Bio 205 Chapter 17 Power Point

BIO 205 Chapter 17

Parasites

Classification and Characteristics of Protists

Protists The Protists Are a Perplexing Group of Microorganisms: •Most are unicellular •Many are free-living, thriving in environments with water •Green algae have chloroplasts and perform photosynthesis •Some dinoflagellates cause red tides

The Protozoa Encompass a Variety of Lifestyles •Some parabasalids live mutualistically in termite guts •Diplomonads, including Giardia intestinatlis, have bilateral symmetry

Trichonympha

•Kinetoplastids include trypanosomes causing sleeping sickness and Leishmania Giardia intestinalis

•Apicomplexans include parasites such as Plasmodium and Toxoplasmosis

Trypanosoma

Amoebozoans are mostly free-living •Amoeboid motion occurs by the formation of pseudopods •Pseudopods also form food vacuoles for ingestion

Amoeba proteus

Ciliates are covered with rows of hair-like cilia The pellicle provides cell structure and stores calcium ions Contractile vacuoles eliminate excess water Ciliates have two types of nuclei: •macronuclei •micronuclei

Paramecium

Sexual Recombination in a Ciliate

Parasite Life Cycles Have Some Unique Features •The infective form of some protozoa is a trophozoite, others a cyst •The sexual cycle occurs in the definitive host •The asexual cycle occurs in the intermediate host

Protozoal Diseases of the Skin, and the Digestive and Urinary Tracts

•Leishmania Can Cause a Cutaneous or Visceral Infection •Several species cause leishmaniasis •It is transmitted by sandflies of the genus Phlebotomus

Phlebotomus, the sandfly that transmits leishmaniasis

L. major causes cuteaneous disease with ulcerative sores

Cutaneous leishmaniasis lesion

L. donovani causes a visceral disease (kala azar) affecting: •white blood cells •spleen •liver

Giardiasis is caused by Giardia intestinalis Transmission occurs through food or water contaminated with sewage containing cysts Trophozoites emerge and attach to the intestinal lining Symptoms appear after about 7 days •nausea •cramps •flatulence

Giardia intestinalis

A Protozoan Parasite Also Infects the Urinary Tract •Trichomoniasis is often transmitted through sexual contact •It is caused by Trichomonas vaginalis

Trichomonas vaginalis

Certain physical and chemical factors can encourage establishment in the female vagina and male urethra and prostate Females experience: •itching •burning •discharge Males may be asymptomatic

Protozoal Diseases of the Blood and Nervous System

The Plasmodium Parasite Infects the Blood Malaria affects 300-500 million people Four species of Plasmodium cause malaria •P. ovale •P. vivax •P. malariae •P. falciparum

malaria cases

Death can occur due to: •loss of RBCs •RBC clustering in small vessels, causing clots •Quinine is used for treatment

Toxoplasma Causes a Relatively Common Blood Infection •Toxoplasmosis is caused by Toxoplasma gondii •Parasites invade all mammalian cells except RBCs Toxoplasma gondii

•Transmission can occur via contaminated beef, pork, and lamb •It can also occur via domestic cats •They pick up cysts from soil, birds, or rodents

No serious illness occurs in most healthy people Parasites may cross the placenta and infect fetal tissues in pregnant women, causing: •neurologic damage •lesion of viscera or retina •spontaneous abortion may occur In AIDS patients, it attacks brain tissue, causing: •inflammation •swelling •cerebral lesions •seizures •death

The Multicellular Helminths and Helminthic Infections

Flatworms (Phylum Platyhelminthes) do not have respiratory or circulatory structures, or a digestive tract •Trematodes, including flukes, have complex life cycles and often 2 hosts •Eggs develop into larvae (miracidia) in water, which invade snails •Trematodes evade the immune system by having a surface similar to host cells A liver fluke, Fasciola hepatica

Cestodes, including tapeworms, have a head region called a scolex

•Fertilized eggs are produced in proglottids distant from the scolex, which break off and spread eggs •Tapeworms generally live in host’s intestine, absorbing nutrients •They have limited host range, but usually at least 2 hosts

SEM of the scolex (head) of the beef tapeworm

Roundworms (Phylum Nematoda) live in every habitat on Earth Damage to the host often occurs by large worms burdens in vessels or intestines

Roundworms in the gut wall of a pig

Humans Are Host to at Least 50 Roundworm Diseases •Pinworm disease is caused by Enterobius vermicularis •Infection of the intestines leads to diarrhea and anal itching •Reinfection can occur if contaminated hands contact food or the mouth •Worms die in a few weeks, even without treatment

Trichinellosis is caused by Trichinella spiralis T. spiralis lives in pig intestines and can encyst in skeletal muscles Transmission to humans occurs by eating raw or poorly cooked pork Symptoms include: •pain •vomiting •nausea •constipation Trichinella spiralis larva encysted in muscle tissue

Larvae can migrate to the tongue, eyes, and ribs

End of Chapter 17