Sex-differential non-specific effects of adjuvanted and non-adjuvanted rabies vaccines versus placebo on all-cause mortality in dogs (NERVE-Dog study): a study protocol for a randomized controlled trial with a nested case-control study.

BACKGROUND: It has been proposed that childhood vaccines in high-mortality populations may have substantial impacts on mortality rates that are not explained by the prevention of targeted diseases, nor conversely by typical expected adverse reactions to the vaccines, and that these non-specific effects (NSEs) are generally more pronounced in females. The existence of these effects, and any implications for the development of vaccines and the design of vaccination programs to enhance safety, remain controversial. One area of controversy is the reported association of non-live vaccines with increased female mortality. In a previous randomized controlled trial (RCT), we observed that non-live alum-adjuvanted animal rabies vaccine (ARV) was associated with increased female but not male mortality in young, free-roaming dogs. Conversely, non-live non-adjuvanted human rabies vaccine (NRV) has been associated with beneficial non-specific effects in children. Alum adjuvant has been shown to suppress Th1 responses to pathogens, leading us to hypothesize that alum-adjuvanted rabies vaccine in young dogs has a detrimental effect on female survival by modulating the immune response to infectious and/or parasitic diseases. In this paper, we present the protocol of a 3-arm RCT comparing the effect of alum-adjuvanted rabies vaccine, non-adjuvanted rabies vaccine and placebo on all-cause mortality in an owned, free-roaming dog population, with causal mediation analysis of the RCT and a nested case-control study to test this hypothesis. METHODS: Randomised controlled trial with a nested case-control study. DISCUSSION: We expect that, among the placebo group, males will have higher mortality caused by higher pathogen loads and more severe disease, as determined by haematological parameters and inflammatory biomarkers. Among females, we expect that there will be no difference in mortality between the NRV and placebo groups, but that the ARV group will have higher mortality, again mediated by higher pathogen loads and more severe disease. We anticipate that these changes are preceded by shifts in key serum cytokine concentrations towards an anti-inflammatory immune response in females. If confirmed, these results will provide a rational basis for mitigation of detrimental NSEs of non-live vaccines in high-mortality populations.

Sex-differential non-specific effects of rabies vaccine in dogs: An extended analysis of a randomized controlled trial in a high-mortality population.

Non-live rabies vaccines have been associated with both beneficial and detrimental effects on host population morbidity and mortality rates to unrelated infections in people and animals, and these non-specific effects may differ by sex. Previous animal studies may have been affected by bias, including selection bias due to loss to follow up in randomized controlled trials (RCTs). We previously reported results of an RCT in dogs on the effect of primary rabies vaccine administered at 6 weeks of age on all-cause mortality over a 7-week follow-up period, in a high-mortality population of owned dogs. Here, we report the results from the same trial of a second vaccination at 13 weeks of age, compared to a primary vaccination. Because a relatively high proportion of study subjects (30%) were lost to follow-up in the RCT, we also conducted an analysis to control for possible selection bias over both periods (6 to 13 weeks and 13 to 20 weeks of age). We found that primary rabies vaccination at 6 weeks of age substantially increased the hazard of death from all causes over the next 7 weeks among females (hazard ratio [HR] 2.69, 95% confidence intervals [CI] 1.27-5.69), but not among males (HR 0.91, 95% CI 0.32-2.59). Among survivors, administration of a second dose of rabies vaccine at 13 weeks of age was associated with a decreased hazard of death among males (HR 0.33, 95% CI 0.10-1.02) but not females (HR 1.64, 95% CI 0.59-4.58), when compared to the group receiving their first dose at this age. Based on our causal assumptions, we show that these results were not affected by selection bias. In this high-mortality dog population, receipt of a non-live rabies vaccine substantially affected all-cause mortality rates, with this effect being strongly modified by sex.

Non-specific effects of veterinary vaccines: a systematic review.

The benefits of vaccines have been centred on their specific effects on subsequent infections by target pathogens. Recent studies, however, have opened up new insights into additional effects of vaccines known as non-specific effects (NSEs) or heterologous effects of vaccines. While several articles have reviewed epidemiological and immunological evidence for NSEs of vaccines in humans, similar works on veterinary vaccines are scarce. The objective of this paper was to review the findings of published studies on NSEs of vaccines developed or repurposed for use in animals. In total 8412 titles were retrieved from PubMed and CABI databases on the 30th of April 2021. After the final stage of screening, 45 eligible articles were included in the review. Data from these articles were summarised and presented here. In general, most of the vaccines studied in the reviewed articles have beneficial NSEs against multiple pathogens and disease conditions. There were, however, fewe studies reporting detrimental NSEs from both non-live and live vaccines which is in contrast to the currently existing evidence of beneficial NSEs of live vaccines and detrimental NSEs of non-live vaccines. This review may be used as a complement for future review of RCT studies of NSEs of vaccines in animals and provide a useful addition to the evolving understanding of the NSEs of vaccines.

Rabies Vaccination of 6-Week-Old Puppies Born to Immunized Mothers: A Randomized Controlled Trial in a High-Mortality Population of Owned, Free-Roaming Dogs.

To achieve global elimination of human rabies from dogs by 2030, evidence-based strategies for effective dog vaccination are needed. Current guidelines recommend inclusion of dogs younger than 3 months in mass rabies vaccination campaigns, although available vaccines are only recommended for use by manufacturers in older dogs, ostensibly due to concerns over interference of maternally-acquired immunity with immune response to the vaccine. Adverse effects of vaccination in this age group of dogs have also not been adequately assessed under field conditions. In a single-site, owner-blinded, randomized, placebo-controlled trial in puppies born to mothers vaccinated within the previous 18 months in a high-mortality population of owned, free-roaming dogs in South Africa, we assessed immunogenicity and effect on survival to all causes of mortality of a single dose of rabies vaccine administered at 6 weeks of age. We found that puppies did not have appreciable levels of maternally-derived antibodies at 6 weeks of age (geometric mean titer 0.065 IU/mL, 95% CI 0.061-0.069; n = 346), and that 88% (95% CI 80.7-93.3) of puppies vaccinated at 6 weeks had titers ≥0.5 IU/mL 21 days later (n = 117). Although the average effect of vaccination on survival was not statistically significant (hazard ratio [HR] 1.35, 95% CI 0.83-2.18), this effect was modified by sex (p = 0.02), with the HR in females 3.09 (95% CI 1.24-7.69) and the HR in males 0.79 (95% CI 0.41-1.53). We speculate that this effect is related to the observed survival advantage that females had over males in the unvaccinated group (HR 0.27; 95% CI 0.11-0.70), with vaccination eroding this advantage through as-yet-unknown mechanisms.

Rabies vaccine is associated with decreased all-cause mortality in dogs.

Evidence suggests that rabies vaccine may have non-specific protective effects in animals and children. We analyzed four years of data (2012-2015) from an observational study of the health and demographics of a population of owned, free-roaming dogs in a low-income community in South Africa. The objective of this analysis was to assess the association between rabies vaccine and all-cause mortality in dogs, stratified by age group (0-3months, 4-11months, and 12months and older), and controlling for the effects of sex and number of dogs in the residence. Rabies vaccination reduced the risk of death from any cause by 56% (95% CI=16-77%) in dogs aged 0-3months, by 44% (95% CI=21-60%) in dogs aged 4-11months and by 16% (95% CI=0-29%) in dogs aged 12months and older. We hypothesize that the protective association between rabies vaccination status and all-cause mortality is due to a protective effect of rabies vaccine against diseases other than rabies. Existence of a strong non-specific protective effect of rabies vaccine on mortality in dogs would have implications for the design of dog rabies control programs that aim to eliminate dog-mediated human rabies cases. Further, we propose that owned domestic dogs in high mortality settings provide a useful animal model to better understand any non-specific protective effect of rabies vaccine in children, due to dogs' high numbers, high morbidity and mortality rates, relatively short lifespan, exposure to a variety of infectious and parasitic diseases, and shared environment with people.

Prevalence of tuberculosis in pigs slaughtered at two abattoirs in Ethiopia and molecular characterization of Mycobacterium tuberculosis isolated from tuberculous-like lesions in pigs.

BACKGROUND: Tuberculosis (TB) is an infectious, granulomatous disease caused by acid-fast bacilli of the genus Mycobacterium. The disease affects practically all species of vertebrates. Although mammalian tuberculosis has been nearly controlled in many developed countries, it is still a serious problem in humans and domestic animals including pigs in developing countries. In Ethiopia, the prevalence of TB in pigs is not known. Therefore, this study was designed to estimate the prevalence of TB in pigs in central Ethiopia and to characterize the causative agents using molecular techniques. RESULTS: The estimated prevalence of TB was 5.8% (49/841). Age and origin of pigs were significantly associated (P<0.001) with the prevalence. In contrast, an association of sex, floor type and water source with the prevalence could not be shown. Culture positivity was confirmed in 30.6% (15/49) of the tuberculous-like lesions. Of the 15 isolates, 12 were acid fast positive while five of the latter were confirmed by multiplex PCR as members of the M. tuberculosis complex. Speciation of the five isolates further confirmed that they were M. tuberculosis, belonging to SIT1088 (two isolates) and SIT1195 (one isolate). The remaining two isolates belong to an identical spoligotype, the pattern of which was not found in the spoligotype database (SpolDB4). CONCLUSIONS: The isolation of M. tuberculosis from pigs suggests a possible risk of transmission between humans and pigs. Hence, establishing feasible control methods is required.