Reverse zoonotic disease transmission (zooanthroponosis): a systematic review of seldom-documented human biological threats to animals

Abstract

Background: Research regarding zoonotic diseases often focuses on infectious diseases animals have given to humans. However, an increasing number of reports indicate that humans are transmitting pathogens to animals. Recent examples include methicillin-resistant Staphylococcus aureus, influenza A virus, Cryptosporidium parvum, and Ascaris lumbricoides. The aim of this review was to provide an overview of published literature regarding reverse zoonoses and highlight the need for future work in this area.

Methods: An initial broad literature review yielded 4763 titles, of which 4704 were excluded as not meeting inclusion criteria. After careful screening, 56 articles (from 56 countries over three decades) with documented human-to-animal disease transmission were included in this report.

Findings: In these publications, 21 (38%) pathogens studied were bacterial, 16 (29%) were viral, 12 (21%) were parasitic, and 7 (13%) were fungal, other, or involved multiple pathogens. Effected animals included wildlife (n = 28, 50%), livestock (n = 24, 43%), companion animals (n = 13, 23%), and various other animals or animals not explicitly mentioned (n = 2, 4%). Published reports of reverse zoonoses transmission occurred in every continent except Antarctica therefore indicating a worldwide disease threat.

Interpretation: As we see a global increase in industrial animal production, the rapid movement of humans and animals, and the habitats of humans and wild animals intertwining with great complexity, the future promises more opportunities for humans to cause reverse zoonoses. Scientific research must be conducted in this area to provide a richer understanding of emerging and reemerging disease threats. As a result, multidisciplinary approaches such as One Health will be needed to mitigate these problems.

Figure 1. Flowchart demonstrating the identification and selection process for publications included in this review.

Figure 2. Timeline and frequency of reverse zoonoses publications included in this review shown by pathogen type.

Figure 3. Proportion of reverse zoonoses scientific reports included in review as illustrated by study location.

Note: Many reports identified several countries therefore each country in this figure does not necessarily represent a single corresponding publication.

Figure 4. Study locations for literature included in review.

A. Proportion of reverse zoonoses scientific reports as illustrated by study location and pathogen type; B. Proportion of reverse zoonoses scientific reports on bacterial pathogens as illustrated by study location; C. Proportion of reverse zoonoses scientific reports on viral pathogens as illustrated by study location; D. Proportion of reverse zoonoses scientific reports on parasitic pathogens as illustrated by study location; E. Proportion of reverse zoonoses scientific reports on fungal pathogens as illustrated by study location.

Figure 5. Animal type and study location included in review literature.

A. Proportion of reverse zoonoses scientific reports as illustrated by study location and animal(s) infected; B. Proportion of reverse zoonoses scientific reports on companion animals as illustrated by study location; C. Proportion of reverse zoonoses scientific reports on livestock as illustrated by study location; D. Proportion of reverse zoonoses scientific reports on wildlife as illustrated by study location.