Download Parasitic Infections

Parasitic Infections
I.
II.
The class of parasitic infectious agents is divided into two parts: Protozoa and Helminths
a. Risk factors for acquisition:
i. Age (children)- fecally contaminated, eat everything
ii. Low socioeconomic status
iii. Poor sanitation, food, water, personal hygiene
iv. International travel
v. Crowding- school, jail, daycare
vi. Co-morbid medical conditions
vii. Gastric hypoacidity- acid not acidic enough
viii. Immunosuppression- AIDs
Protozoa- Single celled animal that characteristically divides and multiplies as a host
i. Transmitted through direct fecal/oral route
ii. Do not cause eosinophilia
b. Organisms:
i. Amoeba: Entamoeba histolytica, naegleria, Acanthamoeba
ii. Protozoa: Giardia lamblia, Cryptosporidium, Balantidium coli, Trichomonas vaginalis
c. Amebiasis is an infection with the intestinal protozoan Entamoeba histolytica
i. Infection is acquired by: ingest viable cysts from fecally contaminated water, hands, and food
ii. Motile trophozoites released from cysts in the small intestine and, in most patients (90%), remain as
harmless inhabitants of the large bowel; in others the trophozoites invade the bowel mucosa, causing
symptomatic colitis(inflammatory diarrhea), or bloodstream, causing distant abscesses of the liver
(MC place to get a cyst from this), lungs, or brain
iii. Infectious cysts are shed in the stool and can survive for several weeks in a moist environment
iv. S/S: asymptomatic, bloody stool, high fever, abdominal pain, anorexia, weight loss
v. Dx: Trophozoites or cysts on stool examination, serological tests (ELISA)
vi. Tx: Metronidazole + iodoquinol; surgery- drainage of abscess, usually the liver
d. Free living amoeba: Found in wide variety of fresh and brackish water, including that from lakes, taps, hot
springs, swimming pools, and heating and air conditioning units
i. Naegleria- Primary amebic meningoencephalitis caused by follows the aspiration of water
contaminated with trophozoites or cysts leading to invasion of the olfactory neuroepithelium; causes:
rhinorrhea of smell, frontal headache, regular signs of meningitis
1. Diagnosis- consider in purulent meningitis without bacteria on gram stain; CSF culture
2. Treatment- high dose amphotericin B and rifampin; poor prognosis
e. Acanthamoeba- also causes encephalitis, but keratitis is associated with: eye trauma or splashed in the eye
with contaminated water, occurs with extended wear contact lenses
1. Treatment: keratitis- topical miconazole, meningoencephalitis-sulfadiazine
f. Giardiasis: Infection follows ingestion of cysts that release organisms into the small bowel. Perfuse watery
diarrhea, does not disseminate outside of the GI tract
i. Because cysts are infectious when excreted or shortly thereafter, person-to-person transmission
occurs where fecal hygiene is poor. Waterborne transmission accounts for episodic infections
(campers, hikers) and massive epidemics. Surface water, ranging from mountain streams to large
municipal reservoirs, can become contaminated with fecally derived Giardia cysts
ii. Reservoirs: carries the organism; beaver, dogs, and cats
iii. S/S: watery diarrhea, N/V, significant malabsorption, lactose intolerance
III.
iv. Dx: Detection of parasite or cysts in feces
v. Tx: metronidazole
g. Cryptosporoidosis: parasitic disease acquired through consumption of cysts (food, water, person-to-person)
that liberate and infect intestinal epithelial cells causing self-limited diarrhea in immune-competent hosts
i. S/S: diarrhea, abdominal pain, anorexia, fever, weight loss, electrolyte abnormalities
1. Boiling water kills the parasite
ii. Tx: paromycin for HIV patients
iii. Dx: with serological titers
h. Balantidiasis- infection with parasite Balantidium coli caused by ingested cysts
i. Reservoirs: Pig
ii. S/S: diarrhea, dysentery (bloody diarrhea), abdominal pain
iii. Dx: detection of cyst or organism in stool; stays in the GI tract
iv. Tx: Tetracycline
i. Trichomoniasis- Trichomonas vaginalis is a pathogen of the GU tract causing symptomatic lower genital
tract infection in both males and females; it is transmitted via sexual intercourse
i. S/S: Frothy yellowish-green malodorous discharge, itchy, erythema, dysuria, dyspareunia
ii. Dx: detection of motile organisms on wet mounts of genital secretions
iii. Tx: metronidazole
Helminths (worms) - multi cellular animals, do not multiply within the host. Eosinophilia on CBC. More
symptoms/invasions, the more eosinophilia
a. Nematodes: elongated, symmetric round worms that predominantly infect either intestines or tissues
i. Symptoms due to invasive larval stage
b. Organisms: ascaris lumbricoides, necator americanus, ancylostoma duodenale and brazillense, toxocara
canis/cati, strongyloides stercoralis, trichinella spiralis, enterobius vermicularis, trichuris trichiura
c. Ascariasis- disease caused by largest intestinal nematode: Ascaris lumbricoides (40cm); clinical disease
arises from larval migration in the lungs or effects of the adult worm in the intestines. Mature female worms
live for 1-2 years and may produce up to 240,000 eggs/day that pass with feces. After infective eggs are
swallowed, larvae hatched in the intestine invade mucosa, migrate through circulation to lungs, break into
alveoli, ascend bronchial tree and return via swallowing to the small intestine
i. S/S: burning substernal chest pain, SOB, hemoptysis, GI tract, asymptomatic, large mass of worms
can form obstruction. Large cream colored worm
ii. Dx/Labs: eosinophilia, pneumonitis with transient CXR changes, detection of eggs or worm (large,
cream-colored) in feces
iii. Tx: abendazole, mebendazole- anti-helminth drug that destroys, paralyzes, or alters worms
permeability
d. Hookworms: it is estimated that ¼ of the world’s population is asymptomatically infected with one of the 2
species: Necator americanus or Ancylostoma duodenale. Infection in same was as Ascariasis. These worms
use teeth or cutting plates to attach to the small bowel mucosa and suck blood (0.2ml/day/adult worm). They
produce thousands of eggs daily and adults may live 6-8 years
i. Hook worm disease from heavy burden of worms, inadequate intake of iron
ii. S/S: iron deficient anemia, transient pneumonitis, epigastric pain, inflammatory diarrhea
iii. Dx/Labs: eosinophilia, iron deficiency, demonstration of eggs in feces
iv. Tx: abendazole, mebendazole, iron replacement
e. Cutaneous larva migrans- skin eruption caused by burrowing larvae of hookworms, Ancylostoma
brazillense; infection occurs after skin contact with soil contaminated with cat and dog feces. Larvae
penetrate the skin and intensely pruritic erythematous lesions from along the tortuous tracts of their
IV.
migration through the dermal-epidermal junction, advancing several cm/day. The larvae does not
mature in humans and dies off in several weeks with resolution of skin lesions
i. Dx: clinically established, skin biopsy
ii. Tx: albendazole
f. Visceral larva migrans- a syndrome caused by nematodes normally parasitic for non-human hosts; in
humans the larvae migrate through host tissues and elicit eosinophilia/inflammation
i. Toxocara canis/cati- two most common forms from cat/dog feces. Can be ingested as well as through
infiltration
1. Larvae invade the intestinal mucosa and spread to the liver, lungs, CNS, and other sites
provoking intense local inflammation
2. S/S: fever, cough, wheezing, SOB, hemoptysis, hepatosplenomegaly, pruritic rash at skin site
3. Dx/Labs: eosinophilia, ELISA antibody titer, transient pulmonary infiltrates on CXR
4. Tx: Usually self-limited, mebendazole, albendazole; steroids for severe inflammation
g. Strongyloidiasis- Strongyloides stercoralis, Threadworm, is distinguished due to its ability to replicate on
the human host permitting ongoing cycles of autoinfection as infection can persist for decades without
further exposure to exogenous infective larvae; it also can undergo a free-living cycle of development in the
soil. It is acquired when larvae in fecally contaminated soil penetrate the skin- disseminate as in Ascariasis.
In reinfection, larvae follow same migration, only penetrating intestinal mucosa
i. S/S: pruritic red rash, abdominal pain, GI bleed, inflammatory diarrhea, intestinal obstruction
ii. Dx/Labs: Demonstration of larvae in feces, eosinophilia
iii. Tx: Ivermectin, albendazole
h. Trichinellosis- disease caused by parasite Trichinella spiralis that occurs after ingestion of meat (pork)
containing cysts; parasite is liberated in small intestine, invades mucosa and matures. Females release larvae
through circulation and infiltrate striated muscle.
i. S/S: asymptomatic, severe enteritis (week 1), periorbital edema (week 2), myositis, fever, rash,
hypersensitivity reaction, myocarditis with dysrhythmias, encephalitis, or pneumonitis
ii. Dx/Labs: eosinophilia, increase IgE, rise in antibody titer (3rd week), muscle biopsy demonstrates
larvae
iii. Tx: mebendazole, albendazole effective only against enteric stage; steroids for severe myositis
i. Enterobiasis- pinworm infection; in the US>40 million people are estimated to be infected (school-age).
Less than a cm and live in a bowel, lays 10,000 eggs a night
i. S/S: asymptomatic. Perianal pruritus and itching worse at night, abdominal pain, weight loss, may
invade the female genital tract causing vulvovaginitis
ii. Dx: scotch tape tape to perianal region in morning demonstrates eggs
iii. Tx: mebendazole
j. Trichuriasis- infection with whipworm Trichuris trichiura, usually asymptomatic
i. S/S: abdominal pain, anorexia, bloody diarrhea, malnourishment
ii. Dx: demonstration of whipworm eggs in stool
iii. Tx: mebendazole
Trematodes: flatworms or “flukes”-Flattened, bilateral symmetric bodies with 2 suckers characterized by
human tissue they invade during their disease course. Infection is by invasion of skin or ingestion.
a. Organisms: Schistosoma species, Clonorchis sp, Fasciola sp, Paragonimus sp
b. Schistosomiasis: human infection from infected snails in freshwater bodies; suckers aid in penetration of
intact skin- organisms undergo transformations in human host to facilitate migration via blood and lymph
vessels reaching the lungs and liver. Their eggs are deposited intravascularly; move through the venous wall
and into the GI or GU tract to be voided in stool or urine
V.
VI.
i. S/S: dermatitis at entry site, Serum sickness like- cytokine release, general lymphadenopathy fever,
hepatosplenomegaly
1. Intestinal species- GI and hepatosplenic disease, portal HTN, abdominal pain and dysentery
2. Vesicular (Egyptian)- GU disease, Dysuria, frequency, hematuria- increased risk of bladder
cancer
3. Other- may affect the cardiopulmonary (pneumonitis) and CNS (encephalitis)
ii. Dx/Labs: eosinophilia, serology for antibodies, FAST-ELISA (Falcon-assay screening test)
iii. Tx: Praziquantel
c. Clonorchiasis: Infection with “Chinese liver fluke” transmitted by ingestion of raw or undercooked
freshwater fish. Released into duodenum and travel to bile ducts
d. Fascioliasis: Infection with “Sheep liver fluke” attached to aquatic plants or ingestion of contaminated
water; parasite released in GI tract, penetrates gut wall and travel through peritoneal cavity to bile ducts
i. S/S: RUQ pain, fever, symptoms of cholangitis/cholecystis, jaundice
ii. Dx: Stool examination for eggs, serology
iii. Tx: Praziquantel
e. Lung Fluke- Infection with Paragonimus sp from reservoirs of wild and domestic felines; human
transmission occurs via ingestion of infected crayfish and freshwater crabs. Exist in the duodenum.
Penetrate gut wall, travel to peritoneum, diaphragm, pleural space into the lung. Eggs are expectorated into
the lungs, swallowed, and passed via the stool
i. Dx: demonstration of eggs in sputum or stool
ii. Tx: Praziquantel
Cestodes- segmented tapeworms; adults reside in GI tract, larvae can be found in almost any organ
a. This worm attaches to intestinal mucosa by means of sucking cups located on the scolex; behind this
structure is a short narrow neck from which segments form
b. As the worm matures, each segment is displaced further back from the neck
c. Segments may be noted in their feces, are often motile and cause perianal discomfort at passage
d. S/S: abdominal pain, nausea, change in appetite, weakness, and weight loss/increased appetite with no
weight gain
e. Dx: demonstration of eggs or segments in feces, serology
f. Organisms:
i. Taenia saginata- beef tape worm
1. Tx: Praziquantel
ii. Taenia solium- pork tape worm
1. May infect the brain, skeletal muscle, subcutaneous tissue, or the eye
2. Tx: Praziquantel; surgery
iii. Taenia Latum- fish tape worm
iv. Fingernail size or larger
v. Neuro complications: seizures, hydrocephalus secondary CSF obstruction, altered mentation
Hemoflagellates: infect blood and tissues
a. Organisms: Leishmania and Trypanosoma
b. Leishmania- transmitted by bite of female sandfly; cause visceral and mucocutaneous disease
i. Visceral disease- “kala-azar=black fever”
1. Skin turns gray, patient gets cachectic, splenomegaly, pancytopenia, peripheral
lymphadenopathy, febrile
ii. Cutaneous disease: papule at bite site, regional lymphadenopathy and ulcerative lesions
iii. Diagnosis: demonstrate pathogen with biopsy + Giemsa stain, culture, serology (PCR)
VII.
iv. Treatment: antimony, amphotericin B, pentamidine
c. Trypansoma- parasitic disease identified via blood smears or serology (PCR)
i. “Chagas Disease”- transmitted by reduvid bugs feces expelled when feeding and transmitted via
breaks in the skin, mucus membranes or conjunctiva
1. Indurated lesion at site of entry (Romana’s signs- periocular swelling), development of
interstitial edema, lymphadenopathy, muscular invasion (including myocardium- thinning
ventricle walls, apical aneurysm, conduction disease), GI dilation, encephalitis
2. Treatment: nifurtimox and benznidazole
ii. “African Sleeping Sickness”- transmitted by tsetse fly bite
1. Indurated lesion at the site of entry followed by systemic febrile illness with dissemination to
the CNS
a. Often have nighttime insomnia
b. Widespread lymphadenopathy and splenomegaly
c. Extra-pyramidal signs- Tremors, tics, chorea, and gait abnormalities
2. Treatment: suramin, pentamidine, and organic arsenicals
d. Toxoplasmosis: opportunistic disease caused by Toxoplasma gondii transmitted via cyst ingestion and
organism is released in the small intestine. Cat feces or raw meat.
i. High risk- HIV and pregnant women( abortion)
ii. S/S: asymptomatic, lymphadenopathy, encephalitis, myocarditis, pneumonitis, CNS involvement
iii. Diagnosis: Serology IgG and IgM antibody, ELISA
iv. Treatment: Pyrimethamine and sulfadiazine
Treatment in general:
a. Nutrient support may be required
i. Lactose free diet, increase fiber, reduce caffeine
b. Educating the patient is important to reduce the risk of reinfection or transmission
c. Bowel paralyzing drugs, for diarrhea caused by invasive organisms, are relatively contraindicated