- Email: [email protected]
Brucellosis in Venezuela
Veterinary Microbiology 90 (2002) 39–44
Brucellosis in Venezuela Francisco J. Vargas O.* Area de Medicina de Grandes Animales, Departamento de Medicina y Cirugı´a, Decanato de Ciencias Veterinarias, Universidad Centroccidental ‘‘Lisandro Alvarado’’, Barquisimeto, Estado Lara 5001, Venezuela
Abstract Brucellosis is a public health problem in Venezuela and affects large numbers of animals. The most important biovar in the country is Brucella abortus. In cattle and buffalo it causes high rates of abortions in females and infertility in males; it is transmissible to occupationally exposed humans. In 1968, an official program was set up for the control and eradication of the disease and it is still in place. Amongst the control provisions, this program provides for the vaccination of female calves with strain 19 and the slaughtering of positive reactors following the official diagnosis (rapid agglutination in plate test). According to the official reports, the positive reactors ranged from 0.8 to 1.2% in the past few years. These values do not corroborate reports showing an average positive rate of 10.5% and even higher values in some areas of the country. The government is working to approve a new resolution that will replace the rapid agglutination in plate test with the Card Test, the use of 2Mercaptoetanol, fixation of complement and competitive ELISA as confirmatory tests. In addition, there will be an obligatory vaccination with B. abortus strain 19 or B. abortus RB51 of all female calves between 3- and 8-month-old and a recommended revaccination at 10–15-month-old and adult cows in high prevalence areas. These measures should allow help to reduce the prevalence of the disease in cattle herds and thus minimize the risk for human populations. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Brucellosis; Venezuela; Card Test; Strain 19; RB51
1. Introduction Brucellosis is an important disease in Venezuela. Since its discovery in 1930, several control and eradication measures have been established. But to date, the disease continues to produce large economic losses, especially in cattle, and constitutes a serious public health problem (Contreras, 2000).
* Tel.: þ58-251-2592420; fax: þ58-251-2592440. E-mail address: [email protected] (F.J. Vargas O.).
0378-1135/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 3 5 ( 0 2 ) 0 0 2 4 3 - 2
40
F.J. Vargas O. / Veterinary Microbiology 90 (2002) 39–44
The most prevalent biovar in the country is Brucella abortus. It has been identified as the causative pathogen of brucellosis in humans and animals. In cattle and water buffaloes (Bubalus bubalis var. bubalis), the disease is characterized by abortions during the last third of gestation, infertility, birth of weak offspring and orchitis in bulls (Contreras, 2000; Carrero, 2000). In humans, the disease (B. abortus) is mainly occupational, affecting workers on cattle, operations, slaughter houses and laboratories where they come in contact with placentas, aborted fetuses and secretions from infected animals (Va´ squez et al., 1999). B. suis has been identified as causing abortions in some swine herds in the center of the country. B. melitensis has been isolated but scarcely studied and its impact in animal and human health is not very well known (Lord et al., 1998b). Other Brucella spp. have not been identified in the country and the disease has been hardly studied in wild animals. In 1968, the Animal Division of Department of Agriculture (MAC) published the Resolution Number 123 entitled ‘‘Control and Eradication Program of Brucellosis’’. The program is still in effect and establishes: the control of cattle shipping, the slaughtering of serologically positive reactors and the obligatory vaccination of female calves (MAC, 1987). Although the program was initially effective, brucellosis exists in a high prevalence in some areas of the country. New efforts are being made for introduction of a new resolution to facilitate more effective control and eradication.
2. Diagnostic tests The resolution currently in place establishes that the official diagnostic test is the rapid agglutination in plate test. The test is performed by veterinarians accredited by the Autonomous Service of Animal Health (SASA). Additional tests for diagnostic confirmation include: Tube Agglutination, Card Test, 2-Mercaptoethanol, Complement Fixation and competitive ELISA, and are being adopted in authorized testing laboratories (MAC, 1987). The percentage of positive cattle reactors in the official tests reported by SASA ranges between 0.8 and 1.2% in the past few years (Gonzalez, 1999). According to such reports, there is very low number of cattle that are positive for brucellosis. In contrast, several studies carried out in different parts of the country using various diagnostic tests show an average rate of 10.5% using ELISA, 8.5% using Complement Fixation, 5% using Card Test and 0.5% using plate and Tube Agglutination tests (Rivera and Curiel, 1993). Other unpublished results show similar rates of positive animals and even higher values in some regions of the country. This is particularly so in the southern part of Maracaibo lake and the states of Zulia, Apure and Monagas where the disease affects cattle and water buffaloes. However, a complete study of the prevalence brucellosis in the country has not been done. The government and others groups are working on a new resolution that will require all female bovines older than 20 months and males older than 6 months to be tested every 6 months using Card Test. The positive reactors will be confirmed with additional tests such as Tube Agglutination, 2-Mercaptoethanol, Complement Fixation and competitive ELISA. The confirmed positive animals will be marked with a letter ‘‘B’’ on the left cheek and sent to the slaughter house within 15 days under supervision. Herds that are negative in two consecutive samplings are granted a ‘‘brucellosis-free’’ certificate and will enter an annual
F.J. Vargas O. / Veterinary Microbiology 90 (2002) 39–44
41
testing program. Herds that are to be shipped within the country will be tested. Other aspects in the proposed resolution include the use of the ring test in the centers of milk collection as epidemiological surveillance (Vargas, 2000). Several herds of water buffalo exhibit a high prevalence of brucellosis even though serological tests, vaccination of calves and slaughtering of positive reactors are being performed. However, it has been observed that serological tests are being interpreted in the same manner as for bovine animals even though there are differences in the immunological responses between these species (Carrero, 2000; Nicoletti, 1994).
3. Vaccination Since 1956, the principle brucellosis vaccine used in the world has been the B. abortus strain 19. In Venezuela, the official resolution in place since 1968 (does the 1987 MAC say 1968?) establishes the obligatory vaccination of female calves from 3 to 8 months old with strain 19 (MAC, 1987). Although this vaccination scheme is utilized, it has some drawbacks including: no constant supply of strain 19, the low quality of the vaccine in terms of colony forming units and the low notification of the vaccinations carried out (Gonzalez, 1999). Furthermore, the other major problem associated with the strain 19 is the production of antibodies that interfere with the diagnostic tests and causes confounding results when used in adult cattle. The slaughtering of positive reactors is undoubtedly the most effective measure for the control and eradication of herd brucellosis (Sutherland and Mackenzie, 1983; Salman and Meyer, 1984). After having compared the results of different serologic tests in animals vaccinated with strain 19 relative to non-vaccinated animals, it has been demonstrated that strain 19 produces false positives in serologic tests, especially in the rapid plate agglutination (Rivera and Curiel, 1993). In addition, vaccinations are not always supervised by accredited veterinarians and sometimes it may be done up to 8 months of age and correlates with the increased numbers of false positives due to vaccination (Gonzalez, 1999). According to Schurig et al. (1991) false positives in the serological tests are due to antibodies against the lipopolysaccharide (LPS) induced by strain 19. A new vaccine strain, B. abortus RB51, has been tested in female cattle and shown to induce protection against brucellosis but not induce antibodies that cause false positives (Schurig, 1999; Olsen, 1999). Several countries have either approved the use of B. abortus strain RB51 for prevention of brucellosis in cattle or they are testing its efficacy, e.g. USA (Ragan, 1999), Mexico (SAGAR, 1998), Chile (SAG, 1998), Colombia (Rodriguez, 1998), Argentina (Samartino et al., 1999), amongst others. In Venezuela, strain RB51 was approved by SASA in 1999. The new official resolution under consideration establishes: vaccination as a requirement for the shipment of animals, the obligatory vaccination of all female calves from 3 to 8 months with strain 19 or RB51, and the recommendation of revaccination with strain RB51 at 10–15 months of age in adult cows from high prevalence areas (Vargas, 2000). The efficacy of strain RB51 vaccination in adult cows has been demonstrated by Olsen et al. (1996). They demonstrated the effectiveness of the vaccine in adult cattle that had been vaccinated with strain 19. Palmer et al. (1997) demonstrated the safety of strain RB51
42
F.J. Vargas O. / Veterinary Microbiology 90 (2002) 39–44
for vaccination of pregnant heifers. In Venezuela, the use of the strain RB51 vaccine in adult cows in high prevalence areas of brucellosis, together with the systematic slaughtering of positive reactors in serological tests, has had an extraordinary impact in the decreasing the incidence of brucellosis. The efficacy of strain RB51 has been tested in Venezuela on cattle ranches with known high and low brucellosis prevalence. Lord et al. (1998a) showed that strain RB51 offered 100% protection against infection with no abortions, regardless of age (calves or heifers) and the amount of dose used (single or double dose), and without producing antibodies that confounded serological tests. A second study carried out by Lord et al. (1998b) demonstrated that the vaccination of swines with strain RB51 protected them against infection with B. suis. Although the use of strain RB51 is not still approved in male cattle, a demonstrated the safety of the vaccine in 20 adult bulls of 3 years of age from a herd with high prevalence of brucellosis study (Vargas et al., 2001). The animals were divided into two groups: a group ðn ¼ 10Þ received a complete dose of 10 billion CFU subcutaneously and another group ðn ¼ 10Þ received saline as a control. The bulls were evaluated through out 90 days during which no excretion of strain was observed in semen nor abnormalities in sperm morphology. After 90 days, the bulls were slaughtered and no significant pathological alterations nor isolations of the strain from the testicles or epididimal, iliacal and inguinal lymph nodes were observed. These results are support those observed in a preliminary study carried out by Edmonds et al. (1999) using six sexually mature bulls vaccinated intramuscularly with a standard dose of strain RB51.
4. Conclusions In Venezuela, brucellosis continues to be a serious disease for animal and human health. The official published reports of positive animals as determined with the plate agglutination test show a low rate. But results obtained with other tests of high sensitivity and specificity such as the ELISA indicate a prevalence of approximately 10.5%. This prevalence is even higher in some areas of the country where the disease produces serious disease in cattle, buffaloes and humans. Currently, a new resolution is being discussed that establishes the obligatory testing of all female bovine animals older than 20 months and males older than 6 months of age by the Card Test and the slaughtering of positive animals under supervision. Other tests that can be used to confirm positive reactor animals include Tube Agglutination, 2-Mercaptoetanol, Complement Fixation and competitive ELISA. The ring test will be performed in the centers of milk collection of as an epidemiological surveillance measure. It will be obligatory for female calves between 3 and 8 months of age to he vaccinated with strain 19 or strain RB51 and revaccination of adult cows between 10 and 15 months of age in high prevalence zones with strain RB51 is recommended. It is expected that these new measures will allow for a more accurate assessment of the prevalence and for better control. However, it is important to note that the main problem encountered by the control program is the related to the lack of co-operation on farms in the slaughtering of reactor positive animals as there is no indemnification scheme to replace affected cattle.
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References Carrero, J.C., 2000. Bufalo Asia´ tico: Un Recurso Inexplotado Para producir Proeı´na Animal. Editado por la Gobernacio´ n del Estado Ta´ chira. San Cristobal, Estado Ta´ chira, Venezuela, pp. 142–157. Contreras, J.A., 2000. Brucelosis en Enfermedades de los Bovinos, Diagno´ stico, Tratamiento y Control, Segunda Edicio´ n. Barquisimeto, Venezuela, pp. 475–489. Edmonds, M.D., Schurig, G.G., Samartino, L.E., Hpyt, P.G., Walker, J.V., Hagius, S.D., Elzer, P.H., 1999. Biosafety of Brucella abortus strain RB51 for vaccination of mature bulls and pregnant heifers. Am. J. Vet. Res. 60 (6), 722–725. Gonzalez, J., 1999. Programa de Brucelosis: Situacio´ n Epidemiolo´ gica y Estrategias para la Prevencio´ n y el Control/Erradicacio´ n en Venezuela. Reunio´ n Consulta de Expertos OPS/OMS Sobre Vacunas y Estrategias de Vacunacio´ n en los Programas de Control/Erradicacio´ n de Brucelosis, Santiago de Chile, 16–18 de Noviembre de 1999, pp. 7–8. Lord, V., Schurig, G., Cherwonogrodzky, J., Marcano, M., Melendez, G., 1998a. Field study of vaccination of cattle with Brucella abortus strains RB51 and 19 under high and low disease prevalence. Am. J. Vet. Res. 59 (8), 1016–1020. Lord, V., Cherwonogrodzky, J., Schurig, G., Lord, R., Marcano, M., Melendez, G., 1998b. Venezuelan field trials of vaccines against brucellosis in swine. Am. J. Vet. Res. 59 (5), 546–551. Ministerio de Agricultura y Cria (MAC), 1987. Resolucio´ n para la Campan˜ a de Control y Erradicacio´ n de la Brucelosis. Resolucio´ n no. 123. Legislacio´ n de Sanidad Animal, Repu´ blica de Venezuela, pp. 53–62. Nicoletti, P., 1994. An update on selected diseases which affect buffaloes. In: Proceedings of the Fourth World Buffalo Congress, Sao Paulo, Brazil, pp. 221–228. Olsen, S., 1999. Available Vaccines for the Control of Brucellosis in Animals. Reunio´ n de Consulta de Expertos de la OPS/OMS Sobre Vacunas y Estrategias de Vacunacio´ n en los Programas de Control/Erradicacio´ n de la Brucelosis, Santiago de Chile, 16 al 18 de Noviembre de 1999, pp. 30–33. Olsen, S., Evans, D., Hennager, S., Cheville, N., Stevens, M., 1996. Serologic responses of Brucella abortus strain 19 calfhood-vaccinated cattle following adult vaccination with strain RB51. J. Vet. Diagn. Invest. 8, 451–454. Palmer, M.V., Steven, C.O., Cheville, N.F., 1997. Safety and immunogenicity of Brucella abortus strain RB51 vaccine in pregnant cattle. Am. J. Vet. Res. 58 (5), 472–477. Ragan, V., 1999. Brucelosis Programs: Epidemiological Situation and Strategies for Prevention and Control/ Erradication in the Countries of the Americas. Reunio´ n de Consulta de Expetos de la OPS/OMS Sobre Vacunas y Estrategias de Vacunacio´ n, Santiago de Chile, pp. 17–20. Rivera, S., Curiel, J., 1993. Epidemiologı´a Serolo´ gica de la Brucelosis Bovina en el Municipio Villa del Rosario, Perija´ , Estado Zulia, vol. 2, part 2. Revista Cientı´fica, Facultad de Ciencias Veterinarias, Universidad del Zulia, pp. 117–124. Rodriguez, I., 1998. Avances en la Prevencio´ n de Brucelosis, vol. 45, part 1. Revista de Medicina Veterinaria y Zootecnia, Universidad Nacional de Colombia, pp. 28–31. Salman, W., Meyer, M., 1984. Epidemiology of bovine brucellosis in the Mexicali Valley, Me´ xico: literature review of the disease-associated factors. Am. J. Vet. Res. 45 (8), 1557–1560. Samartino, L.E., Salustino, E., Gregoret, R., 1999. Evaluacio´ n de la vacuna RB51 de Brucella abortus en hembras bovinas pren˜ adas. Vet. Argentina XVI (152), 2–8. Servicio Agrı´cola Ganadero (SAG), 1998. Introduccio´ n de la vacuna, cepa RB51 en el programa de erradicacio´ n de la brucelosis bovina en Chile. Erradicacio´ n de la Brucelosis. Boletı´n Informativo del Departamento de Proteccio´ n Pecuaria del Servicio Agrı´cola y Ganadero, Santiago de Chile, pp. 1–6. Secretaria de Agricultura, Ganaderia, y Desarrollo Rural (SAGAR), 1998. Experiencia con la vacuna para la prevencio´ n de la brucelosis, cepa RB51 en Me´ xico. In: Proceedings of the IV Seminario Sobre Armonizacio´ n de Registro y Control de Medicamentos Veterinarios, pp. s/n. Schurig, G., 1999. Erradicacio´ n de la Brucelosis y Caracterı´sticas Principales de la Vacuna Brucella abortus cepa RB51. Memorias del Simposio Internacional de Brucelosis, Maracay, Venezuela, 26 al 27 de Mayo de 1999, pp. 27–42. Schurig, G.G., Roop, R.M., Bagchi, T., Boyle, S., Buhrman, D., Sriranganathan, N., 1991. Biological properties of RB51, a stable rough strain of Brucella abortus. Vet. Microbiol. 28, 171–188.
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Sutherland, S.S., Mackenzie, R.M., 1983. Applied serology in the later stages of erradication of bovine brucellosis. Aust. Vet. J. 60 (8), 240–242. Vargas, F., 2000. Inmunologı´a de la Brucelosis y uso de la Vacuna, RB51 en el programa de control y erradicacio´ n de la enfermedad. In: Segunda, J. (Ed.), Enfermedades de los Bovinos: Diagno´ stico, Tratamiento y Control. Editado por Contreras. Barquisimeto, Venezuela, pp. 490–515. Vargas, F., Rivera, S., De Pool, G., Vale-Echeto, O., Montiel, M., Schurig, G., 2001. Histopatologı´a y Bacteriologı´a de Testı´culos, Epidı´dimos y Linfono´ dulos en Toros Vacunados con cepa RB51 de Brucella abortus, vol. XI, part 5. Revista Cientı´fica de la Facultad de Ciencias Veterinarias de la Universidad del Zulia, pp. 423–430. Va´ squez, A., Comach, G., Sa´ nchez, E., Sosa, G., 1999. Aplicacio´ n de la Prueba de ELISA en el Diagno´ stico de Brucelosis en Personas Ocupacionalmente Expuestas. Memorias del Simposio Internacional de Brucelosis, Maracay, Venezuela, pp. 117–124.
Brucellosis in Venezuela Francisco J. Vargas O.* Area de Medicina de Grandes Animales, Departamento de Medicina y Cirugı´a, Decanato de Ciencias Veterinarias, Universidad Centroccidental ‘‘Lisandro Alvarado’’, Barquisimeto, Estado Lara 5001, Venezuela
Abstract Brucellosis is a public health problem in Venezuela and affects large numbers of animals. The most important biovar in the country is Brucella abortus. In cattle and buffalo it causes high rates of abortions in females and infertility in males; it is transmissible to occupationally exposed humans. In 1968, an official program was set up for the control and eradication of the disease and it is still in place. Amongst the control provisions, this program provides for the vaccination of female calves with strain 19 and the slaughtering of positive reactors following the official diagnosis (rapid agglutination in plate test). According to the official reports, the positive reactors ranged from 0.8 to 1.2% in the past few years. These values do not corroborate reports showing an average positive rate of 10.5% and even higher values in some areas of the country. The government is working to approve a new resolution that will replace the rapid agglutination in plate test with the Card Test, the use of 2Mercaptoetanol, fixation of complement and competitive ELISA as confirmatory tests. In addition, there will be an obligatory vaccination with B. abortus strain 19 or B. abortus RB51 of all female calves between 3- and 8-month-old and a recommended revaccination at 10–15-month-old and adult cows in high prevalence areas. These measures should allow help to reduce the prevalence of the disease in cattle herds and thus minimize the risk for human populations. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Brucellosis; Venezuela; Card Test; Strain 19; RB51
1. Introduction Brucellosis is an important disease in Venezuela. Since its discovery in 1930, several control and eradication measures have been established. But to date, the disease continues to produce large economic losses, especially in cattle, and constitutes a serious public health problem (Contreras, 2000).
* Tel.: þ58-251-2592420; fax: þ58-251-2592440. E-mail address: [email protected] (F.J. Vargas O.).
0378-1135/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 3 5 ( 0 2 ) 0 0 2 4 3 - 2
40
F.J. Vargas O. / Veterinary Microbiology 90 (2002) 39–44
The most prevalent biovar in the country is Brucella abortus. It has been identified as the causative pathogen of brucellosis in humans and animals. In cattle and water buffaloes (Bubalus bubalis var. bubalis), the disease is characterized by abortions during the last third of gestation, infertility, birth of weak offspring and orchitis in bulls (Contreras, 2000; Carrero, 2000). In humans, the disease (B. abortus) is mainly occupational, affecting workers on cattle, operations, slaughter houses and laboratories where they come in contact with placentas, aborted fetuses and secretions from infected animals (Va´ squez et al., 1999). B. suis has been identified as causing abortions in some swine herds in the center of the country. B. melitensis has been isolated but scarcely studied and its impact in animal and human health is not very well known (Lord et al., 1998b). Other Brucella spp. have not been identified in the country and the disease has been hardly studied in wild animals. In 1968, the Animal Division of Department of Agriculture (MAC) published the Resolution Number 123 entitled ‘‘Control and Eradication Program of Brucellosis’’. The program is still in effect and establishes: the control of cattle shipping, the slaughtering of serologically positive reactors and the obligatory vaccination of female calves (MAC, 1987). Although the program was initially effective, brucellosis exists in a high prevalence in some areas of the country. New efforts are being made for introduction of a new resolution to facilitate more effective control and eradication.
2. Diagnostic tests The resolution currently in place establishes that the official diagnostic test is the rapid agglutination in plate test. The test is performed by veterinarians accredited by the Autonomous Service of Animal Health (SASA). Additional tests for diagnostic confirmation include: Tube Agglutination, Card Test, 2-Mercaptoethanol, Complement Fixation and competitive ELISA, and are being adopted in authorized testing laboratories (MAC, 1987). The percentage of positive cattle reactors in the official tests reported by SASA ranges between 0.8 and 1.2% in the past few years (Gonzalez, 1999). According to such reports, there is very low number of cattle that are positive for brucellosis. In contrast, several studies carried out in different parts of the country using various diagnostic tests show an average rate of 10.5% using ELISA, 8.5% using Complement Fixation, 5% using Card Test and 0.5% using plate and Tube Agglutination tests (Rivera and Curiel, 1993). Other unpublished results show similar rates of positive animals and even higher values in some regions of the country. This is particularly so in the southern part of Maracaibo lake and the states of Zulia, Apure and Monagas where the disease affects cattle and water buffaloes. However, a complete study of the prevalence brucellosis in the country has not been done. The government and others groups are working on a new resolution that will require all female bovines older than 20 months and males older than 6 months to be tested every 6 months using Card Test. The positive reactors will be confirmed with additional tests such as Tube Agglutination, 2-Mercaptoethanol, Complement Fixation and competitive ELISA. The confirmed positive animals will be marked with a letter ‘‘B’’ on the left cheek and sent to the slaughter house within 15 days under supervision. Herds that are negative in two consecutive samplings are granted a ‘‘brucellosis-free’’ certificate and will enter an annual
F.J. Vargas O. / Veterinary Microbiology 90 (2002) 39–44
41
testing program. Herds that are to be shipped within the country will be tested. Other aspects in the proposed resolution include the use of the ring test in the centers of milk collection as epidemiological surveillance (Vargas, 2000). Several herds of water buffalo exhibit a high prevalence of brucellosis even though serological tests, vaccination of calves and slaughtering of positive reactors are being performed. However, it has been observed that serological tests are being interpreted in the same manner as for bovine animals even though there are differences in the immunological responses between these species (Carrero, 2000; Nicoletti, 1994).
3. Vaccination Since 1956, the principle brucellosis vaccine used in the world has been the B. abortus strain 19. In Venezuela, the official resolution in place since 1968 (does the 1987 MAC say 1968?) establishes the obligatory vaccination of female calves from 3 to 8 months old with strain 19 (MAC, 1987). Although this vaccination scheme is utilized, it has some drawbacks including: no constant supply of strain 19, the low quality of the vaccine in terms of colony forming units and the low notification of the vaccinations carried out (Gonzalez, 1999). Furthermore, the other major problem associated with the strain 19 is the production of antibodies that interfere with the diagnostic tests and causes confounding results when used in adult cattle. The slaughtering of positive reactors is undoubtedly the most effective measure for the control and eradication of herd brucellosis (Sutherland and Mackenzie, 1983; Salman and Meyer, 1984). After having compared the results of different serologic tests in animals vaccinated with strain 19 relative to non-vaccinated animals, it has been demonstrated that strain 19 produces false positives in serologic tests, especially in the rapid plate agglutination (Rivera and Curiel, 1993). In addition, vaccinations are not always supervised by accredited veterinarians and sometimes it may be done up to 8 months of age and correlates with the increased numbers of false positives due to vaccination (Gonzalez, 1999). According to Schurig et al. (1991) false positives in the serological tests are due to antibodies against the lipopolysaccharide (LPS) induced by strain 19. A new vaccine strain, B. abortus RB51, has been tested in female cattle and shown to induce protection against brucellosis but not induce antibodies that cause false positives (Schurig, 1999; Olsen, 1999). Several countries have either approved the use of B. abortus strain RB51 for prevention of brucellosis in cattle or they are testing its efficacy, e.g. USA (Ragan, 1999), Mexico (SAGAR, 1998), Chile (SAG, 1998), Colombia (Rodriguez, 1998), Argentina (Samartino et al., 1999), amongst others. In Venezuela, strain RB51 was approved by SASA in 1999. The new official resolution under consideration establishes: vaccination as a requirement for the shipment of animals, the obligatory vaccination of all female calves from 3 to 8 months with strain 19 or RB51, and the recommendation of revaccination with strain RB51 at 10–15 months of age in adult cows from high prevalence areas (Vargas, 2000). The efficacy of strain RB51 vaccination in adult cows has been demonstrated by Olsen et al. (1996). They demonstrated the effectiveness of the vaccine in adult cattle that had been vaccinated with strain 19. Palmer et al. (1997) demonstrated the safety of strain RB51
42
F.J. Vargas O. / Veterinary Microbiology 90 (2002) 39–44
for vaccination of pregnant heifers. In Venezuela, the use of the strain RB51 vaccine in adult cows in high prevalence areas of brucellosis, together with the systematic slaughtering of positive reactors in serological tests, has had an extraordinary impact in the decreasing the incidence of brucellosis. The efficacy of strain RB51 has been tested in Venezuela on cattle ranches with known high and low brucellosis prevalence. Lord et al. (1998a) showed that strain RB51 offered 100% protection against infection with no abortions, regardless of age (calves or heifers) and the amount of dose used (single or double dose), and without producing antibodies that confounded serological tests. A second study carried out by Lord et al. (1998b) demonstrated that the vaccination of swines with strain RB51 protected them against infection with B. suis. Although the use of strain RB51 is not still approved in male cattle, a demonstrated the safety of the vaccine in 20 adult bulls of 3 years of age from a herd with high prevalence of brucellosis study (Vargas et al., 2001). The animals were divided into two groups: a group ðn ¼ 10Þ received a complete dose of 10 billion CFU subcutaneously and another group ðn ¼ 10Þ received saline as a control. The bulls were evaluated through out 90 days during which no excretion of strain was observed in semen nor abnormalities in sperm morphology. After 90 days, the bulls were slaughtered and no significant pathological alterations nor isolations of the strain from the testicles or epididimal, iliacal and inguinal lymph nodes were observed. These results are support those observed in a preliminary study carried out by Edmonds et al. (1999) using six sexually mature bulls vaccinated intramuscularly with a standard dose of strain RB51.
4. Conclusions In Venezuela, brucellosis continues to be a serious disease for animal and human health. The official published reports of positive animals as determined with the plate agglutination test show a low rate. But results obtained with other tests of high sensitivity and specificity such as the ELISA indicate a prevalence of approximately 10.5%. This prevalence is even higher in some areas of the country where the disease produces serious disease in cattle, buffaloes and humans. Currently, a new resolution is being discussed that establishes the obligatory testing of all female bovine animals older than 20 months and males older than 6 months of age by the Card Test and the slaughtering of positive animals under supervision. Other tests that can be used to confirm positive reactor animals include Tube Agglutination, 2-Mercaptoetanol, Complement Fixation and competitive ELISA. The ring test will be performed in the centers of milk collection of as an epidemiological surveillance measure. It will be obligatory for female calves between 3 and 8 months of age to he vaccinated with strain 19 or strain RB51 and revaccination of adult cows between 10 and 15 months of age in high prevalence zones with strain RB51 is recommended. It is expected that these new measures will allow for a more accurate assessment of the prevalence and for better control. However, it is important to note that the main problem encountered by the control program is the related to the lack of co-operation on farms in the slaughtering of reactor positive animals as there is no indemnification scheme to replace affected cattle.
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