Fly Strike / Myiasis

Fly strike, medically termed myiasis, represents one of the most significant and distressing parasitic conditions affecting farm animals worldwide, characterized by the infestation of living tissue by fly larvae commonly known as maggots. This condition occurs when certain species of flies, primarily blowflies, deposit their eggs on the skin or in wounds of susceptible livestock, with the hatching larvae subsequently burrowing into and feeding upon the animal's living flesh. The resulting tissue destruction causes intense pain, systemic toxicity, and can rapidly progress to life-threatening illness if not promptly identified and treated. Fly strike stands as a major welfare concern in livestock production systems, causing suffering that demands immediate intervention and implementation of comprehensive prevention strategies.

Fly strike affects virtually all livestock species kept in agricultural settings, with sheep being particularly vulnerable due to their dense fleece that creates ideal conditions for fly attraction and larval development. Cattle, goats, pigs, horses, and poultry all experience myiasis to varying degrees depending on geographic location, seasonal conditions, and management practices. Prevalence peaks during warm, humid months when fly populations reach maximum levels, though cases occur whenever environmental conditions support fly activity. Certain geographic regions with consistently warm climates experience year-round risk, while temperate areas see distinct seasonal patterns of fly strike occurrence.

The economic and welfare impact of fly strike extends throughout the livestock industry, causing direct losses through mortality, treatment costs, and reduced productivity alongside indirect losses from prevention program expenses and labor allocation. Affected animals experience rapid weight loss, decreased milk production, wool damage, and reproductive failures that compound immediate treatment costs. The welfare implications are severe, with infested animals suffering intense pain, distress, and systemic illness from toxins released by feeding larvae. Industry estimates suggest fly strike costs livestock producers billions of dollars globally each year when combining direct losses, treatment expenses, and prevention program investments.

Treatability of fly strike depends heavily on early detection and prompt intervention, with cases identified before extensive tissue damage generally carrying favorable prognosis for recovery. The importance of early detection cannot be overstated, as larval feeding and tissue destruction progress rapidly once infestation establishes. Animals receiving treatment within the first day or two of infestation typically recover completely with appropriate wound care and supportive therapy. However, advanced cases involving extensive tissue necrosis, secondary bacterial infection, or systemic toxemia may prove fatal despite aggressive treatment efforts. Prevention through integrated fly management programs offers far better outcomes than relying solely on treatment of established infestations.

The primary cause of fly strike is the parasitic infestation of living tissue by larvae of certain fly species, predominantly blowflies belonging to the family Calliphoridae. Lucilia sericata, the green bottle fly, represents the most common cause of fly strike in sheep and other livestock in temperate regions, while other species including Lucilia cuprina, the Australian sheep blowfly, dominate in warmer climates. Various Calliphora species, known as bluebottle flies, also initiate myiasis in livestock. Screwworm flies, both Old World (Chrysomya bezziana) and New World (Cochliomyia hominivorax) species, cause particularly severe obligate myiasis in regions where they remain endemic. These flies are attracted to livestock by odors emanating from wounds, soiled fleece, body orifices, and other moist areas suitable for egg deposition.

Genetic and breed predisposition to fly strike relates primarily to physical characteristics affecting attractiveness to flies and susceptibility to initiating conditions. Sheep breeds with excessive skin wrinkles, particularly around the breech area, accumulate moisture and fecal contamination predisposing to breech strike. Fine-wool breeds with dense, moisture-retaining fleeces experience higher fly strike rates than breeds with more open wool structures. Cattle breeds with excessive skin folds or pendulous sheaths may experience increased myiasis risk in those anatomical areas. Selection for production traits without consideration of fly strike susceptibility has inadvertently increased vulnerability in some breed populations over generations of breeding.

Environmental and management factors significantly influence fly strike occurrence through effects on both fly populations and animal susceptibility. Warm temperatures combined with humidity create optimal conditions for fly breeding and activity, explaining seasonal patterns of fly strike incidence. Rainfall patterns affect both fly populations and fleece moisture levels in sheep, with conditions following rain often producing fly strike outbreaks. Management practices including shearing timing, crutching, tail docking, and wound care directly impact animal attractiveness to gravid flies seeking oviposition sites. Stocking density and pasture management influence both fly populations and opportunities for early detection of affected animals.

Risk factors for fly strike development encompass animal-level, environmental, and management variables interacting to determine individual and flock susceptibility. Wounds from any cause including shearing cuts, fighting injuries, and footrot lesions attract blowflies seeking oviposition sites. Diarrhea or scouring from any cause creates soiled, moist breech conditions highly attractive to flies. Urine staining in ewes, particularly those with poor conformation, predisposes to pizzle strike in wethers and crutch strike in females. Fleece length and density affect microclimate conditions at the skin surface, with longer fleeces during warm months increasing strike risk. Recent rainfall wetting fleeces dramatically increases susceptibility in sheep populations.

The pathophysiology of fly strike involves progressive tissue destruction by feeding larvae coupled with systemic effects from absorbed toxins. Female flies deposit egg masses containing dozens to hundreds of eggs on susceptible sites, with eggs hatching within hours to days depending on temperature. First-stage larvae initially feed on skin surface debris and wound exudates before molting and beginning tissue invasion. Larval feeding releases proteolytic enzymes that liquefy tissue while simultaneously releasing ammonia and other toxic compounds. Tissue destruction expands rapidly as larvae grow through successive instars, creating progressively larger wounds and attracting additional flies for secondary strike. Bacterial contamination of larval wounds produces additional toxins contributing to systemic illness. Toxin absorption causes fever, depression, metabolic derangement, and potentially fatal toxemia in severe cases.

Early warning signs of fly strike often manifest as behavioral changes before physical lesions become readily apparent, particularly in sheep where dense fleece may conceal initial infestations. Affected animals frequently isolate themselves from the flock, seeking shade or shelter and refusing to graze with herdmates. Restlessness and frequent position changes indicate discomfort, with animals repeatedly lying down then rising unable to find comfortable positions. Tail wagging or twitching in sheep may indicate early breech strike, while head shaking and ear flicking suggest possible poll or ear involvement. Decreased appetite and reluctance to move with the group during normal activities often represent earliest observable indicators of developing fly strike.

Common symptoms of fly strike share fundamental characteristics across species while varying somewhat in presentation based on anatomical differences and typical strike locations. In sheep, crutch strike affecting the breech area represents the most common presentation, characterized by soiled, discolored wool with underlying skin damage and visible larvae in advanced cases. Body strike in sheep appears as patches of discolored, matted fleece often with brownish staining from larval secretions and serum. Cattle more commonly experience wound strike at injury sites or fly worry around eyes, ears, and other facial structures. Goats present similarly to sheep but with less fleece-related concealment. Pigs may develop navel strike in young animals or wound strike at any age, with larvae visible in damaged tissue.

Behavioral changes associated with fly strike become increasingly dramatic as infestations progress beyond early stages. Off-feed behavior progresses to complete anorexia as systemic illness develops from toxin absorption. Affected animals may stand with hunched posture, head lowered, and reluctant to move indicating general malaise and abdominal discomfort. Teeth grinding suggests pain, while excessive vocalization beyond species-normal behavior indicates severe distress. Some animals exhibit self-mutilation behaviors attempting to reach and address irritated areas, potentially causing additional injuries. Recumbency develops in advanced cases as systemic toxemia progresses, with animals unable to rise without assistance.

Physical signs of fly strike include visible changes to skin, fleece, or hair coat along with evidence of larval presence in affected tissues. Initial strike sites show moisture and discoloration before frank tissue damage becomes apparent. Matted, stained fleece or hair surrounds developing wounds, often with characteristic foul odor detectable at distance in advanced cases. Close examination reveals tissue damage ranging from superficial skin erosions to deep cavitating wounds exposing underlying muscle. Larvae at various developmental stages may be visible within wounds, with mature third-stage larvae reaching considerable size. Wound margins show tissue necrosis with progressive undermining of surrounding skin. Serum and blood-tinged exudate drain from affected areas attracting additional flies and creating conditions for secondary strike.

Symptom progression in untreated fly strike follows a predictable pattern of accelerating tissue destruction and systemic deterioration. Initial strikes expand rapidly as larvae consume tissue and additional flies deposit eggs on wounded areas. Wound surface area may double within 24 to 48 hours as multiple generations of larvae feed simultaneously. Toxin absorption produces progressive systemic illness including fever, elevated heart and respiratory rates, dehydration, and metabolic derangement. Body condition deteriorates rapidly as animals cease eating while metabolic demands increase. Skin surrounding wounds becomes increasingly necrotic and may slough in large sections. Terminal cases develop septicemia, shock, and multi-organ failure.

Emergency symptoms requiring immediate veterinary intervention include extensive tissue loss covering large body surface areas, evidence of systemic toxemia with fever and marked depression, and any signs of shock including rapid weak pulse, cold extremities, and collapse. Strike involving critical anatomical structures including eyes, genitalia, or body cavities demands urgent attention to preserve function and prevent life-threatening complications. Animals unable to rise or showing signs of severe dehydration require immediate supportive care. Any struck animal in advanced body condition loss with concurrent illness from other causes faces grave prognosis and requires prompt evaluation for treatment feasibility versus humane euthanasia considerations.

Clinical examination for fly strike combines systematic inspection of at-risk body regions with assessment of behavioral indicators suggesting possible infestation. Visual examination begins with overall animal evaluation from distance, noting posture, behavior, and any obvious areas of fleece or coat discoloration. Close inspection focuses on commonly affected areas including the breech, pizzle region, poll, and any visible wounds or soiled areas. Parting fleece or hair coat reveals underlying skin condition and presence of eggs, larvae, or tissue damage. Palpation may detect heat and swelling associated with tissue inflammation before visual changes become apparent. Systematic examination of all animals during handling opportunities enables early detection improving treatment outcomes.

Diagnostic tests for fly strike primarily involve visual confirmation of larval presence and assessment of wound extent and depth. Wound exploration under appropriate restraint or sedation reveals the full extent of tissue damage often underestimated from surface examination alone. Larvae removed from wounds can be identified to species level through morphological characteristics, useful for epidemiological purposes and prevention program planning. Bacterial culture of wound samples may guide antimicrobial selection when secondary infection complicates myiasis. Blood work including complete blood count and serum chemistry assesses systemic illness severity and guides intensity of supportive care. Necropsy examination of fatal cases documents lesion extent and identifies contributing factors for herd-level prevention efforts.

Differential diagnosis for fly strike includes other causes of skin wounds, fleece abnormalities, and behavioral changes potentially confused with myiasis. Shearing wounds without secondary fly strike may initially resemble early strike before larvae become visible. Skin trauma from fighting, catching on objects, or predator attacks creates wounds attractive to flies that may or may not have progressed to actual strike. Fleece rot produces discolored, matted fleece without larval involvement though often preceding or predisposing to strike. Lumpy wool from bacterial dermatitis creates fleece abnormalities requiring differentiation. External parasites including lice and keds cause fleece damage and behavioral changes distinct from myiasis. Photosensitization creates skin lesions potentially confused with strike in early stages.

Herd-level diagnostics become essential when fly strike affects multiple animals indicating inadequate prevention programs or exceptional environmental conditions. Epidemiological investigation identifies common risk factors among affected animals including age, body condition, fleece length, recent procedures, and pasture location. Environmental assessment evaluates conditions favoring fly populations and animal susceptibility including temperature, humidity, and recent rainfall. Trap monitoring quantifies fly populations and species composition informing prevention strategies. Record review identifies patterns of strike occurrence enabling prediction and prevention of future outbreaks. Comparison with regional reports reveals whether farm-level incidence exceeds expected rates suggesting need for enhanced prevention measures.

Emergency and immediate treatment for fly strike focuses on removing larvae, debriding necrotic tissue, and stabilizing systemically ill animals through supportive care. Physical removal of all visible larvae using forceps or similar instruments represents the essential first step in treatment. Thorough irrigation of wounds with dilute antiseptic solutions dislodges additional larvae and reduces bacterial load. Initial wound assessment determines depth and extent of tissue damage guiding further debridement requirements. Animals showing signs of systemic illness require immediate supportive care including fluid therapy, anti-inflammatory medications, and temperature management. Analgesic administration addresses the significant pain associated with myiasis improving animal welfare and facilitating handling for treatment.

Medical management of fly strike includes topical and systemic treatments targeting remaining larvae while preventing secondary infection and promoting wound healing. Topical larvicidal agents including organophosphates, synthetic pyrethroids, and newer insect growth regulators eliminate remaining larvae and protect against restrike during the healing period. Systemic parasiticides including macrocyclic lactones provide internal protection against remaining larvae while preventing new infestations for defined protection periods. Antimicrobial therapy targets secondary bacterial infection with selection based on likely pathogens and culture results when available. All treatments for food-producing animals require strict attention to withdrawal periods ensuring meat and milk safety for human consumption. Veterinary guidance ensures appropriate product selection and application for specific species and production circumstances.

Surgical options for fly strike primarily involve wound debridement removing necrotic tissue and creating conditions favorable for healing. Extensive wounds may require debridement under sedation or anesthesia to enable thorough removal of all devitalized tissue. Wound margins may be trimmed to healthy tissue creating defined edges more likely to heal successfully. Large wounds may benefit from surgical closure once infection is controlled and granulation tissue has formed. Some wounds heal optimally through second intention with appropriate supportive care and protection from further fly strike. Severe cases involving extensive tissue loss may require reconstructive procedures in valuable animals where economics justify intensive intervention.

Supportive care forms a critical component of fly strike treatment determining outcomes in moderate to severe cases. Fluid therapy addresses dehydration from reduced intake and fluid losses through wound drainage. Nutritional support maintains body condition during recovery periods when appetite may remain suppressed. Pain management continues through the healing process improving welfare and enabling normal behaviors including eating and drinking. Environmental management provides clean, dry conditions protected from further fly exposure. Wound care continues until complete healing occurs, with regular cleaning, appropriate dressing changes, and monitoring for complications.

Herd treatment protocols address flock-level prevention and management when fly strike affects multiple animals or conditions predict outbreak risk. Prophylactic treatments using pour-on or spray formulations protect unaffected animals during high-risk periods. Timing of preventive applications coordinates with seasonal fly activity patterns and management calendar events. Strategic crutching removes soiled wool reducing attractiveness to flies in sheep flocks. Enhanced monitoring frequency during high-risk periods enables early detection improving individual outcomes. Population-level treatments may include premises fly control measures reducing overall fly numbers.

Treatment decision factors in fly strike management include wound severity, systemic illness extent, individual animal value, and likelihood of successful outcome guiding intervention intensity and cull decisions. Mild cases with limited tissue involvement carry excellent prognosis justifying treatment in all animals. Moderate cases require assessment of wound extent, response to initial treatment, and economic factors in determining treatment intensity. Severe cases with extensive tissue loss, systemic toxemia, or poor initial treatment response may warrant humane euthanasia rather than prolonged treatment unlikely to succeed. Economic analysis compares treatment costs including veterinary fees, medications, and labor against animal value and probability of productive recovery. Welfare considerations mandate that all animals receive appropriate pain management and either adequate treatment or humane euthanasia rather than suffering without intervention.

Recovery timeline for fly strike varies substantially based on initial wound severity, treatment timing, and development of complications. Mild cases detected and treated within 24 hours of initiation typically show rapid improvement with complete healing within two to three weeks. Moderate cases involving more extensive tissue damage require four to six weeks for complete wound resolution with appropriate ongoing care. Severe cases surviving initial treatment may require months of wound management before achieving complete healing, with some animals retaining permanent defects or scarring. Animals developing systemic complications including septicemia face extended recovery periods even after wound healing occurs.

Post-treatment care and monitoring ensure continued progress toward healing while enabling early detection of complications or restrike. Wounds require regular inspection for signs of secondary infection, appropriate granulation tissue formation, and absence of new larval activity. Dressing changes maintain clean wound environment when direct bandaging is feasible for specific anatomical locations. Fly repellent application protects healing wounds from restrike which would dramatically set back recovery. Nutritional support continues through recovery promoting tissue regeneration and immune function. Gradual return to normal activities follows wound healing progress avoiding reinjury of healing tissues.

Prognosis factors influencing fly strike outcomes include treatment timing, wound extent and location, systemic illness severity, and individual animal resilience. Early intervention consistently produces better outcomes than delayed treatment, with prognosis declining rapidly as wounds expand and systemic effects develop. Wound location affects both healing capability and functional impact, with strikes involving joints, eyes, or body cavities carrying guarded prognosis. Animals in good body condition before strike tolerate illness better than those already compromised by concurrent conditions. Age influences recovery with young animals often healing more rapidly but also developing more severe systemic illness from equivalent strike severity.

Return to production considerations following fly strike recovery balance healing status against production system requirements. Meat animals may return to finishing programs once wounds are healed and withdrawal times for any treatments have elapsed. Breeding animals can resume reproductive activities once general condition supports successful conception and completion of breeding season activities. Dairy animals may return to milking when any udder involvement is fully resolved and withdrawal times are complete. Wool sheep require assessment of fleece regrowth and skin healing before return to normal fleece production expectations. Sale or show animals need complete cosmetic recovery including hair or fleece regrowth before marketing.

Vaccination protocols for fly strike prevention remain limited as myiasis results from parasitic infestation rather than infectious disease susceptible to immunization. However, research continues on potential vaccines targeting fly larvae antigens that might reduce establishment or survival of larvae in immunized animals. Current prevention relies on physical, chemical, and management interventions rather than vaccination. Vaccination programs targeting conditions predisposing to fly strike, such as footrot vaccines reducing hoof wounds attractive to flies, contribute indirectly to fly strike prevention. Consultation with veterinarians ensures appropriate vaccine programs for conditions increasing fly strike susceptibility on individual farms.

Biosecurity measures for fly strike focus on reducing fly populations and protecting animals from fly contact rather than preventing introduction of flies themselves since relevant species occur naturally throughout livestock production regions. Premises fly control through appropriate waste management, removal of decaying organic matter, and strategic use of fly traps or baits reduces overall fly numbers. Timing of operations such as shearing, marking, and mulesing to periods of lower fly activity reduces wound-related strike risk. Prompt treatment of any wounds or health conditions causing discharge or soiling eliminates attractants drawing flies to individual animals. Sourcing policies ensuring new animals arrive free of active fly strike prevents introduction of heavy infestations to established flocks.

Nutritional prevention strategies support overall animal health and reduce conditions predisposing to fly strike. Appropriate parasite management prevents diarrhea and subsequent breech soiling from gastrointestinal parasitism. Balanced diets avoid nutritional scours that create conditions attractive to gravid flies. Adequate trace mineral nutrition supports immune function and wound healing should strikes occur. Body condition management ensures animals have metabolic reserves to withstand illness and recover from treatment. Feeding management reduces competition and stress that might contribute to diarrhea or reduced grooming.

Management practices preventing fly strike address both animal susceptibility and fly population control. Strategic shearing timing maintains shorter fleeces during peak fly activity periods in sheep operations. Regular crutching removes soiled wool from breech areas reducing strike susceptibility between shearings. Tail docking and mulesing, where practiced under appropriate welfare guidelines, reduce breech soiling and wool coverage in highly susceptible anatomical areas. Wound management including prompt treatment of any injuries, surgical wound care, and appropriate post-procedure protection prevents wound-initiated strike. Breeding programs incorporating fleece type, body conformation, and breech wrinkle traits reduce inherent susceptibility across generations.

Quarantine and testing protocols support fly strike prevention through identification and treatment of affected or high-risk animals before they contribute to fly populations or experience progressive disease. New arrivals undergo inspection for active strike or predisposing conditions before mixing with established groups. Isolation facilities allow observation and treatment of animals during weather or seasonal conditions producing high fly strike risk. Monitoring programs using fly traps establish activity thresholds triggering enhanced prevention measures. Record systems document strike occurrence enabling identification of high-risk individuals, locations, and time periods for targeted prevention efforts.

Daily management and monitoring for fly strike prevention integrates observation into routine farm operations ensuring early detection when strikes occur. Visual inspection during feeding, mustering, or other daily activities identifies behavioral changes suggesting possible strike. Designated high-risk periods trigger enhanced monitoring frequency with specific observation of commonly affected body areas. Staff training ensures all personnel recognize early signs and understand immediate response protocols. Fly activity monitoring through observation or trapping guides timing of preventive treatments and monitoring intensity. Communication systems enable rapid reporting of suspected cases for prompt veterinary assessment.

Housing and environmental management influences fly strike risk through effects on both animal susceptibility and fly populations. Shade provision allows animals to avoid direct sun during peak fly activity hours reducing fly-animal contact. Drainage management prevents accumulation of standing water and organic matter supporting fly breeding. Vegetation management around facilities reduces shelter for adult flies while maintaining air movement through livestock areas. Waste management including prompt removal and proper disposal of manure, carcasses, and other organic materials eliminates fly breeding sites. Facility design incorporating smooth, cleanable surfaces reduces accumulation of attractive materials.

Herd health programs incorporating fly strike prevention provide systematic frameworks for risk reduction. Seasonal calendars identify high-risk periods triggering implementation of prevention protocols. Standard operating procedures define preventive treatment timing, products, and application methods. Record systems document strike occurrence, treatments applied, and outcomes achieved. Program review enables continuous improvement based on farm-specific experience. Integration with other health programs ensures fly strike prevention complements overall herd health management. Veterinary involvement provides expert guidance on product selection, timing, and emerging prevention technologies.

Record keeping and monitoring systems support evidence-based fly strike management through documentation and analysis of farm-specific patterns. Individual animal records identify high-risk animals for targeted monitoring or management intervention. Incident records capture strike occurrence by date, location, severity, and outcome enabling pattern identification. Treatment records ensure withdrawal time compliance and provide data for efficacy assessment. Economic tracking quantifies costs including prevention programs, treatments, losses, and labor enabling cost-benefit analysis. Benchmarking against industry standards or neighboring operations identifies improvement opportunities.

Economic considerations in fly strike management encompass prevention investments, treatment costs, and productivity losses requiring ongoing cost-benefit evaluation. Prevention programs including labor, products, and facilities require upfront investment justified by reduced strike incidence and severity. Treatment costs combine veterinary fees, products, and labor with indirect costs of animal monitoring and wound care. Productivity losses include mortality, reduced growth rates, decreased wool quality and quantity, and reproductive impacts in affected animals. Insurance options may offset some losses while incentivizing implementation of prevention programs. Economic modeling supports decisions regarding prevention investment levels optimizing returns while maintaining acceptable welfare outcomes.

High-risk breeds and species for fly strike demonstrate susceptibility patterns related to physical characteristics, environmental adaptation, and management system requirements. Merino sheep and Merino-derived breeds carrying genes for dense, fine wool face highest fly strike risk due to fleece characteristics creating warm, moist microenvironments at skin level. Sheep breeds with excessive skin wrinkles, particularly in the breech region, experience increased soiling and moisture retention predisposing to crutch strike. British breed sheep with open fleeces generally experience lower strike rates than fine-wool breeds under equivalent environmental conditions. Cattle breeds with light pigmentation and thin skin may experience increased susceptibility to fly worry and wound strike compared to thicker-skinned breeds.

Production type considerations influence fly strike risk through management intensity, fleece or coat characteristics, and environmental exposure patterns. Wool sheep managed primarily for fiber production maintain longer fleeces creating extended high-risk periods compared to meat breeds shorn more frequently. Dairy cattle with higher metabolic rates and more intensive management may experience different fly exposure patterns than extensively managed beef cattle. Feedlot cattle face concentrated fly populations around feeding and watering areas potentially increasing strike risk despite shorter coats. Sheep in extensive range systems may receive less frequent monitoring potentially allowing strikes to progress further before detection compared to intensively managed flocks.

Genetic selection and testing offer opportunities for reducing fly strike susceptibility within sheep populations particularly through selection for breech conformation and fleece characteristics. Australian Sheep Breeding Values include fly strike resistance indicators enabling selection for reduced susceptibility. Breeding programs selecting against excessive breech wrinkle have demonstrated reduced fly strike incidence in subsequent generations. Fleece rot resistance correlates with fly strike resistance since fleece rot predisposes to body strike. Bare breech genetics bred into some Merino lines substantially reduce breech strike susceptibility without requiring mulesing. Genomic tools increasingly enable identification of animals carrying favorable alleles for strike resistance supporting accelerated genetic improvement.

Commonly co-occurring conditions with fly strike include predisposing factors creating attractiveness to flies and complications arising from larval feeding and wound presence. Fleece rot produces the discolored, moist wool conditions highly attractive to blowflies for oviposition, with many body strikes initiated in areas of existing fleece rot. Dermatophilosis or lumpy wool creates similar predisposing conditions through bacterial infection of wool follicles. Diarrhea from any cause including gastrointestinal parasitism, dietary upset, or infectious disease creates soiled breech conditions highly attractive to flies. Footrot and other causes of lameness produce wound sites and discharge potentially initiating strike on lower limbs. Pinkeye and other conditions causing ocular discharge may predispose to head strike around eyes.

Conditions with similar symptoms requiring differentiation from fly strike include other causes of skin wounds, behavioral changes, and fleece abnormalities. Shearing wounds without secondary strike may initially resemble early myiasis before larvae become visible, requiring close inspection for differentiation. Skin trauma from any source creates wounds potentially confused with strike until examination confirms or rules out larval presence. Fleece rot without progression to strike produces discolored matted wool requiring inspection to determine if larvae are present. Wool slip from various causes creates fleece loss potentially confused with fly-damaged fleece. Other external parasites including lice, keds, and mites cause fleece damage, itching, and skin changes distinct from myiasis but requiring appropriate diagnosis.

Complications and sequelae of fly strike include direct consequences of larval feeding as well as secondary effects of wound presence and systemic illness. Secondary bacterial infection invariably accompanies fly strike wounds, potentially progressing to deeper tissue infection, abscess formation, or septicemia. Extensive tissue loss may result in permanent scarring, altered function of affected areas, or chronic wounds failing to heal completely. Toxemia from absorbed larval toxins and bacterial products can produce lasting metabolic effects in surviving animals. Secondary strike occurring during wound healing dramatically increases tissue damage and mortality risk. Chronic fly strike wounds may predispose to neoplasia in some cases. Psychological effects of severe fly strike experience may alter animal behavior in ways affecting subsequent management.