Evidence that ectoparasites influence the hematological parameters of the host: a systematic review

Ectoparasites are important to the one health concept because their parasitism can result in the transmission of pathogens, allergic reactions, the release of toxins, morbidity, and even death of the host. Ectoparasites can affect host physiology, as reflected in immune defenses and body condition as well as hematological and biochemical parameters. Thus, evidence that ectoparasites influence host hematological parameters was systematically reviewed, and the methodological quality of these studies was analyzed. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines were followed, and the studies included were limited to those that evaluated changes in hematological tests in ectoparasite-infested and non-infested animals, and bias and methodological quality were evaluated using the Animal Research: Reporting of In Vivo Experiments guideline. Thirty-four studies were selected and information about the host, ectoparasite infestation, blood collection, and analysis was collected and compared whenever possible. In this review, the presence of ectoparasites influenced both the red series and the white series of hematological parameters. Among the main parameters analyzed, hematocrit, red blood cells, hemoglobin, and lymphocytes showed reductions, probably due to ectoparasite blood-feeding, while including eosinophils, neutrophils, and basophils increased in infested animals due to the host immune response. However, methodologic improvements are needed to reduce the risk of bias, enhance the reproducibility of such studies, and ensure results aligned with the mechanisms that act in the ectoparasite-host relationship.

Automated summary

Ectoparasites are important for the concept of one health because they can transmit pathogens, cause allergic reactions, release toxins, and lead to morbidity and even death in the host. They can also affect the host's physiology, including immune defenses and blood parameters. A systematic review of studies evaluating the influence of ectoparasites on hematological parameters found that the presence of ectoparasites led to reductions in hematocrit, red blood cells, hemoglobin, and lymphocytes, possibly due to blood-feeding, while eosinophils, neutrophils, and basophils increased in response to the host immune response. Methodological improvements are needed to ensure unbiased and reproducible results aligned with the ectoparasite-host relationship mechanisms.