Seroprevalence of leptospiral antibodies among dairy cattle kept in communal corrals in periurban areas of Bamako, Mali, West Africa

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Elsevter Science B.V.

Seroprevalence of leptospiral antibodies among dairy cattle kept in communal corrals in periurban areas of Bamako, Mali, West Africa Mamadou Niang a'1, Loren A. Will *'b, Mamadou Kane a, Alpha A. Diallo a, Manzoor Hussain c aCentral Vetennary Laboratory, B P 2295, Bamako, Malt b2270A, Extenston Vetennary Medtctne, College of Veterma~ Medtctne, Iowa State Untverstty, Ames, IA 50011, USA ~Department of Mtcroblology, Immunology, and Preventive Medtcme. College of Vetertnary Medtcme, Iowa State Umverstty, Ames, IA 50011, USA (Accepted 16 July 1993)

Abstract

Sera obtained from dairy cattle m communal corral herds located near the o t y of Bamako in Mah, West Africa were screened using the m~croscopxc agglutination test against 26 serovars representing 15 serogroups ofLeptosptra mterrogans. Forty-five percent (44 8%, 288/642) were positive to one or more serovars. Thas seroprevalence rate hkely reflects mfectmn since vaccination agamst leptosplral lnfectmn has not been practiced m Mah The rate was higher among females. The most common tlters were against antigens of serovars cynoptert (14.7%), hardjo ( 13.3% ), pomona (9.2%), nona ( 8.1% ), kambale (6 5%), grtppotyphosa (6.4%), hebdomadts (6.2%), andpyrogenes (5.2%)

Introduction Mali is a major producer of livestock in West Africa. The situation regarding leptospirosis in most of Africa is largely unknown (Myburgh et al., 1989 ). The purpose of this survey was to determine the seroprevalence of leptospiral antibodies among dairy cattle herds kept in communal corrals in the periurban areas of Bamako in Mali, West Africa. Farmers in these areas specialize in dairy production to serve the city. The cattle in these periurban herds account for a small portion of the nation's cattle population which is estimated at 5 000 000 (Food and Agriculture Organization, 1992). *Corresponding author. T r e s e n t address: D e p a r t m e n t o f Microbiology, Immunology, a n d Preventive Medicine, College o f Veterinary Medicine, Iowa State University, Ames, IA 50011, USA

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Materials and methods

The cattle which were the subject of this investigation were kept in communal corral milk herds located in the periurban area of Bamako, Mali's capital city. The system of communal corral dairy production is in contrast to traditional village dairy systems and individually owned, modern milk production system farms which are more distant from the city center (International Livestock Centre for Africa (ILCA), 1989 ). The climate of this area is rainy during the summer months (June through October) and dry during the remainder of the year when only the main river channels flow with water. The communal corrals are well managed but less efficient than the private system units. They have difficult access to supplementary feed supplies, but the farmers utilize the well-organized state and private veterinary services extensively to assist production. Cattle drink from rivers. Communal corrals are located on government property and are re-located as the City of Bamako expands. The predominant dairy cattle in Bamako are Zebu, N'dama, and ZebuN'dama crosses (ILCA, 1989). By tradition a herd is comprised of animals belonging to several farmers. The typical size of dairy herds in the district may be 50-100 cattle. Cattle owners pay professional herdsmen to tend the animals. Herdsmen are the primary husbandrymen, managers and information keepers for the cattle. Hand-milking is the norm. Milk is sold either to the one dairy plant in Bamako for processing or, more often, unprocessed directly to consumers. To accomplish the leptospiral serosurvey blood samples were taken from a convenience sample of the male and female dairy cattle in eight major communal corrals. The number of communal corrals fluctuates as some are split and others re-form. Owners occasionally may move their cattle from one corral to another. Blood samples were collected during March-April of 1987. Because cattle bore no identification, attempted selection of a representative sample for bleeding relied on an estimate of each herd's age and sex structure. Individuals were chosen by the investigators to conform to their perceived profile of each herd. Selection of the cattle for bleeding was without investigator knowledge of any individual animal's ownership since the herds were communal. The number sampled varied; proportionately more cattle were selected from the smaller herds than from the larger ones. In each case, however, the sample consisted of more than half of all cattle in the herd. Of the 642 cattle bled, 75 were males and 567 were females. Ages ranged from less than 3 to over 9 years of age. Age was determined by tooth wear, number of horn rings, and as given by the herdsmen. Female cattle are not bred or used for milk production generally until about 3 years of age. Sera were screened at 1:100 dilution against 26 live antigens representative of 15 Leptospira interrogans serogroups (provided by the Leptospirosis Ref-

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erence Laboratory, National Veterinary Services Laboratories, Ames, IA, USA: see Table 2 ) using the microscopic agglutination test (MAT) as described by Cole et al. ( 1979 ). Selection of the antigens was based on the WHO recommendation (Faine, 1982). Positive sera were those that developed 50% or greater agglutination. Saline and negative serum controls were conducted Table 1 S u m m a r y o f serological results for leptosplral antibodies by sex a n d age Age (years)

Females

Males

No. tested

No. p o s m v e

(%)

No. tested

No posmve

(%)

<3 3-9 >9

132 341 94

25 216 31

19.0 a 63.3 b 33.0 c

13 44 18

0 12 3

0a 27 3 e 15 8 f

Total

567

273

48.1 x

75

15

20 0 z

T h e a versus b, a v e r s u s c, b v e r s u s c, x v e r s u s z, a n d b v e r s u s e differences are significantly different ( P < 0 0001; all Z 2 ~ 15.13), o v e r u s e is significantly dlffernt (P-3.84) Table 2 Prevalence o f a n t i b o d i e s against leptospIral antigens in bovine sera Serogroups

Serovars

No. posxtive

Seroprevalence (%)

Cynopten Sejroe Pomona Hebdomadls Hebdomadls Gnppotyphosa Hebdomadls Pyrogenes Icterohamorrhagiae Ballum Mira Hebdomadls Austrahs Batavlae Autumnahs Camcola Autumnahs Icterohamorrhaglae Camcola Javanlca Tarassovl Icterohamorrhagme Icterohamorrhagiae Hebdomadls Camcola Camcola

cynoptert hardjo pomona nona kamble grtppothyphosa hebdomadls pyrogenes m wogolo ballum mtm jules austrahs batavlae autumnahs kamttuga butembo ndambart benjamin javamca tarassovt naam copenhagenl kaburu bafant cantcola

104 94 65 57 46 45 44 37 33 24 23 21 20 18 17 14 14 10 5 5 3 3 2 1 0 0

14 7 13.3 9.2 8.1 6.5 6.4 6.2 5.2 4.7 3.4 3.3 3.0 2 8 2.5 24 19 19 14 0 7 0.7 0.4 0.4 0.2 0 1 0 0

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routinely. Screen test positive sera were titrated in serial two-fold dilutions from 1:100. All sera for which the MAT titer was 100 or greater against one or more of the 26 antigens were considered to be positive. Seroprevalence differences between communal corral herds and female and male dairy cattle were assessed using Z 2 corrected for continuity (Snedecor and Cochran, 1967) and Fisher's exact procedure where numbers were small (Fisher, 1963 ). Results

The overall leptospiral seroprevalence among cattle in the eight herds was 45% (288/642) with a herd specific range of 30.9% to 55.8% reactors. Of these, 87.9% reacted with a reciprocal titer greater than or equal to 400. Of the 288 positive sera, 230 (79.8%) reacted against multiple leptospiral serovars. The differences between herds were not significant ( P > 0.05 ). The proportion of sera positive for leptospiral antibodies was significantly higher ( P < 0 . 0 0 0 1 ) in female (48.1%) than in male cattle (20.0%) (Table 1 ). Among females and males the leptospiral seroprevalence rate was highest in cows (63.3%) and bulls (27.3%) in the 3- to 9-year-old age group. The most frequently detected antibodies were against serovars cynoptert (14.7%), hardjo (13.3%), and pomona (9.2%) (Table 2). There were no titers detected against serovars bafam or canicola. Discussion

The results of this serosurvey demonstrated uniformly high leptospiral reactor rates among dairy cattle kept by Bamako dairy farmers in periurban c o m m u n a l corral herds. Since vaccination of cattle against leptospires was not practiced in Mali, serologic response likely reflected natural exposure. Serologic studies of cattle conducted in Zimbabwe (Feresu, 1988 ) and Malawi (Myburgh et al., 1989) showed seroprevalences of 27% and 21%, respectively. The prevalence of leptospiral infection based on serology alone may not be accurate, and the rate of cultural isolation may be comparatively low (Miller et al., 1991 ). Bovine leptospiral infections may occur in the absence of detectable agglutination titers, unrelated and unknown or excluded serovars may be missed, and microscopic agglutination (the usual test ) lacks sensitivity and is not reproducible (Feresu, 1992). Despite its limitations, the MAT is the preferred test in surveys for leptospiral activity (Ellis et al., 1982: Feresu, 1992). As in the present study, antibodies against multiple leptospiral serovars have been frequently identified in individuals, for example, Feresu (1988) reported 47% multiple serovar reactions in Zimbabwean cattle. Many authors

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have suggested (Hathaway et al., 1981; Grant et al., 1988) that some serologic reactivity may be due to cross-reactions among closely related serovars. As with other investigations in sub-tropical and tropical cattle (Ellis, 1984; Ezeh et al., 1989), the results of the present study suggest that serovars belonging to the Hebdomadis serogroup, which once included serovar hardjo, were also prominent in Bamako. According to Ellis (1984), strains such as serovar hardjo which are adapted to and maintained by cow-to-cow transmission are independent of region and rainfall. Genital tract carriage of serovar hardjo by bulls has also been described (Ellis et al., 1986). Strains such as serovar cynopteri, which are maintained by other domestic and free-living animals, are incidental and dependent upon the animal species present in the area, the serovars they maintain, and farm management systems. The high seroprevalence of serovar cynopteri antibodies in Bamako communal corral cattle apparently has not been identified elsewhere. Feresu (1988 ) reported a seroprevalence rate of 2% in Zimbabwe cattle, and Ellis and others ( 1982 ) found that 3.6% of aborting cows in Northern Ireland had antibodies against serovar cynopteri. The source of serovar cynopteri in Bamako is unknown but is thought to be rodent associated. Leptospires can be venereally transmitted by infected semen, as well as by contact with aborted fetuses, urine, and contaminated water and m u d (Turner, 1969; Hanson, 1982; Smith and Easmon, 1990). Transmission may be more rapid in concentrated groups of animals (Miller et al., 1991 ). Cattle, for example, seroconverted within 4-10 weeks after introduction of carriers into herds shedding serovar hardjo (Leonard et al., 1992). Cattle in communal corrals exist in concentrated herds. High rates of leptospire shedding could produce high seroprevalence rates. Leonard et al. ( 1992 ) found that, whether by supraconjunctival or intrauterine routes, natural infection with serovar hardjo results in prolonged urinary excretion. The large portion of high titers against leptospires displayed by the communal corral cattle in Bamako may be remarkable. Ellis et al. (1982) reported that 58% of cows producing leptospire-infected fetuses versus 20% of cows aborting non-infected fetuses had reciprocal microscopic agglutination titers greater than or equal to 300. In Bamako the fact that communal corral cattle usually drank from rivers and streams could explain the high seroprevalence of leptospiral antibodies, but if this were the case, the titers would be expected to be present about equally in both sexes early and rise in the population with age rather than diminish later as they do in the current case. The decrease in seroprevalence with age may not be easily explained, but Ellis et al. ( 1981 ) found that leptospirosis occurred more frequently in young cattle. They suspected that this related to a more important role played by the young animals in the epidemiologic features of infection. The results of a study by Prescott et al. ( 1988 ) indicate that titers rise or fall in older age groups of beef and dairy cattle. Titers ordinarily diminish with age (Turner, 1967).

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A greater seroprevalence among female than male dairy and beef cattle has previously been reported but not explained (Miller et al., 1991 ). Likewise, we cannot explain from our data the higher seroprevalence found among the female compared with male cattle in Bamako. It may be that serovar cynopteri can be carried in the male genital tract like serovar hardjo, in which case the unmanaged breeding in the Bamako herds would allow for frequent mating of cows with carrier bulls. The results of this serosurvey provide evidence that antibodies against numerous leptospiral serovars and probable infection occur among cattle in Bamako. Systematic microbiological, epidemiological and socioeconomic studies are necessary to provide a better account of the impact of leptospirosis on dairy production and public health in Bamako, Mall.

Acknowledgements We are grateful to David A. Miller and Linda K. Schlater (US Department of Agriculture, National Veterinary Services Laboratory, Ames, IA 50010) for technical assistance and for providing antigens used in this study, to George W. Beran, (Department of Microbiology, Immunology and Preventive Medicine, College of Veterinary Medicine, Iowa State University) and David A. Miller for their expert editorial review of the manuscript, and to Lie Ling Wu (Department of Statistics, College of Liberal Arts and Sciences, Iowa State University) for statistical assistance.

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