Objectives

To determine the time to cessation of Ascaris suum egg shedding, the percent of animals that stop shedding, and to estimate the reduction in environmental burden from eggs shed in naturally infected female breeding swine after different treatment levels of fenbendazole to better determine timing of anthelmintic use prior to movement into a farrowing environment. To determine the ovicidal activity of different fenbendazole levels on Ascaris suum eggs shed from naturally infected commercial breeding female swine.

Materials and methods

Study 1 - Egg shedding

Five experiments across three commercial sow farms known to be infected with A suum were conducted. Breeding gilts and sows were identified with natural A suum infections and allocated to one of 4 treatments: CNT = untreated controls, TX1 = 545.5 mg fenbendazole for one day, TX2 = 545.5 mg fenbendazole daily, for 3 consecutive days (1636.5 mg total), and TX3 = 1636.5 mg fenbendazole for one day (TX3 only in experiment 5). Fecal samples were collected on various days and evaluated using the modified Wisconsin sugar flotation technique, with at least 1 EPG considered a positive sample. Time-to-negative was evaluated using Kaplan-Meier survival analysis with Log-Rank test and censoring of animals that reached the end of the study period still shedding. Percent negative at the end of the experiment was evaluated by Chi-square analysis using Fisher's exact test. Environmental burden (BURD), a calculation of eggs observed versus eggs expected, was evaluated by ANOVA and Tukey's studentized test.

Study 2 - Embryonation

Three experiments were conducted on a commercial breeding farm infected with A suum. Breeding gilts and sows were identified with natural A suum infections and allocated to one of 4 treatments: CNT = untreated controls, TX1 = 545.5 mg fenbendazole for one day, TX2 = 545.5 mg fenbendazole daily, for 3 consecutive days (1636.5 mg total), and TX3 = 1636.5 mg fenbendazole for one day (TX3 only in experiment 3). Eggs were isolated from fecal samples at various days post-treatment (dpt) by experiment and incubated in 0.1 N H2SO4 at room temperature for 60 days. Embryonation rates (ER) for each animal were determined by counting the number of eggs with fully developed larvae out of 100 eggs counted.

Results

Study 1 - Egg shedding

Mean time-to-negative shedding ranged from 9.3 to 13.1 for TX1, 8.9 to 13.1 days and 9.8 for TX3 with 0 to 10 percent censored, while CNT ranged from 13.4 to 28.2 with 70 to 100 percent censored. For all fenbendazole treatment groups, 90 to 100 percent of sows were negative by the end of the study, compared to 0 to 28.6 percent for CNT. Mean BURD range was 7.0 to 60.9 for TX1, 13.9 to 60.8 for TX2, 29.3 for TX3 and 60.4 to 219.0 for CNT. All fenbendazole treatment values were different from CNT (P<0.05) but not from each other for time-to-negative, percent negative and BURD.

Study 2 - Embryonation

ER of A suum eggs shed from CNT animals ranged from 90.3 to 99.3 percent across all experiments and sampling days. ER were significantly (P<0.0001, ANOVA) reduced to 29.3 and 30.5 percent for TX1 and TX2 in A suum eggs shed at 8 dpt, and 26.6 percent for TX3 in eggs shed at 6 dpt. Differences in ER between treatments was only seen in eggs shed at 4 dpt; TX1=75.4, TX2=70.9, and TX3=47.0. In addition, many of the A suum eggs shed from treated animals had atypical character, such as abnormal cell division, granular appearance and irregular shapes.

Implications

* Fenbendazole is an effective anthelmintic for the treatment of Ascaris suum in naturally infected breeding gilts and sows.

* When using fenbendazole for the control of A suum transmission from dams to offspring, treatment should begin approximately 14 days prior to movement into clean farrowing facilities.

* Fenbendazole was effective at all treatment levels used in decreasing the number of A suum eggs shed into the environment.

* Fenbendazole is ovicidal against A suum in eggs shed from naturally infected breeding gilts and sows.

* Use of fenbendazole provides additional epidemiological benefits in control of A suum through reduced effective environmental contamination due to the reduced number of eggs shed and those that develop to an infectious larvae.