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Incidence of babesiosis and anaplasmosis infections in cattle sampled monthly in the Mexican states of Nuevo Leon and San Luis Potosi
Preventive Veterinary Medicine, 3 (1985) 427--435
427
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
INCIDENCE OF BABESIOSIS AND ANAPLASMOSIS INFECTIONS IN C A T T L E SAMPLED M O N T H L Y IN T H E MEXICAN S T A T E S OF NUEVO LEON AND SAN LUIS POTOSI
R.F. T E C L A W
I, Z. G A R C I A 2, S. R O M O
3 and G.G. W A G N E R
l
~Department of Veterinary Microbiology and Parasitology, Texas A&M University, College Station, TX 77843 (U.S.A.) 2 Centro Nacional de Parasitologia Animal, Jiutepec, MoreIos (Mexico) 3Faeultad de Medicina Veterinaria Universidad Autonoma de Nuevo Leon, Monterrey (Mexico)
(Accepted for publication 2 July 1985)
ABSTRACT Teclaw, R.F., Garcia, Z., R o m o , S. and Wagner, G.G., 1985. Incidence of babesiosis and anaplasmosis infections in cattle sampled monthly in the Mexican states of Nuevo Leon and San Luis Potosi. Prey. Vet. Med., 3: 427--435. Serum samples from 200 cattle of various ages and breeds from five ranches in the Mexican states of Nuevo Leon and San Luis Potosi were collected monthly (with occasional omissions) between February 1983 and November 1983. These samples were tested for the presence of antibody activity to Babesia bovis and B. bigemina using the indirect fluorescent antibody test and to Anaplasma marginale using the card test. There were seroconversions to Babesia spp. on two of the five ranches. O n one ranch, five of 37 animals originally negative for B. bigemina became positive in late s u m m e r and fall. O n the other ranch, 32 of 36 animals seroconverted to B. bigemina throughout the study period with a moderate peak in mid-summer. Only four of 35 animals became seropositive to B. bovis on this same ranch. Seroconversions to A. rnarginale were detected on four of the five ranches with the majority occurring on the same ranches with Babesia infections.
INTRODUCTION Single-sample serologic surveys have the disadvantage o f n o t providing information on the approximate time of seroconversion. If animals are exposed to new infections at a constant rate, then the age structure o f the population that is infected will give some indication of the disease dynamics (Lobel and Kagan, 1978). However, f r e qu ent l y a constant infection rate cannot be assumed or the age structure of the population is unknown. Although expensive in time and m o n e y , one solution is to sample from the same animals at regular intervals. In this way epidemic curves and temporal effects can be determined directly. As part of a seroepidemiological study
0167-5877/85/$03.30
© 1985 Elsevier Science Publishers B.V.
428
of hemoparasitic diseases in northeastern Mexico (Teclaw et al., 1985a, b), m o n t h l y field visits to five ranches were conducted over a period of 10 months in 1983. The purpose of this paper is to report the results of the indirect fluorescent antibody test (IFAT) for babesiosis and the card test (CT) for anaplasmosis from animals on these ranches. MATERIALS AND METHODS
Ranches The Fidiecomiso Campana Nacional Contra la Garrapata (National Tick Eradication Campaign) of the Mexican government provided contact with five ranchers in the states of Nuevo Leon and San Luis Potosi. The ranches were not chosen at random but were selected according to the owners' willingness to assemble the cattle each m o n t h for an extended period of time. Thirty-five Brown Swiss, 2-year-old heifers imported from Texas into Mexico (Ranch 6) were also included in the study. We had intended to take serum samples from these latter animals each m o n t h , but only a pre-shipment sampling in Texas and one sampling 10 weeks after their arrival in Mexico were completed. The locations of the six ranches in relation to the study area of the previously described survey is shown in Fig. 1. Animals Forty, 46, 50, 19 and 45 animals on Ranches 1--5, respectively, were identified with plastic eartags. These animals were not randomly selected
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429 nor did they consist of the entire herd. Only adult animals were sampled on Ranches 1 and 5, while approximately equal numbers of adults and calves were tested on the other ranches. Zebu and zebu-cross cattle predominated on Ranches 1--4 and constituted about half of the animals on Ranch 5. The remainder of animals on Ranch 5 were Brown Swiss.
Sampling It was planned to visit each ranch once a m o n t h to take blood samples. However, due to problems beyond our control, not all ranches were sampled each m o n t h and a o t every animal was assembled during each visit.
Serology The IFAT was used to determine antibody activity to Babesia bovis and B. bigemina as described earlier (Todorovic and Long, 1974; Teclaw et al., 1985a). Sera from the first and last sample dates for each animal were tested at 2-fold dilutions beginning at 1:80. When a 4-fold increase in antibody titer was found, the intervening samples for that animal were tested to determine the approximate date of seroconversion. The date was determined by taking the mid-point of the interval between the last negative test and the first positive test and then subtracting the number of days required for test reactivity to occur after infection. These periods are approximately 15 days for Babesia spp. (Ross and Lohr, 1968; Kuttler et al., 1977). The CT was used to test for antibody activity to Anaplasma marginale (Amerault and Roby, 1968) in the same manner except that dilutions were not made and 21 days was used for the number of days required for a positive test after infection (Gonzalez et al., 1978). RESULTS There were seroconversions to Babesia spp. in Ranches 1 and 2. Both herds are about 400 km south of the main study area reported earlier (Teclaw et al., 1985a, b). The remaining 3 herds, in which no seroconversions for Babesia spp. were detected, were located within the main study area. In Herd 1, five of 37 animals at risk (previously uninfected based on negative IFAT) to B. bigemina infection had seroconversions. Exposures were estimated to have occurred close to the following dates: 1 August, one animal; 1 October, one animal; and 1 November, three animals. In Herd 2, 22 of 36 animals at risk of B. bigemina infection had seroconversions at various times t h r o u g h o u t the test period. Figure 2 illustrates the incidence for Herd 2 of B. bigemina infections (new infections divided by remaining animals at risk) vs. date for the period from 1 February 1983 to 15 October 1983. A rolling incidence (3 period average) was used to even o u t random variations. Four of 35 animals in Herd 2
430 originally at risk to B. bovis infection had seroconversions at the approximate dates indicated in Fig. 2. The sera collected each m o n t h from animals which seroconverted during the study were tested against both Babesia antigens, even if seroconversion occurred to only one of them. It was noticed that sera originally negative to both B. bovis and B. bigemina at a 1:80 dilution became positive to both during the same month. The B. bigemina titers were usually ~>1:2560 while the B. bovis titers were 1:80 or 1:160. These low titers to B. bovis were considered to be cross-reactions and were therefore graded negative. Of the four animals which had strong seroconversions to B. bovis at high titer, two had seroconversions to B. bigemina during the same m o n t h and two remained negative to B. bigemina. Most of the animals in the five serially-sampled herds which had antibody titers at the start of the survey either had a 1- or 2-fold drop in titer or remained at the same titer but with lowered intensity of fluorescence by the end of the study. This was observed for both B. bovis and B. bigemina and indicates that antibody titers to these two organisms remain relatively stable for />10 months. Only 11 of 108 animals from all five herds which started the study with antibody titers to B. bigemina had become negative at the end; of these, 10 originally had titers of 1:80 and one had a titer of 1:160. Only six of 73 animals which started the survey with antibody titers
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Fig. 2. Ranch 2 (1983). Seroeonversions to B. bigemina vs. estimated dates of exposure as percentage of remaining animals at risk (solid line) and rolling average (3 period) of the same data (broken line). Triangles (A) designate estimated dates of seroconversion to B. boris.
431
to B. bovis had become negative by the end, and of these six animals, five had titers of 1:80 and one had a titer of 1:160 originally. In Herd 2, in which the incidence of B. bigemina infections was very high, only one animal of the 10 with antibody titers at the start of the survey experienced a 4-fold rise in antibody titer at the end. All of these animals were probably exposed to reinfections, but no change was apparent in the IFAT, except in the single animal. This indicates that superinfection did not noticeably increase antibody titers on the IFAT. On Ranch 5, only 4% and 17% of the animals < 1 year of age at the start of the study were positive to B. bovis and B. bigemina, respectively, while 96% of the adults were positive for each species. This indicates that Babesia spp. were circulating in the herd no sooner than 1 year before the start of the study but had not been active since that time. On Ranch 4, all of the animals tested were adults and 100% had antibody titers to B. bigemina. Thirty-two percent reacted positively for B. bovis, all at low titers. This is the greatest difference in prevalence rates between Babesia spp. seen on any of the ranches in this or the previous study (Teclaw et al., 1985a). This suggests that B. bovis may no longer be active in this herd and that only B. bigemina remains. Animals on Ranches 1--3 and 5 seroconverted from negative to positive on the anaplasmosis CT during the study period. The changes in CT reaction for anaplasmosis between the first and last sample for each of the five herds are shown in Table I. Most of the seroconversions occurred in Ranches 1 and 2. The approximate dates of exposure for the animals on these ranches are shown in Figs. 3 and 4, respectively. Although these two ranches are 30 km apart and were very similar in breed composition, climate, management, and pasture type, new cases at Ranch 1 were concentrated in the spring and fall while at Ranch 2 new cases occurred throughout the year. Of the 35 Brown Swiss cows imported from Texas to a ranch in far southern Vera Cruz state, 28 of 31 (90.3%) and 12 of 31 (38.7%) had seroconversions to B. bigemina and B. bovis, respectively, during the 10week interval between blood samples. Four animals died and most of the TABLE
I
Change in A. marginale card test status b e t w e e n February and November, 1 9 8 3 Ranch
Number Persistent o f animals negative
Seroconversion - to +
Persistent positive
Seroconversion + to -
1 2 3 4 5
38 46 50 19 45
8 11 3 0 1
1 2 0 1 0
2 1 6 1 0
27 32 41 17 44
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Fig. 4. Seroconversionsto A. rnarginale vs. estimated date of exposure (1983) on Ranch 2. rest had signs c o n s i s t e n t w i t h a n a p l a s m o s i s a n d / o r babesiosis. Intensive t r e a t m e n t by t h e herd veterinarian w i t h a variety o f drugs apparently prev e n t e d further losses. On arrival all animals w e r e negative to b o t h Babesia spp. and t o Anaplasma. T h e herd veterinarian v a c c i n a t e d for anaplasmosis, and all animals w e r e p o s i t i v e o n t h e CT after 10 w e e k s . A n acaricide dip w a s used every 7 days. DISCUSSION T h e results indicate that there w a s little activity for either Babesia spp. or A. marginale in the n o r t h e r n part o f the s t u d y area. This w a s u n e x p e c t e d since t h e results f r o m an earlier report indicated that n e w i n f e c t i o n s w e r e occurring in ranches in t h e s a m e area as t h o s e studied here ( T e c l a w
433 et al., 1985a). Since the number of ranches from this area which were sampled m o n t h l y is small (three) it may be that they were not typical of the ranches from the area in general. Ideally, Babesia transmission levels should be determined by serial sampling, as in the five herds followed in this study. However, this is costly in terms of time and m o n e y and severely limits the numbers of herds that can be tested. Also, chance plays an important role because during the 10 m o n t h s of this study, only Herd 2 had a substantial change in exposure status to babesiosis, and then only to B. bigemina. A single sampling one year earlier would have shown a herd with a very low prevalence rate, and a study one year later would have shown a herd with a very high prevalence rate but with little indication as to when transmission had occurred. The cause of the high seroconversion rate for Ranch 2 during the course of the study is not known. Rainfall was below normal for the period, but humidity levels remained high. The data from Ranch 2 indicate that cattle were being exposed to B. bigemina throughout the course of the study, yet Boophilus ticks were seen on only a total of three or four animals during all the visits to this ranch. In addition, all the animals in the study herd were reportedly dipped at ~<3-week intervals. During one visit, a bull which was n o t normally assembled with the other animals was brought up and was seen to be infested with m a n y Boophilus ticks. It is possible that the bulls on this ranch were not regularly dipped and thus seeded the pastures with infected larvae. B. bigemina could have been transmitted by the nymphs (Callow and Hoyte, 1961) which were undetected by us and which were prevented from reaching adulthood by the frequent dipping. Additional field studies are needed to determine the number of ticks necessary to maintain B. bigemina in a herd. A mathematical model for B. bovis by Smith (1983) predicts that infestation by 2--8 adult ticks per day are required to have an epidemiologically unstable situation. Below this level, B. bovis was not maintained in the cattle population, and at > 8 adults per day most cattle are infected before 9 months of age. It should be expected that the seroconversion of 32 of 36 animals for B. bigemina during the study period would have been accompanied by the presence of numerous ticks, especially when infection rates of ~ n l y 0.0004 and 0.0023 for B. bovis and B. bigemina, respectively, are f o u n d in field-collected larvae (Mahoney and Mitre, 1971). Adult cattle are more susceptible to clinical symptoms of Babesia and Anaplasma infections (Latif et al., 1979; Riek, 1968; Smith et al., 1978; Ristic, 1960). From the numerous seroconversions for B. bigemina at Ranch 2 in both young and old animals and from the lack of reports of sick animals by the rancher or by us during our m o n t h l y visits, it can be assumed that under the conditions prevailing on this ranch, B. bigemina and A. marginale did not cause noticeable health problems. The four B. bovis seroconversions included three calves and one adult. Again the lack
434
of reports of sick animals suggests a low pathogenicity, but the numbers involved are too small for a more definitive statement. The results from the imported cattle indicate how rapidly infections can occur in a highly endemic area. B. bigemina was transmitted at a faster rate than B. bovis, an observation also made by others (Friedhoff and Smith, 1981). A mortality rate of 4/35 (11.4%) despite an intensive treatment program points to the need for the development and implementation of programs to prevent losses in the importation of valuable breeding stock into endemic areas of Mexico. 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.
REFERENCES Amerault, T.E. and Roby, T.O., 1968. A rapid card agglutination test for bovine anaplasmosis. J. Am. Vet. Med. Assoc., 153: 1828--1834. Callow, L.L. and Hoyte, H.M.D., 1961. Transmission experiment using Babesia bigemina, Theileria rnutans, Borrelia sp. and the cattle tick Boophilus microplus. Aust. Vet. J., 37: 381--390. Friedhoff, K.T. and Smith, R.D., 1981. Transmission of Babesia by ticks. In: M. Ristic and J.P. Kreier (Editors), Babesiosis. Academic Press, New York, pp. 267--321. Gonzalez, E.F., Long, R.E. and Todorovic, R.A., 1978. Comparison of the complement-fixation, indirect fluorescent antibody and card agglutination tests for the diagnosis of bovine anaplasmosis. Am. J. Vet. Res., 39: 1538--1541. Kuttler, K.L., Adams, L.G. and Todorovic, R.A., 1977. Comparison of the complementfixation and indirect fluorescent antibody reactions in the detection of bovine babesiosis. Am. J. Vet. Res., 38: 153--156. Latif, B.M.A., Said, M.S. and Ali, S.R., 1979. Effect of age on the immune response of cattle experimentally infected with Babesia bigemina. Vet. Parasitol., 5: 307-314. Lobel, H.O. and Kagan, I.G., 1978. Seroepidemiology of parasitic disease. Annu. Rev. Microbiol., 32: 329--347. Mahoney, D.F. and Mirre, G.B., 1971. Bovine babesiosis: estimation of infection rates in the tick vector Boophilus microplus (Canestrini). Ann. Trop. Med. P~rasitol., 65: 309--317. Rick, R.F., 1968. Babesiosis. In: D. Weinman and M. Ristic (Editors), Infectious Blood Diseases of Man and Animals. Vol. II, Academic Press, New York, pp. 219--268. Ristic, M., 1960. Anaplasmosis. Adv. Vet. Sci., 6: 111--192. Ross, J.P.J. and Lohr, K.F., 1 9 7 0 . 0 b e r t r a g u n g und Verweildauer yon Kolostral erworben an Babesia bigemina- und Anaplasma marginale-Antikorpen. Z. Tropenmed. Parasitol., 21: 401--411.
435 Smith, R., 1983. Babesia boris. Computer simulation of the relationship between the tick vector, parasite, and bovine host. Exp. Parasitol., 56: 27--40. Smith, R., Osorno, B.M., Brener, J., De La Rosa, R. and Ristic, M., 1978. Bovine babesiosis: severity and reproducibility of Babesia boris infections induced by Boophilus microplus under laboratory conditions. Res. Vet. Sci., 24 : 287--292. Teclaw, R.F., Romo, S., Garcia, Z., Castaneda, M. and Wagner, GG., 1985a. A seroepidemiologic study of bovine babesiosis in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila. Prey. Vet. Med., 3: 403--415. Teclaw, R.F., Romo, S., Garcia, Z. and Wagner, G.G., 1985b. A serological survey for anaplasmosis in cattle in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila using the card test. Prey. Vet. Med., 3: 417--425. Todorovic, R.A. and Long, R.F., 1976. Comparison of indirect fluorescent antibody (IFA) with complement fixation (CF) tests for diagnosis of Babesia spp. infections in Columbian cattle. Tropenmed. Parasitol., 27: 169--181.
427
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
INCIDENCE OF BABESIOSIS AND ANAPLASMOSIS INFECTIONS IN C A T T L E SAMPLED M O N T H L Y IN T H E MEXICAN S T A T E S OF NUEVO LEON AND SAN LUIS POTOSI
R.F. T E C L A W
I, Z. G A R C I A 2, S. R O M O
3 and G.G. W A G N E R
l
~Department of Veterinary Microbiology and Parasitology, Texas A&M University, College Station, TX 77843 (U.S.A.) 2 Centro Nacional de Parasitologia Animal, Jiutepec, MoreIos (Mexico) 3Faeultad de Medicina Veterinaria Universidad Autonoma de Nuevo Leon, Monterrey (Mexico)
(Accepted for publication 2 July 1985)
ABSTRACT Teclaw, R.F., Garcia, Z., R o m o , S. and Wagner, G.G., 1985. Incidence of babesiosis and anaplasmosis infections in cattle sampled monthly in the Mexican states of Nuevo Leon and San Luis Potosi. Prey. Vet. Med., 3: 427--435. Serum samples from 200 cattle of various ages and breeds from five ranches in the Mexican states of Nuevo Leon and San Luis Potosi were collected monthly (with occasional omissions) between February 1983 and November 1983. These samples were tested for the presence of antibody activity to Babesia bovis and B. bigemina using the indirect fluorescent antibody test and to Anaplasma marginale using the card test. There were seroconversions to Babesia spp. on two of the five ranches. O n one ranch, five of 37 animals originally negative for B. bigemina became positive in late s u m m e r and fall. O n the other ranch, 32 of 36 animals seroconverted to B. bigemina throughout the study period with a moderate peak in mid-summer. Only four of 35 animals became seropositive to B. bovis on this same ranch. Seroconversions to A. rnarginale were detected on four of the five ranches with the majority occurring on the same ranches with Babesia infections.
INTRODUCTION Single-sample serologic surveys have the disadvantage o f n o t providing information on the approximate time of seroconversion. If animals are exposed to new infections at a constant rate, then the age structure o f the population that is infected will give some indication of the disease dynamics (Lobel and Kagan, 1978). However, f r e qu ent l y a constant infection rate cannot be assumed or the age structure of the population is unknown. Although expensive in time and m o n e y , one solution is to sample from the same animals at regular intervals. In this way epidemic curves and temporal effects can be determined directly. As part of a seroepidemiological study
0167-5877/85/$03.30
© 1985 Elsevier Science Publishers B.V.
428
of hemoparasitic diseases in northeastern Mexico (Teclaw et al., 1985a, b), m o n t h l y field visits to five ranches were conducted over a period of 10 months in 1983. The purpose of this paper is to report the results of the indirect fluorescent antibody test (IFAT) for babesiosis and the card test (CT) for anaplasmosis from animals on these ranches. MATERIALS AND METHODS
Ranches The Fidiecomiso Campana Nacional Contra la Garrapata (National Tick Eradication Campaign) of the Mexican government provided contact with five ranchers in the states of Nuevo Leon and San Luis Potosi. The ranches were not chosen at random but were selected according to the owners' willingness to assemble the cattle each m o n t h for an extended period of time. Thirty-five Brown Swiss, 2-year-old heifers imported from Texas into Mexico (Ranch 6) were also included in the study. We had intended to take serum samples from these latter animals each m o n t h , but only a pre-shipment sampling in Texas and one sampling 10 weeks after their arrival in Mexico were completed. The locations of the six ranches in relation to the study area of the previously described survey is shown in Fig. 1. Animals Forty, 46, 50, 19 and 45 animals on Ranches 1--5, respectively, were identified with plastic eartags. These animals were not randomly selected
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429 nor did they consist of the entire herd. Only adult animals were sampled on Ranches 1 and 5, while approximately equal numbers of adults and calves were tested on the other ranches. Zebu and zebu-cross cattle predominated on Ranches 1--4 and constituted about half of the animals on Ranch 5. The remainder of animals on Ranch 5 were Brown Swiss.
Sampling It was planned to visit each ranch once a m o n t h to take blood samples. However, due to problems beyond our control, not all ranches were sampled each m o n t h and a o t every animal was assembled during each visit.
Serology The IFAT was used to determine antibody activity to Babesia bovis and B. bigemina as described earlier (Todorovic and Long, 1974; Teclaw et al., 1985a). Sera from the first and last sample dates for each animal were tested at 2-fold dilutions beginning at 1:80. When a 4-fold increase in antibody titer was found, the intervening samples for that animal were tested to determine the approximate date of seroconversion. The date was determined by taking the mid-point of the interval between the last negative test and the first positive test and then subtracting the number of days required for test reactivity to occur after infection. These periods are approximately 15 days for Babesia spp. (Ross and Lohr, 1968; Kuttler et al., 1977). The CT was used to test for antibody activity to Anaplasma marginale (Amerault and Roby, 1968) in the same manner except that dilutions were not made and 21 days was used for the number of days required for a positive test after infection (Gonzalez et al., 1978). RESULTS There were seroconversions to Babesia spp. in Ranches 1 and 2. Both herds are about 400 km south of the main study area reported earlier (Teclaw et al., 1985a, b). The remaining 3 herds, in which no seroconversions for Babesia spp. were detected, were located within the main study area. In Herd 1, five of 37 animals at risk (previously uninfected based on negative IFAT) to B. bigemina infection had seroconversions. Exposures were estimated to have occurred close to the following dates: 1 August, one animal; 1 October, one animal; and 1 November, three animals. In Herd 2, 22 of 36 animals at risk of B. bigemina infection had seroconversions at various times t h r o u g h o u t the test period. Figure 2 illustrates the incidence for Herd 2 of B. bigemina infections (new infections divided by remaining animals at risk) vs. date for the period from 1 February 1983 to 15 October 1983. A rolling incidence (3 period average) was used to even o u t random variations. Four of 35 animals in Herd 2
430 originally at risk to B. bovis infection had seroconversions at the approximate dates indicated in Fig. 2. The sera collected each m o n t h from animals which seroconverted during the study were tested against both Babesia antigens, even if seroconversion occurred to only one of them. It was noticed that sera originally negative to both B. bovis and B. bigemina at a 1:80 dilution became positive to both during the same month. The B. bigemina titers were usually ~>1:2560 while the B. bovis titers were 1:80 or 1:160. These low titers to B. bovis were considered to be cross-reactions and were therefore graded negative. Of the four animals which had strong seroconversions to B. bovis at high titer, two had seroconversions to B. bigemina during the same m o n t h and two remained negative to B. bigemina. Most of the animals in the five serially-sampled herds which had antibody titers at the start of the survey either had a 1- or 2-fold drop in titer or remained at the same titer but with lowered intensity of fluorescence by the end of the study. This was observed for both B. bovis and B. bigemina and indicates that antibody titers to these two organisms remain relatively stable for />10 months. Only 11 of 108 animals from all five herds which started the study with antibody titers to B. bigemina had become negative at the end; of these, 10 originally had titers of 1:80 and one had a titer of 1:160. Only six of 73 animals which started the survey with antibody titers
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Fig. 2. Ranch 2 (1983). Seroeonversions to B. bigemina vs. estimated dates of exposure as percentage of remaining animals at risk (solid line) and rolling average (3 period) of the same data (broken line). Triangles (A) designate estimated dates of seroconversion to B. boris.
431
to B. bovis had become negative by the end, and of these six animals, five had titers of 1:80 and one had a titer of 1:160 originally. In Herd 2, in which the incidence of B. bigemina infections was very high, only one animal of the 10 with antibody titers at the start of the survey experienced a 4-fold rise in antibody titer at the end. All of these animals were probably exposed to reinfections, but no change was apparent in the IFAT, except in the single animal. This indicates that superinfection did not noticeably increase antibody titers on the IFAT. On Ranch 5, only 4% and 17% of the animals < 1 year of age at the start of the study were positive to B. bovis and B. bigemina, respectively, while 96% of the adults were positive for each species. This indicates that Babesia spp. were circulating in the herd no sooner than 1 year before the start of the study but had not been active since that time. On Ranch 4, all of the animals tested were adults and 100% had antibody titers to B. bigemina. Thirty-two percent reacted positively for B. bovis, all at low titers. This is the greatest difference in prevalence rates between Babesia spp. seen on any of the ranches in this or the previous study (Teclaw et al., 1985a). This suggests that B. bovis may no longer be active in this herd and that only B. bigemina remains. Animals on Ranches 1--3 and 5 seroconverted from negative to positive on the anaplasmosis CT during the study period. The changes in CT reaction for anaplasmosis between the first and last sample for each of the five herds are shown in Table I. Most of the seroconversions occurred in Ranches 1 and 2. The approximate dates of exposure for the animals on these ranches are shown in Figs. 3 and 4, respectively. Although these two ranches are 30 km apart and were very similar in breed composition, climate, management, and pasture type, new cases at Ranch 1 were concentrated in the spring and fall while at Ranch 2 new cases occurred throughout the year. Of the 35 Brown Swiss cows imported from Texas to a ranch in far southern Vera Cruz state, 28 of 31 (90.3%) and 12 of 31 (38.7%) had seroconversions to B. bigemina and B. bovis, respectively, during the 10week interval between blood samples. Four animals died and most of the TABLE
I
Change in A. marginale card test status b e t w e e n February and November, 1 9 8 3 Ranch
Number Persistent o f animals negative
Seroconversion - to +
Persistent positive
Seroconversion + to -
1 2 3 4 5
38 46 50 19 45
8 11 3 0 1
1 2 0 1 0
2 1 6 1 0
27 32 41 17 44
432 Seroconver sions []
•
Rolling average
(3 Deriocl) 4 x \ \
\ \ \
o
.-.-.-
3"
\ \ \ %\\ \ \ \ \ \ \ \ \ \
o
o
2
\ \ x \ \ \
i
i
"'"
i
15
15
15
Feb.
Mar.
April
1
f 15 June
15 May
,
-
T 15 July
i
-
i - , 15 August
15
15
15
Sept,
Oct.
Nov.
Fig. 3. Seroconversions to A. marginale vs. estimated date of exposure (1983) on Ranch 1. 5-
Seroconversions
[]
Rolling average (3 D e r i o d )
o
3 x \ \ xx~
x \ \ xxx x \ \
\ x \ xxx
\ \ \
15 Feb.
Mar.
15
15
15
15
15
15
15
15
April
May
June
July
August
Sept.
Oct.
Nov.
Fig. 4. Seroconversionsto A. rnarginale vs. estimated date of exposure (1983) on Ranch 2. rest had signs c o n s i s t e n t w i t h a n a p l a s m o s i s a n d / o r babesiosis. Intensive t r e a t m e n t by t h e herd veterinarian w i t h a variety o f drugs apparently prev e n t e d further losses. On arrival all animals w e r e negative to b o t h Babesia spp. and t o Anaplasma. T h e herd veterinarian v a c c i n a t e d for anaplasmosis, and all animals w e r e p o s i t i v e o n t h e CT after 10 w e e k s . A n acaricide dip w a s used every 7 days. DISCUSSION T h e results indicate that there w a s little activity for either Babesia spp. or A. marginale in the n o r t h e r n part o f the s t u d y area. This w a s u n e x p e c t e d since t h e results f r o m an earlier report indicated that n e w i n f e c t i o n s w e r e occurring in ranches in t h e s a m e area as t h o s e studied here ( T e c l a w
433 et al., 1985a). Since the number of ranches from this area which were sampled m o n t h l y is small (three) it may be that they were not typical of the ranches from the area in general. Ideally, Babesia transmission levels should be determined by serial sampling, as in the five herds followed in this study. However, this is costly in terms of time and m o n e y and severely limits the numbers of herds that can be tested. Also, chance plays an important role because during the 10 m o n t h s of this study, only Herd 2 had a substantial change in exposure status to babesiosis, and then only to B. bigemina. A single sampling one year earlier would have shown a herd with a very low prevalence rate, and a study one year later would have shown a herd with a very high prevalence rate but with little indication as to when transmission had occurred. The cause of the high seroconversion rate for Ranch 2 during the course of the study is not known. Rainfall was below normal for the period, but humidity levels remained high. The data from Ranch 2 indicate that cattle were being exposed to B. bigemina throughout the course of the study, yet Boophilus ticks were seen on only a total of three or four animals during all the visits to this ranch. In addition, all the animals in the study herd were reportedly dipped at ~<3-week intervals. During one visit, a bull which was n o t normally assembled with the other animals was brought up and was seen to be infested with m a n y Boophilus ticks. It is possible that the bulls on this ranch were not regularly dipped and thus seeded the pastures with infected larvae. B. bigemina could have been transmitted by the nymphs (Callow and Hoyte, 1961) which were undetected by us and which were prevented from reaching adulthood by the frequent dipping. Additional field studies are needed to determine the number of ticks necessary to maintain B. bigemina in a herd. A mathematical model for B. bovis by Smith (1983) predicts that infestation by 2--8 adult ticks per day are required to have an epidemiologically unstable situation. Below this level, B. bovis was not maintained in the cattle population, and at > 8 adults per day most cattle are infected before 9 months of age. It should be expected that the seroconversion of 32 of 36 animals for B. bigemina during the study period would have been accompanied by the presence of numerous ticks, especially when infection rates of ~ n l y 0.0004 and 0.0023 for B. bovis and B. bigemina, respectively, are f o u n d in field-collected larvae (Mahoney and Mitre, 1971). Adult cattle are more susceptible to clinical symptoms of Babesia and Anaplasma infections (Latif et al., 1979; Riek, 1968; Smith et al., 1978; Ristic, 1960). From the numerous seroconversions for B. bigemina at Ranch 2 in both young and old animals and from the lack of reports of sick animals by the rancher or by us during our m o n t h l y visits, it can be assumed that under the conditions prevailing on this ranch, B. bigemina and A. marginale did not cause noticeable health problems. The four B. bovis seroconversions included three calves and one adult. Again the lack
434
of reports of sick animals suggests a low pathogenicity, but the numbers involved are too small for a more definitive statement. The results from the imported cattle indicate how rapidly infections can occur in a highly endemic area. B. bigemina was transmitted at a faster rate than B. bovis, an observation also made by others (Friedhoff and Smith, 1981). A mortality rate of 4/35 (11.4%) despite an intensive treatment program points to the need for the development and implementation of programs to prevent losses in the importation of valuable breeding stock into endemic areas of Mexico. 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.
REFERENCES Amerault, T.E. and Roby, T.O., 1968. A rapid card agglutination test for bovine anaplasmosis. J. Am. Vet. Med. Assoc., 153: 1828--1834. Callow, L.L. and Hoyte, H.M.D., 1961. Transmission experiment using Babesia bigemina, Theileria rnutans, Borrelia sp. and the cattle tick Boophilus microplus. Aust. Vet. J., 37: 381--390. Friedhoff, K.T. and Smith, R.D., 1981. Transmission of Babesia by ticks. In: M. Ristic and J.P. Kreier (Editors), Babesiosis. Academic Press, New York, pp. 267--321. Gonzalez, E.F., Long, R.E. and Todorovic, R.A., 1978. Comparison of the complement-fixation, indirect fluorescent antibody and card agglutination tests for the diagnosis of bovine anaplasmosis. Am. J. Vet. Res., 39: 1538--1541. Kuttler, K.L., Adams, L.G. and Todorovic, R.A., 1977. Comparison of the complementfixation and indirect fluorescent antibody reactions in the detection of bovine babesiosis. Am. J. Vet. Res., 38: 153--156. Latif, B.M.A., Said, M.S. and Ali, S.R., 1979. Effect of age on the immune response of cattle experimentally infected with Babesia bigemina. Vet. Parasitol., 5: 307-314. Lobel, H.O. and Kagan, I.G., 1978. Seroepidemiology of parasitic disease. Annu. Rev. Microbiol., 32: 329--347. Mahoney, D.F. and Mirre, G.B., 1971. Bovine babesiosis: estimation of infection rates in the tick vector Boophilus microplus (Canestrini). Ann. Trop. Med. P~rasitol., 65: 309--317. Rick, R.F., 1968. Babesiosis. In: D. Weinman and M. Ristic (Editors), Infectious Blood Diseases of Man and Animals. Vol. II, Academic Press, New York, pp. 219--268. Ristic, M., 1960. Anaplasmosis. Adv. Vet. Sci., 6: 111--192. Ross, J.P.J. and Lohr, K.F., 1 9 7 0 . 0 b e r t r a g u n g und Verweildauer yon Kolostral erworben an Babesia bigemina- und Anaplasma marginale-Antikorpen. Z. Tropenmed. Parasitol., 21: 401--411.
435 Smith, R., 1983. Babesia boris. Computer simulation of the relationship between the tick vector, parasite, and bovine host. Exp. Parasitol., 56: 27--40. Smith, R., Osorno, B.M., Brener, J., De La Rosa, R. and Ristic, M., 1978. Bovine babesiosis: severity and reproducibility of Babesia boris infections induced by Boophilus microplus under laboratory conditions. Res. Vet. Sci., 24 : 287--292. Teclaw, R.F., Romo, S., Garcia, Z., Castaneda, M. and Wagner, GG., 1985a. A seroepidemiologic study of bovine babesiosis in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila. Prey. Vet. Med., 3: 403--415. Teclaw, R.F., Romo, S., Garcia, Z. and Wagner, G.G., 1985b. A serological survey for anaplasmosis in cattle in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila using the card test. Prey. Vet. Med., 3: 417--425. Todorovic, R.A. and Long, R.F., 1976. Comparison of indirect fluorescent antibody (IFA) with complement fixation (CF) tests for diagnosis of Babesia spp. infections in Columbian cattle. Tropenmed. Parasitol., 27: 169--181.