Medical Entomology: Family Muscidae

Suborder Cyclorrhapa

• Family Muscidae includes house flies, greater house flies, and stable flies
• 4200 species and 170 genera in the family, with 3 medically important species:
  • Musca domestica (house-fly)
  • Muscina stabulans (greater house-fly)
  • Stomoxy calcitrans (stable-fly)

Musca domestica (house-flies)

• Morphology:
  • Medium size, non-metallic, 6-9mm long
  • Color varies from black to dark grey
  • Four broad black longitudinal stripes on thorax
  • Antennae with 3 segments and a prominent hair (arista) on the distal part
  • Proboscis consists of labella and pseudotrachaea, adapted for sucking fluid
• Life cycle:
  • Lay eggs on decomposing materials (animal manure, poultry dung, carcasses, rubbish dumps, etc.)
  • 75-150 eggs laid, with one female able to oviposit 5-10 times during its life
  • Eggs are creamy white, banana-shaped, and hatch after 10-16 hours
  • Larva (maggot) has cylindrical body, with hooks and cephalopharyngeal skeleton in the head
  • Larva feed on decomposing organic material and measure 8-14mm long before becoming a pupa
  • Pupa is barrel-shaped and adult fly emerges after 3-5 days
• Medical importance:
  • Can transmit pathogens to humans through contaminated feet, body hairs, and mouthparts
  • Can transmit over 100 pathogens, including viruses, bacteria, protozoans, and helminths

Control of house-flies

• Divided into three categories: physical and mechanical control, environmental sanitation, and insecticidal control
• Physical and mechanical control:
  • Installing screens on windows and other openings
  • Using air currents or fans to keep flies from entering
  • Using UV light traps
  • Using sticky traps
• Environmental sanitation:
  • Minimizing breeding sites by tightly closing garbage and regularly collecting it
  • Burning or burying garbage if not collected
• Insecticidal control:
  • Using larvicides, adulticides, residual sprays, insecticidal cords, and toxic baits
  • Examples of insecticides used: malathion, pirimiphos-methyl, fenchlorophos, permethrin, cypermethrin, and deltamethrin

Muscina stabulans (greater house fly)

• Distributed worldwide
• Slightly larger than Musca domestica (7-10mm long)
• Wing venation slightly different from house fly
• Posterior spiracles of the maggot are circular
• Late larval stage (maggots) are predaceous and feed on other fly larvae
• Life cycle and medical importance similar to Musca domestica

Stomoxy calcitrans (stable fly)

• Distributed worldwide
• Also known as biting-house flies or dog flies
• Adults have four longitudinal stripes on thorax
• Forward-projecting, rigid proboscis
• Wing venation similar to Muscina stabulans
• Both male and female stable flies feed on blood
• Mainly exophagic and can carry Dermatobia hominis eggs, a myiasis-producing fly
• Control methods similar to house flies

Family Calliphoridae

• Circular-seamed flies with aristate antennae
• Medically important mainly due to its capability in producing myiasis
• Two groups of calliphorids: non-metallic and metallic flies

Cordylobia anthropophaga (tumbu or mango fly)

• Non-metallic fly
• Distributed in Ethiopia, west, east, and south of Africa
• Large flies (9-12mm long), dull to yellowish brown in color
• Myiasis causing fly
• Female lays 100-300 banana-shaped eggs in feces/urine contaminated areas
• Larva can live 9-15 days without hosts
• Larva attach to host or to clothing laid on ground
• Larva burrow into skin, posterior spiracles exposed for breathing
• Matured after 8-12 days and drop to the ground to pupate
• Become adult after 8-15 days

Medical importance of Cordylobia anthropophaga

• Larva cause boil-like (furuncular) swellings on the body
• Infested site becomes sore, inflamed, hard, and exude fluids
• Infestation usually with few larvae and up to 60 larvae
• The larva head and body are in tissues
• The spiracles are exposed for breathing

Control of Cordylobia anthropophaga

• Removal of larvae by covering the site with liquid paraffin or Vaseline
• Larva will emerge from the site to breathe, then it can be removed with forceps or by pressing
• To prevent infection, avoid drying clothes on the ground where the larva can attach
• Iron clothes to ensure no living larva on clothes

Metallic flies

• Cochliomyia hominivorax (New world screwworm)
• Chrysomya bezziana (Old world screwworm)
• Lucilia spp. (greenbottle flies)
• Calliphora spp. (bluebottle flies)

Cochliomyia hominivorax

• Distributed in south USA, Mexico, Central America, Caribbeans, and north part of South America
• Eradication program has successfully eradicated Cochliomyia from USA, Mexico, the Virgin Island, Curacao, and Central America (except Panama)
• Obligatory parasite of living tissues (must have host to survive)

Chrysomya bezziana

• Distributed in tropical Africa, west coast of Persian Gulf, Indian subcontinent, Southeast Asia, and Papua New Guinea
• Obligatory parasite of living tissues (must have host to survive)### Life Cycle of Flies
• After 2-4 days, larva reaches 3rd instars
• After 4-10 days, larva matures and leaves the wound to drop to the ground and become a pupa
• Adult emerges after 7-10 days (warm weather) or weeks to months (cooler climate)

Screwworm Flies

• Family Calliphoridae
• Cochliomyia hominivorax (New World screwworm)
• Chrysomya bezziana (Old World screwworm)
• Both cause obligatory myiasis
• Larva has hooks on the mouthpart to hold onto host tissues

Medical Importance of Screwworms

• Cause myiasis, which leads to damage, disfigurement, and excruciating pain
• Infestation can occur in various parts of the body, including the face, causing impairment of speech
• Infestation in the nasal area can affect the mouth palate

Treatment of Myiasis

• Must be treated immediately due to rapid development of larvae
• Manual removal of maggots or larvae
• Irrigation of wound sites with ethanol or chloroform mixed with vegetable oil
• Ivermectin can be used to kill larvae
• Surgery may be necessary for deeply embedded larvae

Control and Prevention of Screwworms

• Use of topical repellents and proper clothing for personal protection
• Maintain self-hygiene
• Create barriers, such as house screening, to prevent flies from entering homes
• Adopting housefly control methods is recommended
• Eradicating screwworm flies using the sterile male technique has been successful in the USA and Mexico

Metallic Flies (Blowflies)

• Family Calliphoridae
• Cochliomyia spp. (New World screwworms)
• Chrysomya spp. (Old World screwworms)
• Lucilia spp. (greenbottle flies)
• Calliphora spp. (bluebottle flies)

Lucilia spp. (Greenbottle Flies)

• Adult are metallic or coppery green in color
• Size: ~ 10mm long
• Less bristly than bluebottle flies
• Lucilia serricata is the most common species, occurring worldwide

Calliphora spp. (Bluebottle Flies)

• Adult are dull metallic bluish or bluish black in color
• Robust flies with a size of ~ 8-14mm long
• Thorax has a more well-developed bristle than Lucilia spp.
• Abdomen is more shiny than thorax

Medical Importance of Lucilia spp. and Calliphora spp.

• Both are associated with facultative myiasis
• Attracted to foul-smelling wounds and ulcerations
• Used in maggot therapy

Oestridae (Bot Flies)

• Subfamily Cuterebrinae contains 57 species that cause obligatory myiasis in animals such as rodents, monkeys, and livestock
• Dermatobia hominis causes myiasis in humans
• Life cycle of Dermatobia hominis

Medical Importance of Oestridae

• Cause myiasis, which induces an inflammatory response
• Characteristic lesion is a painful and swollen skin known as cutaneous myiasis
• Larva can often be seen at the center of the pore
• Patients may report a sense of movement within the lesion

Treatment of Myiasis Caused by Oestridae

• Surgical removal of the larva is the most common mode of treatment
• Manual extraction can be performed if the larva is visible
• Petroleum jelly can be used to induce hypoxia in the larva, causing it to migrate to the surface

Prevention of Myiasis Caused by Oestridae

• Limit exposure to flies, especially in tropical areas
• Wear clothing that covers the extremities
• Use mosquito netting when sleeping
• Use insect repellent on exposed skin

Sarcophagidae (Flesh Flies)

• Only two genera, Sarcophaga and Wohlfahrtia, are medically important
• Cause myiasis and act as mechanical vectors for pathogens
• Distributed worldwide

Sarcophaga spp.

• Large greyish flies with hairy and non-metallic appearance
• Thorax has 3 black longitudinal stripes
• Abdomen has a chequer-board appearance
• Female is larviparous, depositing ~ 30-60 larvae per batch
• Larvae are laid on carcasses, feces, rotting food, human, and wounds

Wohlfahrtia spp.

• Adults are hairy flies with a smaller size (8-15mm) than Sarcophaga spp.
• Appearance is greyish with prominent black lines on the thorax
• Abdomen has roundish lateral spots and triangular shape markings along the midline
• Adult female is larviparous, depositing 120-170 larvae in several batches

Medical Importance of Sarcophagidae

• Cause myiasis, which leads to discomfort and pain
• Species of Sarcophaga and Wohlfahrtia are distributed in the Americas, Europe, Africa, and Asia

Myiasis

• Invasion of organs and tissues of living humans or other vertebrate animals by fly larvae
• Types of myiasis: accidental, obligatory, and facultative
• Treatment of myiasis: occlusive and suffocation methods, surgery, medication
• Prevention of myiasis: use of insect repellent, maintenance of high levels of hygiene, ironing of clothes, and covering wounds### Glossina sp: The Life Cycle
• After mating and taking a blood meal, a single egg completes maturation in one of the two ovaries and passes down the common oviduct into the uterus, where it is fertilized by sperm from the paired spermathecae.
• The egg hatches within the uterus after 3-4 days into a larva, which receives all its nutrients from secretions from milk glands.
• The larval development takes about 9 days, during which the larva goes through three instars.
• The female selects shaded sites for larviposition, and about 15 minutes after the 3rd instar larval skin contracts and hardens to form a puparium, in which the larva pupates.
• The puparial period is about 4-5 weeks.

Adult Behaviour

• Adult flies feed depending on host availability, taking blood meals every 2-3 days in ideal conditions or every 10 days in cool, humid conditions.
• Feeding is restricted during the daytime, and vision, as well as olfactory cues emanating from host breath and urine, are important in host location.
• Adult flies are particularly attracted to dark moving objects.

Classification and Distribution

• There are three groups of Glossina sp: Fusca (forest flies), Morsitans (savannah flies), and Palpalis (riverine and forest flies).
• Fusca (forest flies) have 13 species, are 10.5-15mm long, and rarely feed on people or transmit sleeping sickness.
• Morsitans (savannah flies) have 5 species, are 7.5-11mm long, and include vectors of sleeping sickness such as G. morsitans, G. pallidipes, and G. swynnertoni.
• Palpalis (riverine and forest flies) have 9 species, are about 6.5mm long, and include vectors of sleeping sickness such as G. palpalis, G. fuscipes, and G. tachinoides.

Transmission of Trypanosomiasis

• There are approximately 30,000 new cases of trypanosomiasis per year, with an estimated 400,000 new cases per year and 55,000 deaths.
• The disease occurs in 36 African countries, with a patchy distribution.
• There are two subspecies of trypanosomes causing human sleeping sickness: T. brucei gambiense and T. brucei rhodesiense (zoonosis), which are morphologically undistinguishable but different in clinical symptoms.
• Important vectors of trypanosomiasis include G. palpalis, G. fuscipes, G. tachinoides, G. morsitans, and G. pallidipes.

Control of Tsetse Flies

• Control methods target adult flies.
• Culling of reservoir hosts, such as bovids, wild pigs, reptiles, and birds, is one method.
• Destruction of surrounding vegetation is another method.
• Insecticidal control involves spraying insecticides such as endosulfan, permethrin, deltamethrin, and cypermethrin onto vegetation, which remains effective for about 2-3 months.
• ULV aerial insecticidal spraying requires re-spraying 5-6 times at 12-18-day intervals.
• Spraying or dipping cattle with pyrethroid insecticides reduces the number of human trypanosomiasis cases.

Family Tabanidae (Horse Flies)

• Tabanidae is a family of medium to large biting flies, comprising 4300 species and subspecies, and 133 genera.
• Important genera include Tabanus (some known as greenhead), Haematopota (clegs and stout), and Chrysops (deer flies).
• Tabanidae have been incriminated in the spread of anthrax and tularaemia and might be involved in the transmission of Lyme disease.

Chrysops sp (Deer Flies)

• Chrysops are robust and heavily built, medium-sized flies (6-12mm).
• They have iridescent eyes, commonly with spots of red, green, or purple.
• Their wings are partially held over the abdomen in an open scissor-like fashion, with one or more brownish transverse bands.
• The abdomen is blackish with orange or yellow patches or bands.
• Antennae are the best feature to differentiate Chrysops from other Tabanids.
• Female Tabanidae have stout and adapted mouthparts for biting, which hang down from the head.

Life Cycle of Chrysops sp

• Eggs are laid in a single large mass (lozenge-shaped pattern) on the underside of objects, firmly glued in an upright position.
• Eggs hatch after 4-14 days, and the wriggling larvae drop down onto the underlying mud or water.
• Larvae are cylindrical, creamy white, brown, or greenish in colour, and have darkish pigmentation near the borders of the segments.
• Chrysops larvae are mainly scavengers, feeding on detritus and organic matter.
• Larval development takes about 1-2 years, with 10-16 instars.
• Pupae are partially buried in mud or soil, in an upright position, with a distinctively curved body and large ear-shaped spiracles on the cephalothorax.

Medically Important Species in Tabanidae Family

• Chrysops sp is the only genus in Tabanidae family that transmits Loa loa nematode to humans when blood feeding.
• C. silaceus and C. dimidiatus are the main vectors of Loa loa in humans.
• Other medically important species include C. distinctipennis, C. longicornis, C. centurionis, and C. langi.

Geographical Distribution of Loasis in Africa

• Loasis is present in many African countries, with a patchy distribution.

Control of Horse Flies

• Control of larvae is difficult due to unknown breeding sites.
• Practical measures to control tabanid flies include efficient drainage of larval habitats, local control using attractant traps, and personal protection using insect repellents.

Learn about the morphology, life cycle, and medical importance of the Family Muscidae, including house flies, greater house flies, and stable flies. Understand control methods and their significance in medical entomology.