Metazoans and ExoparasitesPart II

Three Classes

Trematodes (flukes-flat worms)

Cestodes (tape worms)

Nematodes (round worms)

Major Stages of Life Cycle

Ova

Adult (Mature Parasite)

Monecious - having male and female reproductive organs

in the same animal.

Diecious - sexually distinct; denoting species in which male and female genitals do not occur in the same individual

Most trematodes have complex life cycles, with larval stages parasitizing one or more species that are different from host of adults.

Larval stages of some medically important species include miracidium, redia, cercaria, and metacercaria.

Most trematodes are endoparasites.

They include several parasites that have an enormous impact on human populations,

such as human liver flukes and the blood flukes.

Clonorchius sinesis

causes hepatic portaldisease, very painful, affects liver

Schisotosoma mansoni

blood flukes that targets organs that are fed by blood.

Fasciola hepatica,

also known as the common liver fluke or sheep liver fluke, is a Parasitic flatworm of the class Trematoda, phylum Platyhelminthes that infects

liver of various mammals, including humans.

Cestoda is a class of parasitic flatworms, commonly called Tapeworms.

Tapeworms live in the digestive tract of vertebrates as adults

and often in the bodies of variousanimals as juveniles.

Taenia saginata

The beef tapeworm can grow

up to 40 feet long (12 m); other species may grow to over 100 feet (30 m).

Taenia solium

This infection is caused by ingestion of eggs shed in the feces of a human tapeworm carrier.

Pigs and humans become infected by ingesting eggs or gravid proglottids.

Humans are infected either by ingestion of food contaminated with feces containing eggs, or by autoinfection

Echinococcus granulosus

Hydatid worm parasitizes the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes hydatid disease.

Hydatid disease is treated with surgery, taking special care to leave the cyst intact so new cysts do not Form.

Nematoda , phylum consisting of about 12,000 known species, and many more predicted species of worms (commonly known as roundworms or threadworms).

Nematodes live in the soil and other terrestrial habitats as well as in freshwater and marine environments.

Many are damaging parasites of plants and animals, including humans.

Ascaris lumbricoides –

fairly long, get together in balls and start breeding

Necator americanus

hook worm. Likes to penetrate in soft skin between toes then

migrates from there to other site in the body.

Trichinella spiralis

Trichinellosis, also calledtrichinosis, is caused by eating raw or undercooked meat of animals infected with the larvae.

Infection occurs commonly in certain wild carnivorous (meat-eating) animals but may also occur in domestic

pigs.

Enterobius vermicularis

Pin worms

Lays eggs on the anus.

Causes a very itchy bum and

prolapsed rectum.

These don’t really causeInfection.

They are responsible for infestations.

Insecta (6 legs) – fleas, Lice

Arachnidia (8 legs) – ticks, mites

Pediculus humanusLice are six-legged blood-sucking parasitic insects that live near the surface of the skin, often clinging to the shafts of human hair.

They can travel quickly, up to 10 inches per minute, which explains why they are so contagious.

Infestation with lice is called “pediculosis.” In the U.S., head lice and pubic (crab) lice are the most

common forms of pediculosis.

Direct and prolonged head-to-head

contact is the usual mode of head lice

transmission; as such, lice are typically

spread between people who know each

Other

Sharing of inanimate objects that come in

contact with the hair or scalp, such as hats,

scarves, or hairbrushes, may also cause

the spread of head lice, though this is less

Common.

Contrary to popular belief, lice cannot

jump from one head to another, and they

cannot survive for long off of the human

Body.

Pthirus pubis

Pubic lice (or crab lice) are usuallytransmitted sexually and are among the most contagious of STDs.

Condoms do not prevent the spread of pubic lice.

Nonsexual transmission of public lice

is also possible.

Body louse claw are adapted for round hair

common with body and head hair.

Crab louse claw is adapted for oval shaped

hair common with pubic hair and eye lashes.

Bed bugs, Cimex lectularius , are blood feeding parasites of humans, chickens, bats and occasionally domesticated animals (Usinger 1966).

Bed bugs are suspected carriers of leprosy, oriental sore, Q-fever, and brucellosis (Krueger 2000) but have never been implicated in the spread of disease to humans (Dolling 1991).

Ticks are blood-feeding parasites that are often found in tall grass and shrubs where they will wait to attach to a passing host.

A tick will attach itself to its host by inserting its chelicerae(cutting mandibles) and hypostome(feeding tube) into the skin.

The hypostome is covered with recurved teeth and serves as an

anchor.

Scabies is a contagious ectoparasite skin infestation characterized by superficial burrows and intense pruritus (itching).

It is caused by the mite Sarcoptes scabiei. The word scabies itself is derived from the Latin word for

"scratch" (scabere).

Scabies is highly contagious and can be spread by scratching, picking up the mites under the fingernails and simply touching another person's skin.

They can also be spread onto other objects like keyboards, toilets, clothing, towels, bedding, furniture, and anything else that the mite may be rubbed off onto, especially if a person is heavily infested.

The parasite can survive up to 14 days away from a host, but often do not survive longer than two or three days away from human skin.[

Insects and arachnids are much more important as vectors that as parasites.

Mosquitoes transmit malaria

Ticks transmit Lyme’s disease

Fleas transmit plague