Lecture #25 & #26
CVM 713: Mosquitos, Midges, and Flies (Order Diptera)
Lecture Overview
This course covers the ecological implications and pathologies associated with various Diptera species that inflict illness on companion animals and domestic production animals.
Lecture Objectives
Clinical Importance: Recognize the pathogenic potential of Diptera species (mosquitos, midges, & flies).
Morphological Features: Identify basic morphologic and biologic traits of select genera/species of flies including horse flies, house flies, and bot flies.
Lifecycle Understanding: Employ knowledge of lifecycle to diagnose infections and mitigate risk of infectious diseases, knowing where species deposit eggs and determining the parasitic stages on hosts.
Therapeutics: Recall general chemotherapies for treating infected animals and recommend prevention strategies.
Mechanism of Action: Know therapeutic families, product names, and spectrum of activity including species and lifecycle stages.
General Information on Flies (Order Diptera)
Species Diversity: Approximately 100,000 individual species.
Includes: House flies, horse flies, and mosquitos.
Biological Variability: Variation in morphology, lifecycle biology, and pathogenicity across species.
Roles: Act as obligate intermediate hosts and mechanical vectors for various infectious agents.
General Morphology of Flies
Wings: Two pairs of wings used for flying and balancing.
Antennae: Well developed for sensory functions.
Legs: Six legs, adapted for various functions.
Body Structure: Segmented bodies; mouthpart morphology reflects feeding strategies:
Piercing/Sucking: For blood feeding.
Sponging: For consuming liquids.
Vestigial: Non-functional mouthparts.
Developmental Stages
Parasitic Stages: Include adult and larvae; rarely coexist.
Vectors and Intermediate Hosts: Main groups include:
Mosquitoes
Horse flies
House flies
Bot flies
Specific Groups of Flies
Sand Flies, Mosquitos, Midges
Characteristics: Small, delicate flies that are weak fliers and inhabit aquatic environments. Only female adults are blood-sucking.
Lutzomyia/Phlebotomus: Intermediate hosts for Leishmania sp.; prefer moist, dark habitats.
Culicoides: Found in stagnant water, vectors for equine Onchocerciasis, Bluetongue virus, and Queensland Itch associated with hypersensitivity reactions.
Simulium (Black Flies): Known for painful bites and large swarms; can cause depression, dysorexia, and subcutaneous edema. They prefer clean, fast-flowing water. Control measures include avoiding aquatic habitats.
Mosquitoes
Impact: Considered nuisances that pose significant risks for infectious disease transmission, globally.
Common Species: Aedes albopictus as the predominant backyard species, introduced in the US in 1985.
Competence as Vectors:
In 1995, identified as competent vectors for canine heartworm disease (CHWD) in Louisiana (2% of surveyed mosquitos) and 2.3% in Georgia in 2010.
Metamorphosis: Complex life cycle includes aquatic and non-parasitic larvae; only females require a blood meal for ovarian development, acting as obligate intermediate hosts for various diseases, such as:
Canine Heartworm ( extit{Dirofilaria immitis})
Malaria caused by Plasmodium species
Numerous arboviruses like Zika, Dengue, West Nile, and Yellow fever.
Mosquito Control Measures
Preventive Strategies: Essential to reduce breeding by removing standing water, cleaning gutters, and managing vegetation. Use of repellents and carbon dioxide traps during outdoor activities is recommended.
Horse Flies and Relatives
Characteristics: Large, robust flies, active during the day, strong fliers but develop slowly with one generation per year.
Repetitive Feeding: Females of species such as Tabanus (horse fly) and Chrysops (deer fly) exhibit painful biting behavior with slashing mouthparts.
Economic Impact: Significant reductions in livestock productivity (66-100% decline) with losses estimated around $25 million. Average daily weight gains improved to 2.3 lbs with adequate control measures.
Infectious Disease Vectors: Tabanus linked to Equine Infectious Anemia and Bovine Leukosis virus. They breed in water and decaying organic matter.
House Flies and Relatives
Morphology: Medium to small flies exhibiting similar superficial features.
Ovipositional Tendency: Prefer moist organic materials; both biting and non-biting varieties exist.
Non-Biting Flies
Primary Example: Musca domestica (common house fly) recognized as a mechanical vector carrying 1 to 6 million bacteria and over 100 pathogens including Salmonella.
Obligate Intermediate Hosts: D. habronema (causing stomach worms).
Major Issues: Musca autumnalis (face fly) introduced from Europe in 1948, significantly annoying livestock and acting as a vector for Thelazia and causing cattle pink eye.
Oviposition is typically in fresh feces.
Biting Flies
Examples and Effects:
Hematobia irritans (horn fly): the most crucial ectoparasite of cattle, causing economic loss through weight gain reductions ($800 million per year).
Stomoxys calcitrans (stable fly): closely resembling house flies but known for painful bites, with up to 40-60% declines in milk production (losses of $400 million). They oviposit in old feces and moist organic materials, with environmental sanitation crucial for control.
Myiasis- Producing Flies
Types: Include blowflies (Calliphoridae) and flesh flies (Sarcophagidae).
Myiasis: Characterized by tissue invasion by larval flies, divided into:
Primary Myiasis: Initial invasion of healthy tissues, e.g., Cochliomyia hominivorax (American Screwworm).
Secondary Myiasis: Invasion of infected or necrotic tissues. Flies from Calliphoridae and Sarcophagidae exhibit this.
Bot Flies
Characteristics: Large, robust flies with non-feeding adults; larvae are parasitic within host tissues and are highly host-specific.
Examples: Horse, dog/cat/squirrel bot flies, and Dermatobia hominis (human bot fly) mostly found in Latin America.
Treatment and Prevention Strategies
For Bot Flies
Methods: Surgical removal of bot larvae from companion animals, prophylactic “pour on” macrocyclic lactone drugs for cattle, avoiding adverse reactions and treating before larval migration to overwintering sites.
Nasal bots in sheep generally remain untreated, though GI bot treatment is common.
For Face/Horn Flies and Stable Flies
Control Measures: Incorporate dust bags, insecticide-impregnated ear tags, and rotating insecticides to prevent resistance. Environmental sanitation, feed management, and proper insecticides are fundamental.
Summary of Fly Pests
Notable Fly Types:
Equine Bot Fly (Gastrophilous): Non-feeding adults, larvae within the stomach.
Horse Fly (Tabanus): Vicious blood feeders.
Bot Flies (Cuterebra): Associated with migrating larvae in cats, dogs, and cattle.
Reportable Diseases
American Screwworm (Cochliomyia hominivorax): Infamous for causing severe tissue degradation, previously eradicated in North America; strict federal regulations exist regarding its control due to significant livestock impact.
Lecture Overview
This course provides a comprehensive examination of the ecological implications and pathologies associated with various species within the Order Diptera, particularly focusing on those that inflict illness on companion animals and domestic production animals. Students will engage with both theoretical concepts and practical applications related to these mosquitoes, midges, and flies, exploring their biological characteristics as well as their impacts on animal health and welfare.
Lecture Objectives
Clinical Importance: Cultivate an understanding of the pathogenic potential of species within the Diptera order, including the mechanisms by which they transmit diseases to animals and the significance of these diseases in veterinary practice.
Morphological Features: Gain proficiency in identifying basic morphological and biological traits of select genera and species of flies, including key distinguishing features of horse flies, house flies, and bot flies. This includes a detailed examination of their anatomical structures that relate to their role in disease transmission.
Lifecycle Understanding: Develop an understanding of the lifecycle stages of Diptera, focusing on how this knowledge aids in the diagnosis of infections and mitigation of risk for infectious diseases. This includes knowledge of oviposition sites, growth conditions for larvae, and endurance capabilities of adults in various environments.
Therapeutics: Familiarize with various chemotherapies used to treat infected animals, and develop skills in recommending effective prevention strategies tailored to specific Diptera species and the pathogens they carry.
Mechanism of Action: Understand the mechanisms of action of therapeutic families, recall product names, and identify the spectrum of activity, including the efficacy across various species and their lifecycle stages.
General Information on Flies (Order Diptera)
Species Diversity: The Order Diptera comprises approximately 100,000 individual species, with significant ecological roles. This extensive diversity includes major vectors for zoonotic diseases such as West Nile virus, malaria, and heartworm disease in canines.
Notable species include house flies (Musca domestica), horse flies (Tabanus), and various species of mosquitos, each associated with unique ecological niches and impacts on health.
Biological Variability: Significant variability exists in morphology, lifecycle biology, and pathogenicity across species, influencing their roles as vectors and their interactions with both their environment and host organisms.
Roles: Diptera species function both as obligate intermediate hosts and mechanical vectors, facilitating the transmission of various infectious agents through blood feeding and environmental contact. Their roles in ecosystems are multifaceted, contributing to nutrient recycling and serving as food sources for other organisms.
General Morphology of Flies
Wings: Flies typically possess two pairs of wings, which are critical for flight, balancing, and performing complex maneuvers. The structures and alignment of these wings vary greatly across species, influencing flight patterns and feeding behavior.
Antennae: Flies have well-developed antennae equipped for sensory functions, allowing them to detect chemical signals (pheromones) and navigate their environment effectively.
Legs: Flies exhibit six legs that are adapted for various functions, including gripping surfaces, feeding strategies, and complex movements essential for avoiding predators.
Body Structure: The bodies of flies are segmented, with mouthpart morphology reflecting diverse feeding strategies:
Piercing/Sucking: Adaptations for blood feeding found in species such as mosquitoes.
Sponging: Used by species like house flies to consume liquids through a sponge-like mouthpart.
Vestigial: Some species possess non-functional mouthparts, indicating their evolution and specific life history adaptations.
Developmental Stages
Parasitic Stages: Flies have distinct developmental stages including adult forms and larva, which seldom coexist. Understanding their developmental stages is crucial for controlling populations and managing disease risks.
Vectors and Intermediate Hosts: The main groups of Diptera that serve as vectors or intermediate hosts include mosquitoes, horse flies, house flies, and bot flies, each with unique life-cycle characteristics influencing their role in pathogen transmission.
Specific Groups of Flies
Sand Flies, Mosquitos, Midges
Characteristics: These small, delicate flies are characterized by their weak flying abilities and are typically found in moist aquatic environments. Only female adults engage in blood-sucking activities necessary for ovary maturation.
Lutzomyia/Phlebotomus: Act as intermediate hosts for Leishmania species, preferring humid, shaded habitats that facilitate their life cycle and the survival of their offspring.
Culicoides: Reside in stagnant water, transmitting equine Onchocerciasis and the Bluetongue virus, leading to hypersensitivity reactions.
Simulium (Black Flies): Renowned for their painful bites and aggressive swarming behavior; they thrive in clean, fast-flowing water areas, posing significant health risks to both livestock and humans. Control measures focus heavily on environmental management to reduce habitat availability.
Mosquitoes
Impact: Mosquitoes are significant pests globally and serve as major vectors for a variety of infectious diseases. Their nuisance has both direct and indirect health consequences, influencing livestock and human well-being.
Common Species: Aedes albopictus is a key species known as the predominant backyard mosquito, first introduced to the U.S. in 1985, which significantly contributes to the spread of diseases.
Competence as Vectors:
Mosquitoes have been identified as competent vectors for canine heartworm disease (CHWD), with notable surveys indicating a prevalence of approximately 2% in Louisiana (1995) and an increase to 2.3% in Georgia (2010).
Metamorphosis: The mosquito life cycle is complex, comprising aquatic and non-parasitic larval stages. Only females require a blood meal, which is vital for ovarian development. They serve as obligate intermediate hosts for multiple diseases, including:
Canine Heartworm (Dirofilaria immitis)
Malaria (Plasmodium species)
Various arboviruses, such as Zika, Dengue, West Nile virus, and Yellow fever, underscoring the importance of control measures.
Mosquito Control Measures
Preventive Strategies: Effective mosquito control is paramount in reducing disease transmission. This includes eliminating standing water where mosquitoes breed, regular cleaning of gutters to prevent overflow, managing vegetation to eliminate harboring sites, and using repellents and carbon dioxide traps during outdoor activities to reduce mosquito encounters.
Horse Flies and Relatives
Characteristics: Horse flies are notably large, robust flies that exhibit increased activity during daylight hours and are strong fliers, although their reproductive cycle is prolonged, with one generation developing annually.
Repetitive Feeding: Females of species within the Tabanus (horse fly) and Chrysops (deer fly) genera are infamous for their painful bites, characterized by slashing mouthparts that can break the skin and cause significant distress.
Economic Impact: The presence of horse flies leads to drastic declines in livestock productivity, estimated between 66-100%. Financial losses are projected at around $25 million annually, with control measures aimed at improving livestock performance highlighted through studies indicating an average weight gain improvement of up to 2.3 lbs with proper control practices.
Infectious Disease Vectors: Tabanus species have been linked to serious diseases, including Equine Infectious Anemia and Bovine Leukosis virus, both of which have substantial health and economic implications. These flies prefer to breed in moist organic matter, which also contributes to their life cycle dynamics.
House Flies and Relatives
Morphology: House flies are medium to small in size, with characteristic features that allow for easy identification among domestic flies. Their morphology plays a role in their ecological significance.
Ovipositional Tendency: House flies prefer laying eggs in moist organic materials, which are critical for their larvae's successful development. Some varieties are biting flies, while others are non-biting, with diverse ecological pathways.
Non-Biting Flies
Primary Example: Musca domestica (the common house fly) is a vital mechanical vector, capable of carrying 1 to 6 million bacteria and over 100 pathogens, including Salmonella. This species emphasizes the health risks of flies in domestic settings.
Obligate Intermediate Hosts: Certain species, such as D. habronema, cause significant health issues by leading to the development of stomach worms in animals.
Major Issues: Musca autumnalis (face fly) was introduced from Europe in 1948 and is a significant annoyance to livestock, serving as a vector for Thelazia and contributing to issues such as cattle pink eye. They usually oviposit in fresh feces, indicating the necessity of managing animal waste effectively.
Biting Flies
Examples and Effects:
Hematobia irritans (horn fly) represents the most significant ectoparasite of cattle, causing economic losses through reductions in weight gain, estimated at around $800 million annually across the industry.
Stomoxys calcitrans (stable fly) closely resembles house flies yet is known for inflicting painful bites, resulting in declines in milk production of up to 40-60%, equating to substantial financial losses ($400 million). Proper management requires close attention to environmental conditions conducive to their oviposition in old feces and moist organic material.
Myiasis-Producing Flies
Types: Myiasis is notably produced by blowflies (Calliphoridae) and flesh flies (Sarcophagidae).
Myiasis: This condition features tissue invasion by larval flies, categorized into:
Primary Myiasis: Characterized by the initial invasion of healthy tissues, exemplified by Cochliomyia hominivorax (American Screwworm).
Secondary Myiasis: Involves the invasion of infected or necrotic tissues following a primary infection. This is commonly seen with flies from the Calliphoridae and Sarcophagidae families.
Bot Flies
Characteristics: Bot flies are large, robust in appearance with non-feeding adults; their larvae exhibit parasitic behavior within host tissues and show a high level of host specificity, which can complicate treatment and management strategies.
Examples: This group includes horse bot flies, dog/cat/squirrel bot flies, as well as Dermatobia hominis, known as the human bot fly, primarily found in Latin America. Understanding the life cycles and behaviors of these flies is crucial for effective veterinary interventions.
Treatment and Prevention Strategies
For Bot Flies
Methods: Treatment involves the surgical removal of bot larvae from infected companion animals; proactive measures include the prophylactic use of macrocyclic lactone drugs, particularly in cattle, to avert adverse reactions and manage larvae before they migrate to overwintering sites, which can complicate their removal.
In sheep, nasal bots are usually left untreated, though gastrointestinal bot treatments are more commonly practiced and emphasize the importance of regular veterinary assessments.
For Face/Horn Flies and Stable Flies
Control Measures: Integrated pest management includes utilizing dust bags, insecticide-impregnated ear tags, and practices of rotating insecticides to minimize resistance development. Implementing environmental sanitation, effective feed management practices, and proper insecticide application is crucial to controlling fly populations and preventing associated health problems.
Summary of Fly Pests
Notable Fly Types:
Equine Bot Fly (Gastrophilous): Recognized for their non-feeding adult forms, with larvae residing within the stomach of equines.
Horse Fly (Tabanus): Noteworthy for their vicious blood-feeding behavior, they present considerable problems to livestock.
Bot Flies (Cuterebra): Significantly associated with migrating larvae in various host animals including cats, dogs, and cattle, leading to serious health challenges.
Reportable Diseases
American Screwworm (Cochliomyia hominivorax): This species is notorious for causing severe tissue degradation and has historically led to significant mortality in livestock. Methods for controlling this species are strictly regulated under federal law due to its previous eradication successes in North America, highlighting its potential impact on agriculture and animal health on a broader scale.