Research Note: Evaluation of boric acid as a chemoprophylaxis candidate to prevent histomoniasis

Abstract

Histomoniasis, caused by the protozoan parasite Histomonas meleagridis, is a disease to which turkeys are especially susceptible. Currently, no chemoprophylaxis compounds are available to mitigate this disease. Boric acid (BA) exhibits antifungal, antiseptic, and antiviral properties and has been used in the treatment of yeast infections. Based on these characteristics, an experiment was conducted to evaluate whether BA might be an efficacious prophylaxis against challenge with wild-type H. meleagridis (WTH). On day-of-hatch, poults were randomly assigned to either a basal control diet or a BA diet (basal diet + 0.2% BA). Groups consisted of a nonchallenged control (NC; basal diet), 0.2% BA + challenge (BA; 0.2% BA diet), and a positive-challenged control (PC; basal diet). On day 21, challenged groups were intracloacally inoculated with 2 × 10⁵ WTH cells/turkey, and lesions were evaluated on day 14 postchallenge. Individual body weights were recorded on day 0, 21, and 35 to calculate the prechallenge and postchallenge body weight gain (BWG). The BA group resulted in lower prechallenge day 0 to day 21 BWG (P = 0.0001) than the NC group. Postchallenge day 21 to day 35, BWG was also lower (P = 0.0503) in the BA group than the PC group. No differences between the BA and PC groups were detected for mortalities associated with histomoniasis. Moreover, liver and cecal lesions were not statistically different between the BA and PC groups. Taken together, these data suggest that BA was not efficacious in the prevention or reduction of histomoniasis disease severity when provided at 0.2% dietary concentration under these experimental conditions.

Keywords: Histomonas meleagridis; blackhead; boric acid; boron; histomoniasis.

Figure 1

Histomoniasis lesion scoring system developed at the University of Arkansas Poultry. Health Laboratory. Classic lesions associated with histomoniasis for liver and cecae were evaluated on a scale of “0” to “3.” A score of “0” indicates no detectible lesions; “1” indicates lesions not clinically relevant; “2” indicates intermediate lesions suggesting significant pathology but not imminent mortality; “3” indicates confluent or nearly confluent lesions deemed likely to be fatal.

Figure 2

Body weight gain (BWG) at (A) prechallenge from day 0 to day 21 and (B) postchallenge from day 21 to day 35. BWG data expressed as mean ± SEM and were analyzed using Student 2-tailed t test in JMP Pro 14. (C) Percentage of mortalities associated with histomoniasis postchallenge. No difference was detected when analyzed with a chi-square test. Cumulative lesion scores associated with histomoniasis from day 10 to day 14 postchallenge for (D) liver and (E) cecae. A lesion score of “0” is indicative of a healthy bird with no disease whereas a score of “3” indicates classically severe histomoniasis. No differences between mean lesion scores were detected with SAS Proc Mixed Procedure for either liver or cecal lesions. Numbers within columns indicate the total poults per evaluated lesion score. Poults in challenged groups received 2 × 10⁵Histomonas meleagridis cells/turkey on day 21 via intracloacal administration. Abbreviations: NC, nonchallenged control; BA, 0.2% boric acid diet + challenge; PC, positive-challenged control. Boric acid (Product #B6768, Sigma-Aldrich, St. Louis, MO).