Med Ent Exam 2 Study guide

• Homopterans have the same wings

• Homopterans do not only eat plant juices

• Heteropterans have different wing pairs

• Blood-feeding heteropterans spread pathogens

Kissing Bugs (Reduviidae)

• Triatomines are kissing bugs
• They are obligate blood feeders
• Transmit Chagas (Trypanosoma cruzi)
• Hemimetabolous development with 5 nymphal instars, no larval stage
• Single female lays ~200 eggs; peaks at 1000 in lifetime
• Can undergo arrested development or non-mammalian hibernation
• The 3 habitat groups are sylvatic (nests and burrows), peri-domestic (feeds on domestic animals) and domestic (human habitats)
• At least one substance in saliva has analgesic properties
• Some types of saliva can cause allergic reactions

Chagas Disease (American Trypanosomiasis)

• Protozoan parasite Trypanosoma cruzi causes the disease
• Transmitted by triatomine bugs
• Acute and chronic phases are lifelong if untreated
• Debilitating or life-threatening problems develop in 20-30% of cases
• Lifecycle
  • Bug feeds, metacyclic trypomastigotes in bug feces enter wound
  • Metacyclic trypomastigotes enter various cells and transform to amastigotes
  • Amastigotes multiply in infected tissues
  • Intracellular amastigotes transform into trypomastigotes and burst out of cells into bloodstream, cycle repeats
  • Triatomine bug takes blood meal, ingesting trypomastigotes
  • Trypomastigotes become epimastigotes in bug midgut and multiply
  • Epimastigotes become metacyclic trypomastigotes in hindgut, cycle then repeats
• Triatoma infestans is most responsible for transmission to humans in South America
• Development in the triatomine gut lumen takes 6-15 days
• Bacteria essential for the development of T. cruzi is passed down, but it does NOT pass to offspring
• Identified via blood smear
• Most serious parasitic disease in South America

Chagas: Prevention and Control

• Spray insecticides in endemic areas
• Screen blood donations for Chagas
• Early detection and treatment are important
• Drugs for acute cases include nifurtimox and benznidazole, but have high odds of side effects

Bed Bugs (Cimicidae)

• Cimicids
• Obligate blood feeders
• Not a known vector
• Cimex lectularius
• Hemimetabolous development (5 nymphal instars, no larval stage)
• Not proven to be vectors, but infected with 20+ human pathogens
• Allergic reactions can develop due to saliva
• The signs of bed bugs are bites, blood spots, shed skins, dead and alive bed bugs, or rust spots

Bed Bugs: Control strategies

• Education
• Fumigation
• Pest control
• Proper hygiene and cleaning

Beetles (Coleoptera)

• Largest order of insects
• Holometabolous
• Hardened outer wings
• Cause respiratory allergies
• Canthariasis is tissue invaded by beetle larvae
• Scarabiasis is tissue invaded by adult beetles
• Cantharidin secreted from hemolymph is poisonous to humans

Fleas (Siphonaptera)

• Adults are exclusive bloodsuckers
• Hind legs adapted for jumping (can be attached or mobile)
• Pulex irritans is a human flea
• Xenopsylla cheopis is an oriental rat flea
• Sensillum detects vibrations and temperature gradients
• Male genitalia have paired claspers to secure female while mating
• Female stores sperm in spermatheca
• Mouthparts pierce (stylets) and suck (laciniae)
• Many imbibe more blood than they can hold, excrete blood-rich feces
  • Rickettsia typhi (murine typhus) is voided in feces
• Holometabolous
• Xenopsylla cheopis (oriental rat flea) is the primary urban plague vector
• Pulex irritans (human flea) is an occasional epidemic plague vector
• Nosopsyllus fasciatus (northern rat flea) is an epidemic plague, murine typhus
• Diamanus montanus is an endemic plague vector in west US
• Tiny purple spots characterize the bites and is marked by slightly swollen skin; women receive more bites than men

Fleas: Importance

• Cause irritation and discomfort
• Serves as vector of murine typhus and bubonic plague
• Considered a primary pest of domestic animals

Cestodes

• Dog tapeworm
• Flea larvae ingest tapeworm eggs found in feces, fleas mature into adults
  • Host ingests mature flea containing tapeworm

Murine Typhus: Causation and Vectors

• Pathogen: Rickettsia typhi
• Vector: Xenopsylla cheopis
• Reservoir: roof rat and Norway rat
• Transmitted by flea feces

Plague: Causation and Vectors

• Pathogen: gram-negative coccobacillus
• Vector: Xenopsylla cheopis
• Reservoir: roof rat
• The flea transmits through regurgitation of blood meal or crushing
• Treatable with antibiotics
• 90% mortality rate if the disease develops into pneumonic stage

Urban Plague: Causation and Vectors

• Pathogen: Yersinia pestis
• Vector: Xenopsylla cheopis
• Reservoir: domestic rodents, especially roof rats

Rural Plague: Causation and Vectors

• Pathogen: Yersinia pestis
• Vector: numerous flea species
• Reservoir: a bunch

Flea Control

• Sanitation
• Chemical insecticides
• Insect growth regulators

Flies (Diptera)

• Most species-rich, ecologically exploitative order of insects

Culicidology

• Malaria, filariasis, leishmaniasis, onchocerciasis affect half a billion, 3.5 billion at risk
• Group includes mosquitoes, black flies, biting midges, annoying
• Nematocera (long antennae) and Brachycera (short antennae) are the two suborders
• Diptera exhibit holometabolous development
• Most are oviparous
• Some are larviparous or pupiparous
• Most nematocera have 4 larval instars
• Can be anautogenous or autogenous
• For host feeding, they can detect CO2 emissions
• K-strategists invest heavily in few offspring
• R-strategists invest little in many offspring

Moth Flies (Psychodinae)

• Non-biting; no role in disease transmission

Sand Flies (Phlebotominae)

• Transmit two protozoan diseases
• Visceral and cutaneous leishmaniasis
• Phlebotomus in the Old World; Lutzomyia in the Americas
• Lutzomyia longipalpis and Phlebotomus papatasi have undergone whole genome sequencing - Medically important

Sand Flies: Identification and Classification Methods

• Electron micrography
• Isoenzyme electrophoresis
• Cuticular hydrocarbon
• Molecular hybridization
• Nucleotide sequencing and oligonucleotide mapping; used for identification

Sand Flies: Morphology

• Elongate, dark brown and shiny eggs: 400 micrometers
• Mature larvae are whitish with dark head; up to 5 mm long
• Adults are hairy and grayish-brown; less than 5mm long

Sand Flies: Life History

• Humid terrestrial habitats
• Autogenous or anautogenous
• Eggs hatch in 20 days
• Larvae: 30-60 days
• Pupal: 7-8 days
• Adult: 2-6 weeks

Sand Flies: Epidemiology and Risk

• Leishmaniasis is most neglected disease, limited investment in Dx, Tx and Control
• 500,000 new visceral leishmaniasis cases each year
  • 90% in India, Bangladesh, Nepal, Sudan, Ethiopia, Brazil
• 1.5 million new cutaneous leishmaniasis cases each year
  • 90% in Afghanistan, Algeria, Iran, Saudi Arabia, Syria, Brazil, Colombia, Peru, Bolivia
• Climate change expands range of disease/vectors
• Genus Leishmania causes the disease
• Common form is cutaneous, appears as painless ulcers
• Visceral: a febrile illness, with weight loss, enlargement of spleen/liver, decreased blood cell production
  • Almost always fatal without treatment
• Rare mucocutaneous: develops months/years after cutaneous ulcer, affecting mucous tissue

Parasite Infection Life Stages through Sandflies

• Sandfly takes blood meal, injects promastigote stage into skin
• Macrophages phagocytize promastigotes
• Promastigotes turn into amastigotes inside macrophages
• Infected cells burst after amastigotes multiply, parasite released
• Sandfly takes blood meal, ingests infected macrophages
• Amastigotes transform to promastigote stage in sandfly midgut after parasitized cell ingested
• Midgut divides and then migrates towards the proboscis

Sand Fly Diagnosis and Treatment

• Diagnosis: blood smear or tissue/bone marrow biopsy
• Cutaneous leishmaniasis treatment
  • Lesions resolve in 5-6 months without treatment
  • Other treatment methods: freezing/burning lesions, fluconazole once daily for 6 months, sodium stibogluconate (>90% chance of cure but bad side effects and destabilizes thiol bonds)
• Visceral leishmaniasis treatment
  • AmBisome (only drug approved by FDA)
  • Sodium stibogluconate

Sand Fly Prevention and Control methods

• Avoid outdoor activities dusk to dawn
• Minimize exposed skin outdoors
• Apply insect repellent
• Stay in screened or air conditioned areas
• Insecticides
• Bed nets

Biting Midges (Ceratopogonidae)

• Commonly known as "no see ums" due to small size and painfulness of bite
• Vectors that carry viral diseases such as Oropouche fever in humans; bluetongue disease & episodic hemorrhagic disease in ruminants; African horse sickness in equids
• Nematodes transmitted can lead to Mansonellosis in humans and onchocerciasis in animals
• Mansonella perstans L3 enters the midge bite wound
  • Adults in peritoneal or pleural cavity produce unsheathed microfilariae that reach bloodstream
  • Ingested by Midge, which penetrates midgut and migrates to the thoracic muscles
  • Proceeds through L1, L2, and L3, which migrates to the midge's proboscis

Biting Midges: Morphology

• Slender larvae are between 2-5mm
• White bodies and has a yellow-brown head capsule
• Adults are less than 1-2.5 mm

Biting Midges: Life History

• Females are typically anautogenous
• Egg development takes 7-10 days
• 30-450 eggs per female
• Autogenous females tend to produce fewer eggs
• Larvae hatch in 2-7 days
• Larval development is 2 weeks to over a year (4 instars)
  • Can overwinter or be dormant during summer
• Small percentage of females can obtain second blood meal and produce a second batch of eggs
• Generation time is ~6 weeks
• Culicoides paraensis carries oropouche