A brief review on the laboratory diagnosis of leptospirosis

The association between natural drinking water sources and the emergence of zoonotic leptospirosis among grazing beef cattle herds during a human outbreak

Leptospirosis is a zoonotic bacterial disease associated with water abundance in tropical and temperate climate zones. Bacterial spread may also occur in dry and warm weather conditions when humans and animals are forced to share depleted water sources. In such settings, farm animals such as beef cattle, which may be present in large numbers in natural water sources, can play a major role in disease spread. However, the risk factors for their infection and the potential control measures to prevent the disease spread have not been adequately studied.

In the face of an emerging human leptospirosis outbreak in the dry and warm Israeli 2018 summer, we tested seropositivity to Leptospira serovar Pomona in grazing beef cattle and wild boars located in proximity to the contaminated streams. Additionally, we used the natural setting of the outbreak to identify risk factors for seropositivity in beef cattle.

We found high seropositivity to serovar Pomona in grazing beef cattle (233/845), and in wild boars (7/13). Seropositivity was significantly associated with beef cattle drinking from natural water sources compared to beef cattle drinking from water troughs with fresh water supply (Multivariable logistic regression; odds ratio = 18.6, 95% confidence interval = 3–116, p-value<0.01).

One Health approach is necessary for mitigating zoonotic Leptospira infections, in which interactions between humans, animals, and the environment play a major role. As the global warming crisis results in severe climate changes, dry and warm weather conditions may become more common worldwide. Under such conditions, reducing inter-species interactions in contaminated natural water sources is essential for protecting public health. Our study demonstrates the role of natural water as a source for beef cattle infection and disease spread. Furthermore, we suggest using water troughs with freshwater supply for preventing future outbreaks in animals and humans in such settings.

•

Leptospirosis spread through depleted water sources shared by humans and animals

•

Dry and warm weather may become more common due to global warming crisis

•

During human outbreak, high seropositivity was found in beef cattle and wild boars

•

Drinking sources were significantly associated with seropositivity in beef cattle

•

Using water troughs with freshwater supply may prevent future outbreaks

Serologic titers to Leptospira in vaccinated pigs and interpretation for surveillance

Diagnosis and surveillance of pathogenic Leptospira is difficult as organisms may be intermittently shed and in small numbers. Therefore, serologic testing by the microscopic agglutination test (MAT) is the primary screening method for leptospirosis. While a MAT titer ≥1:100 is considered to be a positive result, interpretation is complicated by the use of commercial vaccines in pigs. Most guidelines for interpretation of MAT titers in pigs were published in the 1970’s and 1980’s, prior to the development of the current multivalent vaccines. We evaluated MAT titers in routinely vaccinated healthy research pigs compared to their unvaccinated cohorts. Our study confirmed previous reports that the Pomona serovar elicits minimal antibody response even after a second booster 6 months after initial vaccination. However, MAT titers of ≥1:3,200 were detected as early as 4 weeks post initial vaccination for serovars Bratislava and Icterohaemorrhagiae and remained as high as ≥1:1,600 prior to booster at 24 weeks post vaccination. Our study determined that high levels of MAT titers can occur from vaccination alone and high titers are not necessarily indicative of infection. Therefore, the interpretation of MAT titers as indicators of Leptospira infection should be readdressed.

Leptospira Interrogans Serogroup Sejroe Serovar Hardjo in Aborting Cows: Two Herd Cases in Sicily (Italy)

Introduction

The aim of this study was to present two outbreaks of bovine abortion due to Leptospira infection in cattle herds located in the northern part of Sicily (Italy). The animals were positive for Leptospira interrogans serogroup Sejroe serovar Hardjo in a microscopic agglutination test (MAT).

Material and Methods

A total of 23 Charolaise cows (farm A) and 75 Limousine bulls and Cinisara and Modicana cows (farm B) were enrolled in this study. The blood samples were collected from all subjects at the following time points: before a cycle of intramuscular treatment with oxytetracycline dihydrate (T0), after 5–6 weeks from the treatment (T1), and every 10 weeks until seronegativisation (T2 in Farm A and T3 in Farm B). A serological test (MAT) was used for the diagnosis of leptospirosis.

Results

Two samples from farm A (2/23) and 29 samples from farm B (29/75) were positive to Leptospira interrogans, serogroup Sejroe, serovar Hardjo in the MAT. Leptospira spp. DNA was detected by real-time PCR in the urine sample of one positive cow on farm A, and in placenta and brain samples belonging to one aborted foetus on farm B.

Conclusion

It is important to use serological and molecular diagnostic techniques complementarily to identify infected individuals.

Evaluation of an in-house LipL32 polymerase chain reaction for diagnosis of leptospirosis and its correlation with various serological diagnostic techniques

Background

Leptospirosis is a zoonotic disease of ubiquitous distribution. During rainy seasons, in spring and summer and also during harvest times, the risk of leptospirosis increases as there are chances of frequent contact with infected rat population which is common in Karnataka as farming is a main source of income to the people here. There is a paucity of data regarding the prevalent serovars from Karnataka. This study was undertaken as an attempt to compare a battery of tools such as immunochromatographic test (ICT), microscopic agglutination test (MAT), immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA) and in-house polymerase chain reaction (PCR) to detect leptospirosis.

Settings and Design

This study using consecutive sampling technique was conducted in a tertiary care centre, Mysore, Karnataka.

Subjects and Methods

Samples from 783 suspected cases of leptospirosis in and around Mysore between April 2013 and April 2016 were processed. Samples from 783 patients suspected of leptospirosis were subjected to ICT, IgM ELISA, MAT and in-house PCR.

Statistical Analysis Used

The statistical analysis was carried out using SPSS software version.

Results

Among 783 samples tested, only 14 (1.7%) were positive by ICT, 341 (44%) were positive by IgM ELISA, 368 (47%) were positive by MAT and 393 (50.2%) were positive by in-house PCR.

Conclusions

Mysore can be considered endemic for leptospirosis. The in-house PCR based on LipL32 gene proved to be useful in the early diagnosis of leptospirosis.

Protection of sheep by vaccination against experimental challenge with Leptospira borgpetersenii serovar Hardjo and L. interrogans serovar Pomona

AIMS

To evaluate a multivalent leptospiral and clostridial vaccine for prevention of renal colonisation and urinary shedding in sheep, following experimental challenge with New Zealand strains of Leptospira borgpetersenii serovar Hardjo type Hardjobovis and L. interrogans serovar Pomona.

METHODS

Two separate but similarly designed studies were conducted. In both studies, Romney-cross lambs, aged 9-11 weeks, were randomly allocated to a vaccinated group and a control group. Vaccinated lambs each received two 1.5-mL S/C doses of a multivalent leptospiral and clostridial vaccine, 4 weeks apart, and animals in the control groups received the same dose of saline. Groups of 12 vaccinated and 12 control lambs were randomly selected in each study for challenge with serovars Hardjo or Pomona. Challenge was initiated 16 weeks following the second vaccination with three daily doses of live leptospires by intranasal and conjunctival routes. Following challenge, urine samples were collected weekly for 6 weeks, for dark field microscopy and leptospiral culture; 6 weeks after challenge the lambs were slaughtered and kidneys collected for leptospiral culture.

RESULTS

In lambs challenged with serovar Hardjo, 8/12 unvaccinated lambs had ≥1 urine or kidney sample that was positive for leptospires following culture, compared with 0/12 lambs in the vaccinated group (p=0.001). In lambs challenged with serovar Pomona, 9/12 unvaccinated lambs had ≥1 urine or kidney sample that was positive following culture, compared with 0/12 lambs in the vaccinated group (p<0.001). Prevention of renal colonisation and urinary shedding, expressed as the prevented fraction, was 100 (95% CI=61.7-100)% and 100 (95% CI=68.3-100)% against challenge with serovars Hardjo and Pomona, respectively, at 4 months after vaccination.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of a multivalent leptospiral and clostridial vaccine demonstrated protection against challenge from New Zealand strains of serovars of Hardjo and Pomona 4 months after vaccination in lambs first vaccinated at 9-11 weeks of age. Further studies are required to assess the duration of immunity against challenge in sheep.

Prevalence of renal lesions in slaughtered cattle in Shiraz, Iran, and detection of Leptospira in them by nested PCR-RFLP

Renal diseases in cattle are frequently not recognized due to the subclinical conditions. Some species of Leptospira are the main cause of infectious agents that damage the kidneys and lead to abortion and economic losses in cattle and are also of major concern in the public health. This study was aimed to assess the prevalence of renal lesions of slaughtered cattle in the Shiraz abattoir and to determine the correlation between rejected kidneys and infection with Leptospira using nested PCR-restriction fragment length polymorphism (RFLP) techniques. Out of 1000 inspected animals, 205 (20.5 %) revealed the renal lesions. Chronic nephritis (7.5 %), white-spotted kidney (7.3 %), and petechial hemorrhage (3.5 %) were the most prevalent forms of the lesions. A direct correlation between increasing the age and significant increase in the rate of lesions was also observed (P = 0.03). Using nested PCR-RFLP assay, 40.8 % of the tested kidneys were turned to be infected to the pathogenic species of Leptospira. The risk of infection of the kidneys with white spot to pathogenic species of Leptospira (53.8 %) was more than that of the kidneys with other lesions (25.0 %) (P = 0.014). The odd ratio indicates that the kidneys with white spot lesions are likely to be infected with pathogenic species of Leptospira, five times greater than other lesions. This study showed that renal lesions especially white-spotted kidney, which were considerably associated with Leptospira in slaughtered cattle in Shiraz, were very high. This is important in terms of public health and in particular, increases the risk of transmission of disease to human specially in the high-risk careers including farmers, veterinarians, and abattoir workers.

Prozone effects in microscopic agglutination tests for leptospirosis in the sera of mice infected with the pathogenic Leptospira interrogans serovar Canicola

Mice experimentally infected with a pathogenic strain of Leptospira interrogans serovar Canicola produced false negative results (prozone effect) in a microscopic agglutination test (MAT). This prozone effect occurred in several serum samples collected at different post-infection times, but it was more prominent in samples collected from seven-42 days post-infection and for 1:50 and 1:100 sample dilutions. This phenomenon was correlated with increased antibody titres in the early post-infection phase. While prozone effects are often observed in serological agglutination assays for the diagnosis of animal brucellosis and human syphilis, they are not widely reported in leptospirosis MATs.

Interlaboratory and between-specimen comparisons of diagnostic tests for leptospirosis in sheep and cattle

A study was performed to investigate interlaboratory test agreement between a research and a commercial veterinary diagnostic laboratory on blood and urine samples, and to investigate test agreement between blood, urine, and kidney samples (research laboratory) for leptospirosis diagnosis. Samples were sourced from 399 sheep and 146 beef cattle from a local abattoir. Interlaboratory agreement for real-time quantitative polymerase chain reaction (qPCR) results on urine samples was almost perfect (kappa = 0.90), despite the use of different amplification targets (DNA gyrase subunit B gene vs. 16s ribosomal RNA gene), chemistries (SYTO9 vs. TaqMan probe), and pre-PCR processing. Interlaboratory agreement for microscopic agglutination test (MAT) positivity was almost perfect (kappa = 0.93) for Leptospira borgpetersenii serovar Hardjo subtype Hardjobovis (Hardjobovis) but moderate (kappa = 0.53) for Leptospira interrogans serovar Pomona (Pomona). Among animals that had different titers recorded, higher Hardjobovis and lower Pomona titers were reported by the commercial laboratory than by the research laboratory (P < 0.005). These interlaboratory comparisons can assist researchers and diagnosticians in interpreting the sometimes discrepant test results. Within the research laboratory, the comparison of qPCR results on urine and kidney showed almost perfect agreement (kappa = 0.84), suggesting that the qPCR on these 2 specimens can be used interchangeably. The agreement between MAT positivity and urine and kidney qPCR results was fair (kappa = 0.32 and kappa = 0.33, respectively). However, the prevalence ratio of urine and kidney qPCR positivity in Hardjobovis-seropositive versus Hardjobovis-seronegative sheep indicated that Hardjobovis seropositivity found in sheep may be able to predict shedding or renal carriage.

Shedding and seroprevalence of pathogenic Leptospira spp. in sheep and cattle at a New Zealand Abattoir

A cross-sectional study was carried out on sheep and cattle slaughtered at a New Zealand abattoir from September to November 2010 to investigate the supplier-specific shedding rate, renal carriage rate and seroprevalence of leptospires. In the 2008/2009 season, this abattoir experienced three human leptospirosis cases from 20 staff, of which two were hospitalized. Urine, kidney and blood samples were collected from carcasses of 399 sheep (six suppliers, 17 slaughter lines) and 146 cattle (three suppliers, 22 slaughter lines). The urine and kidney samples were tested by quantitative real-time PCR (qPCR), while serum samples (from coagulated blood samples) were tested by microscopic agglutination test (MAT). In total, 27% (73/274; 95% CI: 18-37) of urine samples tested positive by qPCR. Species-specific shedding rates (prevalence of positive urine qPCR) were 31% (95% CI: 17-48) for sheep and 21% (95% CI: 14-30) for cattle. For 545 kidney samples tested, 145 were qPCR positive (27%; 95% CI: 17-39). The average prevalence of kidney qPCR positivity was 29% (95% CI: 17-45) for sheep and 21% (95% CI: 15-28) for cattle. Three hundred and thirty of 542 sampled sheep and cattle had antibodies against Leptospira borgpetersenii serovar Hardjobovis (Hardjobovis) and/or Leptospira interrogans serovar Pomona (Pomona), based on reciprocal MAT titre ≥1 : 48 (overall seroprevalence of 61%; 95% CI: 48-73). Seroprevalence was 57% (95% CI: 40-72) for sheep and 73% (95% CI: 59-83) for cattle. Among the seropositive animals, 41% (70/170; 95% CI: 30-54) were shedding (tested positive by urine qPCR) and 42% (137/330; 95% CI: 30-54) had renal carriage (tested positive by kidney qPCR). Some risk management options for abattoirs or farms to prevent human leptospirosis infections include vaccination of maintenance hosts, the use of personal protective equipment, and the application of urine qPCR to detect shedding status of stock as surveillance and as an alert.

Serosurveillance for livestock pathogens in free-ranging mule deer (Odocoileus hemionus)

Routine disease surveillance has been conducted for decades in mule deer (Odocoileus hemionus) in California for pathogens shared between wildlife and domestic ruminants that may have implications for the animal production industry and wildlife health. Deer sampled from 1990 to 2007 (n = 2,619) were tested for exposure to six pathogens: bluetongue virus (BTV), epizootic hemorrhagic disease virus (EHDV), bovine viral diarrhea virus (BVDV), Leptospira spp., Anaplasma spp. and Brucella spp. We evaluated the relationship between exposure to these pathogens and demographic risk factors to identify broad patterns in seroprevalence across a large temporal and spatial scale. The overall seroprevalence for the entire study period was 13.4% for BTV, 16.8% for EHDV, 17.1% for BVDV, 6.5% for Leptospira spp., 0.2% for Brucella spp., and 17% for Anaplasma spp. Antibodies against BTV and EHDV were most prevalent in the deer populations of southern California. Antibodies against Leptospira spp. and Anaplasma spp. were most prevalent in coastal and central northern California whereas antibodies against BVDV were most prevalent in central-eastern and northeastern California. The overall seroprevalence for Anaplasma spp. was slightly lower than detected in previous studies. North and central eastern California contains large tracts of federal land grazed by livestock; therefore, possible contact between deer and livestock could explain the high BVDV seroprevalence found in these areas. Findings from this study will help to establish baseline values for future comparisons of pathogen exposure in deer, inform on long-term trends in deer population health and provide relevant information on the distribution of diseases that are shared between wildlife and livestock.

Evaluation of a SYTO9 real-time polymerase chain reaction assay to detect and identify pathogenic Leptospira species in kidney tissue and urine of New Zealand farmed deer

A SYTO9 real-time polymerase chain reaction assay for detection of pathogenic Leptospira spp. based on amplification of DNA gyrase subunit B (gyrB) gene has been optimized and evaluated for sensitivity and specificity on kidney and urine samples of New Zealand farmed deer. The detection limit was 10(3) cells/ml (2-10 copies/reaction). Comparison of the assay on deer kidneys (n = 268) with culture as the gold standard revealed a sensitivity and specificity of 85% and 99.2%, respectively. For deer urine (n = 113), the assay was compared with known inoculated samples and revealed a sensitivity and specificity of 96.7% and 100%, respectively. The assay was applied for quantifying pathogenic leptospires shed naturally in deer urine and revealed a detectable concentration of 3.7 × 10(3) to 1.7 × 10(6) cells/ml. To assess the assay's capability for identifying pathogenic Leptospira spp., 14 field isolates of L. borgpetersenii serovar Hardjo-bovis and L. interrogans serovar Pomona were amplified for polymerase chain reaction (PCR) product, purified, and sequenced. When compared with the National Center for Biotechnology Information database, sequence data matched with L. borgpetersenii serovar Hardjo-bovis in 13 samples and L. interrogans serovar Pomona in 1 sample, which was consistent with the microscopic agglutination test (MAT). Sequence analysis of purified PCR product amplified directly from kidney and urine samples also yielded serovar-comparable MAT results. Results suggest that the assay is rapid, sensitive, and specific for detection of pathogenic leptospires in deer clinical samples. The developed assay can also be used for estimating the concentration of leptospires and identifying Leptospira spp. in combination with DNA sequencing.

Assessment of occupational exposure to leptospirosis in a sheep-only abattoir

This study estimated the frequency of exposure of meat workers to carcasses infected with Leptospira serovars Hardjobovis or Pomona in a sheep-only abattoir in New Zealand. A stochastic spreadsheet model was developed to assess the daily risk of exposure of eviscerators, meat inspectors and offal handlers to live leptospires in sheep carcasses from May to November 2004 (high-risk period), and from December 2004 to June 2005 (low-risk period). The average sheep processed per day were 225 for an eviscerator, 374 for a meat inspector, and 1123 for an offal handler. The median daily exposures during high- and low-risk periods were 11 [95% distribution interval (DI) 5-19] and three (95% DI 1-8) infected carcasses/day for eviscerators, 18 (95% DI 9-29) and six (95% DI 2-12) for meat inspectors, and 54 (95% DI 32-83) and 18 (95% DI 8-31) for offal handlers, respectively. Stochastic risk modelling provided evidence that processing of sheep carcasses exposed meat workers regularly to live leptospires with substantial seasonal variation.