Partial strategic tick control within a herd of European breed cattle in the state of Rio Grande do Sul,southern Brazil

A trial is described, in the state of Rio Grande do Sul, southern Brazil, as one of a series suggested to investigate the effects of strategic but selective acaricide treatments of cattle within herds against Boophilus microplus. They are aimed at considering the repercussions of farmer attempts at immediate reductions in acaricide costs and the potential for creation of ‘refugia’ of untreated ticks. Half (Group 1) of a small experimental herd of European breed heifers were treated strategically against ticks, three times during the late spring–early summer and twice during autumn (southern hemisphere), with an injectable avermectin endectocide, designed to act directly against the first and third generations of parasitic B. microplus per ‘cattle tick year’ at this site, respectively. The consequent levels of infestations on all of the member cattle in their common pasture were monitored. Group 1 showed low to zero tick counts during the 28-day treatment interval periods and up to ca. 14 days after the last of such a series. Treated cattle, however, became re-infested outside of these periods and to levels that would be considered as unacceptable by farmers in the state. The untreated cattle (Group 2) showed infestations at generally higher levels, than their contemporaries, within and outside of the treatment periods. There were thus ample sources of larvae in the pasture, derived principally from falling, untreated engorged female ticks, re-infesting both the treated and untreated cattle. Advantages of maintaining chemically untreated cattle ticks within a herd, compared to their disadvantages as contaminants to classical strategic control procedures, merit re-evaluation, especially in relation to the recent, world-wide resurgence of acaricide resistance in B. microplus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic approaches for controlling ratios of related polyketide products in fermentation processes

Simple acyl thioesters are used as precursors for both the initiation and elongation steps in polyketide biosynthetic processes. Several structurally related polyketide products are sometimes made in these processes. These analogs are typically generated by a combination of two factors: availability of structurally similar biosynthetic precursors, and biosynthetic enzymes unable to effectively discriminate between them. Often, only one polyketide product is desired from a fermentation process, requiring a method to control the ratio of these different analogs. Preferential production of one desired analog is accomplished using random mutagenesis and manipulation of fermentation conditions. A genetic enzymatic understanding of polyketide biosynthesis, as well as the pathways that provide the relevant precursors, allows for a rational and more contemporary approach for control of analogs produced in fermentation processes. This approach involves genetic manipulation of either the pathways that provide pools of the acyl CoA thioester precursors, or the function/specificity of the appropriate biosynthetic enzymes. Reviewed herein are three such examples where these approaches have been carried out successfully with polyketide biosynthetic processes. Journal of Industrial Microbiology & Biotechnology (2001) 27, 368–377. Received 01 March 2001/ Accepted in revised form 08 August 2001     

Effects of ivermectin and doramectin faecal residues on the invertebrate colonization of cattle dung

Abstract: The effects of avermectin [ivermectin (IVM) and doramectin (DRM)] faecal residues on dung colonization and degradation by invertebrates were evaluated during late spring in the east of La Pampa province, Argentina. The study was conducted after collection of faecal material from animals (10 steers per group) allocated to the following groups: untreated control group (CG) and groups treated subcutaneously (200 μg/kg) with either DRM (DG) or a long‐acting formulation of IVM (IG). Fifty pats (550 g each) per group were collected, prepared and deposited on the field on days 3, 7, 16 and 29 post‐treatment (pt). Eight pats per group were recovered after 7, 14, 21, 42, 100 and 180 days post‐deposition (pd) on the field. The weight, percentage of dry matter, number of arthropods and nematodes from faeces were determined. The faecal concentrations of IVM and DRM were measured by high performance liquid chromatography (HPLC) throughout the trial period to correlate the pattern of drug degradation in dung with pd time. The total number of arthropods in dungs from CG was higher (P < 0.05) than those counted between days 3 and 29 pt in IG and DG. A decrease in the number of Coleoptera larvae (P < 0.05) between days 21 and 42 days pd was observed in both treated groups. Diptera larvae counts in CG pats were significantly higher (P < 0.05) than those obtained in treated groups in the 7‐ and 14‐day‐old pats. A lower number (P < 0.05) of Collembola, compared with pats from CG, was recovered from IG and DG pats deposited at days 3 and 7 pt and exposed from day 42. The counts of Acari in pats from treated animals were lower (P < 0.05) than those observed in CG pats at 3, 8 and 16 days pt. There were no differences neither in adult Scarabaeidae recovered nor in the proportions of dung buried and destroyed by great dung beetles. Dung specific nematodes were reduced (P < 0.05) in IG and DG pats from 3 and 7 days pt compared with those of CG pats. The comparative results shown here demonstrate that the negative effects of both IVM and DRM on dung colonization are similar. The pattern of drug degradation in the environment was very slow. High residual concentrations of both active parent compounds were recovered in dungs exposed in the field for up to 180 days pd. Concentrations as high as 13 ng/g (IVM) and 101 ng/g (DRM) were measured in faeces obtained from pats deposited on day 27 pt and exposed to the environment during 180 days. The results show a decrease in invertebrate colonization of dung recovered from IVM‐ and DRM‐treated cattle, which is in agreement with the large drug residual concentrations measured in faeces.     

发酵液中多拉菌素的提取和萃取条件研究

采用单因素实验,分别研究提取试剂、发酵液放置时间、pH值和温度对发酵液中多拉菌素提取效果的影响;然后以乙酸乙酯为萃取试剂,研究萃取次数及萃取体积对多拉菌素萃取效果的影响。结果显示,甲醇为最佳提取试剂;发酵液在pH为3～11、温度为20～80℃的条件下放置144 h,多拉菌素均能稳定存在,提取得到的多拉菌素的质量浓度没有显著变化;浓缩提取液液经2倍体积乙酸乙酯萃取2次即可。该条件下多拉菌素的质量浓度和萃取率分别为151.78μg/mL和98.00%。     

Engineering the aveC gene to enhance the ratio of doramectin to its CHC-B2 analogue produced in Streptomyces avermitilis

Avermectin and its analogues are produced by the actinomycete Streptomyces avermitilis and are major commercial products for parasite control in the fields of animal health, agriculture, and human infections. Historically, the avermectin analogue doramectin (CHC-B1), which is sold commercially as Dectomax is co-produced during fermentation with the undesired analogue CHC-B2 at a CHC-B2:CHC-B1 ratio of 1.6:1. Although the identification of the avermectin gene cluster has allowed for characterization of most of the biosynthetic pathway, the mechanism for determining the avermectin B2:B1 ratio remains unclear. The aveC gene, which has an essential role in avermectin biosynthesis, was inactivated by insertional inactivation and mutated by site-specific mutagenesis and error-prone PCR. Several unrelated mutations were identified that resulted in improved ratios of the desirable avermectin analogue CHC-B1, produced relative to the undesired CHC-B2 fermentation component. High-throughput (HTP) screening of cultures grown on solid-phase fermentation plates and analysis using electrospray mass spectrometry was implemented to significantly increase screening capability. An aveC gene with mutations that result in a 4-fold improvement in the ratio of doramectin to CHC-B2 was identified. Subsequent integration of the enhanced aveC gene into the chromosome of the S. avermitilis production strain demonstrates the successful engineering of a specific biosynthetic pathway gene to significantly improve fermentation productivity of a commercially important product.     

Haemaphysalis concinna (Acari: Ixodida): Persistent efficacy of doramectin in rabbits under laboratory conditions

In the present study, the persistent efficacy of doramectin (DOR) in rabbits infested by Haemaphysalis concinna was observed. DOR (200 µg/kg) was administered once to infested rabbits by subcutaneous injection. A total of 15 rabbits were allocated to three groups, which were observed for efficacy. On days 1–7, 8–14, 15–21 and 22–28 post-inoculation, the percent reduction of tick larvae in DOR treated rabbits was 100.0, 100.0, 86.7 and 61.7%, respectively; the percent reduction of nymphs was 100.0, 90.0, 75.0 and 65.0%, respectively; and the percent reduction of adults was 85.0, 65.0, 55.0 and 55.0%, respectively. In comparison, in untreated rabbits at the same time points (control group), the percent reduction of larvae was 5.0, 3.3, 5.0 and 5.0%, respectively, and there was no reduction of nymphs and adults in the untreated rabbits.     

Larvicidal activity of endectocides against pest flies in the dung of treated cattle

Cattle were treated with topical formulations of endectocides to assess the larvicidal activity of faecal residues against horn fly, Haematobia irritans (L.), house fly, Musca domestica L., and stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae). In laboratory bioassays, doramectin, eprinomectin and ivermectin suppressed horn fly in dung of cattle treated at least 4 weeks previously and suppressed house fly and stable fly in dung of cattle treated 1-5 weeks previously. Moxidectin suppressed horn fly in dung from cattle treated no more than one week previously and did not suppress house fly and stable fly. Results combined for the three species across two experiments suggested that, ranked in descending order of larvicidal activity, doramectin > ivermectin approximately = eprinomectin > moxidectin.     

Fly larvicidal activity in the faeces of cattle and pigs treated with endectocide products

Bioassays were conducted to study the effect of a single therapeutic dose of injectable ivermectin, doramectin or moxidectin given to cattle and pigs and excreted in their faeces, against larvae of the housefly, Musca domestica L. (Diptera: Muscidae). Five cattle were treated with each of the test products. Cattle faecal samples were collected before treatment and on days 1, 2, 3, 6, 10, 16, 20, 23 and 28 after treatment. Three groups of pigs, each comprising 12-14 pregnant sows and gilts, were used in the experiment. Pig faeces was collected from each group before treatment and on days 1, 3, 5, 7, 9, 11, 13, 15 and 20 after treatment. Thirty, first-stage larvae were placed into 100 g of faeces. Five replicates were examined for each time-point and for each endectocide group. Evaluation was based on the number of larvae surviving to adult emergence. Low numbers of adults emerged from samples taken from cattle 1 day after treatment, indicating that ivermectin and doramectin were rapidly excreted in the faeces and affected the development of the house fly. A larvicidal effect of both drugs in cattle faeces was present for a period of about 3-4 weeks and lasted a few days longer in cattle treated with doramectin than with ivermectin. In cattle, the larvicidal activity of moxidectin was first observed in faecal samples collected 2 days post-treatment; however, it killed fewer larvae than the other two drugs. The larvicidal effect of moxidectin subsequently decreased. Ivermectin and doramectin exhibited a pronounced larvicidal effect against the house fly in the faeces of pigs. The effect of doramectin was of longer duration. Moxidectin gave the weakest larvicidal effect in pig faeces. The main difference between the results obtained for the two livestock species is that peak toxicity occurred relatively later and for a shorter duration in pig than in cattle faeces.     

Endectocide residues affect insect attraction to dung from treated cattle: implications for toxicity tests

A 3-year study was performed in southern Alberta, Canada to assess the effect of endectocide residues on the attractiveness of cattle dung to colonizing insects. In 2003 and 2004, insect captures were compared between pitfall traps baited with dung of untreated cattle and paired traps baited with dung of cattle that had been treated 7 days previously with topically applied doramectin, eprinomectin, ivermectin or moxidectin. Faecal residues associated with each compound affected insect captures in both spring and autumn of each year. Effects were detected (P < 0.05) for a total of 94 cases representing 27 insect taxa from 13 families in three orders (Coleoptera, Diptera, Hymenoptera). Two-fold differences in captures were common. Up to six-fold differences were observed. Eleven cases of attraction and 11 cases of repellency were associated with residues of doramectin. Eprinomectin tended to repel insects, with decreased captures for 19 of 29 cases of effect. Ivermectin showed a strong attractive effect, with increased captures for 17 of 25 cases. Moxidectin also showed a strong attractive effect, with increased captures for 17 of 18 cases. Comparisons between compounds suggested that results for doramectin best predicted results for eprinomectin and vice versa. In 2005, insect captures were compared between pitfall traps baited with dung of untreated cattle and traps baited with dung from cattle treated 3, 7 or 14 days previously with topically applied doramectin. Effects were detected in 14 cases plus one case of near significance (P= 0.053). Significant differences between control vs. days 3, 7 and/or 14 dung were detected in nine cases. Residues enhanced captures in seven of these cases. Day 14 dung affected captures in six of these cases. This study shows that endectocide residues can affect the number of insects attracted to colonize and oviposit in dung. Hence, the emergence of their offspring from field-colonized dung of untreated vs. endectocide-treated cattle should not be used as a measure of residue toxicity per se, but rather as a measure of 'insect activity'. Insect activity is a composite measure of residue toxicity, the number and species composition of insect colonists, and the mortality factors (e.g. predation, parasitism, competition) associated with the co-occurrence of these species in the dung pat.