Leptospirosis: I. Clinical investigation of the infection in dairy cattle in the Waikato district of New Zealand

An investigation was made into the prevalence of leptospiral infection in cattle. An area 50 km radius was selected in a region where leptospirosis was reputedly common. Farmers volunteered 250 herds with 39 500 cows for testing and 7 500 animals were selected and sampled. Twenty-nine cows (0.4%) on 14 (5.6%) of the farms had leptospiruria at the first examination. Leptospirae were cultured from the urines of nine of these animals and all were Leptospira interrogans serovar hardjo. Serologically 12.5% of cows had titres of 1:200 or greater to hardjo and 3.5% titres of 1:200 or greater to pomona. In the Spring of 1977, there was evidence of clinical leptospirosis in calves associated with only one of the herds and no clinical leptospirosis in the 250 lactating herds, although leptospiral titres were found in 88% of them. This indicated that clinical disease was much less common than infection. We concluded that leptospirosis was of minor economic importance in dairy cattle, although it could be significant in individual herds, and a health hazard to farm workers.     

Leptospirosis: II. Investigation of clinical disease in dairy cattle in the Waikato district of New Zealand

Investigations were carried out in 1975, 1976 and 1977 in 16 dairy herds where leptospiral abortions were suspected and in five other herds where clinical disease was not present. Both Leptospira interrogans serovars pomona and hardjo were isolated from cattle in herds with leptospirosis, but only pomona was recovered from those that had aborted. There was no evidence that hardjo caused clinical disease in dairy cattle in the Waikato district. It was found that 73% of the cows that aborted and 19% of other animals in the same herds had microscopic agglutination test titres to pomona of 1:2,000 or greater. By contrast, only 2% of cattle in herds without clinical evidence of leptospirosis had such titres. One cow retained a titre of 1:2,000 or greater to pomona for 7 months; titres of this order had a shorter duration in other cows. Leptospiruria occurred in 50% of cows that had aborted and in 9% of in-contact cows in the same herds. Only 0.7% of cows had leptospiruria in the herds with no clinical disease. Ten of 35 cows shedding pomona still had leptospiruria one month later. It was concluded that clinical leptospirosis should be diagnosed by testing a sample of the herd, rather than just individual cows, because of the variability and persistence of leptospiruria and serological titres in cows with and without clinical signs. Although hardjo is common in cattle in the Waikato district, it was not found to cause abortion in cattle.     

Leptospirosis: II. Investigation of clinical disease in dairy cattle in the Waikato district of New Zealand

Investigations were carried out in 1975, 1976 and 1977 in 16 dairy herds where leptospiral abortions were suspected and in five other herds where clinical disease was not present. Both Leptospira interrogans serovars pomona and hardjo were isolated from cattle in herds with leptospirosis, but only pomona was recovered from those that had aborted. There was no evidence that hardjo caused clinical disease in dairy cattle in the Waikato district.

It was found that 73% of the cows that aborted and 19% of other animals in the same herds had microscopic agglutination test titres to pomona of 1:2 000 or greater. By contrast, only 2% of cattle in herds without clinical evidence of leptospirosis had such titres. One cow retained a titre of 1:2 000 or greater to pomona for 7 months; titres of this order had a shorter duration in other cows. Leptospiruria occurred in 50% of cows that had aborted and in 9% of in-contact cows in the same herds. Only 0.7% of cows had leptospiruria in the herds with no clinical disease. Ten of 35 cows shedding pomona still had leptospiruria one month later.

It was concluded that clinical leptospirosis should be diagnosed by testing a sample of the herd, rather than just individual cows, because of the variability and persistence of leptospiruria and serological titres in cows with and without clinical signs. Although hardjo is common in cattle in the Waikato district, it was not found to cause abortion in cattle.     

Seroprevalence and association with abortion of leptospirosis in cattle in Ontario.

Sera were collected using a systematic random sampling from 348 cattle herds in Ontario, in proportion to the cattle population in different areas. One cow in five from 296 dairy herds and one in three from 52 beef herds were sampled. The sera were analyzed for prevalence of antibodies to Leptospira interrogans serovar grippotyphosa, hardjo, icterohaemorhagiae and pomona using the microscopic agglutination test. Herd seroprevalence (one or more animals with titer greater than or equal to 80) in beef and dairy herds combined was grippotyphosa 2%, hardjo 13.8%, icterohaemorrhagiae 10.1% and pomona 25.8%; 39% of all herds showed evidence of leptospiral infection with one or more serovars; 44.2% of 52 beef herds had serological evidence of infection with serovar hardjo compared to 8.4% of 296 dairy herds (P less than 0.0001). Seroprevalence of other serovars was not significantly different between beef and dairy herds. The proportion of beef animals seropositive for hardjo and for pomona increased with age, particularly for hardjo; 26.5% of beef animals aged nine years or over were seropositive for hardjo. Dairy animals showed a significant rise of hardjo but not pomona titers with age. The seroprevalence of pomona infection was significantly higher in dairy cattle in eastern Ontario than in other regions. Thirty-four (6.1%) of 553 aborted bovine fetuses had leptospires detected by immunofluorescence techniques. Sixty-five percent of these fetuses were from submissions made between November and January. Leptospires were identified as serovar hardjo by specific immunofluorescence. There appeared, however, to be a paradoxical serological response in that eight aborting cows had antibody titers to pomona rather than hardjo.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epidemiology of leptospirosis in dairy farm workers in the Manawatu. Part II. A case-control study of high and low risk farms

Subsequent to a cross-sectional serological survey of Manawatu dairy farm workers, a case-control study was carried out to investigate the correlation between titres to leptospiral serovars in workers and those in cattle in their herds. A total of 52 herds was investigated, 25 of which were high risk where milkers had titres of 1:96 or greater, and 27 were case-controls where milkers had no detectable agglutinin titres at a minimum serum dilution of 1:24. The serological prevalence of titres to hardjo in cattle on high risk farms (76.5%) was significantly higher (P<0.05) than on the case-control farms (60.0%). The geometric mean titres of seropositive cattle on high risk farms were also significantly higher (P<0.01) than in the cattle from the case-control farms, especially in the younger cohorts. These findings suggest that there was active endemic hardjo infection in the two- to three-year-old cattle on the high risk farms. Titres to pomona were demonstrated in only 5.2% of the cattle from both types of farm. Workers with titres to pomona tended to be from farms on which stock, especially calves, were bought-in and pigs were kept. Conventional measures for protecting milkers from contact with infected urine appeared to be ineffective and it is concluded that prevention of leptospirosis in dairy farm workers can only be achieved by elimination of infection in the herd by vaccination of cattle.     

The epidemiological interpretation of serological responses to leptospiral serovars in sheep

Serum samples were examined for evidence of leptospiral agglutinins from 928 sheep from 45 lines and kidneys from 12 of these lines for evidence of leptospiral infection. All sheep had been submitted for slaughter at meat works in the Manawatu. Serological results were analysed using the results at a minimum serum dilution in the microscopic agglutination test (MAT) of 1:24 and at a minimum dilution of 1:48. It was shown that a minimum dilution of 1:24 resulted in many non-specific or cross-reactions. A minimum dilution of 1:48 was more accurate for detecting the serological prevalence of specific agglutinins to leptospires in ovine sera. Twenty percent of the sheep had titres of 1:48 or greater to hardjo, 3.8% to pomona, 2.6% to tarassovi, 2.3% to copenhageni and 2.7% to ballum. No titres of 1:48 or greater to australis were detected. Serovar hardjo was isolated from the kidneys of three animals in one line. Eighteen months later 291 serum samples and 95 urine samples were collected from live animals on the property from which the three hardjo infected animals originated. No titres to hardjo were detected in the sera of lambs, but a serological prevalence of 44% and 84% to this serovar was demonstrated in the hoggets and ewes respectively. No leptospires were demonstrated in any of the urine samples. These results show that sporadic infection of sheep with hardjo can occur but they also indicate that infection with this serovar is not endemic and that sheep are unlikely to act as maintenance hosts for hardjo in New Zealand.     

Epidemiology of leptospirosis in dairy farm workers in the Manawatu. Part II. A case-control study of high and low risk farms

Subsequent to a cross-sectional serological survey of Manawatu dairy farm workers, a case-control study was carried out to investigate the correlation between titres to leptospiral serovars in workers and those in cattle in their herds. A total of 52 herds was investigated, 25 of which were ‘high risk’ where milkers had titres of 1:96 or greater, and 27 were case-controls where milkers had no detectable agglutinin titres at a minimum serum dilution of 1:24.

The serological prevalence of titres to hardjo in cattle on ‘high risk’ farms (76.5%) was significantly higher (P<0.05) than on the case-control farms (60.0%). The geometric mean titres of seropositive cattle on ‘high risk’ farms were also significantly higher (P<0.0l) than in the cattle from the case-control farms, especially in the younger cohorts. These findings suggest that there was active endemic hardjo infection in the two- to three-year-old cattle on the ‘high risk’ farms.

Titres to pomona were demonstrated in only 5.2% of the cattle from both types of farm. Workers with titres to pomona tended to be from farms on which stock, especially calves, were bought-in and pigs were kept.

Conventional measures for protecting milkers from contact with infected urine appeared to be ineffective and it is concluded that prevention of leptospirosis in dairy farm workers can only be achieved by elimination of infection in the herd by vaccination of cattle.     

A serological study of bovine leptospirosis in the district of Taranaki

A cross-sectional serological survey of dairy cattle in Taranaki in 1979-80 indicated that 62% (551/891) of the animals had evidence of Leptospira interrogans serovar hardjo infection as disclosed by the microscopic agglutination test. Titres to Leptospira interrogans serovar pomona were demonstrated in only 4% (23/591) of the animals examined. The high prevalence of hardjo infection is suggestive of an endemic infection whilst the low level to pomona is indicative of sporadic infection. In a detailed examination of 10 herds, 9 revealed high (55%-91%) prevalence of serological reactions to hardjo and the herd profiles of titres, indicated that the animals had become infected at one to two years of age. A field strain of hardjo from cattle as well as the usual laboratory strain (hardjoprajitno) was incorporated in the test but there were no significant differences between the results given by the two antigens.     

Haemolytic disease associated with Leptospira interrogans serovar pomona in red deer calves (Cervus elaphus)

Three red deer calves (Cervus elaphus) died with a haemolytic disease associated with infection by Leptospira interrogans serovar pomona. Infection within the herd was more prevalent than disease. Sera from 16 herd mates were tested by the microscopic agglutination test (MAT) and 12 had leptospiral titres, the majority to serovar pomona. A few calves had titres to balcunica and hardjo. Urine was obtained for culture from six of these calves and serovar pomona was isolated from five with titres to pomona, and hardjo from one with a titre to hardjo but not pomona. A fourth calf died with severe nephritis but a diagnosis of leptospirosis was not confirmed in this case.     

A seroepidemiological study of bovine pestivirus in Queensland beef and dairy herds conducted in 1994/95

OBJECTIVE: To describe the distribution and prevalence of cattle herds with detectable antibody to bovine pestivirus in Queensland in 1994/95. MATERIALS AND METHODS: The study used 7,838 serum samples collected from 250 herds in Queensland, as part of a structured animal health surveillance program conducted in 1994 and 1995. Samples were collected from female cattle bred on the property. In each herd, 10 to 20 heifers less than two years of age and 10 to 15 older cows were sampled giving a 95% probability of detecting one or more seropositive animals if the seroprevalence was approximately 10% or greater. Sera were analysed for antibodies to bovine pestivirus using a virus neutralisation test. RESULTS: Total cattle numbers in sampled herds varied from 62 to 24,600 head, while total area of properties sampled varied from 50 to 395,400 hectares. Eleven percent of herds contained no seropositive animals among those sampled, and in 38% of herds, all sampled cattle aged one to two years of age were seronegative. There was a trend for larger herds to have one or more animals seropositive for bovine pestivirus (chi-squared for Linear trend = 3.656, p = 0.056). Herds with more than 500 head of cattle were significantly more likely than herds with less than 500 head to contain one or more seropositive animals in any age group (prevalence ratio = 1.12; 95% confidence interval 1.01 - 1.23; p = 0.026). Age specific seroprevalence increased from around 10% in heifers, to between 75% and 85% in cows aged 10 years. The average annual incidence risk for bovine pestivirus infection varied from 0.12 to 0.24 seroconversions per cattle year at risk, and did not vary with age. The overall crude seroprevalence adjusted for herd size was 45%. There was a wide range of seroprevalence recorded for each level of stocking intensity. CONCLUSIONS: This survey provides valuable baseline data on bovine pestivirus infection in Queensland cattle herds.     

LEPTOSPIRA SEROGROUP HEBDOMADIS INFECTION AS AN AUSTRALIAN ZOONOSIS

Two cases of leptospirosis due to infection with a member of the Hebdomadis serogroup are described in farm workers on a Victorian dairy farm. The source of infection appeared to be the milking herd which had elevated serum antibody titres against a member of the Hebdomadis serogroup. Agglutinin-absorption testing of one patient's serum indicated that the infecting serovar was hardjo .
A survey of 1,144 cattle entering abattoirs throughout the State indicated that 44.3% of these animals showed serological evidence of past or present infection with leptospira of the Hebdomadis serogroup and the potential risk for people with occupational contact with cattle is emphasised. The importance of considering leptospirosis in the differential diagnosis of all patients with influenza-like symptoms or pyrexia of unknown origin and having occupational contact with animals, especially cattle, is discussed.     

Leptospira interrogans serovar hardjo Infection in Cattle in the South Okanagan District of British Columbia

An outbreak of leptospirosis due to Leptospira interrogans serovar hardjo in the South Okanagan District of British Columbia was investigated. The infection was associated primarily with bulls, but serovar hardjo was isolated from both bulls and cows at slaughter. Kidney and cerebrospinal fluid were found to contain leptospires, independently of the presence and level of serum agglutinins. Treatment of a bull twice in six months with dihydrostreptomycin failed to diminish an agglutinin titer (1/200) which persisted for two years without reexposure of the bull. A serological survey of cull cows sold through a central auction mart revealed the presence of hardjo agglutinins in 15.4% of 1300 sera representing 163 herds in 20 locations. Thirty percent of these herds contained reactor cattle. The number of premises from which reactor cattle came in a given locality varied from 4% to 67.7%. Measures to control leptospirosis in the study are suggested.     

Hairy shaker disease of lambs

A serological survey of 213 randomly chosen dairy farm residents in the Manawatu showed that 66 (34%) of the people who milked cows had leptospiral titres ≤ 1:24 by the Microscopic Agglutination Test. Forty-eight (72.7%) of these people had titres to hardjo, while 29 (43.9%) had titres to pomona. Dual hardjo/pomona titres occurred in 12 people. Ballum and Copenhageni accounted for 8% of the titres found. Women milkers and farm residents who did not milk were all serologically negative. A third of the seropositive milkers had a history of clinical leptospirosis. Other factors which significantly correlated with leptospiral titres included the time spent in the dairy shed during milking, the wearing of shorts, the keeping of pigs for sale, and the number of years the individual had been working on a dairy farm. The type of milking shed and the size of the herd were interrelated and both showed strong trends towards a correlation with serological prevalence.     

Leptospirosis associated with serovars hardjo and pomona in red deer calves (Cervus elaphus)

Four red deer calves (Cervus elaphus) died with severe nephritis apparently associated with infection by Leptospira interrogans serovar pomona. The sera of 12 in-contact red deer calves were examined for leptospiral agglutinins and nine showed titres to pomona consistent with recent infection. Two also showed titres of 1:100 to serovar hardjo. The urine of five of these in-contact calves was examined periodically over a period of nine months. All were initially leptospiruric, four being infected with pomona and one with hardjo. In four animals leptospiruria could only be detected for up to six months, but one animal infected with pomona was leptospiruric for at least eight months. The apparent source of infection was from infected cattle, and it is suggested that deer are unlikely to act as maintenance hosts for serovar pomona.     

The role of the common vole (Microtus arvalis) in the epidemiology of bovine infection with Leptospira interrogans serovar hardjo

Control of leptospirosis in cattle depends on the presence of other possible maintenance hosts, with which cattle may have contact. Twenty-seven common voles (Microtus arvalis) were trapped on a dairy farm where the cattle were infected with Leptospira interrogans serovar hardjo (hardjo). In the sera of 11 voles, titres greater than or equal to 100 against serogroup Grippotyphosa were measured with the microscopical agglutination test (MAT). From 8 of these 11 voles, which also showed interstitial lymphoplasmacellular nephritis, Leptospira interrogans serovar grippotyphosa was isolated. We found no evidence that the common vole is a maintenance host for hardjo in this biotope.     

An unusual serological response in cattle after use of a commercial leptospiral combined hardjo-pomona vaccine

Vaccination of four calves with Leptavoid (Wellcome New Zealand Limited) gave rise to Leptospira interrogans serovars hardjo and pomona microscopic agglutination test titres that could not he distinguished in magnitude from post-infection titres. Vaccination of four calves with Lepto-3 (ICI Tasman Limited) gave rise to much lower titres. Revaccination of cows with Leptavoid caused a rise in hardjo titres which was significantly greater than after use of Lepto-3. The possibility that titres were due to the simultaneous infection with serovars pomona and hardjo of only the animals vaccinated with Leptavoid must be discounted.     

Serological evidence of bovine leptospirosis in Malawi

Two hundred and seventy-five serum samples from cattle in Malawi were tested as a pilot survey for Leptospira antibody titres. Fifty-nine (21.4%) of the animals were positive for leptospirosis, while 35 (12.7%) animals reacted inconclusively. Titres to L. hardjo and L. pomona serovars were the most prevalent. Results are also discussed with reference to the areas where samples were collected.     

Evaluation of an ELISA for the diagnosis of experimentally induced and naturally occurring Leptospira hardjo infections in cattle

An enzyme-linked immunosorbent assay (ELISA) for the diagnosis of Leptospira interrogans serovar hardjo (hardjo) infection in cattle was compared with the microscopic agglutination test (MAT). Glutardialdehyde was used in the ELISA to couple sonicated hardjo antigen to the microtiter plate. Mouse monoclonal anti-bovine IgG1 coupled to peroxidase was used as conjugate. Sera from calves experimentally inoculated with hardjo reacted positively in the MAT as early as 10 days after inoculation; these sera did not react positively in the ELISA until 25 days after the first inoculation. Positive and negative field sera from 704 adult cattle on 90 farms were examined by the MAT and the ELISA; a 90% correlation between the two tests was demonstrated. Eighty-six sera from calves inoculated with four Leptospira serogroups other than hardjo and 227 field sera from adult cattle with naturally occurring leptospirosis other than hardjo were examined by the ELISA. Fewer than 1% of these heterologous sera reacted with hardjo antigen in the ELISA. We concluded that the ELISA described in this report is an advantageous alternative to the MAT for diagnosing leptospirosis.     

Leptospira interrogans infection in domestic and wild animals in Fiji

Clinical and serological evidence has indicated that human leptospirosis in Fiji is an important disease, and the prevalence of antibody is exceptionally high. A serological survey of the rural population showed that only 12% of the people studied did not have complement fixing (CF) leptospiral antibody. As the origin of this infection could not be explained by the known distribution of leptospiral infection in domestic and wild animals, a serological survey using the complement fixation test (CFT) was undertaken as the first stage of an epidemiological investigation into human and animal leptospirosis. Sera from domestic and wild animals were tested for CF antibody to 12 leptospiral serovars, namely: pomona, copenhageni, grippotyphosa, hardjo, ballum, tarassovi, canicola, australis, bratislava, autumnalis, pyrogenes and bataviae. Antibody was detected in 27.5% of 480 cattle, 17.1% of 70 sheep, 10.3% of 252 goats, 10.0% of 480 pigs, 57.0% of 100 dogs, 55.8% of 34 rats (Rattus rattus, R. frugivorus, R. exulans and R. norvegicus), 53.1% of 32 mongooses (Herpestes auropunctatus) and 40.0% of 10 mice (species unknown.) Cross-reactivity precluded the identification of infecting serogroups with the exception of pomona in pigs and icterohaemorrhagiae, ballum and australis in dogs. Infection of dogs with a serovar of the australis serogroup may explain the predominance of serological reactions to bratislava in man. The survey revealed a significant level of leptospiral antibody in the animal populations of Fiji and indicated that cattle, dogs, rats, mongooses and mice are probably the most important maintenance hosts. Consequently, further investigation will concentrate on the attempted isolation of leptospires from these species.     

A serological survey on the prevalence of infectious bovine rhinotracheitis in Buckinghamshire, Berkshire and Oxfordshire.

Of the 2368 cattle sera from herds in Buckinghamshire, Berkshire and Oxfordshire examined for infectious bovine rhinotracheitis antibody by an indirect haemagglutination test, 162 (6.8 per cent) proved positive. Positive titres were more prevalent in older cows and they tended to show higher titres. There was little evidence of infection in the bulls tested. The percentage of positive animals in Berkshire and Oxfordshire was 4.7 compared with 10.5 in Buckinghamshire. The infection was not known to be associated with any clinical disease.