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A serological survey for anaplasmosis in cattle in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila using the card test
Preventive Veterinary Medicine, 3 (1985) 417--425 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
417
A SEROLOGICAL SURVEY FOR ANAPLASMOSIS IN C A T T L E IN THE MEXICAN STATES OF NUEVO LEON, TAMAULIPAS AND COAHUILA USING THE CARD TEST
R.F. TECLAW', S. ROMO', Z. G A R C I A 3 and G.G. W A G N E R ' 'Department of Veterinary Microbiology and Parasitology, Texas A & M University, College Station, T X 77843 (U.S.A.) "Facultad de Medicina Veterinaria, Universidad Autonoma de Nuevo Leon, Monterrey
(Mexico) 3Centro Nacional de Parasitologia Animal, Jiutepec, Morelos (Mexico) (Accepted for publication 2 July 1985)
ABSTRACT
Teclaw, R.F., Romo, S., Garcia, Z. and Wagner, G.G., 1985. A serologicalsurvey for anaplasmosis in cattlein the Mexican statesof Nuevo Leon, Tamaulipas and Coahuila using the card test.Prey. Vet. Med., 3: 417--425. Blood samples from 2156 cattle from 40 herds in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila were tested for antibody activity to Anaplasma marginale using the card test. Herd prevalence rates ranged from 0 to 86% with a mean of 22%. Analysis of joint positivity to A. marginale and Babesia boris and to A. marginale and B. bigemina in individual animals resulted in the rejection of the null hypothesis of no association in 7 and 8 of 37 herds, respectively.
INTRODUCTION
T h e rickettsia, Anaplasma marginale, causes e x t e n s i v e e c o n o m i c losses t o c a t t l e p r o d u c e r s in t h e s o u t h e r n and w e s t e r n U n i t e d States, w h e r e t h e disease is e n d e m i c . Several v e c t o r s , including ticks, biting flies a n d m o s q u i t o e s , have b e e n s h o w n t o t r a n s m i t a n a p l a s m o s i s (Ristic, 1968). In Australia t h e cattle tick, Boophilus microplus, is t h e o n l y m a j o r v e c t o r ( R o g e r s a n d Shiels, 1 9 7 9 ) ; h o w e v e r , t h e a b s e n c e o f this species f r o m t h e U n i t e d States and an overall r e a c t o r r a t e t o t h e c o m p l e m e n t f i x a t i o n (CF) t e s t o f 14% ( U S D A , 1 9 7 3 ) d e m o n s t r a t e t h e i m p o r t a n c e o f o t h e r m e a n s o f transmission. A s u r v e y o f p r o d u c e r s and veterinarians in T e x a s ( A l d e r i n k and Dietrich, 1 9 8 2 ) i n d i c a t e d t h a t a n a p l a s m o s i s was an i m p o r t a n t a n i m a l h e a l t h p r o b l e m in t h r e e areas o f t h e state; t h e e x t r e m e n o r t h e a s t , t h e E d w a r d s P l a t e a u in t h e c e n t e r o f t h e s t a t e and t h e u p p e r G u l f coast. T h e p r i n c i p a l v e c t o r s w e r e c o n s i d e r e d to be biting flies in t h e s u m m e r a n d t h e tick, Dermacentor
0167-5877/85/$03.30
© 1985 Elsevier Science Publishers B.V.
418
albipictus, in the winter. The endemic focus along the Gulf coast coincides with the major rice-growing counties of Texas, and the black riceland mosquito, Psorophora columbine, has been suggested to be an important vector in this region. There were few clinical cases of anaplasmosis reported from extreme southern Texas according to the survey. Little information exists on the prevalence of anaplasmosis in northeastern Mexico, an area with similar climate and vegetation to south Texas, but with an endemic population of Boophilus spp. ticks. Osorno and Ristic (1977) reported an overall anaplasmosis reactor rate of 7.9% for the five northern Mexican states of Nuevo Leon, Coahuila, Chihuahua, Durango and Zacatecas. The data for the individual states were not presented. A seroepidemiologic study of hemoparasitic diseases in cattle in northeastern Mexico was carried out. The results for babesiosis were reported earlier (Teclaw et al., 1985). The purpose of this paper is to report the results of a serologic survey for anaplasmosis in 40 cattle herds in northeastern Mexico using the card test (CT) (Amerault and Roby, 1968). MATERIALS AND METHODS Blood samples from 2156 cattle in 40 herds located in and adjacent to the state of Nuevo Leon, Mexico were collected from April 1982 to November 1983. Sampling procedures have been described earlier (Teclaw et al., 1985). The number of samples tested differs from the previous report because not all sera were tested for antibody activity to Babesia spp. when large numbers of sera were collected from the same ranch. Although neither herds nor the animals within the herds were sampled randomly, a broad geographic representation was achieved. The sera were separated and stored at - 2 0 ° C until tested with the anaplasmosis CT (Brewer Diagnostic Kits, Hynson, Westcott and Dunning, Inc., Baltimore, MD). The results were expressed as the percentage positive for each herd. Inoculation rates were calculated for herds for which age data were collected using the formula:
I = 1 - e -ht (Mahoney and Ross, 1972), where I is the proportion positive, e is the base of the natural logarithms, h is the inoculation rate (daily probability of infection for each animal) and t is the average age in days. Since both Babesia spp. and Anaplasma share a vector, Boophilus spp., and since cross-reactions between Babesia spp. and other hemoparasites are known to occur (Ludford et al., 1972), a test of association was performed to determine if a positive reaction to the anaplasmosis CT is associated with a positive reaction to the indirect immunofluorescent antibody test (IFAT) for Babesia. A hypergeometric model suggested by Fager (1957) was used.
419 RESULTS Table I lists the number of animals tested, the prevalence rate and the inoculation rate (20 ranches) for each ranch. Reactor rates ranged from 0 TABLE I Anaplasmosis herd prevalence rates for antibody activityand inoculation rates Herd
No. tested
Proportion positive
Inoculation rate
1 2 3 4
114 98 38 110
0.30 0.04 0.01 0.01
---0.000007
5
200
0.18
--
6
100
0.35
--
7 8 9 I0 II 12 13 14 15
I00
0.54 0.18 0.26 0.15 0.33 0.00 0.31 0.17 0.21
------0.000000 0.000080 0.000250
16 17 18 19
42 27 29 34
0.i0 0.04 0.17 0.09
--0.000180 0.000048
20 21 22
29 15 7
0.55 0.13 0.86
23 24 25 26 27 28 29 30 31 32 33
52 7 142 92 16 8 24 21 21 11 11
0.10 0.43 0.10 0.26 0.06 0.00 0.04 0.10 0.19 0.00 0,36
--0.000047 -0.000057 0.000210 0.000023 0.000000 0.000020 0.000028 -0.000000 0.000290
34 35 36 37 38 39 40
58 15 22 27 15 26 31
0.09 0.40 0.68 0.52 0.13 0.04 0.42
-0.000490 -0.000390 0.000320 0.000025 0.000400
345 50 26 27 19 86 18 43
a
--
aRanches where inoculation rates were calculated based on fewer than the number of animals indicated.
420 to 86% with a ranch mean of 22.3%. T he inoculation rates were calculated from age data and ranged from 0 to 0.00049 infective bites per day from all sources. The location and approximate prevalence rate for each herd are shown in Fig. 1. The location and inoculation rate for 20 ranches are represented in Fig. 2. The relative frequencies of prevalence rates are graphed in Fig. 3. Herds with low prevalence rates predominate. A scatter plot of prevalence vs. inoculation rate is presented in Fig. 4. Because of the different age structures of herds among ranches, inoculation rates varied widely for similar prevalence rates: age-dependent prevalence rates for the 20 herds for which the ages of the cattle were known are presented in Fig. 5. The exact P values for the observed joint positives to A. marginale and B. boris and to A. rnarginale and B. bigernina were c o m p u t e d for 37 ranches using the hypergeometric model suggested by Fager (1957). The P values indicate that the null hypothesis of no association at the = < 0.05 level of significance is rejected in 7 and 8 herds for B. boris and B. bigemina, respectively. 0
(~
(~ TEXAS Nuevo Laredo
COAHUILA
Saffilt
eynosa
PREVALENCE (40 HERDS)X,~ {CARD TEST) (
0 o-,o~ ~-2o~ 2,-3o,
}(
__/
f % )
\
l,,-loo~ N~ I
(1I ~
, .ILO~E,.S , o 20 ,'o 6'o ~o
\
\
}
............
TAMAULIPAS
~
1I I
/
%
O .*
c i ~ a d victo,,a
o
<~" ~
Fig. 1. Herd location and approximate prevalence rates for antibody activity to A. marginale in bovine sera collected during the period April 1981 to November 1983.
421
~ ] ) ~
j
TEXAS
h t-.o-.oo
COAHO,,A ~NUEVO~EON/ L~
•
eynosa
INOCULATIONRATES(20 HERDS) [ O ,~ .(:~OE~ to .0001~00 I .000101to .000200 O .000201to .000300~
(~ t""-/
TAMAULIPAS
._o.=\ 7oo ,000301 to . 0 0 0 4 0 0
+ " I
t
~
I
[ $ ~
~ C"
,
0
c~ w~o.. .,.~o,~,.=, 20 40 60 80
Fig. 2. Herd location and approximate inoculation rates for antibody activity to A. marginale in bovine sera collected during the period of April 1982 to November 1983.
.250] "2251~
.200~
~ .,oo~
6 ~ ,0 ,'s 2'0 2'5 3b 3's 4b .'s 50 5'5 8'0 6'5 7b is s'o Prevalence (percent)
~00
Fig. 3. Relative frequency of herd prevalence rates for antibody activity to .4. marginale.
422 500
450
400 350
300
250
200
150
100 ¸
50-
lo
20
30 Prevalence
4o
so
6o
(percent)
Fig. 4. Scatter plot of inoculation vs. prevalence rates for A. marginale.
60"
~----v'~
50"
"~
40-
~
30"
5
24 ~ ~ 4
4 3 4
> @
~.
5
20-
9
76 45
30
tO.
2
3
4
5
6 7 Months
8
9
10
11
1
2
3
4
5
6
7 Years
8
9
10
11
12 >-13
Fig. 5. Prevalence rates for antibody activity to A. marginale vs. age. N u m b e r s refer to animals at each age.
423 DISCUSSION The data demonstrate that anaplasmosis is widely distributed throughout the study area. No overt spacial pattern to the distribution is readily apparent. The predominance of low prevalence and inoculation rates can be explained by a low transmission rate for anaplasmosis or by a rapid serologic recovery rate as determined by the CT (MacDonald, 1950a, b). When reinfection is absent and infection is cleared with tetracycline, CT reactors begin to become non-reactors by about 6 months (Magonigle and Newby, 1982). Untreated natural and experimental infections have remained positive to the CT for /> 10 months (Gonzalez et al., 1978). Thus if reactor status is lost at about the same rate as new infections are occurring, high serologic prevalence rates will be uncommon. Another result of the short period of CT reactivity is that most of the animals with positive sera must have been carrying Anaplasma within a year of blood collection, indicating that new infections or reinfections were occurring during or immediately prior to the time the samples were collected. Since the age composition of the herds under study differed, inoculation rates were calculated as a means of age adjustment. These rates were used by Mahoney and Ross (1972) to determine the average probability of a tick infected with Babesia feeding on one bovine each day. Because anaplasmosis can be transmitted by several different vectors, inoculation rates do not have the same significance as they do in babesiosis, but they do provide a measure of the rate of occurrence of new infections. The short time period before seroreactivity to the CT is lost means that the estimated inoculation rates for Anaplasma infection are probably much below the true rates. The scatter plot of prevalence vs. inoculation rates (Fig. 4) illustrates how herds with similar prevalence rates but different age structures can have very dissimilar inoculation rates. For example, at prevalence rates of approximately 10, 15 and 40%, h can vary over 60%. The variation in h with constant prevalence is much less for Anaplasma than that found for Babesia where up to 7-fold differences were found (Teclaw et al., 1985). Since the CT recovery rate for anaplasmosis is much greater than the IFAT recovery rate for babesiosis (Magonigle and Newby, 1982; Callow et al., 1976), the effect of age on the prevalence rates should be less in the former. Since these same sera were tested for the presence of antibody activity to Babesia spp., it was of interest to see if any relationship existed between anaplasmosis and babesiosis reactivity in the same animal. The association could be due to test cross-reactions, vector sharing, similar favorable habitats for the two hemoparasites or their vectors, and management factors which favor their propagation. The test of association indicates that for most herds (30 and 29 of 37) at the cc < 0.05 significance level an animal with a positive CT reaction for anaplasmosis is not more likely to be positive on the IFAT for either Babesia species than an animal that is CT negative for anaplasmosis. This is different from saying that herds with a high prevalence
424 of anaplasmosis also have a high prevalence of babesiosis. In the herds in which association occurs, it can be partially explained by the shared vectors, Boophilus spp. ticks. However, ot her vectors are probabl y involved in the transmission o f anaplasmosis in northeastern Mexico. It m ay be that the situation in Mexico is similar to t h a t in Australia where B. microplus is considered the only major vector for anaplasmosis (Rogers and Shiels, 1979). Also, the possibility of cross-reactions between the CT for anaplasmosis and the IFAT for babesiosis must also be considered. ACKNOWLEDGEMENTS This report is based upon work supported by the U.S. D e p a r t m e n t of Agriculture under Agreement No. USDA/OICD/MX-TX-116 and the Texas Agricultural Ex per i m ent Station Project No. TAES-H-6261. Any opinions, findings, conclusions or r e c o m m e n d a t i o n s expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. D e par tmen t o f 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 Alderink, F.J. and Dietrich, R.A., 1982. Economic and epidemiological implications of anaplasmosis in Texas cattle herds. Proc. 86th Annual Meeting of the U.S. Animal Health Association, Nashville, TN, pp. 66--75. 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., Emmerson, F.R., Parker, R.J. and Knott, S.G., 1976. Infection rates and outbreaks of disease due to Babesia argentina in unvaccinated cattle on 5 beef properties in south-eastern Queensland. Aust. Vet. J., 52 : 446--450. Fager, E.W., 1957. Determination and analysis of recurrent groups. Ecology, 38: 586--
595. Gonzalez, E.F., Long, R.F. and Todorovic, R.A., 1978. Comparison of the complementfixation, indirect fluorescent antibody and card agglutination tests for the diagnosis of bovine anaplasmosis. Am. J. Vet. Res., 39: 1538--1541. Ludford, C.G., Hall, W.T.K., Sulzar, A.J. and Wilson, M., 1972. Babesia argentina, Plasmodium vivax, and P. falciparum: antigenic cross reactions. Exp. Parasitol., 32: 317--326. MacDonald, G., 1950a. The analysis of infection rates in diseases in which superinfection occurs. Trop. Dis. Bull., 47: 907--915. MacDonald, G., 1950b. The analysis of malaria parasite rates in infants. Trop. Dis. Bull., 47: 915--938. Magonigle, R.A. and Newby, T.J., 1982. Elimination of naturally acquired chronic Anaplasma marginale infections with a long-acting oxytetracyctine injectable. Am. J. Vet. Res., 43: 2170--2172. Mahoney, D.F. and Ross, D.R., 1972. Epizootiologic factors in the control of bovine babesiosis. Aust. Vet. J., 48: 292--298.
425 Osorno, M. and Ristic, M., 1977. Anaplasmosis bovina con enfasis en control, diagnostico, distribucion de la enfermedad en Mexico y uso de una vacuna atenuada de Anaplasma marginale. Veterinaria (Mexico), 8 : 85--98. Ristic, M., 1968. Anaplasmosis. In: D. Weinman and M. Ristic (Editors), Infectious Blood Diseases of Man and Animals. Vol. II, Academic Press, New York, pp. 473-542. Rogers, R.J. and Shiels, I.A., 1979. Epidemiology and control of anaplasmosis in Australia. J. S. Afr. Vet. Assoc., 50: 363--366. Teclaw, R.F., Romo, S., Garcia, Z., Castaneda, M. and Wagner, G.G., 1985. A seroepidemiologic study of bovine babesiosis in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila. Prey. Vet. Med., 3: 403--415. United States Department of Agriculture, 1973. A national anaplasmosis serologic survey. Unpublished report. Veterinary Services, Animal and Plant Health Inspection Service, USDA, Washington, D.C.
417
A SEROLOGICAL SURVEY FOR ANAPLASMOSIS IN C A T T L E IN THE MEXICAN STATES OF NUEVO LEON, TAMAULIPAS AND COAHUILA USING THE CARD TEST
R.F. TECLAW', S. ROMO', Z. G A R C I A 3 and G.G. W A G N E R ' 'Department of Veterinary Microbiology and Parasitology, Texas A & M University, College Station, T X 77843 (U.S.A.) "Facultad de Medicina Veterinaria, Universidad Autonoma de Nuevo Leon, Monterrey
(Mexico) 3Centro Nacional de Parasitologia Animal, Jiutepec, Morelos (Mexico) (Accepted for publication 2 July 1985)
ABSTRACT
Teclaw, R.F., Romo, S., Garcia, Z. and Wagner, G.G., 1985. A serologicalsurvey for anaplasmosis in cattlein the Mexican statesof Nuevo Leon, Tamaulipas and Coahuila using the card test.Prey. Vet. Med., 3: 417--425. Blood samples from 2156 cattle from 40 herds in the Mexican states of Nuevo Leon, Tamaulipas and Coahuila were tested for antibody activity to Anaplasma marginale using the card test. Herd prevalence rates ranged from 0 to 86% with a mean of 22%. Analysis of joint positivity to A. marginale and Babesia boris and to A. marginale and B. bigemina in individual animals resulted in the rejection of the null hypothesis of no association in 7 and 8 of 37 herds, respectively.
INTRODUCTION
T h e rickettsia, Anaplasma marginale, causes e x t e n s i v e e c o n o m i c losses t o c a t t l e p r o d u c e r s in t h e s o u t h e r n and w e s t e r n U n i t e d States, w h e r e t h e disease is e n d e m i c . Several v e c t o r s , including ticks, biting flies a n d m o s q u i t o e s , have b e e n s h o w n t o t r a n s m i t a n a p l a s m o s i s (Ristic, 1968). In Australia t h e cattle tick, Boophilus microplus, is t h e o n l y m a j o r v e c t o r ( R o g e r s a n d Shiels, 1 9 7 9 ) ; h o w e v e r , t h e a b s e n c e o f this species f r o m t h e U n i t e d States and an overall r e a c t o r r a t e t o t h e c o m p l e m e n t f i x a t i o n (CF) t e s t o f 14% ( U S D A , 1 9 7 3 ) d e m o n s t r a t e t h e i m p o r t a n c e o f o t h e r m e a n s o f transmission. A s u r v e y o f p r o d u c e r s and veterinarians in T e x a s ( A l d e r i n k and Dietrich, 1 9 8 2 ) i n d i c a t e d t h a t a n a p l a s m o s i s was an i m p o r t a n t a n i m a l h e a l t h p r o b l e m in t h r e e areas o f t h e state; t h e e x t r e m e n o r t h e a s t , t h e E d w a r d s P l a t e a u in t h e c e n t e r o f t h e s t a t e and t h e u p p e r G u l f coast. T h e p r i n c i p a l v e c t o r s w e r e c o n s i d e r e d to be biting flies in t h e s u m m e r a n d t h e tick, Dermacentor
0167-5877/85/$03.30
© 1985 Elsevier Science Publishers B.V.
418
albipictus, in the winter. The endemic focus along the Gulf coast coincides with the major rice-growing counties of Texas, and the black riceland mosquito, Psorophora columbine, has been suggested to be an important vector in this region. There were few clinical cases of anaplasmosis reported from extreme southern Texas according to the survey. Little information exists on the prevalence of anaplasmosis in northeastern Mexico, an area with similar climate and vegetation to south Texas, but with an endemic population of Boophilus spp. ticks. Osorno and Ristic (1977) reported an overall anaplasmosis reactor rate of 7.9% for the five northern Mexican states of Nuevo Leon, Coahuila, Chihuahua, Durango and Zacatecas. The data for the individual states were not presented. A seroepidemiologic study of hemoparasitic diseases in cattle in northeastern Mexico was carried out. The results for babesiosis were reported earlier (Teclaw et al., 1985). The purpose of this paper is to report the results of a serologic survey for anaplasmosis in 40 cattle herds in northeastern Mexico using the card test (CT) (Amerault and Roby, 1968). MATERIALS AND METHODS Blood samples from 2156 cattle in 40 herds located in and adjacent to the state of Nuevo Leon, Mexico were collected from April 1982 to November 1983. Sampling procedures have been described earlier (Teclaw et al., 1985). The number of samples tested differs from the previous report because not all sera were tested for antibody activity to Babesia spp. when large numbers of sera were collected from the same ranch. Although neither herds nor the animals within the herds were sampled randomly, a broad geographic representation was achieved. The sera were separated and stored at - 2 0 ° C until tested with the anaplasmosis CT (Brewer Diagnostic Kits, Hynson, Westcott and Dunning, Inc., Baltimore, MD). The results were expressed as the percentage positive for each herd. Inoculation rates were calculated for herds for which age data were collected using the formula:
I = 1 - e -ht (Mahoney and Ross, 1972), where I is the proportion positive, e is the base of the natural logarithms, h is the inoculation rate (daily probability of infection for each animal) and t is the average age in days. Since both Babesia spp. and Anaplasma share a vector, Boophilus spp., and since cross-reactions between Babesia spp. and other hemoparasites are known to occur (Ludford et al., 1972), a test of association was performed to determine if a positive reaction to the anaplasmosis CT is associated with a positive reaction to the indirect immunofluorescent antibody test (IFAT) for Babesia. A hypergeometric model suggested by Fager (1957) was used.
419 RESULTS Table I lists the number of animals tested, the prevalence rate and the inoculation rate (20 ranches) for each ranch. Reactor rates ranged from 0 TABLE I Anaplasmosis herd prevalence rates for antibody activityand inoculation rates Herd
No. tested
Proportion positive
Inoculation rate
1 2 3 4
114 98 38 110
0.30 0.04 0.01 0.01
---0.000007
5
200
0.18
--
6
100
0.35
--
7 8 9 I0 II 12 13 14 15
I00
0.54 0.18 0.26 0.15 0.33 0.00 0.31 0.17 0.21
------0.000000 0.000080 0.000250
16 17 18 19
42 27 29 34
0.i0 0.04 0.17 0.09
--0.000180 0.000048
20 21 22
29 15 7
0.55 0.13 0.86
23 24 25 26 27 28 29 30 31 32 33
52 7 142 92 16 8 24 21 21 11 11
0.10 0.43 0.10 0.26 0.06 0.00 0.04 0.10 0.19 0.00 0,36
--0.000047 -0.000057 0.000210 0.000023 0.000000 0.000020 0.000028 -0.000000 0.000290
34 35 36 37 38 39 40
58 15 22 27 15 26 31
0.09 0.40 0.68 0.52 0.13 0.04 0.42
-0.000490 -0.000390 0.000320 0.000025 0.000400
345 50 26 27 19 86 18 43
a
--
aRanches where inoculation rates were calculated based on fewer than the number of animals indicated.
420 to 86% with a ranch mean of 22.3%. T he inoculation rates were calculated from age data and ranged from 0 to 0.00049 infective bites per day from all sources. The location and approximate prevalence rate for each herd are shown in Fig. 1. The location and inoculation rate for 20 ranches are represented in Fig. 2. The relative frequencies of prevalence rates are graphed in Fig. 3. Herds with low prevalence rates predominate. A scatter plot of prevalence vs. inoculation rate is presented in Fig. 4. Because of the different age structures of herds among ranches, inoculation rates varied widely for similar prevalence rates: age-dependent prevalence rates for the 20 herds for which the ages of the cattle were known are presented in Fig. 5. The exact P values for the observed joint positives to A. marginale and B. boris and to A. rnarginale and B. bigernina were c o m p u t e d for 37 ranches using the hypergeometric model suggested by Fager (1957). The P values indicate that the null hypothesis of no association at the = < 0.05 level of significance is rejected in 7 and 8 herds for B. boris and B. bigemina, respectively. 0
(~
(~ TEXAS Nuevo Laredo
COAHUILA
Saffilt
eynosa
PREVALENCE (40 HERDS)X,~ {CARD TEST) (
0 o-,o~ ~-2o~ 2,-3o,
}(
__/
f % )
\
l,,-loo~ N~ I
(1I ~
, .ILO~E,.S , o 20 ,'o 6'o ~o
\
\
}
............
TAMAULIPAS
~
1I I
/
%
O .*
c i ~ a d victo,,a
o
<~" ~
Fig. 1. Herd location and approximate prevalence rates for antibody activity to A. marginale in bovine sera collected during the period April 1981 to November 1983.
421
~ ] ) ~
j
TEXAS
h t-.o-.oo
COAHO,,A ~NUEVO~EON/ L~
•
eynosa
INOCULATIONRATES(20 HERDS) [ O ,~ .(:~OE~ to .0001~00 I .000101to .000200 O .000201to .000300~
(~ t""-/
TAMAULIPAS
._o.=\ 7oo ,000301 to . 0 0 0 4 0 0
+ " I
t
~
I
[ $ ~
~ C"
,
0
c~ w~o.. .,.~o,~,.=, 20 40 60 80
Fig. 2. Herd location and approximate inoculation rates for antibody activity to A. marginale in bovine sera collected during the period of April 1982 to November 1983.
.250] "2251~
.200~
~ .,oo~
6 ~ ,0 ,'s 2'0 2'5 3b 3's 4b .'s 50 5'5 8'0 6'5 7b is s'o Prevalence (percent)
~00
Fig. 3. Relative frequency of herd prevalence rates for antibody activity to .4. marginale.
422 500
450
400 350
300
250
200
150
100 ¸
50-
lo
20
30 Prevalence
4o
so
6o
(percent)
Fig. 4. Scatter plot of inoculation vs. prevalence rates for A. marginale.
60"
~----v'~
50"
"~
40-
~
30"
5
24 ~ ~ 4
4 3 4
> @
~.
5
20-
9
76 45
30
tO.
2
3
4
5
6 7 Months
8
9
10
11
1
2
3
4
5
6
7 Years
8
9
10
11
12 >-13
Fig. 5. Prevalence rates for antibody activity to A. marginale vs. age. N u m b e r s refer to animals at each age.
423 DISCUSSION The data demonstrate that anaplasmosis is widely distributed throughout the study area. No overt spacial pattern to the distribution is readily apparent. The predominance of low prevalence and inoculation rates can be explained by a low transmission rate for anaplasmosis or by a rapid serologic recovery rate as determined by the CT (MacDonald, 1950a, b). When reinfection is absent and infection is cleared with tetracycline, CT reactors begin to become non-reactors by about 6 months (Magonigle and Newby, 1982). Untreated natural and experimental infections have remained positive to the CT for /> 10 months (Gonzalez et al., 1978). Thus if reactor status is lost at about the same rate as new infections are occurring, high serologic prevalence rates will be uncommon. Another result of the short period of CT reactivity is that most of the animals with positive sera must have been carrying Anaplasma within a year of blood collection, indicating that new infections or reinfections were occurring during or immediately prior to the time the samples were collected. Since the age composition of the herds under study differed, inoculation rates were calculated as a means of age adjustment. These rates were used by Mahoney and Ross (1972) to determine the average probability of a tick infected with Babesia feeding on one bovine each day. Because anaplasmosis can be transmitted by several different vectors, inoculation rates do not have the same significance as they do in babesiosis, but they do provide a measure of the rate of occurrence of new infections. The short time period before seroreactivity to the CT is lost means that the estimated inoculation rates for Anaplasma infection are probably much below the true rates. The scatter plot of prevalence vs. inoculation rates (Fig. 4) illustrates how herds with similar prevalence rates but different age structures can have very dissimilar inoculation rates. For example, at prevalence rates of approximately 10, 15 and 40%, h can vary over 60%. The variation in h with constant prevalence is much less for Anaplasma than that found for Babesia where up to 7-fold differences were found (Teclaw et al., 1985). Since the CT recovery rate for anaplasmosis is much greater than the IFAT recovery rate for babesiosis (Magonigle and Newby, 1982; Callow et al., 1976), the effect of age on the prevalence rates should be less in the former. Since these same sera were tested for the presence of antibody activity to Babesia spp., it was of interest to see if any relationship existed between anaplasmosis and babesiosis reactivity in the same animal. The association could be due to test cross-reactions, vector sharing, similar favorable habitats for the two hemoparasites or their vectors, and management factors which favor their propagation. The test of association indicates that for most herds (30 and 29 of 37) at the cc < 0.05 significance level an animal with a positive CT reaction for anaplasmosis is not more likely to be positive on the IFAT for either Babesia species than an animal that is CT negative for anaplasmosis. This is different from saying that herds with a high prevalence
424 of anaplasmosis also have a high prevalence of babesiosis. In the herds in which association occurs, it can be partially explained by the shared vectors, Boophilus spp. ticks. However, ot her vectors are probabl y involved in the transmission o f anaplasmosis in northeastern Mexico. It m ay be that the situation in Mexico is similar to t h a t in Australia where B. microplus is considered the only major vector for anaplasmosis (Rogers and Shiels, 1979). Also, the possibility of cross-reactions between the CT for anaplasmosis and the IFAT for babesiosis must also be considered. ACKNOWLEDGEMENTS This report is based upon work supported by the U.S. D e p a r t m e n t of Agriculture under Agreement No. USDA/OICD/MX-TX-116 and the Texas Agricultural Ex per i m ent Station Project No. TAES-H-6261. Any opinions, findings, conclusions or r e c o m m e n d a t i o n s expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. D e par tmen t o f 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.
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