Parasitology exam 1

Parasite

Animal or plant which lives in or on another organism and draws its nutrients directly from it.

Endoparasites

Internal infection.

Ectoparasites

External infestation.

Obligate parasite

Must be a parasite and cannot survive on their own.

Accidental/opportunist/facultative parasite

Free living and can live by themselves without parasitizing.

Micro endoparasites

Multiply inside definitive host, leading to an increase in the number of parasites within the host.

Macro endoparasites

Reproduce inside host, mate and offspring develop outside the host, keeping the same number of parasites the host started with.

Intra vs. extracellular

Parasites in cells vs parasites outside of cells.

Infection

Establishment and sometimes multiplication of organisms in body tissues, presence of endoparasite.

Infectious

Caused by or capable of being communicated by infection.

Infective

Form or stage capable of producing infection.

Life cycles

The series of stages in the development of a parasite.

Stage when parasites are able to cause infection

Typically 1 specific stage.

Life cycle

Parasite life history including all stages and hosts.

Direct life cycle

One definite host.

Indirect life cycle

Several hosts (2+).

Host

Animal or plant that harbors and provides sustenance for a parasite.

Definitive host

Host in which parasite becomes adult or reaches reproductive maturity.

Intermediate host

Necessary part of life cycle, immature parasite cannot reach maturity without it.

Transport/paratenic host

Not required to complete the life cycle; no development occurs.

Prepatent period

Time required following infection of the definitive host to reach reproductive maturity.

Patent infection

Time from sexual maturity to death.

Zoonosis

Disease transmitted from animals to humans.

Reservoir host

Animal carrying an infection that can be transmitted to humans.

Vector

Agent, usually arthropod, transmitting disease.

Mechanical vector

Assists in the transfer of parasitic forms between hosts but is not essential in the life cycle of the parasite.

Biological vector

An arthropod in the organism of which the agent of diseases has certain stages of development or reproduction.

70/30 rule

Top 30% of hosts has 70% of parasites.

Parasitic infection

Is not synonymous with parasitic disease.

Immunity

Often prevents disease but not infection/infestation.

Young animals

Usually more susceptible to parasitic infection and disease than adults.

Parasitic stages

Must develop and survive in the environment are at the mercy of the weather.

Desiccate

If you want to kill a parasite in the environment.

Phylum Arthropoda

Bilaterally symmetrical, segmented, chitinous, jointed exoskeleton.

Ticks

Important vectors for pathogens.

Gnathosoma/capitulum

Mouth of the tick.

Idiosoma

Body of the tick.

Scutum

"Shield" over body of the tick.

Tick paralysis

Progressive flaccid ascending paralysis caused by toxin produced by female tick.

Haller's organ

Detects CO2, located on 1st pair of legs of ticks.

Common ticks in US

Dermacentor variabilis, Ixodes scapularis, Amblyomma americanum, Rhipicephalus sanguineus, Haemaphysalis longicornis.

Dermacentor variabilis

American dog tick, 3 host life cycle.

Ixodes scapularis

Nymphs transmit Lyme disease.

Amblyomma americanum

Lone star tick, female has white dot on scutum.

Rhipicephalus sanguineus

Brown dog tick, prefers dogs.

Haemaphysalis longicornis

Asian longhorn tick, invasive species in US.

Tick season

Occurs all year.

How to remove a tick

Grasp with forceps/tweezers next to skin where attached.

Class Insecta

Includes orders with important parasites: Siphonaptera, Phthiraptera, Diptera, Hemiptera.

Order Siphonaptera

Fleas, macroscopic, usually brown, wingless.

Ctenocephalides felis

Most common flea in US, life cycle includes eggs falling off the host.

Flea allergy dermatitis (FAD)

Hypersensitivity to flea saliva antigens.

Integrated pest management (IPM)

Important for flea control on animals.

Felis

Other hosts that will bite people when they can't find anything better but don't carry out life cycle on human blood.

Possible severe hypersensitivity

Treating animals may increase human bites.

Other flea species

Fleas are host specific.

Rodent fleas

Vectors of plague (yersinia pestis) in southwestern US.

Order Phthiraptera

Lice, lots of animals (and humans) have lice.

Characteristics of lice

Small, wingless, dorsoventrally flattened, often white or gray, some brown.

Incomplete metamorphosis

All life stages look similar to adult.

Host specificity of lice

Very host specific, entire life cycle on the host.

Transmission of lice

Transmitted by direct contact or by fomites.

Human lice

Pierce the skin to feed (sucking lice).

Pthirus pubis

Crab louse/pubic louse.

Pediculus humanus capitis

Head louse, 1-2 mm in length, grayish-white.

Eggs of Pediculus humanus capitis

Less than 1mm, yellow to white (viable eggs close to the scalp).

Signs of Pediculus humanus capitis infection

Many infections asymptomatic, signs include itching (may develop secondary bacterial infection).

Transmission of Pediculus humanus capitis

By direct contact or fomites.

Diagnosis of Pediculus humanus capitis

By seeing lice and eggs.

Pediculus humanus corporis

Body louse, 2-4 mm, live in clothing and lay eggs there.

Transmission of Pediculus humanus corporis

Transmitted by direct contact and clothing.

Diseases transmitted by Pediculus humanus corporis

Transmits typhus, trench fever, and relapsing fever.

Pthirus pubis characteristics

About 1.5mm, prefer coarse body hair.

Treatment for Pthirus pubis

Several insecticides used, washing clothes, bed linens.

Order Diptera

Flies, 1 pair of membranous wings (some exceptions), complete metamorphosis.

Adult biting flies

Includes mosquitoes, stable flies, black flies, midges, horse and deer flies.

Myiasis

Any infection due to the invasion of the tissues or cavities of the host by the larvae of dipterous insects.

Cutaneous myiasis

Fly strike, larvae feed on necrotic material.

Fly strike causes

Fly eggs laid in organic material, females attracted by secretions from wounds, fecal material, etc.

Blow flies

Metallic green, blue, bronze.

Flesh flies

Bug house fly-like, often have red tip to abdomen.

Specific ID of fly larvae

Through examination of larval spiracles (breathing plates).

Screwworm

Cochliomyia hominivorax, requires living tissue, produces severe disease.

Lucilia sericata

Common green bottle fly, attacks carrion, used in forensic investigations.

Internal myiasis

Fly larvae called bots, grubs and/or warbles, obligate internal parasites.

Myiasis in horses

Gasterophilus species, eggs laid in equids, remain for 10-12 months.

Myiasis in rodents

Cuterebra species, parasites of rodents, rabbits, develop in SubQ cyst.

Human bot fly

Dermatobia hominis occurs in Latin America, larva develops under the skin of humans.

True bugs

Order Hemiptera, includes bed bugs (Cimex species) and kissing bugs.

Bed bugs

Wingless, brown, about 5-7mm, spend the day in cracks, crevices, mattresses.

Kissing bugs

Have wings, incomplete metamorphosis, transmit Chagas disease caused by protozoan Trypanosoma cruzi.