PARASITES

VOCABULARY

• Medical parasitology: “the study and medical implications of parasites that infect humans”

• Eukaryote: a cell with a well-defined chromosome in a membrane-bound nucleus. All parasitic organisms are eukaryotes

• A parasite: “a living organism that acquires some of its basic nutritional requirements through its intimate contact with another living organism”. 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”

VOCABULARY

• 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

EPIDEMIOLOGY

• 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.

PARASITES

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

• Protozoa

• Helminths

• Ectoparasites

PROTOZOA

• 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

• 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

ECTOPARASITES

• 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)

LIFE CYCLE OF PARASITES

PROTOZOA

GIARDIA

• 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

GIARDIA• 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.

TRANSMISSION

• Infected with Giardia occurs by swallowing Giardia cysts (hard shells containing Giardia) found in contaminated food or water

• swallowing as few as 10 cysts might cause someone to become ill (1,2)

• Fecal-oral transfer of cysts person-to-person

• Animal- to- person transmission

• Often transmitted by asymptomatic carriers

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.

Trophozoite• Colonizes in the intestines of mammals• Definiteve host- Human intestine

• Duodenum and Jejunum

Cyst• Contaminated

material• Definiteve host-

Human colon• Sigmoid colon

GIARDIA

Risks• 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

Prevention• Good hygiene

• Washing hands

• In child care settings- children 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.

CHLORINE DISINFECTION

TIMETABLE

GIARDIA• 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.

GIARDIA

Diagnosis

• Because Giardia cysts can be excreted intermittently, multiple stool collections (i.e., three stool specimens collected on separate days) increase test sensitivity(1)

• Water-like feces• Trophozoite

• Formed feces• Cysts

Treatment

• Several drugs can be used to treat infection

• Effective treatments include metronidazole, tinidazole, and nitazoxanide (2)

• Combination therapy may be effective

1. 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. 2. Drugs for Parasitic Infections: The Medical Letter; 2010

ENTAMOEBA HYSTOLYTICA

• 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

TRANSMISSION

• 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

ENTAMOEBA HYSTOLITICA

Risks• Anyone can get it, but most

common in people who live in tropical regions with poor sanitation

• In the U.S.• People who have traveled to

tropical places that have poor sanitary conditions

• Immigrants from tropical countries that have poor sanitary conditions

• People who live in institutions that have poor sanitary conditions

Prevention• Handwashing (soap & clean water)

• Boiling water used for drinking & food preparation (10-15 minutes)

• When traveling• Drink only bottled or boiled water

• Don’t drink juices, fountain drinks or any drinks with ice cubes

• Don’t drink fresh fruit or vegetables not personally prepared

• Avoid street foods and drinks if possible

CLINICAL SYMPTOMS

• 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 AND TREATMENT

Diagnosis• 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.

Treatment• Several diff. medications

depending on severity and nature of disease

• Asymptomatic- Meds of choice are iodoquinol and paromomyosin

• Symptomatic- Mild, moderate, severe- metronidazole, tinidazole

TOXOPLASMA GONDII

• 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.

TOXOPLASMOSIS

• 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.

TOXOPLASMOSIS-TRANSMISSION

• 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

FOODBORNE TRANSMISSION

• 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

ANIMAL-TO-HUMAN

• 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.

ANIMAL-TO HUMAN• 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

MOTHER-TO-CHILD

• 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

SYMPTOMS• 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

• 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.

TREATMENT• 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

TREATMENT• 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

PREVENTION• 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.

PREVENTION• 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 well-

cooked table food, not raw or undercooked meats.

PREVENTION• 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.