Cattle‐associated risk factors for human tuberculosis in rural livestock‐keeping communities, Uganda

Abstract

Tuberculosis (TB) is a leading infectious cause of human death worldwide. In cattle, TB infection results in productivity losses, trade barriers and zoonotic transmission via milk, meat or direct contact. We conducted a cross‐sectional study in rural communities in Uganda between 2014 and 2016 to evaluate the association between tuberculosis skin test (TST) positivity in humans and cattle‐associated risk factors: household herd positivity and raw milk consumption. Human and cattle TSTs were performed in communities followed by a survey of household practices. TST data were available on 493 humans, 184 (37.3%) with positive results, and 1,441 cattle, 50 (3.5%) with positive results. We fit separate log binomial generalized estimating equation models for the herd positivity‐human TST positivity association, stratified on sex; and for the raw milk consumption‐human TST positivity association, stratified on frequency of milk consumption. Having at least one TST‐positive bovid in the household's herd was significantly associated with lower risk of TB among men (prevalence ratio [PR] 0.66, 95% CI 0.49, 0.87) but was not significantly associated with TB among women (PR 1.21, 95% CI 0.76, 1.95). This apparent protective effect was contrary to our a priori hypothesis of higher exposure effect among men, the primary caretakers of cattle. This finding may be the result of residual confounding by socioeconomic status; wealthier individuals may be less likely to be TB positive, but more likely to have TST‐positive herds by virtue of larger herd sizes, ability to purchase new and possibly infected stock, and propensity to keep more TB‐susceptible European breeds. For raw milk consumption, effect estimates were close to one and not statistically significant. Thus, in settings where bovine TB prevalence is low, such as Uganda, cattle‐associated zoonotic transmission may be rare, and cattle‐associated risk factors may not be important drivers of human TB burden.

Bovine ownership and reduced pulmonary tuberculosis risk in Nepal: A case–control study

“…Consistent with our findings, a study of cattle-owning families in Uganda found that having at least one TST (tuberculin skin test)positive bovine in the household cattle herd was associated with a lower TST positivity among men (prevalence ratio (PR) = 0.66, 95% CI: 0.49, 0.87), but not among women (PR = 1.21, 95%CI: 0.76, 1.95) (Meisner et al, 2019). Traditionally, in Uganda, men look after the cattle.…”

“…There is some evidence that living closely with cattle may be a risk factor for pulmonary tuberculosis (PTB) (Mfinanga et al, 2003;Waziri et al, 2014); however, other evidence suggests that close contact with Mycobacterium bovis-infected cattle may have a protective association with TB in cattle herders (Berg et al, 2015;Meisner et al, 2019). Some illnesses attributed to M. tuberculosis, particularly in high TB burden countries, are caused by M. bovis.…”

Associations between livestock keeping, morbidity and nutritional status of children and women in low- and middle-income countries: a systematic review

“…For example, of the total (n = 81) references reporting on infection and morbidity outcomes, about four out of five (n = 66, 79.5%) of the references indicated that livestock keeping is strongly associated with transmission of various microorganisms and diseases in man. On the other hand, some articles (n = 13, 16%) (47,(152)(153)(154)(155)(156)(157)(158)(159)(160)(161)(162)(163)(164) indicated a lack of association (neutral), while a few (n = 4, 4.9%) (156,(165)(166)(167) showed a protective effect (positive association) between livestock keeping and disease transmission.…”

“…Among bacterial species, Brucellosis (n = 8) (91,96) , Campylobacter (n = 7) (88,91,102,109,168) and Salmonella (n = 3) (90,118,119) were also mentioned as having adverse effects on man from keeping livestock. Other bacterial species including Coxiella (141) , Escherichia (118) , Enterotoxigenic bacteroides fragilis (92) , Mycobacterium tuberculosis (164) , Mycobacterium ulceran (167) and Thermotolerant coliform (TTC) (123) were also identified (Table 4).…”

Notes from the field: Descriptive Exploration of childhood tuberculosis frequency and risk factors of zoonotic bovine tuberculosis in Moroto district, Uganda

“…Indeed, zoonotic M. bovis has been previously isolated from patients with cervical lymphadenitis in this region which emphasizes the risk of human infection with zoonotic M. bovis due to close association of humans with cattle in this region (15,17). The burden of childhood TB in Moroto district remains unreported by TB control program in their weekly bulletins.…”