Control Of Lice Research Articles

Effects of regional coordination of salmon louse control in reducing negative impacts of salmonid aquaculture on wild salmonids

Parasitic salmon lice (Lepeophtheirus salmonis) are a constraint to the sustainable growth of salmonids in open net pens, and this issue has caused production to level off in recent years in the most aquaculture-intensive areas of Norway. The maximum allowed biomass at a regional level is regulated by using the so-called “traffic light” system, where salmon louse-induced mortality of migrating wild salmon post-smolts is evaluated against set targets. As a case study, we have investigated how a specific aquaculture-intensive area can reduce its louse levels sufficiently to achieve a low impact on wild salmon. Analyses of the output from a virtual post-smolt model that uses data on the reported number of salmon lice in fish farms as key input data and estimates the salmon louse-induced mortality of wild out-migrating Atlantic salmon post-smolts, suggested that female louse abundance on the local farms must be halved in spring to reach the goal implied by the traffic light system. The outcome of a modelling scenario simulating a proposed new plan for coordinated production and fallowing proved beneficial, with an overall reduction in louse infestations and treatment efforts. The interannual variability in louse abundance in spring, however, increased for this scenario, implying unacceptably high louse abundance when many farms were in their second production year. We then combined the scenario with coordinated production with other louse control measures. Only measures that reduced the density of farmed salmonids in open cages in the study area resulted in reductions in salmon louse infestations to acceptable levels. This could be achieved either by stocking with larger fish to reduce exposure time or by reducing fish numbers, e.g. by producing in closed units.

Histopathological assessment of Atlantic salmon exposed to calcium oxide particles: a controlled clinical study

Particulate calcium oxide (CaO) has been successfully used for the control of sea urchin and starfish populations. Recent studies have proven its efficacy in killing planktonic copepods, making it a promising and cheap option for salmon louse control in the Atlantic salmon (Salmo salar) farming industry. Additionally, preliminary laboratory tests demonstrated that exposure to 0.2 g/L–0.6 g/L of fine CaO particles induced significant mortality of salmon louse (Lepeophtheirus salmonis) in the planktonic stages. The present study investigated the effects of water treatment with fine CaO particles [0.2 g/L or 127.4 g/m2; 0.1 mm–0.3 mm], conducted twice a week for three consecutive weeks at 5°C and 12°C on Atlantic salmon post-smolt in a flow-through system. The study compared mortality rates and histopathology of skin, eyes, gills, and intestines between treated and untreated control salmon. The results indicated that CaO exposure did not induce fish mortality or histopathological damages in the skin, eyes, or intestines. Although there were no significant effects of CaO exposure on gill inflammation or hyperplasia, the exposure did increase the occurrence of gill vascular injuries and necrosis in small portions of the tissue (< 10% of the respiratory gill tissue in most of the samples) by 60% and 35%, respectively. The effect was not modulated by temperature or time. The results indicate that the CaO treatment protocol used in this study is not lethal to Atlantic salmon and is safe for most analyzed tissues. Nonetheless, the induction of vascular damage and necrosis in the gill, albeit in small tissue portions, emphasizes the need for further research. It is crucial to develop a protocol that avoids such lesions, ensuring the secure application of CaO as an antiparasitic treatment in salmon aquaculture.

Exploring the impact of thermal delousing on gill health and microbiome dynamics in farmed Atlantic Salmon

The economic cost of salmon louse (Lepeophtheirus salmonis and Caligus rogercresseyi) infestations in the Atlantic salmon (Salmo salar) industry has been estimated to be around $900 million annually. This high cost has driven a concerted effort to develop, examine, understand, and implement various methods for louse control. Husbandry interventions utilising warm water exposure have been highly successful in complementing traditional chemotherapeutants, especially as the efficiency of the latter has reduced in recent years. In this study, we sought to examine the impact of thermal delousing on gill health in two commercial sites with different historical husbandry and treatment interventions prior to and post-thermal treatment. Methods to characterise gill health and the response to thermal treatment included a detailed examination of the gill for microparasites using both histology and qPCR and targeted immune gene expression analysis, most notably antigen-presenting cells (mhc ii), proinflammatory cytokines (il-1β and tnf-α) and inhibitory cytokines (tgf-β and il-10). Furthermore, we examined the bacterial communities present on the gill surface using 16S rRNA amplicon sequencing. Data obtained from these trials indicated a minimal impact on gill microparasite prevalence in response to the thermal treatment. The expression of immune markers exhibited a significant decrease across both sites after treatment. Intriguingly, marked differences in the gill bacterial communities in response to treatment between the two sites were clearly observed. This divergence could be attributed to the notable differences in husbandry history and health status of the fish at the two sites prior to the thermal treatment. Our data suggest that microbiome diversity is an informative indicator of fish gill health and could be used to define appropriate interventions when treating sea lice.

Histological confinement of transglutaminase-mediated nit sheath crosslinking is essential for proper oviposition and egg coating in the human head louse, Pediculus humanus capitis

BackgroundHead louse females secrete liquid gel, which is mainly composed of the louse nit sheath protein 1 (LNSP1) and LNSP2, when they lay eggs. The gel is crosslinked by transglutaminase (TG) to form the nit sheath, which covers most of the egg except the top operculum area where breathing holes are located. Knowledge on the selective mechanism of nit sheath solidification to avoid uncontrolled crosslinking could lead to designing a novel method of louse control, but no information is available yet.MethodsTo elucidate the crosslinking mechanisms of nit sheath gel inside the reproductive system of head louse females, in situ hybridization in conjunction with microscopic observation of the oviposition process was conducted.ResultsHistochemical analysis revealed that LNSP1 and LNSP2 are expressed over the entire area of the accessory gland and uterus, whereas TG expression site is confined to a highly localized area around the opening of posterior oviduct. Detailed microscopic observations of oviposition process uncovered that a mature egg is positioned in the uterus after ovulation. Once aligned inside the uterus, the mature egg is redirected so that its operculum side is tightly held by the ventral end of the uterus being positioned toward the head again and its pointed bottom end being positioned toward the dorsal end of the uterus, which functions as a reservoir for the nit sheath gel.ConclusionsPhysical separation of the TG-mediated crosslinking site from the ventral end of the uterus is necessary to avoid uncontrolled crosslinking inside the uterus and to ensure selective crosslinking over only the lower part of egg without any unwanted crosslinking over the operculum during oviposition.Graphical

Effect of Education and Regular Examination on the Prevalence of Head Louse Infestations in Adana

The current study provides training to parents and teachers about pediculosis in schools in three villages in Adana to measure their knowledge level by conducting surveys and to determine the prevalence of pediculosis in these foci. Pre- and post-questionnaires including 30 questions about pediculosis were handed to parents and teachers. The answers were analyzed with the Pearson correlation analysis. Overall, 418 school pupils s were examined for lice. The results of the head louse control were analyzed by the chi-square test and t-test. We observed that the level of awareness increased in parents and teachers. Additionally, the gender of both teachers and parents was determined as the most important factor in increasing this awareness. Because of interventions for the control of head and lice, the prevalence of pediculosis decreased from 15.22% to 1.71%. It is very important that parents and teachers are aware of the health problems related to pediculosis, while regular combing of school children may be essential for the control of this common infestation.

Prevalence of sheep lice and trends in control practices across Australia - Australian sheep parasite control surveys from 2003 to 2019.

The sheep body louse (Bovicola ovis) is a parasite of major economic concern in Australia. This article reports lice incidence and control practices on Australian sheep farms as determined by three cross-sectional surveys of the years 2003, 2011 and 2018. The incidence of live lice detected within a flock was similar across the survey years with a slight decline in 2018 (2003: 20%, 2011: 18.6% and 2018: 13.9%). In an average year, most farmers did not see any direct or indirect evidence of lice infestation (2011: 59.3% and 2018: 69.5%), however, over a five-year period 38.9% (2003), 66.3% (in 2011) and 55.8% (in 2018) reported seeing evidence of lice infestation at least once with significant variation between sheep producing regions in 2011. In an average year, nearly three quarters of respondents treated for lice (2011:73.5% and 2018: 73.3%) with the majority treating immediately following shearing and very few treating sheep with long wool. Even higher percentages treated for lice at least once in the preceding five-year period (2011: 86.2% and 2018: 87.5%). Backliner was the most popular method of chemical application for lice control in sheep off-shears or with short wool (2003: 77%, 2011: 73% and 2018: 74.3%). For long wool treatments, hand jetting declined in popularity from 2003 (64%) to 2011 (54%) and 2018 (8.6%) as backliners became more popular (2003: 36%, 2011: 51% and 2018: 60%). The use of benzoylphenyl urea insect growth regulators (IGR) for off-shears/short wool treatment declined from 2003 (92.8%) to 2011 (51%) and 2018 (2.9%) and were largely replaced by neonicotinoids and spinosad for backliner/spray-on products. The use of organophosphates declined for plunge dipping (2003: 83.8%, 2011: 83% and 2018: 7.7%). Spinosad use for plunge dipping off-shears/short wool increased over the survey years (2003, 0%, 2011: 9% and 2018:46.2%). The use of IGRs declined for backliner application on long wool and were mainly replaced by spinosad in 2011 and 2018. Fewer respondents reported suspected resistance to lice control products in 2018 (8%) compared with 2003 (26%) and 2011 (13%) with most reporting suspected resistance to IGR and synthetic pyrethroids and emerging suspicions of resistance to neonicotinoids in 2018. Resistance to lice control products also reduced in importance as a reason for recurring lice infestations between 2011 (ranked 2nd) and 2018 (ranked 6th). Biosecurity was important to sheep producers with the highest ranked reason for recurring lice infestations being from stray or purchased sheep.

Evolution of salmon lice in response to management strategies: a review

AbstractEctoparasitic salmon lice (Lepeophtheirus salmonis) present a major challenge to Atlantic salmon (Salmo salar) aquaculture. The demand for effective louse control has produced diverse management strategies. These strategies essentially impose novel selection pressures on parasite populations, driving the evolution of resistance. Here we assess the potential for salmon lice to adapt to current prevention and control methods. Lice have evolved resistance to at least four of five chemical therapeutants, and use of these chemicals has declined significantly in recent years. The industry has shifted to alternative non‐chemical approaches, yet lice may adapt to these as well. Early research suggests that phenotypic variation exists in the louse population upon which non‐chemical selection pressures could act and that this variation may have a genetic basis. From the existing evidence, as well as an examination of evolutionary processes in other relevant parasite and pest systems, we conclude that the evolution of non‐chemical resistance is an emergent concern that must be considered by the industry. We recommend areas for focused research to better assess this risk. It is also important to determine whether phenotypic shifts in response to non‐chemical selection may shift the ecological niche of the parasite, as this may have cascading effects on wild salmon populations. We also recommend further research to identify strategy combinations that have antagonistic selective effects that slow louse evolution and those with synergistic effects that should be avoided. Greater understanding of evolutionary processes can inform aquaculture policies that counteract the rise of resistant parasite populations.

Estimation of spatiotemporal transmission dynamics and analysis of management scenarios for sea lice of farmed and wild salmon

Parasite transmission between farmed and wild salmon affects the sustainability of salmon aquaculture in Pacific Canada. Understanding and managing parasites in aquaculture is challenged by spatial and temporal variation in transmission dynamics. We developed a mechanistic model that connects sea louse (Lepeoptheirus salmonis) outbreak and control on farmed salmon (Salmo salar) to spatiotemporal dynamics of sea lice on migrating wild juvenile salmon (Oncorhynchus keta and Oncorhynchus gorbuscha). We fitted the model to time series of sea lice on farmed salmon and spatial surveys of juvenile wild salmon in the Broughton Archipelago. We used the parameterized model to evaluate alternative management scenarios based on the resulting sea louse infestations and predicted mortality of wild salmon. Early and coordinated management of sea lice on salmon farms was most effective for controlling outbreaks in wild salmon, while uncoordinated treatments led to a resurgence of sea lice on salmon farms during the juvenile salmon migration. This study highlights the importance of incorporating spatiotemporal variability when considering infectious disease dynamics shared by farmed and wild hosts, particularly when migratory wildlife are involved.

Mortality caused by aqueous extract of the leaves of Datura stramineus to goat biting louse, Bovicola caprae (Phthiraptera)

Extensive and indiscriminate use of organic lousicides is leading to environmental hazards i.e. persistence of residues, development of resistance and targeting of non-target beneficial organism. Hence, phytotherapy is emerging as effective tool for louse control, due to ecofriendly and biodegradable nature of plant extracts. In the present study the mortality and repellency caused by five concentration of aqueous extract of the leaves of commonly available Datura stramineus were tested against goat biting louse, Bovicola caprae. Fifteen percent concentration of extract prepared from leaves of aforesaid plant imparted 77% mortality and 66% repellency to goat biting louse.

In vitro efficacy of five essential oils against Pediculus humanus capitis.

Treatment of head lice has relied mainly on the use of topical insecticides. Today, conventional topical pediculicides have suffered considerable loss of activity worldwide. There is increasing interest in the use of natural products such as essential oils for head louse control, and many of them are now incorporated into various over-the-counter products presented as pediculicides, often without proper evaluation. The aim of the present study was to assess the in vitro efficacy of five essential oils against adults of Pediculus humanus capitis using a contact filter paper toxicity bioassay. The chemical composition of the essential oils from wild bergamot, clove, lavender, tea tree, and Yunnan verbena was analyzed by gas chromatography-mass spectrometry. All treatments and controls were replicated three times on separate occasions over a period of 11months. In all, 1239 living lice were collected from the scalp of 51 subjects, aged from 1 to 69years. Clove oil, diluted either in coco oil or sunflower oil, demonstrated the best adulticidal activity, reaching > 90% mortality within 2h in lice submitted to a 30-min contact. Yunnan verbena oil diluted in coco oil showed also a significant efficacy. Other essential oils showed a lower efficacy. The oil's major component(s) differed according to the tested oils and appeared chemically diverse. In the case of clove oil, the eugenol appeared as the main component. This study confirmed the potential interest of some of the essential oils tested, but not all, as products to include possibly in a pediculicidal formulation.

A mathematical model for the transmission of louse-borne relapsing fever

We present a detailed derivation and analysis of a model consisting of seven coupled delay differential equations for louse-borne relapsing fever (LBRF), a disease transmitted from human to human by the body louse Pediculus humanus humanus. Delays model the latency stages of LBRF in humans and lice, which vary in duration from individual to individual, and are therefore modelled using distributed delays with relatively general kernels. A particular feature of the transmission of LBRF to a human is that it involves the death of the louse, usually by crushing which has the effect of releasing the infected body fluids of the dead louse onto the hosts skin. Careful attention is paid to this aspect. We obtain results on existence, positivity, boundedness, linear and nonlinear stability, and persistence. We also derive a basic reproduction number R0 for the model and discuss its dependence on the model parameters. Our analysis of the model suggests that effective louse control without crushing should be the best strategy for LBRF eradication. We conclude that simple measures and precautions should, in general, be sufficient to facilitate disease eradication.

A stage-structured Bayesian hierarchical model for salmon lice populations at individual salmon farms – Estimated from multiple farm data sets

Salmon farming has become a prosperous international industry over the last decades. Along with growth in the production farmed salmon, however, an increasing threat by pathogens has emerged. Of special concern is the propagation and spread of the salmon louse, Lepeophtheirus salmonis. To gain insight into this parasite's population dynamics in large scale salmon farming system, we present a fully mechanistic stage-structured population model for the salmon louse, also allowing for complexities involved in the hierarchical structure of full scale salmon farming. The model estimates parameters controlling a wide range of processes, including temperature dependent demographic rates, fish size and abundance effects on louse transmission rates, effect sizes of various salmon louse control measures, and distance based between farm transmission rates. Model parameters were estimated from data including 32 salmon farms, except the last production months for five farms, which were used to evaluate model predictions. We used a Bayesian estimation approach, combining the prior distributions and the data likelihood into a joint posterior distribution for all model parameters. The model generated expected values that fitted the observed infection levels of the chalimus, adult female and other mobile stages of salmon lice, reasonably well. Predictions for the periods not used for fitting the model were also consistent with the observational data. We argue that the present model for the population dynamics of the salmon louse in aquaculture farm systems may contribute to resolve the complexity of processes that drive this host-parasite relationship, and hence may improve strategies to control the parasite in this production system.

Evaluation of Lousicidal Activity of Ziziphus mauritiana Alkaloids and Eucaylptus camaldulensis Terpenoids Leaves Extracts in Chickens: An In Vitro Study

The present study aimed to highlight and assess the in vitro poultry anti-lice properties of Ziziphus mauritiana alkaloids and Eucalyptus camaldulensis terpenoids leaves extracts. In vitro poultry antilouse effects of the extracts of various concentrations (1 mg/mL, 5 mg/mL, and 10 mg/mL) using filter paper contact bioassay was applied. Results revealed that lice mortality was concentration-dependent for both studied extracts. The median lethal concentration (LC50) values were 3.687 and 1.045 for alkaloids and terpenoids extracts respectively. The results indicate that terpenoids extract has strong lousicidal activity. Further steps should be pursued to make these extracts to be tested in vivo then may be used as a novel treatment for poultry lice in future, allowing lice control in a less aggressive way to the environment.

Ovicidal Efficacy of Abametapir Against Eggs of Human Head and Body Lice (Anoplura: Pediculidae).

Studies were undertaken to determine the ovicidal efficacy of 5,5′-dimethyl-2,2′-bipyridyl (abametapir) against eggs of both human head and body lice. Head lice eggs of different ages (0–2, 3–5, and 6–8-d-old eggs) were exposed to varying concentrations of abametapir in isopropanol and concentration-dependent response relationships established based on egg hatch. One hundred percent of all abametapir-treated eggs failed to hatch at the 0.74 and 0.55% concentrations, whereas 100% of 6–8-d-old head louse eggs failed to hatch only at the 0.74% concentration. The LC50 value for abametapir varied, depending on the age of the head lice eggs, from ∼0.10% recorded for 0–2-d-old eggs and increasing to ∼0.15% for 6–8-d-old eggs. Abametapir was also evaluated once formulated into a lotion referred to as Xeglyze (0.74% abametapir) and serial dilutions made. Ovicidal efficacies were determined against head lice eggs 0–8-d-old. Results indicated 100% ovicidal activity at the 0.74, 0.55, 0.37, and 0.18% concentrations. Additional studies undertaken using body lice eggs also demonstrated that abametapir was 100% ovicidal against eggs of all ages when evaluated at a concentration of 0.37 and 0.55%. Given that ovicidal activity is a critical component of any effective treatment regime for louse control, the data presented in this study clearly demonstrate the ability of abametapir to inhibit hatching of both head and body louse eggs as assessed in vitro.

A regional model of sheep lice to study the effect on lice prevalence and costs for Australian farms using a range of treatment efficacy in combination with other lice control strategies

Using a previously developed predictive model, three different management practices were examined in combination with post-shearing chemical treatments for lice, to determine which combinations could provide cost-effective reductions in lice prevalence over a 20-year period. The model included nine sheep production regions across Australia, all of which have different regional flock prevalence of lice and mean numbers of sheep/property. The lice prevalence model simulated the effects of four management options on Australian lice prevalence and on financial return (expressed as net present value) over a 20-year period. Management options modelled in this study were: treatment for eradication, inspection for lice detection, intervention level, and biosecurity of purchased sheep. The costs and benefits of these management options were calculated on the basis of published data or standard industry costs. Combinations of eradication achieved through treatment and biosecurity of purchased sheep provided the greatest modelled reductions in Australian flock lice prevalence at the lowest cost. With current management practices, lice prevalence was estimated as 16.3% of Australian properties infested and lice costs were estimated at 902 cents per sheep over 20 years. The model estimated that with appropriate management, lice prevalence could be reduced to less than 1.5% of properties infested and costs could be halved to 435 cents per sheep over 20 years. With further development, the modelling described herein offers potential guidance for Australian sheep producers in selecting the most effective and cost-efficient combination of management strategies to reduce lice infestation.

A regional model of sheep lice management practices to examine the impact of managing straying sheep combined with other management choices

A model of lice management systems was used to investigate the potential benefits of improved fencing against straying sheep, used in conjunction with other management options for lice control. The impact of combined strategies was simulated over a 20-year period. Management options included in the model were: lice eradication rate, lice detection, intervention level, improved fencing to reduce straying sheep, and biosecurity of purchased sheep. The modelling found it was cost-effective to improve fences for an initial average cost of $20 000/property if the number of properties from which strays could enter was reduced by ≥40%, but for average Australian properties this represents less than 20% of the boundary replaced. In order for fencing to be a cost-effective part of lice management, the fencing must target sections of boundary fence that will provide the greatest protection from contact with neighbouring flocks. The model showed that improved biosecurity against straying sheep combined well with improved eradication rates. However, biosecurity for purchased sheep may be the most cost-effective option.

Effects of different strategies for lice control, a simulation experiment.

Effects of different strategies for lice control, a simulation experiment.

Mixture toxicity effects of sea louse control agents in Daphnia magna

Caligid sea lice are ectoparasites causing major disease problems in industrial salmon farming. Sea louse control currently relies widely on parasiticides. Among non-target species, crustaceans are particularly susceptible to salmon delousing agents. Drug combinations have recently been suggested for sea louse control; however, no information is available on the non-target effects of such mixtures. To obtain first insights into combination effects of salmon parasiticides, acute toxicity tests with the crustacean model species Daphnia magna were conducted. Four compounds, including two organophosphates and two pyrethroids, were tested individually and in all pair-wise combinations at one fixed concentration ratio. For most combinations, observed toxicities were close to predictions assuming concentration additivity. However, deltamethrin and cypermethrin showed greater than predicted combination effects, while the inverse was observed for deltamethrin and malathion. The results demonstrate combination effects of anti-sea louse agents and suggest that predictions based on concentration additivity are in most cases protective.

Head louse control by suffocation due to blocking their oxygen uptake

The present study shows that head lice (Pediculus humanus capitis) are killed by suffocation when submersed into the anti-louse shampoo Licener®, which contains a mild shampoo component and an extract of neem seeds after their oil components had been pressed off. It is shown that the inner tracheal system becomes completely filled by the very fluid product. Within 3-10 min, oxygen uptake is prohibited and death of all thus treated lice stages occurred.

Increased frequency and changed methods in the treatment of sea lice (Lepeophtheirus salmonis) in Scottish salmon farms 2005-2011.

The sea louse is the most economically and environmentally serious ectoparasite of marine salmonids. Sea lice have been largely controlled by treatment with a variety of medicines. In order to understand the sustainability of medicine usage, an analysis of sea louse treatment data has been carried out for all Scottish salmon farms from 2005 to 2011. Overall, there was an increase from 0.156 to 0.282 treatments month(-1) ; treatments could involve one or multiple agents. This increase was mostly in bath treatments (cypermethrin in 2007, largely replaced by deltamethrin and azamethiphos in 2008). Treatments using in-feed treatments (emamectin benzoate and teflubenzuron) increased only slowly. Treatments involving more than one medicine in a single month also increased, as did the probability of follow-up treatments. Treatments were seasonal, with peaks of in-feed treatments in March and August and bath treatments more frequent between August and December. Frequency of sea louse treatment increased substantially, with an increase in multiagent and follow-up treatments. This increase in treatment activity is expensive to the industry and increases exposure of the neighbouring environment. This indicates that earlier louse control practices were not sustainable and so adapted.