Animal- and herd-level risk factors for leptospiral seropositivity among sows in the Mekong delta, Vietnam

In 1998, a total of 424 sows had sera collected in the Mekong delta in Vietnam. Of these, 283 sows were from 151 small-scale family farms in 19 villages, and 141 from seven large-scale state farms. The sera were subjected to the microscopic agglutination test (MAT) for antibodies to 13 Leptospira serovars. The overall leptospiral seroprevalence for titres > or =1:100 and > or =1:400, was 73 and 29%, respectively, and was higher (P=0.001) at small- than at large-scale farms. The highest seroprevalence was recorded for Leptospira interrogans serovar (sv) bratislava (52%). At small-scale farms, higher prevalences were found to serovars L. interrogans sv icterohaemorrhagiae (P=0.04) and L. interrogans sv pomona (P=0.02).Epidemiological information (at the individual-animal and herd-levels) was collected with a questionnaire. The data were analysed using logistic multiple regression. At the animal-level, sows seropositive for L. interrogans sv australis and sv autumnalis had less direct contact with sows in neighbouring pens (odds ratio (OR)=0.3 and 0.4, respectively) and sows seronegative for L. interrogans sv bratislava were of lower age (OR=0.1 for seropositivity). Also, sows seropositive for L. interrogans sv icterohaemorrhagiae had higher odds (OR=5.8) if they had not been born on the farm (had been introduced to it as gilts).Herds seropositive for sv javanica showed association with farms not taking measures to control the local rodent population (OR=7.8). Serovar pomona was also linked to the use of artificial insemination (AI), as opposed to natural-breeding services (OR=11.2).These results indicate that housing and management could affect the seroprevalence of Leptospira infection in pigs.     

Epizootiologic association between feline immunodeficiency virus infection and feline leukemia virus seropositivity

Five hundred twenty-one feline serum samples submitted to the Texas Veterinary Medical Diagnostic Laboratory between Nov 1, 1988, and Jan 31, 1989 were tested for antibody to feline immunodeficiency virus (FIV) by use of an ELISA. The prevalence of FIV infection in this population was 11.3% (95% confidence interval: 8.6 to 14.0%). Serologic test results for FeLV were available for 156 of the 521 cats. A significant (P = 0.008) association between FIV infection and FeLV seropositivity was observed; FeLV-positive cats were nearly 4 times more likely to be seropositive for FIV than were FeLV-negative cats. The association remained statistically significant (P = 0.021) after adjusting for age and gender, using multiple-logistic regression analysis.     

Investigation of possible leptospiral infection in cats in Scotland

Eighty-seven cats from the Glasgow area were investigated to determine the prevalence of leptospiral infection and possible resultant disease. Eight (9-2 per cent) of the cats reacted serologically with the antigens of three serovars. Five of the cats were seropositive to Leptospira hardjo, two to L autumnalis and one cat serocon-verted to L icterohaemorrhagiae. A paired serum sample indicated a recent infection in one of the cats. The major clinical sign shown by this cat was ascites. Four of the cats were from rural areas. This appears to be the first report of a serological survey of leptospiral infection in cats in the Glasgow area.     

Associations between viral infection and respiratory disease in young beef bulls

Blood samples were taken from bull calves at two Meat and Livestock Commission performance testing centres, just after weaning at six months of age and at six weekly intervals until the end of the performance test seven months later. Sera were assayed by specific ELISAS for antibodies to bovine herpes virus 1 (BHV1), respiratory syncytial virus, parainfluenza 3 (Pi3) and adenoviruses A and B. Seroconversions between each sampling were related to the occurrence of clinical respiratory disease using chi-squared (chi 2) and relative risk (RR) analyses. In 294 bulls there were 123 cases of respiratory disease. Seroconversion to bovine respiratory syncytial virus (RR = 4.7, chi 2 = 96.3, P less than 0.001) and adenovirus A (RR = 1.8, chi 2 = 8.9, P less than 0.001) and adenovirus B (RR = 1.9, chi 2 = 5.6, P less than 0.05) were significantly associated with clinical respiratory disease. There was evidence that prior exposure to respiratory syncytial virus (RR = 0.4, chi 2 = 9.8, P less than 0.01) Pi3 (RR = 0.4, chi 2 = 12.8, P less than 0.01) and adenovirus A (RR = 0.7, chi 2 = 7.5, P less than 0.01) conferred some protection against respiratory disease after arrival at the centre. It is concluded that vaccination before weaning, at least against bovine respiratory syncytial virus, would be beneficial.     

Serological survey of leptospiral infection in kennelled dogs in Italy

Two hundred and forty-five dogs were examined serologically for the presence of antibodies against different serovars of Leptospira interrogans. The dogs belonged to five different groups: group 1 was composed of clinically healthy pet dogs referred for a regular veterinary check-up visit or for vaccination; group 2 was composed of stray dogs; and groups 3, 4 and 5 were composed of dogs maintained in three different kennels which had varying standards of hygiene. Seventy-two out of the 245 dogs examined were seropositive for leptospirosis. In group 1, there were 3-4 per cent seropositive dogs; in group 2, 30.3 per cent; in group 3, 13.8 per cent; in group 4, 38.6 per cent; and in group 5, 49.2 per cent. This study demonstrates that leptospiral infection is common in dogs housed in kennels, despite most of them being vaccinated, and that crowding of animals into unsanitary quarters is associated with a high prevalence of infection. The most common infecting serovars found were bratislava and grippotyphosa, confirming recent observations that demonstrate a significant change in the epidemiology of canine leptospirosis.     

An historical view of the experimental leptospiral infection in ruminants

The first experimental infections with Leptospira in ruminants were conducted in the 1950s, primarily assessed the pathogenesis caused by serovar Pomona in cows. Throughout the decades, experimental infections have also demonstrated the clinical aspects of the infection by other strains, mainly Hardjo. Despite the important outcomes observed in experimental infections in ruminants, there is still a large discrepancy regarding the ideal dose, route, strain, model species or animal age that should be used to reproduce the acute and chronic leptospirosis in ruminants. In this context, the present study aimed to review the historical processes involved on the experimental leptospiral infection in ruminants. The inclusion criteria were papers that clearly described inoculation route, strain, dose, clinical signs and animal age. Overall, 37 experiments were noted. The most frequently reported clinical signs were fever, prostration, hematuria and death, with the majority of them occurring in young animals infected by incidental strains. Regarding reproductive problems, they occurred in the majority of the experiments and were also more related to incidental strains. In this context, abortions, retained placenta and weak fetuses were the most frequent symptoms. Noteworthy that although the mechanisms of the clinical acute disease either systemic or reproductive, is reasonably well understood, the physiopathology involved on reproductive problems due to the silent chronic infection is less discussed and remains to be elucidated. In this context, it is evident the need for studies focused on the genital infection and reproductive aspects of leptospiral infection in ruminants.     

Associations between postpartum diseases and milk yield and changes in body condition between drying off and parturition of dairy cows in Argentina

ABSTRACT

Aims: To assess the change in body condition score (BCS) during the early and late dry periods and its association with postpartum diseases and milk yield in grazing dairy cows from central Argentina.

Methods: BCS assessments during the dry period, and cow health and milk production records up to 90 days in milk (DIM), were collated for cows from 28 farms at monthly visits between 2007 and 2008. Cows were categorised into four groups; those in Group 1 (n=7,067) maintained or gained BCS during the early and late dry periods; Group 2 (n=2,615) maintained or gained BCS during the early dry period and lost BCS during the late dry period; Group 3 (n=1,989) lost BCS during the early dry period and maintained or gained BCS during the late dry period; and Group 4 (n=5,144) lost BCS during the early and late dry periods.

Results: Cows in Group 1 had reduced odds of having retained fetal membranes (RFM), metritis, and clinical mastitis up to 90 DIM than cows in Group 2 (p<0.001), but the odds of disease were similar to cows in Group 3. The odds of having RFM or clinical mastitis tended to be lower in cows in Group 1 than cows in Group 4 (p=0.08). The odds of cows being culled or dying during the first 90 DIM were lower for cows in Group 1 than for those in Groups 2, 3, and 4 (p≤0.05). Mean accumulated milk yield up to 90 DIM was higher in cows in Group 1 than Group 2 and Group 4 (p<0.001), but was similar to that of cows in Group 3 (p=0.28).

Conclusions and clinical relevance: Cows that lost BCS during the late dry period had increased odds of being diagnosed with several postpartum diseases and had decreased milk yield compared to cows that maintained or gained BCS during the entire dry period. Loss of BCS during any stage of the dry period was also associated with increased incidence of culling or death during the first 90 DIM. These results should raise awareness among dairy cattle producers of the importance of properly managing cow body condition during the dry period, especially during the late dry period.     

Potency of leptospiral vaccines and protection against chronic infection in golden hamsters

Seven vaccines prepared from pathogenic strains of different origin of Leptospira interrogans [serovars icterohaemorrhagiae (one strain) and copenhageni (6 strains)] were examined in protection tests on golden hamsters. Two of the copenhageni strains were used for challenge. The organs (kidneys, spleen, liver) in the vaccinated animals surviving challenge were protected to a varying degree. Low rates of survival were associated with a high incidence of Leptospira-positive findings, partly connected with focal lesions of the kidneys. On the other hand, in the groups in which all the animals survived, it was not possible to culture leptospires from their organs or to detect leptospiral antigen in these organs by immunohistochemical investigation. A protection of the organs that prevents vaccinated animals from shedding leptospires after infection clearly depends on the vaccine dose administered and the efficacy of the vaccine which can be measured in potency tests based on the survival rate as the relevant parameter.     

A serological and bacteriological survey of leptospiral infection in dogs in Edinburgh and Glasgow

Sera collected from 511 unvaccinated urban dogs were examined for antibodies to serovars of Leptospira interrogans representing nine serogroups found in the United Kingdom. The point estimates of the seroprevalence of leptospiral titres in Edinburgh and Glasgow at a minimum serum dilution of 1:10 were 23-5 per cent and 27-5 per cent, respectively, and, in Glasgow, the seroprevalence was significantly higher in males than females, for both crude and age-adjusted values. Serovar canicola was the dominant strain identified, followed by serovars icterohaemorrhagiae, bratislava and ballum. Antibodies against serovars javanica and hardjo also were detected. Urine samples were collected from 84 of the male blood-sampled dogs, and cultured. Serovars canicola and bratislava were isolated from three and four samples, respectively.     

Associations between farmers' personal characteristics, management practices and farm performance

A survey was carried out in a random sample of 123 dairy farms from the east of Ireland. The monthly mean production per cow was 315 l of milk and 11.5 kg of fat. The mean log herd somatic cell count was 5.45 (arithmetic mean = 372,573 cells/ml), with almost 50% of the monthly counts over 300,000 cells/ml in a 12-month period. Bivariate and multivariate analysis was performed to assess the relative impact of the personal characteristics of the farmer and the management policies he applied on the amount and quality of the milk produced. In five out of six models the group of variables related to farmers' attitudes, values, and sociodemographic profile explained a similar or greater amount (between 14.44 and 34.35%) of the variation of farm performance than the group of management variables (between 14.33 and 25.99%) as measured by the R2. These results stress the importance of the human factors in explaining variation in farm performance.     

Associations of Neospora caninum seropositivity with gestation number and pregnancy outcome in Danish dairy herds.

The prevalence and distribution of seropositivity towards the protozoan parasite Neospora caninum were studied in single blood samples from 1561 cows from 31 Danish dairy herds. Blood samples were analysed by an indirect enzyme-linked immunoassay and an indirect fluorescent-antibody test. Seroprevalence in 15 herds with previous abortions assigned to neosporosis ranged from 1% to 58%, with a mean frequency of 22%. In eight out of 16 herds without a history of N. caninum related abortions, no seroreactors were found. In the remaining eight herds, the seroprevalence ranged from 6% to 59%. The prevalence and distribution of seropositivity, gestation number prior to sampling, and breed were related to abortions and perinatal deaths using a random-effects logistic-regression model. Abortion risk was significantly increased in seropositive animals (OR=3) and in 2nd-gestation cows (OR=3). Perinatal death was significantly influenced by gestation number and breed, but not by serostatus. Reproductive performance and culling risk of cows were not affected by serostatus. Seropositivity increased with “age” (i.e. gestation number) (P=0.02). In open cows, seropositivity tended to decrease with distance from calving (P=0.05). The proportion of seropositive pregnant cows increased with trimester (P=0.02).     

Transmission and control of leptospiral infection in a beef cattle herd in southern alberta

Leptospiral antibodies were detected in unvaccinated cattle on a 17 000 hectare ranch in the arid southeast region of Alberta. Antibody to serovar hardjo was present before the breeding season in 7% of 42 yearling bulls, 86% of 29 two year old bulls and 5% of 519 cows. Pomona antibody was confined to 3.7% of the cows. Bulls were treated once with dihydrostreptomycin, 25 mg/kg. Bulls and cows were vaccinated twice at a six week interval, with pomona-hardjo-gripptotyphosa bacterin before breeding and cows were revaccinated the next year. Leptospires were demonstrated in urine, kidney and spinal fluid of vaccinated and treated cattle. New infections occurred on range in vaccinates. Eighteen months after the last vaccination, hardjo and pomona antibody prevalences in cows were 3.6 and 3.2% respectively. A group of 250 seronegative cows on the same ranch were not vaccinated. They remained seronegative throughout the 2.5 years of the study. These cows, in contrast to infected groups, were excluded from pastures adjacent to perimeter herds and grazing leases, and they were bred by artificial inseminstion. Rotation through pastures in common with infected groups, and exposure to seropositive heat detector bulls, did not result in seroconversion in these cows. The study showed the potential of range bulls to amplify and transmit hardjo infection, limitations to the value of treatment and vaccination with available agents, and the potential of management practices to maintain an uninfected herd in close proximity to cattle carrying hardjo infection.     

Associations of Neospora caninum seropositivity with gestation number and pregnancy outcome in Danish dairy herds

The prevalence and distribution of seropositivity towards the protozoan parasite Neospora caninum were studied in single blood samples from 1561 cows from 31 Danish dairy herds. Blood samples were analysed by an indirect enzyme-linked immunoassay and an indirect fluorescent-antibody test. Seroprevalence in 15 herds with previous abortions assigned to neosporosis ranged from 1% to 58%, with a mean frequency of 22%. In eight out of 16 herds without a history of N. caninum related abortions, no seroreactors were found. In the remaining eight herds, the seroprevalence ranged from 6% to 59%. The prevalence and distribution of seropositivity, gestation number prior to sampling, and breed were related to abortions and perinatal deaths using a random-effects logistic-regression model. Abortion risk was significantly increased in seropositive animals (OR=3) and in 2nd-gestation cows (OR=3). Perinatal death was significantly influenced by gestation number and breed, but not by serostatus. Reproductive performance and culling risk of cows were not affected by serostatus. Seropositivity increased with “age” (i.e. gestation number) (P=0.02). In open cows, seropositivity tended to decrease with distance from calving (P=0.05). The proportion of seropositive pregnant cows increased with trimester (P=0.02).     

Associations between farm characteristics in fattening pigs and occurrence of lesions at meat inspection

A revised inspection system for fattening pigs in the EU has been proposed emphasizing the need for a more detailed documentation of the fattening process. It is supposed that the availability of such information enables a discrimination of conspicuous and non-conspicuous lots of fattening pigs delivered to the abattoir allowing for a modified, only visual inspection of non-conspicuous lots. This proposal motivated a study performed in 1996 on about 22,000 pigs, searching, among other things, for first hints on associations between management/farm conditions for fattening pigs and lesions found at meat inspection, which can be used for discrimination. Taking the two lesions 'pneumonia' and 'callous affections of the legs' as examples this contribution demonstrates the use of regression trees to visualize association structures and to develop hypotheses on relations between lesions and farm characteristics. An association of 'callous affections of the legs' with flooring systems is clearly shown in the generated tree. The occurrence of 'pneumonia' seems to be associated with the application of disinfection measures in this data set. However, this result should be interpreted with caution as some problems for data analysis arise because of the low number of farms in this study in relation to the high number and complexity of farm characteristics considered. A further problem is the high variability of daily deliveries within farms that cannot be explained referring to farm characteristics common to all deliveries. As a conclusion data from this study have been useful to develop hypotheses on associations between farm characteristics and lesions at meat inspection. However, there is need for further, more specific studies before such associations can be utilized to discriminate between conspicuous and non-conspicuous lots of fattening pigs.     

Immunohistochemical identification and pathologic findings in natural cases of equine abortion caused by leptospiral infection

The aim of this study was to examine the utility of immunohistochemistry (IHC) in the diagnosis of leptospiral equine abortion and to compare IHC to silver staining and serology of the aborted mares. Ninety-six fetuses from 57 farms were examined using all 3 diagnostic techniques, revealing evidence of leptospiral infection in 3 fetuses (3.1%) from 3 (5.3%) different farms. A new finding in 1 of these confirmed cases of leptospiral abortion was the presence of macroscopic pinpoint grayish-white nodules that had a histologic correlate of hepatic necrosis; other histologic findings were consistent with those previously reported. IHC performed using 2 different leptospiral antisera (multivalent whole-cell rabbit antiserum and rabbit antiserum against the major outer membrane protein LipL32) yielded similar results. IHC was more sensitive (19/21 [90.5%] tissue samples) than silver staining (8/21 [38.1%] tissue samples), and more specific than serology performed using the microscopic agglutination test. The primary advantage of IHC over silver staining was the ability of IHC to identify leptospiral antigen not only as morphologically intact spiral forms.     

An association exists between bovine herpesvirus-4 seropositivity and abortion in cows

The prevalence of cattle seropositive to bovine herpesvirus-4 (BHV-4) is high in Belgium. In Belgian farms, clinical signs associated with BHV-4 infection essentially involve the genital tract and consist mainly of postpartum metritis or metroperitonitis. The role of BHV-4 in abortion has not been definitively demonstrated but epidemiological and experimental facts suggest its involvement. A seroepidemiological investigation was therefore conducted as a case-control study to compare the seroprevalences of BHV-4 infections in the aborted-cow population and in a randomly selected control group in the province of Liège (Belgium). The seroprevalence (17.2%) in aborted cows was significantly higher than that of the control group (10.0%). The odds ratio (OR) was 1.87 (1.06 < 3.30). BHV-4 infection is therefore considered as a risk factor for abortion in cows.