Stochastic Modeling of Imperfect Salmonella Vaccines in an Adult Dairy Herd

Abstract

Salmonella is a major cause of bacterial foodborne disease. Human salmonellosis results in significant public health concerns and a considerable economic burden. Dairy cattle are recognized as a key source of several Salmonella serovars that are a threat to human health. To lower the risk of Salmonella infection, reduction of Salmonella prevalence in dairy cattle is important. Vaccination as a control measure has been applied for reduction of preharvest Salmonella prevalence on dairy farms. Salmonella vaccines are usually imperfect (i.e., vaccines may provide a partial protection for susceptible animals, reduce the infectiousness and shedding level, shorten the infectious period of infected animals, and/or curb the number of clinical cases), and evaluation of the potential impacts of imperfect Salmonella vaccines at the farm level is valuable to design effective intervention strategies. The objective of this study was to investigate the impact of imperfect Salmonella vaccines on the stochastic transmission dynamics in an adult dairy herd. To this end, we developed a semi-stochastic and individual-based continuous time Markov chain (CTMC) vaccination model with both direct and indirect transmission, and applied the CTMC vaccination model to Salmonella Cerro transmission in an adult dairy herd. Our results show that vaccines shortening the infectious period are most effective in reducing prevalence, and vaccines decreasing host susceptibility are most effective in reducing the outbreak size. Vaccines with multiple moderate efficacies may have the same effectiveness as vaccines with a single high efficacy in reducing prevalence, time to extinction, and outbreak size. Although the environment component has negligible contributions to the prevalence, time to extinction, and outbreak size for Salmonella Cerro in the herd, the relative importance of environment component was not assessed. This study indicates that an effective vaccination program against Salmonella Cerro spread in the herd can be designed with (1) vaccines with a single high efficacy in reducing either the infectious period or susceptibility of the host, or (2) if such single high efficacy vaccines are not available, vaccines with multiple moderate efficacies may be considered instead. These findings are also of general value for designing vaccination program for Salmonella serotypes in livestock.

Antimicrobial resistance patterns of bovine Salmonella enterica isolates submitted to the Wisconsin Veterinary Diagnostic Laboratory: 2006–2015

“…Other biologic products aimed at reducing disease from salmonellosis in cattle, such as gram-negative core and siderophore vaccines, could also have a selection pressure effect. Whereas these Salmonella vaccines have been used to help reduce transmission and mortality associated with salmonellosis in cattle, they are generally regarded as having little to no efficacy at reducing the prevalence of Salmonella at the farm level and providing only partial or waning protection (McGuirk and Peek, 2003;Lu et al, 2014;Cernicchiaro et al, 2016). Some Salmonella vaccines in cattle are also associated with transient negative effects on milk production (Bergeron and Elsener, 2008).…”

Systematic Literature Review of Models Used in the Epidemiological Analysis of Bovine Infectious Diseases

“…In the case of bovines, the infectious diseases that were considered for the analysis (assuming that these are diseases present in many countries [42] and/or that generate social problems [105], economic losses [98], health problems in humans [48], low quality in milk and meat [13,43,120], and restrictions in livestock movement [99]) are tuberculosis [46,65,89], salmonella [69,126], brucellosis [51,55,101], bovine viral diarrhea (BVD) [13,14,32], foot and mouth disease [41,50,91], and bovine mastitis [47,90]. Of the works, 50% are aimed at personnel who are experts in bovine infectious diseases.…”

“…Table 4 shows the relation of the works according to the technique used, such as Bayesian networks [46][47][48]63,73,78], Markov chains [22,41,45,49,67,68,74], logistic regression [14,19,[50][51][52]75], differential equations [19,25,31,33,43,[54][55][56]59,60,62,65,69,76,77,79,115], contact networks [19,62,64,70], and machine learning [13,92,93]. The most-used technique is differential equations, while machine learning is presented in five jobs.…”

The discrete fractional order difference applied to an epidemic model with indirect transmission

“…Motivated by the facts exposed above, in this paper, we consider a discrete-time model established from the Grünwald-Letnikov fractional order derivative. Moreover, we are interested on studying epidemic models that include the indirect transmission of the disease due to the underlying contamination in the space where we have the population, (see [3,[29][30][31][32][33] ). That is, individuals can become infected with residues found in their environment.…”