Number Of Lice Research Articles

Atlantic salmon, Salmo salar L., and Arctic char, Salvelinus alpinus (L.): comparative correlation between iodine-iodide supplementation, thyroid hormone levels, plasma cortisol levels, and infection intensity with the sea louse Caligus elongatus

The interrelationship between plasma cortisol levels, iodine-iodide nutritional supplementation, plasma thyroid hormone levels (tri- and tetra-iodothyronine, T3 and T4 respectively), and infection intensity with the sea louse Caligus elongatus were investigated in Atlantic salmon, Salmo salar L., and Arctic char, Salvelinus alpinus (L.). Cortisol-implanted Atlantic salmon had significantly higher mean intensities of sea lice than salmon not implanted with cortisol. Untreated Arctic char had significantly higher plasma cortisol levels and sea lice infections than untreated salmon. Cortisol-implanted salmon had lower plasma levels of T3 and T4. Salmon and char treated with iodized feed and iodinated water had higher plasma T3 and T4 levels, higher plasma T3/T4 ratios, and lower plasma cortisol levels than controls. Sea lice infections were significantly reduced on salmon treated with either iodized feed (P < 0.05) or iodinated water (P < 0.05). Char treated with iodized feed also had significantly reduced infections (P < 0.05). In general, iodized feed had a greater effect than iodinated water in reducing sea lice numbers. This study indicates that elevated plasma cortisol levels in salmon and char result in lower plasma levels of thyroid hormone and an increased susceptibility to sea lice infections. It is concluded that providing the fish with sufficient iodine-iodide increases thyroid hormone levels, reduces plasma cortisol levels, and reduces susceptibility to sea lice infections.

Spatial distribution and spread of sheep biting lice, Bovicola ovis, from point infestations

The spatial distribution of chewing lice ( Bovicola ovis) on their hosts was examined in Polypay and Columbia ewes initially artificially infested on the midside or the neck. Densities of lice were determined at 69 body sites in eight body regions at approximately monthly intervals for 2 years. In the second year, half of the ewes were mated and lice were counted at 26 body sites on the resulting lambs. Polypay ewes had higher densities of lice than Columbias at most inspections but there was little effect of infestation point or mating on either numbers or the distribution of lice. During periods of high louse numbers densities were generally greatest on the sides or the back. Densities on the head were also high at times and peaked later than overall louse densities. Shearing markedly reduced density but increased the proportion of lice found on the neck, belly and lowleg sites. The distribution of lice on the lambs was similar to that on the ewes except that fewer lice were found on the head. Comparisons of lice per part with the numbers of lice extracted from clipped patches indicated that a sheep with wool bearing area of 1 m 2 and a mean count of one louse per 10 cm fleece parting carried approximately 2000 lice. At most times of the year inspections for sheep lice should be concentrated on the sides and back, but in recently shorn sheep greater attention should be paid to the lower neck and ventral regions. Implications of the observed distributions of lice for the efficacy of chemical treatments are discussed.

Serum and skin surface antibodies and their associations with sheep biting lice, Bovicola ovis, on experimentally infested sheep.

The sheep biting louse (Bovicola ovis) feeds superficially on the skin of sheep but appears to stimulate an immune response. In this study we examined the association between louse infestation and serum and skin surface antibodies. Louse numbers were monitored on experimentally infested Polypay and Columbia ewes for two years and on their lambs in the second year. Serum and skin wash samples were tested for antibodies to soluble extracts of B. ovis, Stomoxys calcitrans and Musca autumnalis by enzyme linked immunosorbent assay (ELISA). In addition, the effects of skin wash extracts on B. ovis were examined in vitro. The titre of anti-B. ovis antibodies in the serum did not differ significantly between infested and naive ewes. However, there was an increase in serum antibody titre which coincided with periods of high louse density in ewes with high louse counts. Infested lambs had higher serum antibody levels than naive lambs. Substantial cross reactivity was evident among extracts of the different insects. Densities of lice on the ewes during population decline were negatively related to the titre of skin surface antibodies. Skin washings collected from sheep during B. ovis population decline reduced the number of louse progeny when incorporated into louse diet. These results indicate that B. ovis stimulates an immune response in sheep and suggest that compounds on the skin surface may play a role in the regulation of louse populations.

Occurrence ofLepeophtheirus salmonis(Copepoda: Caligidae) on sea trout (Salmo trutta) in the inner Oslo Fjord, south-eastern Norway

The occurrence of the parasitic copepod Lepeophtheirus salmonis Kroyer on sea trout Salmo trutta L. was studied in the Askerelva river and in the adjacent Oslo Fjord, south-eastern Norway, where there are no salmon farms. Sampling was carried out in 1992 and 1993. Fishing was started in May, but no sea trout were caught in the river before August. Maximum prevalence (percent infested fish) in the monthly samples from the river was 50%, and the mean intensity (mean number of lice on the infested fish) in all river samples pooled was 19.9 parasites. Most were in the pre-adult or adult stage. The fish from the fjord were larger and had, in general, fewer lice than fish from the river (pooled mean intensity=7.6 lice), but the difference in mean intensity of infestation was not significantly different. There was no correlation between condition factor and the intensity of infestation on trout from the river nor from the fjord.

Pruritis and dermal response to insect antigens in sheep infested with Bovicola ovis

This study examined the relationships among louse density, pruritis and dermal response to insect antigens in sheep infested with Bovicola ovis. Polypay and Columbia ewes were allocated to two groups, infested and naive, and louse densities and pruritis were monitored for 15 months. Ten months after the initial infestation, all sheep were tested for hypersensitivity on the midside and ears by intradermal injection of soluble extracts of B. ovis, Stomoxys calcitrans and Musca autumnalis. The areas of skin reactions were measured at 20 min, 1, 3 and 24 h after injection and skin thickness was measured at 24 h. Louse densities on Polypays were approximately 10 times greater than on Columbias, and pruritis was correlated with louse numbers at most inspections. Most pruritic behaviour was directed to the sides of infested sheep. Wheal and flare reactions developed rapidly to all extracts in both infested and naive ewes. Reactions to louse extract were larger in infested than naive sheep at all four times after injection. In the infested Polypays, reactions to louse extract were greater than to the fly extracts, but in naive sheep there was little difference among extracts. Reactions in naive Columbias were larger than in naive Polypays at 20 min, 1 and 3 h, but had almost completely abated in both groups at 24 h. Reactions in infested Columbias were greater than in infested Polypays at 20 min, but at 24 h reactions in the Polypays were larger. Louse numbers and pruritis were correlated with wheal areas and skin thickness at 24 h, but there was little relationship with the size of reactions at earlier times. These findings are consistent with the development of a hypersensitive response to B. ovis and suggest that dermal reactions to lice may influence sheep susceptibility.

Seasonal dynamics and variation among sheep in densities of the sheep biting louse, Bovicola ovis

Cyclic patterns and variations among sheep in numbers of Bovicola ovis are described in Polypay and Columbia ewes that were initially infested with equal numbers of lice and penned indoors continuously for 2 years. Bovicola ovis populations were censused at 3–4-week intervals at 69 body sites on each animal. In the second year of the study, the ewes were reinfested and half were mated. Louse populations were monitored on the resulting lambs from birth until 25 weeks of age. Strong seasonal cycles in louse numbers were observed on the ewes, with peaks in spring and troughs in summer. These cycles occurred in the absence of shearing, direct solar radiation or rainfall. Populations began to decline when daily mean and maximum temperatures were 11.5°C and 15°C, respectively, well below temperatures thought to cause warm season decline. Louse densities on Polypay ewes were approximately 10 times higher than on Columbias at most inspections. There were also large differences among sheep within breeds and sheep counts were highly correlated among dates, both within and between years. One third of the ewes failed to become infested despite having lice applied on five separate occasions and being penned together with other infested sheep. Pregnancy and lactation did not significantly affect louse numbers on the ewes. There was a significant negative correlation between louse counts and weight gains in the lambs, and lamb counts were significantly correlated with those of their dams up until, but not after, weaning. It is suggested that sheep may exert regulatory influences on lice which contribute to cycles in B. ovis populations.

Open-ocean infestation by salmon lice (Lepeophtheirus salmonis): comparison of wild and escaped farmed Atlantic salmon (Salmo salar L.)

Salmon lice (Lepeophtheirus sabnonis) infestation was investigated in 128 salmon (S&IO s&r L.) caught on floating long-lines in the Norwegian Sea during NovemberMarch 199331995. Overall prevalence was 99.2% and abundance 29.5 lice per salmon. Most lice were adults (90%) and 72% of these were ovigerous females. These adult lice were estimated to be at least 3 months old based on prevailing sea-surface temperatures at the sampling site: 7°C in November and 3°C in March. The prevalence and abundance of lice on one sea winter (1SW) salmon were significantly higher on escaped farmed fish than on wild salmon. However, no difference in abundance was observed between 2SW farmed and wild salmon. The average number of lice per surface area of fish (density) was significantly higher in 2SW wild salmon than in 1SW wild salmon, indicating an accumulation of lice on the salmon in the oceanic phase. No differences in density were observed between 1SW and 2SW farmed salmon. The prevalence of Cakgus elongutus was low (5.5%), with an abundance of 0.9 lice per salmon. 0 1997 International Council for the Exploration of the Sea

Evaluation of three automatic jetting races for control of the sheep body louse Bovicola ovis

Fine wool Merino sheep with short (4 mm) or long (30-80 mm) wool and moderate to heavy infestations of lice (Bovicola ovis) were treated with cyhalothrin at a concentration of 50 mg/L, applied using Alison, Aussie Dip and Boral Cyclone Superace automatic jetting races. Each machine was set up and operated by representatives of the manufacturer. With all 3 machines, arithmetic mean louse counts before and after treatment showed that in the sheep with short wool, lice numbers were reduced by > 98% at 8-12 weeks after treatment but were not eliminated. In the sheep with long wool, the maximum reductions in mean louse counts were 79, 68 and 98% for Alison, Aussie Dip and Boral Cyclone Superace machines at 7, 5 and 8 weeks after treatment, respectively. The Alison and Aussie Dip machines were each tested in alternative configurations which affected the disposition of the jetting fluid on the fleece. The distribution of live lice on the bodies of the shorn sheep after treatment using the Alison machine and 1 configuration of the Aussie Dip machine, indicated that more insecticide may have been delivered to the left side of the body than to the right. There were no significant differences between sides in sheep treated in the Boral Cyclone Superace machine. Our results suggest that the jetting races tested would control infestations of lice for at least 12 weeks in sheep treated within 2 weeks after shearing, but would be unlikely to eradicate lice from an infested flock. The machines differed markedly in their ability to control moderate to heavy infestations of lice in sheep with long (30-80 mm) wool, but in all cases there was evidence of a resurgence in lice numbers beyond 12 weeks after treatment.

Python™, Yt–615, and Optimizer™ Ear Tags for Winter–Time Control of Cattle Lice in Wyoming, 1992

Abstract The objective of this study was to evaluate PYthon™, YT𠄣615, and Optimizer™ ear tags applied at one tag per animal, and PYthon™ ear tags at two tags per animal for winter-time control of cattle lice. The experiment was performed at the University of Wyoming Research and Extension Center, Torrington, Wyoming. The experimental cattle were born in the spring of 1991. All were male castrates and were primarily Gelbvieh X Angus crosses. Animals were individually identified by numbered ear tags in both ears. The cattle were housed in ten separate pens at the rate of 5 or 6 animals per pen. Each pen was 20 X 60 ft with a 20-ft feed bunk across one end. Each animal received a finishing ration, free-choice, average weight gain was 2 lb per head per d. Salt, mineral mix, and water were provided ad libitum. Lice infestations were naturally acquired. Most cattle were infested with Linognathus vituli and Bovicola bovis. A few animals were infested with Solenopotes capillatus. Prior to treatment, the pens were ranked by total counts of L. vituli. The five pens with the highest mean counts and the five pens with the lowest mean counts were randomly assigned to one of the five ear tag treatments. All species of lice present on the animals were counted. Counts were performed by visual inspection of the cattle on d 0 (pretreatment), and 14, 28, 42, and 56 DAT. Lice were counted in eight examination sites on each animal. Specimens were identified by species and life stage (either adult or nymph). Examination sites and dimensions were as follows: topline 5 X 15 cm, withers 5 X 15 cm, around right eye 10 X 15 cm, around left eye 10 X 15 cm, right cheek 5 X 10 cm, left cheek 5 X 10 cm, muzzle 5 X 25 cm and dewlap 5 X 15 cm. These sample sites include predilection areas of L. vituli, B. bovis, and S. capillatus. For purposes of examination, cattle were individually restrained in a squeeze chute with a head catch. A high intensity light provided illumination. Total lice counts were transformed using In (total count + 1). A general linear model procedure (SAS) was used to analyse the transformed counts. Total variation in the lice count was partitioned into that attributable to the treatment, animal within treatment, sampling d, treatment X sampling d interaction, and residual. Geometric means for lice counts were estimated for each treatment group on each sampling d. Percentage reduction in lice numbers from the first to the last d of the study were calculated from the geometric means of the treated and untreated cattle using the formula:

In‐vivo Synergism of Cypermethrin by Piperonyl Butoxide in Bovicola ovis (L.) (Phthiraptera: Trichodectidae)

ABSTRACTMixtures of existing formulations of piperonyl butoxide (PBO) and cypermethrin were poorly suited for use as sheep dips. Mixture ratios of up to 10:1 PBO:cypermethrin did not offer a significant advantage over cypermethrin alone. A novel formulation of PBO and cypermethrin (5:1) which contained 49% wetting agent provided a much greater degree of control in small scale field trials using sheep infested with highly pyrethroid‐resistant lice. At 10 weeks after treatment, lice numbers on sheep treated with cypermethrin alone had returned to pretreatment levels, whereas a greater than 80% reduction in lice numbers was recorded on sheep dipped in the PBO:cypermethrin mixture. Although impressive, this improvement in efficacy is not sufficient to make PBO:cypermethrin mixtures a realistic proposition for controlling highly pyrethroid‐resistant sheep lice. At present, when highly resistant strains of lice need to be controlled the most cost‐effective option available to Australian woolgrowers is to dip with an organophosphate product.

Evaluation of non-conventional treatments for control of the biting louse (Bovicola ovis) on sheep.

A variety of non-conventional treatments was applied to biting louse (Bovicola ovis) infested sheep in order to evaluate ways in which farmers could control the louse infestations and still maintain Organic Production Standards. In one trial, louse scores of sheep shorn but kept dry or wetted by water alone or with water plus detergent were compared with unshorn sheep treated similarly. Shearing alone accounted for a 35.7-66.3% reduction in mean louse scores. Wetting alone either with water or with water and added detergent accounted for a 26.9-35.3% reduction in mean louse scores. The combined effects on mean louse scores of shearing and wetting, as opposed to shearing alone, were statistically significant on two of the three farms at 32-35 days post-treatment. The effects persisted for the duration of the trial (between 48 and 52 days), at which point shearing and wetting with detergent provided 95.3-99.6% control of lice. In a second trial, a range of insecticidal substances considered acceptable by Organic Production Standards, azadirachtin (neem), pyrethrum, soap, was applied to louse-infested sheep and their efficacy compared with that of a commercial formulation of cypermethrin. The sheep treated with azadirachtin and pyrethrum had significantly fewer lice than either the control or soap treated sheep over the 48 days of the trial. Neither azadirachtin nor pyrethrum were significantly less effective than cypermethrin. Control (reduction in louse score) of 85.0-100% was achieved over the period of the trial. It is concluded that most of the non-conventional treatments evaluated had a useful and cost-effective role to play in reducing louse numbers on sheep for at least 40-50 days. The lack of persistence compared with that obtained with conventional insecticides was the only apparent drawback.

Proliferative responses of lymphocytes in Bovicola ovis-infested lambs

Proliferative responses of peripheral blood and prescapular lymph node lymphocytes from 8 B. ovis-infested and 8 valve lambs to concanavalin A (Con A) and soluble antigen of B. ovis were examined in vitro. The numbers of lice and the extent of cockle were also assessed on each lamb. Prescapular lymph node lymphocytes from infested lambs showed significantly higher responses to B. ovis antigen than those from naive lambs. Only a marginal difference was observed between infested and naive lambs in the response of lymphocytes from peripheral blood. Proliferative responses to Con A by prescapular lymph node or blood cells were not significantly different between groups. The results indicated a relationship between the intemity of louse infestation and the proliferative response of prescapular lymph node lymphocytec to B. ovis antigen.

Preliminary investigations into the aetiology and treatment of cockle, a sheep pelt defect

A defect of sheep pelts known as cockle, detectable after depilation, but usually first noted only in the pickled pelt or tanned stage of processing, was studied to established causal factor(s) and effective treatments. In addition, data on the histology and seasonal prevalence of the disease were obtained. Samples collected soon after slaughter from pelts identified at the pickled pelt stage as having cockle, had a superficial dermatitis with infiltration of eosinophils. This may represent an immediate hypersensitivity reaction of the sheep to lice. Treatments of sheep with either insecticides, disinfectants or shearing showed that where biting lice ( Bovicola ovis) were removed, cockle lesions had either disappeared or regressed on pickled pelts. In Trial 1 diazinon reduced cockle prevalence and severity substantially; cypermethrin had a less pronounced effect. In Trial 2 diazinon, cypermethrin, Hibitane ® and Savlon ® were equally effective in reducing biting louse numbers as shown by counts of lice at 35 and 63 days post-treatment. Reduction of cockle on pelts from sheep slaughtered at 39 days post-treatment was achieved best by both diazinon and shearing. Examination of other pelts at 67 days post-treatment showed diazinon and Hibitane to be equally effective in reducing cockle. Furthermore, shearing in the absence of insecticides reduced the severity and extent of lesions on cockled pelts. The diazinon excipient and zinc sulphate were consistently poor at removing lice and reducing cockle prevalence and severity. The results have important implications for the leather industry in that shearing and good dipping practice with appropriate chemicals at the right time can lead to improved pelt quality. However, an incentive scheme for farmers, and a means of identifying individul pelts to the farms or origin, are both necessary before a marked improvement is likely to occur.

Evaluation of Max-Con® and Optimizer® Ear Tags Applied at 2 Tags Per Animal for Control of Cattle Lice in Wyoming, 1992

Abstract The experiment was performed with 1-yr-old heifer and steer calves at Laramie, WY, and with 2-yr-old steers at Torrington, WY. Average weights of the animals were 211 and 467 kg, respectively. At Laramie, the cattle were heavily infested with Bovicola bovis. At Torrington, Linognathus vituli, Haematopinus eurysternus and Solenopotes capillatus were the dominant species. Cattle were housed in separate pens in groups of five at both locations. Cattle were ranked according to lice density, and similarly infested cattle were then randomly assigned to one of three treatment groups. Five animals per treatment were used in the study at Laramie and 15 per treatment at Torrington. Hair was parted and lice density was estimated by observing and recording the numbers of lice of each species at sample sites on selected body regions of the host. Body regions examined were; one 5 x 15 cm area on the topline; one 5 x 15 cm area on the withers; two 10 X 15 cm areas surrounding the right and left eyes; two 5 x 10 cm areas on the right and left cheeks; one 5 x 25 cm area on the muzzle; and one 5 x 15 cm area on the dewlap. Each animal was tagged in both ears. Cattle at Torrington were tagged on 27 Dec, and cattle at Laramie were tagged on 19 Feb.

Distribution and structure of the population of sea lice, Lepeophtheirus salmonis Krøyer, on Atlantic salmon, Salmo salar L., under typical rearing conditions

Abstract. Samples of Atlantic salmon, Salmo salar L., held in sea cages and tanks with running water were examined for presence of sea lice, Lepeophtheirus salmonis. The number of lice, their sex stage (only post-chalimus stages) and location on the fish body were recorded. A new method has been used to express parasitic intensity in fish of different size. Effects of different factors on the degree and character of infestation (structure of the lice population), such as fish size, habitat and chemical treatment, have been studied. Different lice categories have shown different susceptibility to delousing with dichlorvos. Second pre-adults are most susceptible, and males generally more than females. Running water has been found to‘flush out’the lice from the fish body. Pre-adults are flushed out easier than adults, and males generally easier than females. Adult males show high tolerance to water of lowered salinity and great mobility manifested in occasional transfer between hosts. The higher activity level of adult males may partly explain a drop in proportion of males after delousing and in running water. Frequency of mating has been found to increase with parasitic intensity.

Effect of insecticidal ear tags on populations of lice (Damalinia ovis) infesting sheep.

Polymer matrix ear tags containing 13.7% w/w tetrachlorvinphos or 8.5% w/w cypermethrin were applied to Merino wethers infested with lice and carrying two months wool. The cypermethrin tags reduced louse numbers by a maximum of 89% in comparison to controls at 16 weeks after treatment and by 85% at the conclusion of the experiment 38 weeks after application. Lice were not eradicated from any sheep. The number of lice counted on sheep treated with tetrachlorvinphos-impregnated tags was not significantly different from controls.

Efficacy of 10% Flucythrinate Swine Ear Tags for Control of Hog Lice, 1986

Abstract American Cyanamid Guardian® swine ear tags containing 10% flucythrinate were evaluated in Buckingham County, Virginia, for control of hog lice on brood sows maintained on pasture. Forty sows were tagged with 1 tag per ear 3 Oct. The efficacy of the tags was determined by counting the number of lice on one side of the body of 15 treated sows and 10 untreated gilts on 3 Oct. Lice counts were made at monthly intervals thereafter for 4 mo. Treatment and control groups were maintained in separate pastures throughout the test. The data were subjected to a general linear models procedure (SAS) and the means separated by a Duncan’s Multiple Range Test (P = 0.05).

Oral Administration of a Levamisole—Famphur Paste for Cattle Lice Control, 1984-85

Abstract Five mixed-breed cattle were randomly assigned to each of 5 treatments to evaluate the effectiveness of varying rates of famphur in combination with levamisole paste for lice control. Levamisole dosage was constant at 8 mg/kg. Warbex (famphur) pour-on at 40 mg/kg was used as a treatment comparison. All treatments were applied 28 Feb. Pretreatment lice populations were quantified by making two 3-cm hair partings in 18 sites and counting the lice present. Sites checked included ears, eyes, muzzle, jaws, brisket, shoulders, backline, tailhead, and hips. The actual sucking and chewing lice numbers found were recorded. Posttreatment lice counts were at 2, 4, 7, 18, 23, 28, and 35 days.

Ear Tags for Control of Cattle Lice, 1984

Abstract Two insecticide-impregnated ear tags, fenvalerate and flucythrinate, were evaluated for control of cattle lice on yearling steers. Each treatment group contained 6 yearlings, which were tagged with 2 tags per head; six untreated yearlings served as controls. Lice counts were made prior to tagging and at weekly intervals for 8 wk. Total number of lice were recorded from 2 to 3-cm hairparts from each of the following locations: ears, eyes, muzzle, jaw, shoulder, backline, tailhead and hips. Lice viability was determined by microscopic examination of specimens. Because of uneven pretreatment lice numbers, an analysis of covariance with the pretreatment lice count as the covariable was performed to assist in interpreting the posttreatment significance of the ear tag treatments.

Recovery of sheep lice (Damalinia ovis) from baled wool: A technique enabling nation-wide surveillance of louse ridden flocks

Abstract Wool from pre-sale core samples was examined for sheep body lice. Wool was dissolved in boiling 20% NaOH, and the lice were collected by washing the treated sample over a 75 μm sieve. A total of 1112 samples from throughout New Zealand were processed. Six percent of these samples had more than 20 lice per 20 g of greasy wool, 3% had 16–20, 4% had 11–15, 9% had 6–10, and 78% had 5 or fewer lice per 20 g of greasy wool. The incidence of lice in baled wool was highest in the north of the North Island, and generally decreased from north to south. Samples gathered from 7 previous trials, for which the nocks' scoured wool yields had been recorded, were processed in a similar manner to determine the relationship between louse numbers and wool yield. There was a high correlation between louse numbers and loss in yield: 1 louse per g of greasy wool represented a loss of about 1%, 2 lice per g — about 4%, and 6 lice per g — about 5%. An estimate of the current annual louse-related loss of marketable fibre, based on the trial and survey data, is 0.2% of the national clip. The dissolution method we used could easily be adapted for routine louse surveillance.