[MDENTOM] Lecture 1-6

• Medical Entomology is a scientific discipline that studies the impact of arthropods and arthropod-borne diseases on public and human health
• Class Insecta:

  • Order Blattaria: cockroaches
  • Order Phthiraptera: lice
  • Order Hemiptera: true bugs
  • Order Coleoptera: beetles
  • Order Siphonaptera: fleas
  • Order Diptera: mosquitos and flies
  • Order Hymenoptera: ants, wasps, & bees
  • Order Lepidoptera: caterpillar, butterflies, & moths
• Class Arachnida:

  • Order Scorpionida: scorpions
  • Order Araneae: spiders
  • Order Acari: mites & ticks
• Arthropod Anatomy:

  • Characteristics for arthropods under this phylum:
  • Bilaterally symmetrical
  • Segmented bodies/joint appendages
  • Exoskeleton composed of chitin
  • Have/Do not have antennae or wings
  • Morphological parts:
  • Class Insecta:
  • Bilaterally symmetrical: YES
  • Segmented bodies: 3-body regions (Head, Thorax, Abdomen)
  • Exoskeleton: YES
  • Wings: Present
  • Antennae: Present
  • Class Arachnida:
  • Bilaterally symmetrical: YES
  • Segmented bodies: 2-body regions (Cephalothorax, Abdomen)
• • Exoskeleton: YES
  • Wings: Absent
  • Antennae: Pedipalp
• Mouthparts of Insects:

  • Labrum: front lip
  • Mandible: pair of jaws for crushing or grinding
  • Hypopharynx: tongue-like process
  • Maxilla: paired appendages with Cardo, Stipes, Gale, and Lacinia
  • Labium: back lip with Postmentum and Prementum divided into glossae and paraglossae
• Chewing Mouthparts:

  • Found in cockroaches and beetles
  • Function: feeds directly on host tissues, destroys/minces host tissue
• Piercing & Sucking Mouthparts:

  • Found in medically important insects like mosquitoes
  • Mosquitoes have a long needle-like structure for piercing skin
  • Examples: Solenophages in mosquitoes, Telmophages in certain flies
  • Found in mosquitoes and flies
• Piercing & Sucking Mouthparts (cont.):

  • Found in fleas with stylets for piercing skin
  • Found in true bugs with styliform maxillae and mandibles within a sheath-like labium
  • Found in lice with a highly modified labrum forming a snout-like haustellum
• Mouthparts of Arachnids:

  • Arachnids have chelicerae for mouthparts
  • Mites have modified mouthparts for piercing, anchoring, and drawing blood
  • Ticks have similar mouthparts to mites, anchoring to host and causing pain when removed
• Leg Parts:

  • Typical insect leg: Coxa, Trochanter, Femur, Tibia, Tarsus
  • Fleas have modified legs for jumping remarkable distances
  • Lice have legs adapted for grasping host hair, like pubic lice or head lice
• Sensory parts found in insects and arachnids that are medically important include: antennae, large eyes, sensilium, trichobothria, and Haller's organ
• Antennae in blood-feeding insects have receptors that detect chemicals emanating from the skin and exhaled breath of potential hosts
• Large eyes in certain insects like Dipterans are used for light perception and vision to locate or orient towards potential host animals
• Sensilium in fleas is a sensory organ specialized for detecting host-associated cues such as vibrations and temperature gradients
• Trichobothria are specialized sensory setae found in the tarsus or last portion/segment of the leg for detecting airborne and substrate vibrations and tactile cues
• Haller's organ in mites and ticks is a complex sensory structure located on the dorsal aspect of the tarsus of the first pair of legs, detecting temperature, air movements, host odors, and other cues to know they are at the host and can feed on its blood
• Problems caused by arthropods include: annoyance, allergic reactions, invasion of host tissues, fear of arthropods, delusional disorders, food contaminants, and toxins and venom
• Annoyance is caused by arthropods pestering, biting, hovering around, flying into ears/eyes/nose, and contaminating food
• Allergic reactions from arthropod bites and stings can cause localized skin allergies and respiratory allergies
• Invasion of host tissues by immature arthropods like mosquitoes or flies allows them to exploit different host niches and grow by feeding on the host's blood
• Fear of arthropods can lead to psychological effects like entomophobia, arachnophobia, and acarophobia
• Delusional disorders may cause people to believe they are being bitten by parasites, leading to conditions like Ekbom syndrome, Elliot disease, and Morgellons disease
• Food contaminants from arthropods can spoil food, carry pathogens causing gastrointestinal diseases, and accidentally be ingested with food
• Certain arthropods produce toxins and venom, with toxins being fat-soluble and water-repellent, and venom being a mixture of compounds injected into animal tissues via specialized morphological structures like stings or modified spines
• Examples of arthropods that produce venom include bees, hornets, wasps, and ants, with bees having a barb that can cause them to die after stinging
• Nature of toxins and venoms vary, with ants secreting formic/acetic acid, blister beetles having cantharidin, honey bees containing melittin, and funnelweb spiders having atracotoxin
• Toxins are typically fat-soluble and water-repellent (hydrophobic), aiding in penetrating the integument on contact
• Venom is water-soluble and consists of complex mixtures with other chemicals that facilitate the spread and effectiveness of toxic components once they penetrate the integument
• Yellow jackets/hornets:

  • Kinins hemolyze blood and cause pain
  • Phospholipase is an enzyme that causes allergic reactions
  • Mastoparans are enzymes that destroy mast cells
• Blister beetles:

  • Melittin inhibits protein kinases and ion transport across the cell membrane
  • Cardiotoxic Phospholipase A creates lung congestion and allergic reactions
• Urticating caterpillars have urticates/hair that contain certain enzymes:

  • Proteolytic enzymes break down fibrinogen in blood causing hemorrhaging
  • Thaumetopoein causes dermatitis, rash, conjunctivitis, and respiratory distress
• Scorpions:

  • Scyllatoxin is a neurotoxin that blocks Ca-activated K channels
  • Agitoxin blocks K channels
• Black widow spiders:

  • a-Latrotoxin is a neurotoxin that acts on presynaptic nerve terminals, causing muscle cramps and paralysis
• Brown recluse spider:

  • Sphingomyelinase D breaks down sphingomyelin in plasma membranes, causing cell destruction and necrotic skin lesions
• Arthropod-borne diseases involve parasites/pathogens that can develop and multiply within both vertebrate host and vector tissues
• Intrinsic incubation is when the pathogen is infecting inside the insect, while extrinsic incubation is when the pathogen is infecting outside the insect
• Three families considered as pest or medically-important in the Order Blattodea are:

  • Family Blaberidae
  • Family Blattelidae
  • Family Blattidae
• Common cockroach species include:

  • Periplaneta australasiae (Australian cockroach)
  • Blatella germanica (German cockroach)
  • Blatella asahinai (Asian cockroach)
• Characteristics of a primary vertebrate host:

  • Accessibility: must be abundant and available to become infected
  • Susceptibility: must be susceptible to infection with a parasite and permissive to its development