Herd level risk factors for Mycobacterium avium subsp. paratuberculosis infection and clinical incidence in dairy herds in Chile

Association between the severity of histopathological lesions and Mycobacterium avium subspecies paratuberculosis (MAP) molecular diversity in cattle in southern Chile

The objective was to evaluate the association between the severity of histopathological lesions caused by Mycobacterium avium subspecies paratuberculosis (MAP) infection and the molecular diversity of this pathogen. Blood, ileum, and mesenteric lymph node samples were collected at slaughter, from 1,352 adult cattle [source population 1 (SP1)]. In addition, 42 dairy herds (n = 4,963 cows) were followed for 2 years, and samples from compatible paratuberculosis clinical cases [source population 2 (SP2)] were collected. MAP infection was confirmed using an ELISA test, liquid media culture, and PCR. Isolates were genotyped using five MIRU-VNTR markers. Tissues from confirmed samples were subjected to a histopathological examination. A histopathological severity score (HSS) system was developed and used to grade (0 to 5) the magnitude of lesions caused by MAP. In general, the HSS system assesses the number of foci and degree of macrophage infiltration, together with the presence of multinucleated giant cells (MGCs) and acid-fast bacilli (AFB), in addition to the fusion of the intestinal villi and hyperplasia of the crypts. Despite the large sampling effort, only 79 MAP isolates were successfully genotyped, where 19 different haplotypes were described. A mixed-effect Poisson regression model was used to assess the relationship between haplotypes and HSS values. The model was controlled by animal age, and the farm was used as a random effect. Haplotypes were grouped based on their relative frequency: the most frequent haplotype (group i, 49.4%), the second most frequent haplotype (group ii, 12.7%), and all other haplotypes (group iii, 37.9%). Model outputs indicated that group i had significantly higher HSS values than group iii. In addition, group i was also associated with higher optical density (OD) values of the ELISA test. These results support the existence of differences in pathogenicity between MAP haplotypes. However, results were based on a relatively small sample size; thus, these should be taken with caution. Despite this, study findings suggest that haplotypes would be associated with differences in disease progression, where the dominant haplotype tends to generate more severe lesions, which could be linked to a greater shed of MAP cells than non-dominant haplotypes, increasing their chances of transmission.

Prevalence of infectious diseases on dairy farms classified on the basis of their biosecurity score

Introduction

The aim of the study was to investigate the relationship between biosecurity as scored on the Italian National Animal Welfare Reference Centre (Centro di Referenza Nazionale per il Benessere Animale – CReNBA) checklist and the prevalence of Mycobacterium avium subsp. paratuberculosis, Chlamydophila abortus and Neospora caninum on dairy farms located in Ragusa, Italy.

Material and Methods

The checklist was used to assign an animal welfare score to 31 dairy farms. Twenty-one farms with a moderate score (>33%, <66%) formed group 1, and 10 farms with a high score (>66%) were group 2. Blood samples were collected from all cows on each farm to investigate the titres of antibodies against the relevant pathogens. Two-way analysis of variance was applied to assess differences between the two experimental groups and the Mann–Whitney test was applied to evaluate prevalence differences in the tested parasites between the groups.

Results

All tested farms had a score that classified them as either good or excellent. A higher incidence of Neospora caninum was observed in group 1. The incidences of the other two parasites were no different between the two groups.

Conclusion

The CReNBA checklist represents an impartial, reproducible, functional and smart instrument based on risk analysis and assigns a farm a mathematical animal welfare score. Among the parasites tested for, only Neospora caninum had prevalence influenced by biosecurity. Our preliminary results highlighted the positive associations between good animal welfare, high levels of biosecurity, and the prevention of the infectious diseases caused by the parasites in our focus, which are common on dairy farms.