Entamoeba histolytica

·         Intestinal protozoan      

·         Worldwide (10%-15% in tropic region and about 2% of total population in the US).

·         Fecal-oral transmission.

·         Our understanding is in transition.

·         Mis-identified cases.

·         Seen in travellers as well.

·         liver abscess

·         ulcer in colonic mucosa

Cryptosporidia

·         intestinal protozoan

·         Worldwide.

·         Epidemic contamination of municipal water.

·         1%-3% in developed countries, up to 10% in developing countries; increased in AIDS patients, children, day cares.

·         Zoonosis – founded in most mammals; esp. bovine, cattle, cats, dogs, etc.

·         Resistant to chlorination

·         Must boil water or filter water to remove organism

Trichomonas vaginalis

·         Urogenital protozoan

·         Name tells where found

·         No cyst - doesn’t survive in environment and human as its only host (a strictly human parasite).

·         Since transmission is by intimate sexual contact, this protozoan needs (or has adapted to) a trophozoite form only.

·         Worldwide, 10% to 25% in adult women become infected sometime and 2% to 10% in adult men.

Plasmodium

·         Blood and tissue protozoan

·         Kills 1-3 million/year.

·         Mostly in the tropic region (Africa).

·         Economic and social burden.

·          Vaccines slow.

·         Mosquitoes.

·         Swamps.

·         Life cycle

o   From mosquito salivary gland to human liver to RBCs to gut of mosquito back to salivary gland of mosquito

Toxoplasma gondii

·         Blood and tissue protozoan

·         Infects both human and domestic animals worldwide.

·         Transmission is by inhalation/ingestion of infective oocysts by grazing animals or from infected cat litter or by ingestion of animal muscle tissue containing pseudocysts (don’t eat steak tartare!).

·         Rack of lamb is served rare

·         Felines are the definitive hosts

·         Congenital infections -> prevent pregnant women from handling cat litter

Ascaris lumbricoides

·         Animalia -> Helminth -> Nematode (roundworm)

·         The most common helminthic infection worldwide, -1 billion.

·         Prevalent in areas where human faeces are used as fertilizer.

·         A adult female may lay up to 200,000 eggs per day for as long as a year.

·         Ingestion of food contaminated with the eggs.

Lymphatic Filariasis

·         Epidemiology

o   120m people infected in >80 countries in Africa, Asia, the Pacific islands and South and Central America.

o   40m of those infected are disfigured or severely incapacitated.

o   95% cases due to Wuchereria bancrofti; other species include Brugia malayi and Brugia timori

·         Life cycle

o   Wuchereria bancrofti is mainly transmitted by:

§  Culex mosquitoes in Asia.

§  Anopheline mosquitoes in Africa.

o   B. malayi and B. timori are transmitted mainly by Mansonia mosquitoes.

o   When the mosquito bites, the infective parasites enter the bite wound.

o   Parasites migrate to the lymphatics and lymph glands.

·         Pathology and lymphatic filariasis

o   Adult worms live in the afferent lymphatic vessels and cause severe disruption to the lymphatic system.

o   Scrotal damage and massive swelling may occur when adult parasites lodge in the lymphatics of the spermatic cord.

·         Late stage disease is typified by elephantiasis – painful and disfiguring swelling of the limbs

Taenia saginata

·         Animalia -> Helminth -> Cestode (tapeworm)

·         Common name: beef tapeworm.

·         Worldwide; one of the most common causes of cestode infections in US.

·         Insufficiently cooked beef.

Adult size: 4-6 meters

Schistosomes

·         Epidemiology

o   200m people in 74 countries, 85% of whom live in sub-Saharan Africa.

o   S. haematobium – Africa, middle east.

o   S. mansoni - Africa and Latin America.

o   S. japonicum – Pacific region.

·         Life cycle

o   Transmission occurs in fresh water.

o   Cercariae released from snails.

o    Cercariae penetrates the skin of people. Adult worm live in the veins and release eggs into water.

o   Eggs develop into miracidia which then infect snails

·         Pathology

o    Schistosoma eggs become trapped in the tissues of the urinary tract (S. haematobium) and intestines (S. mansoni, S. japonicum).

o   This results in inflammatory response and tissue damage.

o   Liver failure occurs because the parasites releases million of eggs, which remain trapped in liver tissue causing extensive damage, including liver fibrosis

·         Prevention and control

o   Educate people to not urinate or defecate in fresh water supplies.

o   Eliminate snail vectors by making the water habitat unsuitable.

o   Provide piped water to avoid direct contact with cercariae.

o   Provide mass drug treatment of communities to reduce reservoir of infection

Arthropods

·         Pubic lice

·         Head louse

·         Bed Bugs

o   Disappeared due to DDT use, recent return

o   Oval, flat, wingless

§  1/16 - 1/4 " long

§  brown to purplish-red

o   Bite similar to mosquito bites

§  singly or sometimes clusters or rows

·         Ticks

o   Tick is the common name for the small arachnids. Ticks are ectoparasites (external parasites).

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

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

o   Deer ticks can transmit Lyme disease to humans.