Vaccination practices for Leptospira spp. on New Zealand dairy farms

AIMS

To describe leptospiral vaccination practices in dairy herds in New Zealand and evaluate conformity with best practice guidelines issued by the New Zealand Veterinary Association using data from a questionnaire administered by participating veterinary practices.

METHODS

A cross-sectional study of 200 randomly selected dairy farms stratified by herd size and region throughout New Zealand was conducted from January to April 2016 to investigate leptospiral vaccination practices in dairy herds in New Zealand. Using a pre-tested questionnaire administered during a face-to-face interview, vaccination practice details such as vaccine types, time, and age of vaccination and whether vaccines were administered by veterinary or farm staff, were collected.

RESULTS

Leptospiral vaccination programmes had been implemented on 199/200 (99.5 (95% CI = 97.2-99.9)%) farms, and on 178 (89.4%) of those, programmes had been running for ≥5 years. Most farmers used bivalent vaccines containing antigens for leptospiral serovars Pomona and Hardjo (144/179 (80.4%) in calves, 112/167 (60.7%) in heifers, and 112/163 (68.7%) in cows), rather than trivalent vaccines which also include antigens for L. interrogans serovar Copenhageni. In total, 123/200 (61.5%) of farmers purchased only vaccinated animals but 51/199 (25.6%) were unsure of the vaccination status of purchased cattle. Sixty-one percent (105/172) of farmers had other livestock on their farms and of them, 78/186 (42%) vaccinated some or all for Leptospira spp. Leptospiral vaccines were administered always or sometimes with other animal remedies on 30/190 (15.8%) and 91/190 (47.9%) of farms, respectively. Most farmers had not made changes to their vaccination programme in the previous 5 years. Timing of first vaccination of calves ranged from 2 weeks to 10 months of age, with 112/189 (59.3%) vaccinating by 4 months of age. Approximately half of the farms followed the best practice guideline for the timing of vaccinations for calves (high-risk farms; 67/162; 41.4%) heifers (72/165, 43.6%), and cows (171/184; 92.9%).

CONCLUSIONS

The results of this survey suggest that there is almost universal adoption of leptospiral vaccination for dairy cattle in New Zealand. However, there remain areas for improvement regarding the proportion of farmers following best practice guidelines and refinement of vaccination programmes, particularly with respect to timing of vaccination in calves.

AN AGE STRUCTURE MODEL WITH IMPULSE ACTIONS FOR LEPTOSPIROSIS IN LIVESTOCK CATTLE

As a zoonotic disease, leptospirosis has now been identified as one of the emerging infectious diseases. In this paper, we analyze the propagation of leptospirosis and find a schedule for control programs to eradicate the disease in a cattle ranch. A mathematical model has been built with ordinary differential equations (ODEs) to understand the epidemiology of leptospirosis and main factors on its transmission. We investigated the disease free equilibrium of the model and its stability using the basic reproduction number, [Formula: see text], and target reproduction number, [Formula: see text]. Then, the model incorporates vaccination and recruitment control programs in the form of impulse actions as measures to prevent the propagation of leptospirosis in the ranch. Parameter estimation and sensitivity analysis are presented as a part of this study.

Bovine Immune Response to Vaccination and Infection with Leptospira borgpetersenii Serovar Hardjo

This study examined the humoral and cellular response of cattle vaccinated with two commercial leptospiral vaccines, Leptavoid and Spirovac, and a novel bacterin vaccine using Seppic Montanide oil emulsion adjuvant. Vaccination was followed by experimental challenge. All vaccinated cattle were protected from colonization of the kidney and shedding of Leptospira in urine, as detected by culture and immunofluorescence assay. Agglutinating antibody titers were detected in vaccinated cattle at 4 weeks following vaccination, with small anamnestic response detected following experimental challenge. Only animals vaccinated with the oil emulsion-adjuvanted bacterin produced significant IgG2 titers following vaccination, and nonvaccinated animals produced serum IgA titers after experimental challenge. CD4⁺ and γδ T cells from vaccinated cattle proliferated when cultured with antigen ex vivo. Cellular responses included a marked proliferation of γδ T cells immediately following experimental challenge in vaccinated cattle and release of gamma interferon (IFN-γ), interleukin 17a (IL-17a), and IL-12p40 from stimulated cells. Proliferative and cytokine responses were found not just in peripheral mononuclear cells but also in lymphocytes isolated from renal lymph nodes at 10 weeks following experimental challenge. Overall, effects of leptospirosis vaccination and infection were subtle, resulting in only modest activation of CD4⁺ and γδ T cells. The use of Seppic Montanide oil emulsion adjuvants may shorten the initiation of response to vaccination, which could be useful during outbreaks or in areas where leptospirosis is endemic.

IMPORTANCE Leptospirosis is an underdiagnosed, underreported zoonotic disease of which domestic livestock can be carriers. As a reservoir host for Leptospira borgpetersenii serovar Hardjo, cattle may present with reproductive issues, including abortion, birth of weak or infected calves, or failure to breed. Despite years of study and the availability of commercial vaccines, detailed analysis of the bovine immune response to vaccination and Leptospira challenge is lacking. This study evaluated immunologic responses to two efficacious commercial vaccines and a novel bacterin vaccine using an adjuvant chosen for enhanced cellular immune responses. Antigen-specific responsive CD4 and γδ T cells were detected following vaccination and were associated with release of inflammatory cytokines IFN-γ and IL-17a after stimulation. CD4 and γδ cells increased in the first week after infection and, combined with serum antibody, may play a role in clearance of bacteria from the blood and resident tissues. Additionally, these antigen-reactive T cells were found in the regional lymph nodes following infection, indicating that memory responses may not be circulating but are still present in regional lymph nodes. The information gained in this study expands knowledge of bovine immune response to leptospirosis vaccines and infection. The use of oil emulsion adjuvants may enhance early immune responses to leptospiral bacterins, which could be useful in outbreaks or situations where leptospirosis is endemic.

Poly(diaminosulfide) Microparticle-Based Vaccine for Delivery of Leptospiral Antigens

Leptospirosis is a debilitating infectious disease that detrimentally affects both animals and humans; therefore, disease prevention has become a high priority to avoid high incidence rates of disease in the herd and break the transmission cycle to humans. Thus, there remains an important unmet need for a prophylactic vaccine that can provide long-term immunity against leptospirosis in cattle. Herein, a novel vaccine formulation was developed where poly(diaminosulfide) polymer was employed to fabricate microparticles encapsulating the antigen of Leptospira borgpetersenii serovar Hardjo strain HB15B203 (L203-PNSN). A prime-boost vaccination with a L203-PNSN microparticle formulation increased the population of L203-specific CD3⁺ T cells and CD21⁺ B cells to levels that were significantly higher than those of cattle vaccinated with L203-AlOH or the vehicle control (empty PNSN microparticles and blank AlOH). In addition, L203-PNSN was demonstrated to stimulate durable humoral immune responses as evidenced by the increases in the antibody serum titers following the vaccination. It was also found that cattle vaccinated with L203-PNSN produced higher macroscopic agglutinating titers than cattle in other groups. Thus, it can be concluded that L203-PNSN is a novel first-in-class microparticle-based Leptospira vaccine that represents a powerful platform with the potential to serve as a prophylactic vaccine against leptospiral infection in cattle.

Dynamics of humoral response in naturally-infected cattle after vaccination against leptospirosis

Vaccination is one of the most important measures for the control of bovine leptospirosis. Despite the broad usage of vaccination against leptospirosis in cattle worldwide, the dynamics of the post-vaccine immune response remain controversial and many aspects are still unclear, particularly in naturally-infected animals. Thus, the objective of this study is to describe the dynamics of humoral response in naturally-infected cattle after vaccination against leptospirosis. A total of 162 cows were studied, consisting of 129 included in the experimental group (G1), and subdivided into two groups, vaccinated with two different brands of bacterins, as well as 33 in the control group (G2). Serology (MAT) was performed in all cows on D0 (vaccination), then 60 and 120 days post-vaccination. Vaccination significantly elicited the production of anti-leptospiral antibodies. Seroreactivity increased rapidly but was of short duration (up to D60). Significantly, that increase was notably higher in the vaccinated group than in the controlled. Both vaccines elicited a similar response with a higher rate of seroreactive animals, but predominately against different serogroups. In this context, our results reinforce that, although of limited duration, vaccination against leptospirosis significantly elicits a specific humoral response in naturally-infected animals. The two studied vaccines presented similar seroconversion levels, but predominantly to different serogroups, being one against Icterohaemorrhagiae and the other against Sejroe.

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.

Meta-analysis of the efficacy of Leptospira serovar Hardjo vaccines to prevent urinary shedding in cattle

Leptospirosis is a zoonosis often associated with occupational exposure from livestock that can be prevented by animal vaccination. Several trials have assessed vaccine efficacy in livestock but there have been no attempts to evaluate these trials jointly. This systematic review and meta-analysis aimed to estimate vaccine efficacy to prevent urinary shedding of Leptospira serovar Hardjo (Hardjo) in cattle. Three databases were used to search for relevant papers published from 1980 to 2015 evaluating commercial vaccines to prevent urinary shedding of leptospires after artificial conjunctival or natural challenge. A total of 1237 articles were initially identified. Eight articles containing information from nine trials that assessed vaccine efficacy to prevent Hardjo urinary shedding, as per bacteriological culture, were included in the meta-analysis. Fixed effects Mantel-Haenszel (MH) and a Bayesian random effects meta-analyses were used to estimate the efficacy of vaccination to prevent Hardjo shedding in urine. Vaccine efficacy against Hardjo challenge was 88.7% (95% CI 81.0%-93.2%) in the MH meta-analysis and 89.9% (95% probability interval 80.6%-94.9%) in the Bayesian random effects meta-analysis. There was no evidence of heterogeneity of study results (p = 0.17). The estimated vaccine efficacy to prevent urinary shedding of Hardjo in cattle may be sufficient to reduce disease incidence in animals and exposure risk of people working in close contact with cattle.