Bovine abortion associated with Leptospira interrogans serovar hardjo infection

During 1981, 265 bovine abortions were investigated by serological and histological methods for evidence of leptospiral infection. Leptospires were demonstrated in the tissues of 10 foetuses by a Levaditi silver impregnation technique. Serological testing of maternal sera indicated that Leptospira interrogans serovar hardjo was associated with 5 of the abortions while the remaining 5 were due to L. interrogans serovar pomona infection. In cases of abortion associated with L. interrogans serovar hardjo leptospires were readily demonstrated in foetal liver, kidney, intestine and heart. They were demonstrated less often in lung and placenta and could not be found in foetal brain. Autolysis did not appear to interfere with the demonstration of leptospires by silver impregnation. No lesions attributable to leptospiral infection were seen in placentas but mild interstitial nephritis was found in some of the foetuses. Fourteen other cows had serological evidence of recent leptospiral infection but leptospires were not detected in foetal tissues. Histological examination of silver impregnated foetal tissues in combination with the microscopic agglutination test was shown to be an effective method for diagnosing abortion associated with L. interrogans serovar hardjo in cattle.     

Restriction endonuclease analysis of Leptospira interrogans serovar hardjo isolates from cattle

The genomes of 253 strains of Leptospira interrogans serovar hardjo were examined by restriction endonuclease analysis of their DNA. The strains had been isolated from cattle at an abattoir (190), milk of agalactic cows (seven) and from aborted bovine fetuses (56). Two distinct genome types, Hardjoprajitno and Hardjobovis, were detected. The majority (91 per cent) of isolates from abattoir cattle were of the Hardjobovis type while most (76 per cent) of the isolates from clinical/pathological material were similar to Hardjoprajitno.     

Problems associated with the serological diagnosis of Leptospira interrogans serovar hardjo infection in bovine populations

Data combining sequential bacteriology and serology from a longitudinal study of a dairy herd were used to demonstrate the limitations of serology as a diagnostic method in cross-sectional sampling of bovine populations. Whole-herd point serological prevalences showed considerable variation over a two-year sampling period (38.8 to 76.2 per cent), and this was mainly due to varying age-specific prevalence. Owing to the rapid decline in titres and the varying persistence of infection, point serological prevalences failed to approximate to cumulative infection rates (either past or present) at different times of the year. A higher estimate of the number of susceptible animals in the herd than is the case results in inaccurate information on true incidence rates and can confuse assessments of the susceptibility of different age groups, especially if only small numbers are sampled. A sampling exercise demonstrated that a 10-cow sample usually provided little useful information other than establishing the presence or absence of hardjo in the herd. Increasing the sample size markedly improved epidemiological information, investigations of clinical disease, assessments of vaccination needs and public health tracebacks. Preferably 10 sera from each of the yearling, first calver, second calver and older age groups should be tested. Serology was an inadequate indicator of infection in individual animals. Group geometric mean titres taken from a mean serological response curve were shown to have limited application in the interpretation of field data, unless infection had occurred in the previous two months.     

Experimental Leptospira borgpetersenii serovar hardjo infection of pregnant cattle

Objective To observe the effect upon the foetus of experimental infection of pregnant cattle with Leptospira borg-petersenii serovar hardjo .
Design A disease transmission study using pregnant cattle.
Procedure Fourteen heifers serologically negative to L hardjo were artificially inseminated and later challenged with a north-Queensland isolate of L hardjo by conjunctival inoculation. The heifers were serologically monitored and their urine examined for the presence of leptospires using culture and fluorescent-antibody tests at appropriate intervals. Elective caesarean sections were performed on pregnant heifers at 6.5 weeks after the challenge. Foetuses were examined using serological, histopathological, microbiological and fluorescent-antibody tests.
Results Ten of the heifers became pregnant, but three subsequently aborted before challenge. After challenge, all 14 heifers seroconverted and L hardjo was isolated from the urine of 6 of the 7 pregnant heifers. No evidence of foetal L hardjo infection was detected. Two of the foetuses had histopatho-logical lesions consistent with Neospora s p infection.
Conclusion It is likely that the isolate of L hardjo used in this study does not normally infect the foetus. Neospora s p may be a more significant cause of bovine reproductive wastage.     

Antimicrobial drug susceptibility of Leptospira interrogans serovar hardjo isolated from cattle.

The susceptibility to commonly used drugs of 18 isolates of Leptospira hardjo from the kidneys of feedlot cattle from different sources was determined quantitatively. All isolates were susceptible to penicillin G, ampicillin, tetracycline, erythromycin and streptomycin. Susceptibility to sulphamethazine was ambiguous. No drug resistance was detected and the results were similar to those described for other serovars.     

Prevention of Leptospira interrogans serovar pomona infection in cattle

A commercial hardjo-pomona vaccine which has previously been shown to be effective against hardjo infection was tested against pomona. Following challenge all 11 six-month-old non-vaccinated calves seroconverted and pomona was isolated from blood or urine on at least one occasion from nine of them. Pomona was isolated once only, on the third day after challenge, from the blood of one of 11 vaccinated calves.     

Prevalence of Leptospira interrogans serovar hardjo in the genital and urinary tracts of non-pregnant cattle

In a bacteriological investigation of 60 cows and heifers from an abattoir Leptospira interrogans serovar hardjo was isolated from 39 (65 per cent) animals. The genital tract (57 per cent) appeared to be as important a site of hardjo localisation as the urinary tract (62 per cent). This is believed to be the first report of genital hardjo infection in naturally infected cattle.     

Excretion of Leptospira interrogans serovar hardjo following calving or abortion

Leptospira interrogans serovar hardjo was demonstrated in the vaginal discharges of 12 experimentally infected heifers for up to eight days after abortion or calving. Organisms were recovered from the oviducts of heifers examined at slaughter eight to 22 days after calving or 32 to 91 days after infection. They were also recovered from the uteri of four heifers eight to 22 days after calving.     

Comparison of three techniques to detect Leptospira interrogans serovar hardjo type hardjo-bovis in bovine urine

Nucleic acid hybridization, bacteriologic culture, and a fluorescent antibody test were compared for detection of Leptospira interrogans serovar hardjo type hardjo-bovis in bovine urine. Seventy-five urine samples were collected from pregnant cows challenge exposed with type hardjo-bovis. Twenty samples were collected from steers not exposed to hardjo-bovis. Sediments from each sample were examined, using fluorescent antibodies and a repetitive sequence element nucleic acid probe, to detect the presence of leptospires. Urine samples were processed for bacteriologic culture, using standard techniques. Under laboratory conditions typically used for these techniques, leptospires were detected in 60 of 75 urine samples from challenge exposed cows by nucleic acid hybridization, in 24 samples by fluorescent antibody test, and in 13 samples by bacteriologic culture. Leptospires were not detected in the urine of steers not exposed to hardjo-bovis.     

Dihydrostreptomycin treatment of bovine carriers of Leptospira interrogans serovar hardjo

Ten non-pregnant heifers, experimentally infected with Leptospira interrogans serovar hardjo, were each given an intramuscular injection of dihydrostreptomycin at a dose rate of 25 mg kg-1. In five of these animals this treatment was repeated after 14 days. Treatment failed to remove established genital or renal infection in seven of the 10 heifers, although the number of organisms persisting was apparently reduced in these animals. Serovar hardjo infection persisted for at least 83 days in the oviduct and uterus and these tissues may be as important carrier sites for serovar hardjo as bovine kidney tissue.     

Leptospira interrogans serovar hardjo associated with bovine abortion in South Africa

Leptospira interrogans serovar hardjo was isolated from urine from dairy cattle in the Onderstepoort area. This was the first successful isolation of this serovar as sole agent causing an abortion storm in the Republic of South Africa. Abortions occurred as early as at 4 months' gestation.     

Protection of cattle against natural challenge with Leptospira interrogans serovar hardjo using a hardjo-pomona vaccine

The hardjo component of a bivalent hardjo/pomona vaccine prepared from cultures grown in a protein-free medium was tested in calves which experienced a natural challenge about 7 months after vaccination. A significant degree of protection was obtained using either seroconversion or positive urine cultures as in-dicators of infection. Seroconversion occurred in 10/10 non-vaccinates and 2/9 vaccinates (p <0.01), Leptospires of serovar hardjo were isolated from the urine of 6/10 non-vaccinated calves and 0/9 vaccinated animals (p <0.05).