Human–livestock contacts and their relationship to transmission of zoonotic pathogens, a systematic review of literature

Abstract

BackgroundMicro-organisms transmitted from vertebrate animals – including livestock – to humans account for an estimated 60% of human pathogens. Micro-organisms can be transmitted through inhalation, ingestion, via conjunctiva or physical contact. Close contact with animals is crucial for transmission. The role of intensity and type of contact patterns between livestock and humans for disease transmission is poorly understood. In this systematic review we aimed to summarise current knowledge regarding patterns of human–livestock contacts and their role in micro-organism transmission.MethodsWe included peer-reviewed publications published between 1996 and 2014 in our systematic review if they reported on human–livestock contacts, human cases of livestock-related zoonotic diseases or serological epidemiology of zoonotic diseases in human samples. We extracted any information pertaining the type and intensity of human–livestock contacts and associated zoonoses.Results1522 papers were identified, 75 were included: 7 reported on incidental zoonoses after brief animal–human contacts (e.g. farm visits), 10 on environmental exposures and 15 on zoonoses in developing countries where backyard livestock keeping is still customary. 43 studies reported zoonotic risks in different occupations. Occupations at risk included veterinarians, culling personnel, slaughterhouse workers and farmers. For culling personnel, more hours exposed to livestock resulted in more frequent occurrence of transmission. Slaughterhouse workers in contact with live animals were more often positive for zoonotic micro-organisms compared to co-workers only exposed to carcasses. Overall, little information was available about the actual mode of micro-organism transmission.ConclusionsLittle is known about the intensity and type of contact patterns between livestock and humans that result in micro-organism transmission. Studies performed in occupational settings provide some, but limited evidence of exposure response-like relationships for livestock–human contact and micro-organism transmission. Better understanding of contact patterns driving micro-organism transmission from animals to humans is needed to provide options for prevention and thus deserves more attention.

Antimicrobial usage and resistance in beef production

“…These demonstrate that the most convincing molecular and epidemiological AMR links are found when the infected human is directly connected to the animal population on farms or via farm workers [211, 216, 217]. Direct exposure to livestock is a known risk factor for zoonotic transmission (reviewed in [218]).…”

Review of Antimicrobial Resistance in the Environment and Its Relevance to Environmental Regulators

“…A recent review of the academic literature that address the issue of antibiotic use in agriculture suggests that only seven studies (five percent) argued that there was no link between antibiotic consumption in animals and resistance in humans, while 100 (72%) found evidence of a link (O’Neill and The Review on Antimicrobial Resistance, 2015). The degree to which this transmission from animals to humans, and vice-versa, is of great interest and has significant implications for public and animal health (Weir et al, 2012; Woolhouse et al, 2015; Klous et al, 2016). The relevance of theses pathways to the environment will be discussed, as this is the main remit and interest of environmental regulators.…”

Limited awareness of animal influenza prevention and control among Dai Lue smallholder farmers in Southwest China

“…Dai society is obviously not the 'risk society' that characterises the so-called post-industrial modern societies, as the farmers did not seem to care about the risks associated with influenza. Some Dai cultural traditions likely augment zoonotic infection, for example, the attribution of influenza to supernatural beliefs such as evil spirits, which reduces confidence in the utility of veterinary services, and the close proximity of farmers and animals in old-style houses, as physical closeness to animals is associated with zoonotic risk (Klous et al 2016). This reveals important information about the types of contact between humans and livestock for disease transmission in this group of people.…”