• Medical parasitology: “the study and medical implications of parasites
• Eukaryote: a cell with a well-defined chromosome in a membranebound nucleus. All parasitic organisms are eukaryotes
• A parasite: “a living organism that acquires some of its basic nutritional
Parasites may be simple unicellular protozoa or complex multicellular metazoan
• Protozoa: unicellular organisms
• Metazoa: multicellular organisms
• An endoparasite: “a parasite that lives within another living organism”

• An ectoparasite: “a parasite that lives on the external surface of another living organism” –
• Definitive host: “the organism in which the adult or sexually mature stage of the parasite lives”
• Intermediate host: “the organism in which the parasite lives during a period of its development only”
• Zoonosis: “a parasitic disease in which an animal is normally the host - but which also infects man”
• Vector: “a living carrier (e.g.an arthropod) that transports a pathogenic organism from an infected to a non-infected host

• Several diseases falling it this field only occur in the tropics, but many parasite disease are/were very common in temperate climates
• Overall there is a much stronger association with the level of:
• housing, nutrition, sanitation and general public health than climate
• Parasitic diseases are in their majority the diseases of the poor around the globe
• Poverty is a major risk factor for disease – but disease is also a major contributor to poverty.

• There are three main classes of parasites that can cause disease in humans:
• Protozoa
• Helminths
• Ectoparasites

• Protozoa are microscopic
• One-celled organisms that can be free-living or parasitic in nature
• They are able to multiply in humans
• contributes to their survival
• Transmission of protozoa that live in a human intestine to another human typically occurs through a fecal-oral route
• Protozoa in the blood or tissue of humans are transmitted to other humans by an arthropod vector (for example, through the bite of a mosquito or sand fly).

• Helminths are large, multicellular organisms that are generally visible to the naked eye in their adult stages
• Can be either free-living or parasitic in nature
• In their adult form, helminths cannot multiply in humans
• There are three main groups of helminths that are human parasites:
• Flatworms, Thorny headed worms, roundworms

• This term is generally used more narrowly to refer to organisms such as:
• ticks, fleas, lice, and mites that attach or burrow into the skin and remain there for relatively long periods of time
(e.g., weeks to months)

• Microscopic parasite
• Protozoal flagellate parasite
• Single-celled, bi-nucleated intestinal parasite
• Has trophozoite and cyst phases
• Causes diarrheal illness- Giardiasis
• Also know as
• Giardia intestinalis
• Giardia lamblia or
• Giardia duodenalis

• Found on surfaces or soil, food, or water that has been contaminated with feces
(poop) from infected humans or animals
• Protected by an outer shell that allows it to survive outside the body for long periods of time and makes it tolerant to chlorine disinfection .

•
• swallowing as few as 10 cysts might cause someone to become ill (1,2)
•
•
•
1.CDC. Giardiasis surveillance - United States, 2006-2008. MMWR Morb Mortal Wkly Rep. 2010;59(SS06):15-25.
2. 6.Rendtorff RC. The experimental transmission of human intestinal protozoan parasites. II. Giardia lamblia cysts given in capsules. [PDF - 12 pages] Am J Hyg. 1954;59(2):209-20.

Cyst
• Contaminated material
• Definiteve host- Human colon
• Sigmoid colon
Trophozoite
• Colonizes in the intestines of mammals
• Definiteve host- Human intestine
• Duodenum and Jejunum

• Traveling to countries where it is common
• People in child care settings
• Close contact with someone with disease
• People who swallow contaminated drinking water
• Backpackers or campers who drink untreated water from lakes or rivers
• People who have contact with animals who have the disease
• Good hygiene
• Washing hands
• In child care settingschildren with diarrhea should be removed from setting until diarrhea has stopped
• In pools- if you have diarrhea do not go swimming, shower before entering water
• Do not swallow water while swimming in pools, hot tubs, interactive fountains, lakes, rivers, springs, ponds, streams or the ocean.

• Incubation period 1-2 weeks
• Onset is gradual
• Signs and symptoms may vary and can last for 1 to 2 weeks or longer [2,3]
• In some cases, people infected with Giardia have no symptoms [2-4]
• Acute Symptoms
• Diarrhea, Gas, Greasy stools that tend to float, Stomach or abdominal cramps, nausea, vomiting, dehydration
• Sometimes, the symptoms of giardiasis might seem to resolve, only to come back again after several days or weeks.
2.Robertson LJ, Hanevik K, Escobedo AA, Morch K, Langeland N. Giardiasis--why do the symptoms sometimes never stop? Trends Parasitol. 2010;26(2):75-82.
3. 5.Escobedo AA, Cimerman S. Giardiasis: a pharmacotherapy review. Expert Opin Pharmacother. 2007;8(12):1885-1902.
4. 4.Gardner TB, Hill DR. Treatment of giardiasis. Clin Microbiol Rev. 2001;14(1):114-28.

• Because Giardia cysts can be excreted intermittently, multiple stool collections (i.e., three stool specimens collected on separate days) increase test sensitivity (1)
• Several drugs can be used to treat infection
• Effective treatments include metronidazole, tinidazole, and nitazoxanide (2)
• Water-like feces
• Trophozoite
• Formed feces
• Cysts
• Combination therapy may be effective
1.
2.
1.Clinical and Laboratory Standards Institute. Procedures for the recovery and identification of parasites from the intestinal tract; approved guideline. [PDF - 7 pages] CLSI document M28-A2. 2nd ed. Wayne, PA: Clinical Laboratory Standards Institute; 2005.
Drugs for Parasitic Infections: The Medical Letter; 2010

• Protozoal infection
• Causes: Amebiasis
• Morphology
• Trophozoite
• Cysts- Killed by desiccation or boiling
• Entamoeba spp: Infects ~ 10 % of world’s population
• Geographic distribution is worldwide
• Found where sanitation is poor
• High incidence in developing countries
• In the U.S ~ 4%
• Hosts are humans, cats, dogs, and rats

• Fecal-oral-route
• Ingestion of food & water contaminated with feces
• Putting anything into one’s mouth that has touched the feces (poop) of a person who is infected with E.
histolytica.
• Swallow E. histolytica cysts (eggs) picked up from contaminated surfaces or fingers.

Excystation: happens in the small intestine
• This leads to a trophozoites
• Can cause liver absess, amoebic colitis
• Asymptomatic colonization
Encystation: happens in the colon
• Gets excreted in feces

• Anyone can get it, but most common in people who live in
• In the U.S.
• People who have traveled poor sanitary conditions
• Immigrants from tropical sanitary conditions
• People who live in institutions conditions
• Handwashing (soap & clean
• Boiling water used for drinking &
• When traveling
• Drink only bottled or boiled water
• Don’t drink juices, fountain drinks
• Don’t drink fresh fruit or prepared
• Avoid street foods and drinks if

• Incubation period: 2-4 weeks
• Only about 10% to 20% of people who are infected with
E. histolytica become sick from the infection
• Acute symptoms- sudden high fever, chills, abdominal cramping, bloody stool
• Chronic symptoms- 1-4 years with periodic symptoms same as acute
• Complications may lead to more serious illness including abscess of the liver

• Diagnosis can be very difficult
• Other parasites and cells can look very similar to E. histolytica when seen under a microscope
• Your health care provider will ask you to submit fecal samples
• E. histolytica is not always found in every stool sample, you may be asked to submit several stool samples from several different days.
• Several diff. medications depending on severity and nature of disease
• Asymptomatic- Meds of choice are iodoquinol and paromomyosin
• Symptomatic- Mild, moderate, severe- metronidazole, tinidazole

• Protozoan parasite
• Causes Toxoplasmosis
• Toxoplasmosis is considered to be a leading cause of death attributed to foodborne illness in the United
States
• > 60 million men, women, and children in the U.S. carry the Toxoplasma parasite
• very few have symptoms because the immune system usually keeps the parasite from causing illness.

• In various places throughout the world, it has been shown that up to 95% of some populations have been infected with Toxoplasma.
• In, women newly infected with Toxoplasma during pregnancy and anyone with a compromised immune system should be aware that toxoplasmosis can have severe consequences.

• Not passed from person-to-person
• Except in mother-to-child, blood transfusion, organ transplantation
• People typically become infected by three principal routes of transmission.
• Foodborne
• Animal-to-human (zoonotic)
• Mother-to-child (congenital)
• Rare instances

• Tissue form of parasite (microscopic cyst) can be transmitted to humans by food
• By eating undercooked, contaminated food (pork, lamb, and venison)
• Accidental ingestion of undercooked, contaminated meat after handling it and not washing hands thoroughly

• Cats play an important role in spreading toxoplasmosis
• They become infected by eating infected birds, or rodents, or other small animals
• The parasite is then passed in the cat's feces in an oocyst form
• Kittens and cats can shed millions of oocysts in their feces for as long as 3 weeks after infection.

• People can accidentally swallow the oocyst form of the parasite. People can be infected by:
• Accidental ingestion of oocysts after:
• cleaning a cat's litter box when the cat has shed Toxoplasma in its feces
• touching or ingesting anything that has come into contact with a cat's feces that contain Toxoplasma
• Accidental ingestion of oocysts in contaminated soil (e.g., not washing hands after gardening or eating unwashed fruits or vegetables from a garden)
• Drinking water contaminated with the Toxoplasma parasite

• Generally if a woman has been infected before becoming pregnant, the unborn child will be protected because the mother has developed immunity.
• If woman becomes infected while pregnant may not have symptoms, but there can be severe consequences for the unborn child such as:
• diseases of the nervous system (mental disability, seizures)
• Potential visual loss

• Very few have symptoms because a healthy person's immune system usually keeps the parasite from causing illness
• If acquired in first trimester of pregnancy:
• Often results in stillbirth
• Many problems may arise
• Ex: hydrocephalus
• Acute:
• Similar to those for mononucleosis
• Immunodeficient patients may have generalized infection with encephalitis, fever, headache, vomiting, delirium, convulsions, and rash

• Diagnosis typically made by serologic testing
• Test that measures IgG
• For time of infection: measures of IgM
• Less frequent techniques used:
• Direct observation of the parasite in stained tissue sections, cerebrospinal fluid (CSF), or other biopsy material.

• Healthy people (nonpregnant)
• Most recover w/o treatment
• Persons who become ill may be treated w/ combination of drugs such as pyrimethamine and sulfadiazine, plus folic acid
• Pregnant women, newborns, infants
• Can be treated although parasite not completely eliminated
• The parasites can remain within tissue cells in a less active phase

• Persons with ocular disease
• Sometimes prescribed meds to treat active disease by ophthalmologist
• Whether or not medication is recommended depends on the size of the eye lesion, the location, and the characteristics of the lesion (acute active, versus chronic not progressing)
• Immunocompromised
• Need to be treated until they show improvement in their condition

• Reduce risk from food
• Cook food to safe temps
• Do not sample meat until well cooked
• For Whole Cuts of Meat (excluding poultry)
• Cook to at least 145° F (63° C) as measured with a food thermometer placed in the thickest part of the meat. Allow the meat to rest* for three minutes before carving or consuming.
• For Ground Meat (excluding poultry)
• Cook to at least 160° F (71° C); ground meats do not require a rest* time.
• For All Poultry (whole cuts and ground)
• Cook to at least 165° F (74° C), and for whole poultry allow the meat to rest* for three minutes before carving or consuming.

• Reduce risk from environment
• Avoid drinking untreated water
• Wear gloves when in contact with soil as it may contain cat feces
• Wash hands with soap and warm water
• Keep outdoor sandboxes covered
• Feed cats only canned or dried commercial food or wellcooked table food, not raw or undercooked meats.

• Change the litter box daily if you own a cat.
• The Toxoplasma parasite does not become infectious until 1 to 5 days after it is shed in a cat's feces.
• If you are pregnant or immunocompromised :
• Avoid changing cat litter if possible. If no one else can perform the task, wear disposable gloves and wash your hands with soap and warm water afterwards
• Keep cats indoors
• Do not adopt or handle stray cats, especially kittens
• Do not get a new cat while you are pregnant.