Jerome A. Klavons

Therapeutic and persistent efficacy of a long-acting (LA) formulation of ivermectin against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) and sera concentration through time in treated cattle.

The concentration-time profile, therapeutic, and persistent efficacy of a single subcutaneous injection of cattle with a long-acting (LA) formulation of ivermectin at a concentration of 630microg/kg of body weight were determined against Rhipicephalus (Boophilus) microplus. Ivermectin sera concentration in treated cattle increased to 13.0ppb within 1d after treatment, and peaked at 26.2ppb at 11d post-treatment. Ivermectin sera levels remained above the threshold level for control of feeding ticks (>or=8ppb) for 42.6d after treatment. Therapeutic efficacy of ticks on treated animals was >99.9%, and tick number, index of fecundity, engorgement weight, and egg mass weight of ticks from treated animals remained dramatically less than ticks from untreated animals. Tick number and reproductive capacity of ticks infested on treated animals at 14 and 28d post-treatment were less than for ticks on untreated animals, whereas engorgement weight and egg mass weight of treated ticks remained lower than that of untreated ticks 49d post-treatment. However, the level of control against ticks infested at 14d after treatment (99.9%) was the only post-treatment infestation interval that provided the required 99% control necessary for use in the U.S. tick eradication program. The 14d post-treatment infestation was also the only interval at which infested ticks were exposed to ivermectin levels above the threshold level of 8ppb for the entire parasitic development period. Cattle would have to be treated at intervals of no more than 31d apart to ensure that no viable ticks could reach repletion and detach from the host. Although this treatment interval is >2-fold longer than the present treatment requirement (14d), it is dramatically less than the label claim for the LA ivermectin formulation of 75d of prevention against re-infestation.

Efficacy of a Single Doramectin Injection Against Adult Female Boophilus microplus (Acari: Ixodidae) in the Final Stages of Engorgement Before Detachment

Abstract The efficacy of injectable doramectin applied at 200 &mgr;g/kg was evaluated against adult female Boophilus microplus (Canestrini) (Acari: Ixodidae) in the later stages of engorgement before detachment. Lethal levels of doramectin in the serum of treated cattle (9.7–36.6 ppb) were reached and sustained within 24 h after treatment. However, treatment at 19 or 20 d postinfestation allowed greater tick survival and reproductive capability (IF) than at 18 d postinfestation, indicating that a significant portion of the ticks were able to engorge and detach before obtaining a lethal dose of doramectin. Thus, treatment at 18 d after infestation provided significantly higher overall control (99.5%) than treatment at 19 or 20 d postinfestation (95.8 and 89.1%, respectively). Analysis of control on a daily basis demonstrated that treatment at 18 d postinfestation provided >99% on each day of the evaluation. Conversely, treatment at 19 or 20 d postinfestation produced levels of control ranging from 22.6 to 85.6% during the first 2 d of female detachment, and ≥99% control was not achieved until after the fourth day of female detachment, where it remained throughout the study. Therefore, application of injectable doramectin at ≤18 d after tick infestation was the only treatment regime considered acceptable for use in the U.S. Boophilus Eradication Program. Treatment intervals >18 d postinfestation could pose a substantial risk of dispersing viable ticks to tick-free areas outside the permanent quarantine zone that has been established along the Texas–Mexico border.

A Sustained Release Gel Formulation of Doramectin for Control of Lone Star Ticks (Acari: Ixodidae) and Horn Flies (Diptera: Muscidae) on Cattle

ABSTRACT A gel formulation formed by incorporating technical doramectin into a 10% hydroxypropyl methylcellulose aqueous solution was used to subcutaneously inject steers at varying dosages. Doramectin serum concentration of steers receiving 600 µg (AI)/kg body weight declined from 21.9 ppb at 0.5 wk to below detectable at 8 wk postinjection. The 1,200 µg (AI)/kg injection resulted in serum concentrations of 29.1 ppb at 0.5 wk and declined to 0.5 ppb at 8 wk postinjection. Both the 600 and 1,200 µg (AI)/kg injections provided 100% inhibition of index of fecundity (IF) in adult lone star ticks, Amblyomma americanum L. (Acari: Ixodidae) through week 8, after which inhibition declined to 79.4 and 45.3%, respectively, during the 12th week posttreatment. For steers treated at 600 µg (AI)/kg, mortality of adult horn flies, Hematobia irritans L. (Diptera: Muscidae), declined from 16.9% during week 2 to 3.1% during week 7 postinjection. The blood from steers treated at 1,200 µg (AI)/kg resulted in a similar decline in mortality of blood fed adult horn flies from 29.4% during week 1 to 4.0% during week 7. The 600 µg (AI)/kg treatment provided complete control of larval horn flies in the manure for 9 wk, whereas the 1,200 µg (AI)/kg injection gave complete control for 14 wk posttreatment. The doramectin gel formulation provided long-lasting delivery of doramectin to cattle and extended control of lone star ticks and larval horn flies. Such a simple and inexpensive formulation could be useful in tick eradication programs by reducing the frequency of gathering cattle.

Release of Piperonyl Butoxide and Permethrin from Synergized Ear Tags on Cattle and Effects on Horn Fly Mortality

Abstract A study was conducted to determine the release rates of piperonyl butoxide (PBO) and permethrin from synergized insecticidal cattle ear tags and their effects on mortality of the horn fly, Hematobia irritans irritans (L.) (Diptera: Muscidae). PBO was released from the ear tags at a higher rate than permethrin in both winter and summer trials. The cumulative release of PBO and permethrin from the ear tags at the end of 18 wk in the winter trial was 50.4 and 30.3%, respectively. The cumulative release of PBO and permethrin from the ear tags at the end of 18 wk in the summer trial was 66.7 and 44.7%, respectively. There was a significant correlation between the cumulative daily high ambient temperature (°C) and the cumulative release of both PBO and permethrin. Compared with the susceptible horn fly strain, the permethrin-resistant strain demonstrated 7.9- and 12.8-fold resistance to permethrin at the levels of LC50 and LC90, respectively. When exposed to filter paper wipes taken from the shoulders of cattle treated with the PBO-synergized permethrin tags from the summer trial, the resistant strain demonstrated reduced mortality compared with the susceptible strain. The mortality of the resistant strain at 2- and 3-h exposure exhibited a pattern of declining fly mortalities as a result of the decreased release of PBO and permethrin, as well as the decline in the ratio of PBO:permethrin released from the tags after 8 wk. A similar decline in horn fly mortalities was observed in the susceptible strain at 30-min exposure time that coincided with the pattern of reduced release of PBO and permethrin from the ear tags over the course of summer trial.

Liquid Chromatographic Detection of Permethrin from Filter Paper Wipes of White-tailed Deer

White-tailed deer, Odocoileus virginianus (Zimmermann), are keystone hosts for the adult stage of lone star ticks, Amblyomma americanum (L.), (Patrick and Hair 1978, J. Parasitol. 64:1100 -1106; Bloemer et al. 1986. J. Econ. Entomol. 79: 679 683) and blacklegged ticks, Ixodes scapularis Say, (Barbour and Fish 1993, Science 260: 1610-1616), both of which transmit a variety of agents that cause disease in humans, including Lyme disease, human ehrlichioses, and human babesiosis in the eastern U.S. (Lockhart et al. 1996, J. Med. Entomol. 33: 153 158; Varela et al. 2004, J. Clin. Microbiol. 42:1163 1169). White-tailed deer are also marginal hosts of the cattle tick, Rhipicephalus (Boophilus) annulatus (Say), and the southern cattle tick, R. (B.) microplus (Canestrini), particularly in the absence of cattle (Cooksey et al. 1989, J. Med. Entomol. 26: 155 158). Increasing populations of white-tailed deer along the Texas-Mexico border are compromising efforts by federal agencies to prevent the reestablishment of these vectors of bovine babesiosis from Mexico, where these disease vectors are endemic (George 1990, J. Agric. Entomol. 7:119 -125, Pound et al. 2010, J. Econ. Entomol. 103:211 -218). In an effort to manage the disease risks posed by the increasing numbers of whitetailed deer and subsequent tick populations in the northeastern U.S. and reinfestations of cattle fever ticks (southern cattle ticks and cattle ticks) in South Texas, the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) developed two passive treatment devices designed to apply permethrin acaricide onto the ears