numbers tested and numbers positive are shown in Fig. 1. Most of the infected herds appear to be clustered to the north and east of the city of Monterrey, Nuevo Leon. DISCUSSION
The proportion of herds with antibody activity to Brucella abortus in northeastern Mexico is higher than in the adjacent area of south Texas, 35% vs 1.6% (Texas Animal Health Commission, 1983). Both areas are ecologically and climatically similar. The low number of infected animals in the infected herds indicates that, as detected by ELISA and under the conditions found in northeastern Mexico, brucellosis is not highly contagious within herds. The stocking density in this area of Mexico is on the average lower than in south Texas, and since stocking densities are directly correlated with exposure potential (Nicoletti, 1980), a higher prevalence rate would be
447 expected in Texas. Also, Kellar et al. (1979) found that dairy herds infected with B. abortus were more likely to have frequent additions than non-infected herds. Since Mexican herds tend to be more stable in terms of additions than the Texas herds, a higher herd infection rate would again be expected in Texas. An obvious explanation for the differences in herd infection rates in south Texas and northeastern Mexico is the success of the brucellosis eradication program in Texas, and although the data support that conclusion they do not prove it: other explanations can be made for the difference. The herds sampled in the Mexican study were not selected at random but were included because the owners had contact with university veterinarians and were willing to cooperate. Such owners tended to be more progressive than average and thus more likely to have improved pastures with higher stocking densities and to make more frequent purchases of replacements for genetic improvement. Thus a bias in the survey methods may have
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PREVALENCE
I Reynosa
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2
I
A
TAMAULIPAS
(> [
~
/
,O0/78 CiudadVictoria
0/580
Fig. 1. Ranch location, approximate herd prevalence rate o f antibody activity and reactors per animal tested for B. abortus. " D " = Dairy.
448
resulted in an inflated level of infected herds. On the other hand, the Texas data are based on almost 100% of the herds in the area and thus are less likely to have sampling biases. One of the reasons for testing the Mexican sera for antibody activity to Brucella was to assess the threat of the importation (legal and illegal) or straying of Mexican cattle into the United States. Based on the data from 40 herds in northeastern Mexico, it can be stated that entry of cattle from this area into the United States should be accompanied by careful testing, isolation and retesting to avoid the introduction of Brucella. ACKNOWLEDGEMENTS
This report is based upon work supported by the U.S. Department of Agriculture under Agreement No. USDA/OICD/MX-TX-116 and the Texas Agricultural Experiment Station Project No. TAES-H-6261. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture. We wish to thank Dr. Benjamin A. Jara Guillen, Director General of Animal Health for the Secretary of Agriculture, Mexico, for permission to publish this paper and Roberta Pugh for technical assistance.
REFERENCES Byrd, J.W., Heck, F.C. and Hidalgo, R.J., 1979. Evaluation of the enzyme-linked immunosorbent assay for detecting Brucella abortus antibodies. Am. J. Vet. Res., 40: 896--898. Heck, F.C., Williams, J.D. and Pruett, J., 1980. Interpretation of spectrophotometric absorbance values to define results of enzyme-linked immunosorbent assays. J. Clin. Microbiol., 11 : 398--401. Kellar, J., Marra, R. and Martin, W., 1979. Brucellosis in Ontario: a case control study. Can. J. Comp. Med., 40: 119--128. National Research Council, 1977. Brucellosis research; an evaluation. Subcommittee on Brucellosis, Committee on Animal Health, Board on Agriculture and Renewable Resources, Commission on Natural Resources, Washington, DC. Nicoletti, P., 1980. The epidemiology of bovine brucellosis. Adv. Vet. Sci. Comp. Med., 24: 69--98. Teclaw, R.F., Romo, S., Garcia, Z., Castaneda, M. and Wagner, GG., 1985. A seroepidemiologic study of bovine babesiosis in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila. Prey. Vet. Med., 3: 403--415. Texas Animal Health Commission, 1983. Quarterly Report, Texas Bovine Brucellosis Program, May 31, 1983. Austin, TX.