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• Fundamentals of Human Body II
• Basic Infection, Infection Control and Vectors of Disease Transmission
• Main topic: Arthropoda

Arthropoda and Parasitology

• Parasitology includes the study of Helminths, Protozoa, and Arthropoda.
• Arthropoda are further divided into Insecta, Arachnida, and Crustacea classes.

Classification of Arthropods

• Medical Entomology studies arthropods that cause or transmit diseases to humans.
• Arthropods are invertebrate animals with articulated body parts.
• Three key classes: Insecta, Arachnida (Acarina), and Crustacea.
• Insects have 3 pairs of legs, and a body divided into the head, thorax, and abdomen.
• Arachnids have 4 pairs of legs, and a body that isn't well differentiated.
• Crustaceans have a cephalothorax and a segmented abdomen.

Key Distinctions Between Classes

• Insecta: Body has a head, thorax, and abdomen; 1 pair of antennae; 1 or 2 pairs of wings (may be absent); e.g., mosquitoes, flies, fleas, lice, and bugs.
• Arachnida: Body has a cephalothorax and abdomen; no antennae; no wings; e.g., ticks, mites, and scorpions
• Crustacea: Body has a cephalothorax and abdomen; 2 pairs of antennae; no wings; e.g., Cyclops, crabs, and crayfish.

Arthropods of Medical Importance

• Insecta: Mosquitoes (Anopheles, Culex), flies (houseflies, sandflies, Tsetse, blackflies), human lice, fleas, and Reduviid bugs.
• Arachnida: Ticks (hard and soft ticks) and mites (Trombiculid and itch mites).
• Crustacea: Cyclops.

Metamorphosis Types in Arthropods

• Complete Metamorphosis (Holometabolous): Developmental stages are completely different from the adult (egg → larva → pupa → adult), seen in mosquitoes.
• Incomplete Metamorphosis (Hemimetabolous): The immature nymph stage resembles the adult but is sexually immature (egg → nymph → adult), seen in lice.

Medical Importance of Arthropods

• Arthropods impact human health by causing diseases and discomfort, transmitting disease agents, and inducing entomophobia.
• Causing Diseases::
  • Envenomization occurs through inoculation of poisons (e.g., ticks, spiders, scorpions).
  • Tissue invasion (e.g., scabies, myiasis).
  • Dermatitis and allergic skin lesions (e.g., mosquitoes, fleas, lice, mites).
  • Nuisance, annoyance, and disturbance from painful bites (e.g., bugs).
• Transmitting disease: act as vectors that transmit diseases to humans, causing vector-borne illnesses.
• Entomophobia: exaggerated fear of insects or arthropods may lead to nervous disorders; for example, cockroaches and scorpions.
• Examples of venomous arthropods are wasps, bees, spiders, centipedes, and scorpions.

Arthropod-Borne Diseases

• Mosquitoes transmit malaria, filaria, viral encephalitis, and viral fevers like Dengue and West Nile.
• Houseflies transmit typhoid fever, diarrhea, dysentery, cholera, amebiasis, and helminthic infestations.
• Sandflies transmit Kala-azar, Oriental sore, and Sandfly fever.
• Tsetse flies transmit sleeping sickness.
• Lice transmit epidemic typhus and relapsing fever.
• Rat fleas transmit bubonic plague and endemic typhus.
• Hard ticks transmit tick typhus, viral encephalitis, and tularemia.
• Soft ticks transmit Q fever and relapsing fever.
• Mites transmit scrub typhus and scabies.
• Cyclops transmit Guinea-worm disease.

Transmission of Arthropod-Borne Diseases

• Direct Contact: occurs through close contact, for example, scabies and pediculosis.
• Mechanical Transmission: disease agents are mechanically transmitted by arthropods, such as food poisoning by houseflies.
  • Direct: inoculation during insect feeding (e.g., Stomoxys Trypanosomes). -Indirect: contamination by organisms carried on the hairs or body of non-biting arthropods.
• Biological Transmission: disease agents multiply or develop within the arthropod:
  • PROPAGATIVE: number of organisms increases inside the vector (e.g., plague in fleas).
  • CYCLO-PROPAGATIVE: both number and morphology change (e.g., malaria parasites in female Anopheles).
  • CYCLO-DEVELOPMENTAL: only morphology changes inside the vector (e.g., Wuchereria bancrofti in female Culex).
  • TRANS-OVARIAN: Organism passes vertically to offspring (e.g. Zika Virus in female Aedes)

Flies Classification

• Class: Insecta (head, thorax, abdomen, 3 pairs of legs)
• Order: Diptera (having 1 or 2 pairs of wings)
• Four main families: Muscidae, Calliphoridae, Sarcophagidae, and Oestridae (Gastrophilus).

Scientific Classification of Musca Domestica

• Kingdom: Animalia
• Phylum: Arthropod
• Class: Insecta
• Order: Diptera
• Family: Muscidae
• Genus: Musca
• Species: Musca domestica

Family Muscidae

• Musca domestica (House fly): cosmopolitan distribution, 7-10 mm size, grey color; sucking retractile proboscis; 4 longitudinal dark stripes on the thorax, 4 segments, median dark stripes on its abdomen.
• Stomoxys calcitrans (Stable fly) cosmopolitan distribution, 7-10 mm size, grey color, piercing and sucking rigid non-retractile proboscis. 4 longitudinal dark stripes on the thorax, 4 segments with dark round spots on the abdomen.
• Glossina palpalis, Glossina morsitans (Tsetse fly): west and east Africa; 10-15 mm size; Black or Brown color; Piercing and sucking rigid non-retractile proboscis. 8 segments with transverse bands on its abdomen

Fly Anatomy and Adaptations

• Biting flies have piercing and sucking proboscis (Stomoxys and Glossina).
• Non-biting flies have proboscis adapted for sucking only.

Transmission and Breeding

• Musca domestica carries out indirect mechanical transmission in the form of parasitic, viral, and bacterial diseases and undergoes accidental myiasis.
• Stomoxys calcitrans carries out direct mechanical transmission in the form of animal trypanosomes.
• Glossina palpalis and Glossina morsitans carry out Cyclopropagative transmission in the form of African trypanosomes. Breeding locations:
• Musca domestica favors garbage and manure.
• Stomoxys calcitrans favors horse dung.
• Glossina palpalis and Glossina morsitans favor soil, shaded water and open land.

Medical Importance by Fly Type

• Musca domestica (House fly):
  • It is a vector for accidental myiasis.
  • It is a factor for indirect mechanical transmission of microorganisms in typhoids shingella, hepatitis.
  • Vector for parasitic infections.
• Stomoxys calcitrans (Stable fly):
  • Direct mechanical transmission of blood parasites causing African sleeping and Leishmaniasis.
  • Vector for accidental myiasis.
  • It causes painful bites.
• Glossina species (Tsetse fly):
  • Vectors for intermediate hosts of African sleeping sickness.
  • Glossina transmits Gambian sleeping sickness and Rhodesian sleeping sickness.

Life Cycle and Pathogen Transmission

• Flies undergo complete metamorphosis (egg → larva → pupa → adult).
• Musca Domestica carries pathogens on their body parts, contaminating food and causing food-borne illnesses.

Control of Houseflies

• Health education on garbage disposal.
• Control measures against adult flies include wire screens, fly nets, insecticides, and UV light traps.
• Control measures against breeding: eliminate breeding places, sanitary disposal of excreta, spraying insecticides, and using sterilized males

Calliphoridae and Sarcophagidae

• Calliphoridae (Calliphora/Lucilia): metallic flies that are slightly larger than Musca, are blue/green and exhibit a sucking nature.
• Sarcophagidae (Sarcophaga/Wohlfahrtia): flesh flies that are larger than Musca, are Grey and exhibit a sucking nature.

Anatomy and Lifecycle

• Calliphoridae feature a Metallic thorax, a shining metallic abdomen.
• Sarcophagidae exhibit a thorax with longitudinal stripes, a Chess Board/Spotted abdomen.
• As larvae, they undergo triangular with complete peritreme on calliphoridae species.

Medical importance of Calliphoridae and Sarcophagidae

• Calliphoridae and Sarcophagidae undergo semi-specific myiasis.
• The flies lay their eggs or larvae either on decaying animal or plant matter, but more commonly on animals such as wounds.
• Unlike regular flies, the flies are able to perform Facultative Sarcobiots.

Myiasis

• An infection resulting from an invasion of bodily tissue from larval flies.
• Classified based on biological larval behavior and the clinical kind of tissues that are infected.
• Obligatory species are solely living tissue parasites.
• A host can be infected via tissue, aural, opthalmitic and several other ways.

Specific/Obligatory Myiasis

• Specific species of flies can use their hosts to feed even if the tissues are viable, as well as obligatory species.
• Usually caused by species such as Oestrus, Wohlfahrtia, and Cordylobia.

Semi/Facultative Myiasis

• Semi species of flies are still able to infect tissues due to an abundance of their Larvae, but may eventually die if viable species are not found.
• Usually done by faculative flies such as Sarcophaga

Accidental Myiasis

• Caused by accidental swallowing of flies with live larvae.
• Likely contributed to species such as Musca, Stomoxys, and Fannia.

Clinical myiasis

Usually they will pass in the stomach due to a non favorable environment. Larvae may accidentally remain in the intestine through oral-anal openings.

• Signes may be Nausea and diarrhea; living larvae can be found in bodily stool.
• Flies such as e.g. Calliphora, Lucilia, Musca and Sarcophaga., and Gastrophilus have been attributed to Gastric and Intestinal myiasis.

Urogenital Myiasis

• Flies are able to infect or deposit near the urethral-genital openings.
• Usually occurs if the host defecates near flies, or during the sleep periods.
• Can cause great pain and discomfort; species include Fannia flies.

Dermal Myiasis

• Can be caused by Hypoderma and result in creepy eruptions if larvae is accidently moved to the skin.
• Dermatobia can also cause furuncular issues due to injuries.
• Wohlfahrtia, Calliphora, Sarcophaga and Chrysomia can also contribute if left to be severely infected.

Orbital & Atrial Myiasis

• Orbital: Infection of the eyes can cause loss of vision and requires surgical intervention with antiseptics.
• Atrial: Infections near the ears and nearby sinus regions; again can be fatal but requires surgical assistance.

Diagnosis

• Diagnostic is usually accomplished through isolation such as looking in discharge.
• Shapes such as paterns of the posterior spiracles may also be used to identify the types of larvae in a host's system.

Treatment

• Intestinal species of flies can usually be removed via purgatation.
• Species near open areas can usually be removed through surgical intervention as well as antiseptcs and antibiotics
• Ivermectin tablets may also be used to prevent further infections.

Preventions

• Preventative practices include proper hygiene, particularly in vulnerable populations like youths and the elderly.
• Sanitation and wound coverage may also prevent furthers infection from occurring.
• Sterilization is also a potential option to eradicate certain species of flies in certain areas.