Arthropod Diseases (12)

arthropods

(vector transmission)

• Kingdom Animalia

  • Phylum Arthropoda

    • class insecta: lice, fleas, mosquito

    • class arachnida: spiders, mites, ticks

arthropod disease interaction

1. host/reservoir (human/animal)

2. pathogen/parasite

3. vector (arthropod)

• animal reservoir (w/ a pathogen) → vector (arthropod) → host (human)

• ex. infected rat → infected rat flea → infects human (ex. plague)

arthropod vector adaptation (overview)

goal: enhanced survival of arthropod vector

1. multiple developmental stages/complex life-cycle

2. diverse habitats (ex. water & land)

3. several types of vertebrate hosts (rodent, humans)

3 types of arthropod vector adaptation

1. physiological adaptations:

• kissing bug detects host’s chemicals (CO2 → bites around mouth)

• mosquito bites the host/release certain chemical before/after a blood meal (numb area → dissolve clot → form clot)

2. behavioral adaptations:

• mosquito bites host at appropriate times (@ night)

3. structural adaptations

• wings: locate nutrient source/escape from predators

• compound eyes: multiple lenses → see 360 → escape predators

• needles: take a blood meal/deliver pathogens to host

• sensory bristles: detect vibrations (nutrients/predators/mates)

bacterial arthropodborne diseases

1. plague

2. lyme disease

3. epidemic typhus

4. rocky mountain spotted fever (RMSF)

parasitic arthropodborne diseases

1. malaria (kingdom protista)

arboviral arthropodborne diseases (7)

1. west nile encephalitis

2. st. louis encephalitis

3. eastern equine encephalitis

4. zika virus disease

5. yellow fever

6. dengue

7. ebola virus disease (viral disease but NOT transmitted by arthropods)

plague (black death)

• cause: Yersinia pestis, gram — bacillus

• reservoir: 1 rats, wild rodents; 2 human

• arthropod vector: rat flea

• MOT: pathogen in rat → infected rat flea → bite human

• types:

  • bubonic plague: bact. growth in phagocytes → bacteremia → lymph nodes

    • s/s: painful/swollen lymph nodes in axilla & groin (buboes), fever, chills, body aches, bleeding into skin (skin turns black), most common, 50-75% mortality

  • septicemic plague: septic shock d/t bacteremia

  • pneumonic plague: airborne/droplet transmission (human → human), bact. → lungs, ~100% mortality w/n 3 days if untreated

• dx: serology, sputum sample, fluid from buboes

• predisposing factor: poor sanitation (rats)

• prevention: eliminate reservoir (rats), plague vaccine for ↑ risk people (only effective for bubonic plague)

• tx: high dose abx

• misc: endemic to parts of U.S.

lyme disease

• cause: Borrelia burgdorferi, spiral bact. (spirochete), motile

• reservoir: 1 field/deer mice, 2 deer

• arthropod vector: tick

• MOT: mouse/deer → tick → human

• s/s:

  • 1st phase: bull’s-eye rash

  • 2nd phase: flu-like sxs, irregular heartbeat, encephalitis, facial paralysis

  • 3rd phase: arthritis

• dx: clinical sxs, geographic location, serology

• prevention: protective clothing, tick repellent, avoid rodents/deer

• tx: abx (1st phase), harder to tx in later stages

• misc: known since 1975, most common tick-borne dz in US, northeast US, summer months

4 developmental stages (forms) for tick

year 1

1. egg (U)

2. larvae (U/I)

year 2

3. nymph (I) → human/host gets lyme dz

4. adult (I)

how many blood meals? (ticks)

1. larvae (U) → infected field mouse

2. nymph (I) → uninfected pet/human host

3. adult (I) → uninfected deer

tick vector stage?

(stage 8)

infected adult female tick lays uninfected eggs in the ground during spring year 1

tick vector stage?

(stage 1)

uninfected egg hatches & develops into uninfected larvae in spring year 1

tick vector stage?

(stage 2)

uninfected larvae take 1st blood meal on infected wildlife host, such as field mice (natural reservoirs) who are infected with Borrelia burgdorferi in summer year 1 (uninfected larvae → infected larvae)

tick vector stage?

(stage 3)

after 1st blood meal, infected larvae w/ B. burgforferi detaches from wildlife host (field mice) & drops to ground & remains dormant during fall/winter year 1 (d/t colder weather & field mice not being available)

tick vector stage?

(stage 4)

the infected larvae come out of dormant stage & develop into an infected nymph during spring year 2

tick vector stage?

(stage 5)

the infected nymph takes its 2nd blood meal on uninfected human/pets who are usually outdoors during summer year 2, infecting human/pet w/ B. burgdorferi

• human now develop Lyme Disease

tick vector stage?

(stage 6)

the infected nymph detaches from human/pets after blood meal & develops into infected adult tick in fall year 2

tick vector stage?

(stage 7)

the infected adult tick has its 3rd blood meal on wild animal (deer) in fall year 2, infecting the deer w/ B. burgdorferi. the adult ticks mate.

rickettsial diseases: Epidemic Typhus & Rocky Mountain Spotted Fever

• Genus Rickettsia (bacterium)

  • causative agent of “Typhus Fever” group & “Spotted Fever” group of dz (diff. clinical sxs)

• gram — bacillus or coccobacillus

• obligate intracellular parasite (replicate in human cells only)

• spotted flat rash on body

• reservoir = arthropod vector

epidemic typhus (typhus fever)

• cause: Rickettsia prowazekii, gram — bacillus/coccobacillus, obligate intracellular parasite

• reservoir/vector: human body louse

• MOT: louse feces rubbed into bite wound

• s/s: prolonged HIGH fever, spotted red rash (chest/trunk → extremities)

• dx: rash type/location, serology

• predisposing factors: wars, homelessness, crowded jails, concentration camps (unsanitary conditions)

• prevention: good personal hygiene

• tx: abx

• misc: ↑ mortality if untreated

rocky mountain spotted fever (RMSF)

• cause: Rickettsia rickettsii, gram — bacillus/coccobacillus, obligate intracellular parasite

• reservoir/vector: tick

• MOT: (nymph) tick → human

  • transovarian passage: infected female tick lays infected eggs → larvae hatch already infected

• s/s: fever, spotted red rash (palms & soles → chest/trunk)

• dx: rash type/location, serology

• predisposing factors: outdoor activities (hiking)

• prevention: protective clothing, tick repellent

• tx: abx

• misc: common in southeast US, appalachian mountains

lyme disease vs. rocky mountain spotted fever

• lyme disease (Borrelia): infected adult female tick → UNINFECTED eggs → uninfected larvae (only infected after 1st blood meal → field mouse)

• RMSF (Rickettsia): infected adult female tick (transovarian passage) → INFECTED eggs → infected larvae

malaria

• cause: Genus Plasmodium, kingdom protista, subkindom protozoa, protozoan parasites (found in RBC’s/liver cells)

  • Plasmodium vivax → mildest & most common

  • Plasmodium ovale → endemic

  • Plasmodium malariae → endemic

  • Plasmodium falciparum → most deadly, severe anemia/encephalitis (cerebral malaria)

• VF: complex lifecycle of Plasmodium pathogen w/ 2 hosts

  • long/slow blood cycle

  • frequent gene mutations → ↑ drug resistance

• reservoir: human (intermediate host / asexual reproduction)

• arthropod vector: mosquito (definitive host / sexual reproduction)

• MOT: plasmodium (pathogen) in human → mosquito → different human dz

• sxs (paroxysyms): intermittent fever (spike every 48 or 72 hours), chills, sweating, fatigue, weakness, anemia (d/t plasmodium infect/destroy RBC → rupture → release merozoites)

• dx: RBCs w/ ring form of Plasmodium (merozoites)

• predisposing factors: tropical climates, stagnant water

• prevention: vector control, mosquito repellant, mosquito nets, clearing stagnant water (no vaccine in US atm)

• tx: antiparasitic/antimalarial durgs

  • chloroquine: limit d/t ↑ drug resistance

  • artemisinin derivatives: chinese herb

• misc: 300 mil worldwide, 500,000 deaths annually, top 3 deadliest infectious dz worldwide

life cycle of the plasmodium pathogen (summary)

4 developmental stages (forms) - for Plasmodium

1. Sporozoite

2. Merozoite

3. Male & Female Gametocytes

4. Zygote

• human: all except zygote

• mosquito: all except merozoite

• both hosts: sporozoite & gametocyte

• schizogony: asexual reproduction in human liver; 1 sporozoite divides into 8 merozoites

(stage 1)

• infected female mosquito has sporozoites of Plasmodium parasite in her salivary glands

• infected female mosquito bites/has blood meal on uninfected human

• sporozoites from mosquito’s salivary gland enter human bloodstream, then reach human liver

(stage 2)

• occurs in intermediate (human) host as part of asexual reproduction

• sporozoites undergo “Schizogony” ( division of 1 sporozoites into 8 merozoites) in human liver cells

• merozoites are produced in the liver

(stage 3)

• merozoites are released from the liver into bloodstream & can infect new RBCs

(stage 4)

• merozoites develop into the “Ring Stage” inside RBCs

• observing RBCs w/ “ring-formed” merozoites in blood smear is most common diagnostic method for malaria

(stage 5)

• “ring-stage” of Plasmodium (merozoites) grow and divides, producing more merozoites

(stage 6)

• d/t rapid divison of Plasmodium (merozoites) in RBCs → RBCs rupture and release the merozoites

• leads to Paroxysms (intermittent fever & chills in humans)

  • some merozoites infect new RBCs in bloodstream

  • some merozoites develop into male & female gametocytes (sex cells to carry out sexual reproduction in definitive (mosquito) host)

(stage 7)

• an uninfected (different) mosquito take blood meal from infected human carrying Plasmodium (gametocytes)

• mosquito becomes infected by ingesting gametocytes that travel & found in mosquito’s GI tract

(stage 8)

• in infected mosquito’s GI tract, the gametocytes (male & female) unite to form a zygote

• sexual reproduction occurs in definitive (mosquito) host

(stage 9)

• zygotes develop into sporozoites that migrate to salivary glands of mosquito

  • adaptive for Plasmodium parasite to be delivered into next host when mosquito takes another blood meal

• Plasmodium parasite that remains in mosquito GI tract not helpful b/c cannot pass along parasite

arboviral diseases

• arbovirus: arthropodborne virus (belong to several viral families)

• arthropod vector: usually mosquitos (mosquito-borne viruses)

• some considered EIDs (ebola, zika)

• sxs subclinical to severe:

  • neurological → encephalitis

  • vascular damage → hemorrhagic fevers

arboviral encephalitis

1. west nile encephalitis

2. st. louis encephalitis

3. eastern equine encephalitis

4. zika virus dz: more neurological sxs than hemorrhagic fever sxs

arboviral hemorrhagic fevers

1. yellow fever

2. dengue

3. ebola virus dz: hemorrhagic fever sxs, no arthropod transmission!

west nile encephalitis

• cause: west nile encephalitis virus

• sxs: (most asxs) fever, HA, neurological sxs (brain inflammation), polio-like paralysis (sometimes)

• reservoir: birds (crows), rodents

• MOT: mosquito bite

• prevention: vector control, no vaccine

• misc: portal of entry = skin, all over US

st. louis encephalitis

• cause: st. louis encephalitis virus

• sxs: fever, HA, neurological sxs (brain inflammation)

• reservoir: birds

• MOT: mosquito bite

• prevention: vector control, no vaccine

• misc: portal of entry = skin, usually adults over 40 yo, central us

eastern equine encephalitis

• cause: eastern equine encephalitis virus

• sxs: fever, HA, neurological sxs (brain inflammation)

• reservoir: horses & birds

• MOT: mosquito bite

• prevention: vector control, no vaccine

• misc: portal of entry = skin, over 30% mortality in humans, southeast US

yellow fever (jungle fever)

• cause: yellow fever virus

• sxs: fever, muscle pain, rash, jaundice, blood vessel damage, hemorrhage (severe cases)

• reservoir: wild monkeys

• MOT: mosquito bite

• prevention: vector control, vaccine

• misc: portal entry = skin

dengue

• cause: dengue virus

• sxs: fever, muscle pain, rash, blood vessel damage, hemorrhage (severe cases)

• reservoir: humans

• MOT: mosquito bite

• prevention: vector control, no vaccine

• misc: portal entry = skin

ebola virus disease

• cause: ebola virus

• sxs: fever, muscle pain, rash, blood vessel damage, PROFUSE hemorrhage (severe cases)

• reservoir: cave-dwelling fruit bats

• MOT: spread by contact w/ animal blood & waste products

  • spread by infected human body fluids

  • NO arthropod transmission

• prevention: vaccine

• misc: portal entry = skin, mortality rate 90%, originated from ebola river region in Africa

zika virus disease

(similar to viruses that cause viral hemorrhagic fevers)

• cause: zika virus

• sxs: (mild) fever, muscle pain, rash, pink eye (conjuctivitis), mostly neurological sxs, some blood vessel damage

• reservoir: wild monkeys

• MOT: mosquito bite

  • sexual, mother to fetus, blood transfusions

• prevention: vector control, no vaccine

• misc: portal entry = skin, infection during pregnancy → microcephaly (small brain in infants), originated from zika forrest region in Africa, 2015 outbreak in Brazil