Arthropods Flashcards
insects vs ticks/mites
Insects:
* adult: 3 body parts (head, thorax, abdomen)
* adults: 6 legs, larvae: 6 or none
* life stages: egg, larva, pupa, adult
ticks/mites:
* adult: 2 body parts (gnathosoma, idiosoma)
* adults and nymphs: 8 legs, larvae: 6 legs
* life stages: egg, larva, nymph, adult
class insects
Morphology
* Adults have 6 legs
* 3 body segments: head, thorax, and abdomen
Life cycle: metamorphosis
* Simple or incomplete: immature stages look like small adults
* Complex or complete: marked differences in morphology and structure between adults and immature stages
Siphonaptera
insects, fleas
Macroscopic, usually brown
Wingless
Laterally compressed
Complex metamorphosis
life cycle:
1. eggs
2. larvae
3. pupae
4. adult
Ctenocephalides felis
insecta, Siphonaptera, cat flea
Hosts: dogs, cats, ferrets, occasionally other animals
Most common flea of cats and dogs. Two other species occasionally found on small animals, much less common
Worldwide
Immature stages (environment) prefer high humidity and warm temperatures, don’t survive freezing
Ctenocephalides felis - Life cycle
Once on host, adults considered permanent ectoparasites
1. Females begin feeding as soon as they find a host
2. Then, mate and begin egg laying after 24 hours
1 female can lay up to 1000 eggs although most females don’t live long enough to do that
3. Eggs (0.5 mm) laid on the host, but fall off
Usually hatch in a few days (up to 6 days)
Warm and humid conditions, nearly all eggs hatch
4. Larva is slender, white, 2-5 mm, may have dark appearance from blood in intestine
Eat organic debris but requires flea feces, limited movement
Love high humidity
5. Pupa
Larva forms sticky, cocoon, debris sticks - camouflage
Adult can stay in pupa for up to 6 months
Toughest stage, not killed by pesticides
Ctenocephalides felis - Diagnosis
Usually diagnosed by observation
* Adults
* Flea dirt
* Scratching
Ctenocephalides felis - Clinical importance
- Hypersensitivity reaction to flea saliva antigens - Flea allergy dermatitis (FAD)
- Range of pruritus and hair loss
- From animals that show no evidence of fleas to severe hypersensitivity
- Possible cause of hot spots
Vector of
* Tapeworms: Dipylidium caninum
* Acanthocheilonema reconditum
* Bartonella henselae (and other Bartonella spp.): cat scratch fever
Anemia, especially in young animals
Ctenocephalides felis - other hosts
Can adapt to other hosts under some circumstances
* Serious infestations reported in confined calves, goats, etc.
* Originate from heavy contamination from barn cats
Humans
* Humans don’t sustain life cycle, but fleas will bite if they need a meal
* Possible severe hypersensitivity
* Treating animals with products with repellent activity may increase human bites temporarily
Rodent fleas
several species
Will bite dogs/cats if they go on them
Vector of Yersinia pestis: Plague
Sticktight flea (Echidnophaga gallinacea)
Usually a bird parasite, sometimes on dogs and cats
Female flea stays attach
Phthiraptera
insecta, lice
Similar across hosts
Characteristics
* Small
* Wingless
* Dorsoventrally flattened
* Often white or gray, some brown
* host specific
2 types of lice:
sucking: mammals, head narrower than thorax
biting (chewing): mammals and birds, wider head
lice life cycle
- egg
- 1st nymph
- 2nd nymph
- 3rd nymph
- adult
no larval stage
Entire life cycle spent on the host
Eggs glued to feathers or hairs
Life cycle generally about 4 weeks
Lice - Transmission
Transmission by direct contact or fomites
Very host specific
Usually site specific
Lice cannot survive long off the host
Biting (chewing) lice may survive several days if cool and humid
Populations increase in winter on animals kept outside
* Hair coat and body temperature favorable
* More close contact
* May be more stress: nutritional, weather
Carrier animals
Stressed animals most susceptible to heavy louse burdens
Lice - Diagnosis
Observation of lice and eggs
Predilection sites
Pruritus
Hair loss and poor hair coat
Lice clinical importance
In severe cases: Anemia, Debilitation
Infestations generally not severe in healthy animals
* Small animals: uncommon in well cared for pets
* Horses: uncommon but easily introduced, spread
* Food animals: common
* Birds
Wild: common
Pets: uncommon, more in poultry
* Wild mammals: common
* Zoonotic? NO host specific
Diptera
Insects
Adults have 1 pair of membranous wings (some exceptions)
Complex (complete) metamorphosis
Musca domestica
housefly
Not parasites
Annoyance can interfere with normal behavior (eating, etc.)
Can serve as disease vectors (mechanical)
Eggs often laid in decaying organic material
Short generation times (House fly: 2 weeks)
Musca autumnalis
face fly
Females eat secretions (especially tears) for protein
Eggs laid in fresh manure
Primarily affects ruminants, horses
Importance
* Fly worry
* Irritation of eye mucosa: inflammation, tearing
* Transmits Moraxella bovis (casual agent of bovine pink eye)
Haematobia irritans
Horn fly
Small flies, sit on dorsum (ventrum when hot) of cattle, (horses - lesser extent)
Adults are resident parasites - spend all their life on the host
Eggs: fresh manure
Complete cycle: 10-12 days
Annoyance, each fly feeds up to 20 times/day
Importance
* FW, FBD
* May carry bacteria causing mastitis
* Most important external parasite of cattle in the US
Stomoxys calcitrans
Stable fly
Looks like house fly with protruding proboscis
One of the most important biting flies, especially around barns or stables
Life cycle:
* Visits host 1-2 times/day
* Prefers to bite lower body, feet legs of livestock
* Lay eggs in decaying organic material
* Duration: about 28-30 days
Importance
* FW, FBD
* Not an important disease vector in the US
Family Tabanidae
Horse fly, deer fly
In general, big flies, big eyes, stout body
Deer flies often have stripped wings
Life cycle
* Lay eggs near water
Importance
* Annoyance, very painful bites
* Excellent mechanical vectors of diseases
culicidae
mosquitos
Small, long body, wings and mouthparts
Life cycle
* Eggs laid in water
* Wide variation in species preferences for egg environment: impacts control
Importance, varies with region
* FW, FBD
* Disease vector: heartworm, encephalitis viruses, avian malaria, West Nile Virus
Exotic species introduced, may have impact on disease transmission
Simuliidae
Black flies, buffalo gnats (hump-backed)
Eggs laid in rapidly moving water
Intense FW: can interrupt feeding, cause stampedes in large numbers
FBD
Disease vector: limited in the US.
* Avian hemoprotozoa, EEE, vesicular stomatitis
Problem in Northeast, Canadian plains, other areas regionally
Culicoides
midges
Tiny flies - can pass through insect wire screens
Larvae in moist soil or water
FW, FBD in horses, sometimes called “sweet itch”
Transmits bluetongue in ruminants, some nematodes
tick/mite structure
Mouthparts: important in tick ID (Gnathosoma or Capitulum)
Everything else (Idiosoma)
Leg numbers
* Adults, nymphs
* Larvae
Sarcoptic mites
subsurface mites
Round bodies: last 2 pairs of legs short
Burrowing mite, females lay eggs in tunnels in epidermis
Life cycle takes about 3 weeks
Easily transmitted between individuals of host species
Sarcoptes scabiei
subsurface mites
Separate varieties for dogs, pigs, cattle, horses (Host specific)
* Common cause of mange in dogs
* Uncommon to rare in cattle (REPORTABLE) and horses
Mites like hairless or thin haired areas: lesions may appear first on face, ears, legs
Intense pruritus, alopecia, inflammation
Chronic sarcoptic mange:
* Alopecia, thickened, wrinkled skin
* Pyoderma
* Self inflicted trauma
May be difficult to find mites in skin scraping, scrape several areas
Hypersensitivity reaction elicited by a few mites
Treatment/Control
* Several effective drugs available
* Environmental treatment? Not important, mostly lives on host
Demodex spp.
subsurface mite
“Cigar with legs”
Very host specific species in domestic animals, humans, others
Some animals have more than one species
Hair follicles or sebaceous glands
Common species can be thought of as part of normal skin fauna
Transmission occurs shortly after birth from dam
cause demodicosis
demodicosis
Demodex (sub surface mite)
seen most often in dogs
Clinical signs occur when mites proliferate beyond normal levels
* Balance between mite and host immune response
* Non-contagious
* NO pruritus
* Interfere with follicle, gland function
* Can lead to inflammation, secondary infection
Several treatments available
Otodectes, Chorioptes
surface mites
Surface dwellers, not burrowers
Look like sarcoptic mites but oval, not round, longer legs
Life cycle: minimum 2 weeks
Otodectes cynotis
Surface mite
Worldwide parasite of the ear canal of dogs, cats, ferrets
* Seen most often in cats, easily transmitted cat to cat
* Not clear if easily transmitted across species
Causes otitis externa, can be intensely pruritic
* Exudate looks like coffee grounds in ear
Diagnosis with swab of ear and microscope ID or with otoscope
Treatment: clean, use miticide
Ixodidae
hard ticks, important ones
Hard, shiny appearance
Mouthparts projected forward
Scutum (hard plate) on the dorsal surface allows to distinguish males and females
tick life stages
Life stages
* Egg
* Larva (3 pairs of legs)
* Nymph
* Adult
One blood meal in each stage
Molt between stages
All of our common ticks are 3-host ticks (can be same animal)
Leave host after each blood meal
Molt in the environment
Female lays eggs in environment then die
Hatched larval tick called “seed tick”
* Small, 6 legs
* Often hard to identify genus
* Find a host, feed a few days
* 3-host ticks: leaves after feeding, molts
3-host tick life cycle
