MAJOR PARASITIC DISEASES OF HUMANS
AN INTRODUCTION TO MEDICAL PARASITOLOGY

INTRODUCTION
Parasitism
-Symbiotic relationship that is of benefit to one party (parasite) and usually detrimental to the other party (host).
Parasites
-Organisms that live on or in other living organisms (host) at whose expense they gain some advantage
a. Ectoparasites – parasites that live on the outside of the host’s body
b. Endoparasites – parasites that live inside the host’s body
Host
- Organism that harbors the parasite
a. Definitive Host – harbors the adult or the sexual stage of the parasite
b. Intermediate Host – harbors the larval or asexual stage of the parasite
Helminth
- Parasitic worm
Has two major divisions:
1.Round worms – nematodes
2.Flat worms – platyhelminths 2 Divisions:
Cestodes – tapeworms
Trematodes – flukes Has three typical stages in the life cycle: Egg Larva Adult worm

Parasitic Infections of the Gastrointestinal Tract
Amebiasis, Amebic Dysentery, Amebic Abscesses, Amebomas
A protozoal gastrointestinal infection that may be asymptomatic, mild or severe
Often with dysentery, fever, chills, bloody or mucoid diarrhea or constipation, and colitis
Amebae may invade the mucous membranes of the colon, forming abscesses and granulomas (amebomas)
Amebae may also be disseminated via the bloodstream to extraintestinal sites, leading to abscesses of the liver, lung, brain, and other organs. Depending on their location, extraintestinal amebic abscesses can be fatal
Agent: Entamoeba histolytica
Occurs as: Cyst - dormant infective stage Trophozoite – motile reproducing stage
Mode of Transmission: Symptomatic or asymptomatic humans; fecally contaminated food or water. Transmission is by ingestion of fecally contaminated food or water containing cysts from feces to food, soiled hands of infected food handlers, oral-anal sexual contact
Precaution – most important precaution are careful handwashing after each toilet visit and proper disposal of sewage. Homosexual males should refrain from intimate sexual contact until effectively treated.

Giardiasis
A protozoal infection of the duodenum (uppermost portion of the small intestines)
Disease may be asymptomatic, mild or severe, with diarrhea, steatorrhea (loose, pale, malodorous, fatty stool), abdominal cramps, bloating, abdominal gas, fatigue and possible weight loss
Agent: Giardia lamblia – a flagellated protozoan
Trophozoites attach by means of a ventral sucker to the mucosal lining of the duodenum. The trophozoites and cysts are expelled in the feces.
Reservoir and Mode of Transmission: infected humans, possible beaver and other wild and domestic animals that may have consumed water containing giardia cyst; fecally contaminated water and recreational water
Transmission is by the fecal-oral route; ingestion of cysts in fecally contaminated water or foods, person to person by soiled hands to mouth
Large community outbreaks have resulted from drinking treated but unfiltered water. Filtration is necessary because the concentration of chlorine used in routine water treatment do not kill giardia cysts, especially in cold water.

Ascariasis
Ascaris lumbricoides – large intestinal worm of humans reaching a maximum length of about 35 cm (14 inches).
Humans are the only hosts
Male and female live in the small intestines. Female worms release eggs which pass in the feces (200,000 egg / day)
Humans become infected by ingesting eggs, often by ingesting unwashed and inadequately washed vegetables
In the human body the adult worm could live for about 1 year
Ascariasis is most common in areas where human feces is used to fertilize crops (night soil)
Infection occurs through ingestion of food contaminated with feces containing Ascaris eggs. The larvae hatch, burrow through the intestine, reach the lungs and finally migrate up the respiratory tract. From there, they are reswallowed and mature in the intestines, growing up to 35 cm