Protozoal and Helminth Infections Flashcards
Learning objectives: (suggested to utilize)
helminth infestations
malaria
pinworms
toxoplasmosis
Enterobiasis aka “Pinworms”
Transmitted person-to-person via
Ingestion of eggs after contact with the hands or perianal region of an infected individual (P for perianal and P for pinworms)
Food or fomites that have been contaminated by an infected individual
Infected bedding or clothing
Pinworms:
Eggs hatch in the duodenum and larvae migrate to the cecum, setup camp
Females mature in about a month and remain viable for about another month
During this time they migrate through the anus to deposit large numbers of eggs on the perianal skin
Due to the relatively short lifespan of these helminths, continuous reinfection is required for long-standing infection (child scratching perianally without washing hands)
Pinworms:
Eggs hatch in the duodenum and larvae migrate to the cecum, setup camp
Females mature in about a month and remain viable for about another month
During this time they migrate through the anus to deposit large numbers of eggs on the perianal skin
Due to the relatively short lifespan of these helminths, continuous reinfection is required for long-standing infection
pinworms: signs and symptoms
itching in and around anus (most important, obvious)
malaise/unwell
restless sleep
eggs visualized
vaginal inflammation
pain, rash, skin irritation
abdominal pain
nausea
pinworms: demographics
Enterobius vermicularis common cause of intestinal infections worldwide
Maximal prevalence in school-age children (bolded)
pinworms: signs and symptoms
Most are asymptomatic
Nocturnal perianal pruritus (itching) is common
Insomnia, restlessness, and enuresis (involuntary urination) are common in children
Perianal scratching may result in excoriation and impetigo (highly contagious skin infection)
Serious sequelae are uncommon
But colonic ulceration and eosinophilic colitis have been report
pinworms: lab tests
Pinworm eggs usually not found in stool
Diagnosis is made by finding adult worms or eggs on the perianal skin
“Scotch Tape Test”:
Apply clear cellophane tape to the perianal skin in the early morning, followed by microscopic examination for eggs
The sensitivity of this test is about 90% for three tests
Nocturnal examination of the perianal area or gross examination of stools may reveal adult worms, which are about 1 cm in length
Eosinophilia is rare(!!!)
pinworms: meds & therapeutics
Single oral dose of:
albendazole (400 mg),
mebendazole (100 mg)
or pyrantel pamoate
(“the -bendazoles”)
Other infected family members or contacts should be treated concurrently
Standard handwashing and hygiene practices are helpful in limiting spread
Perianal scratching should be discouraged
Washing of clothes and bedding should kill pinworm eggs
Fasciolopsiasis aks “Intestinal Flukes”
Fasciolopsis buski is a common parasite of pigs and humans in eastern and southern Asia(!!!)
Eggs shed in stools and hatch in fresh water
Followed by infection of snails and release of cercariae that encyst on aquatic plants
Humans are infected by eating uncooked water chestnuts, bamboo shoots, and watercress
Adult flukes mature in about 3 months and live in the small intestine attached to the mucosa, leading to local inflammation and ulceration
Intestinal flukes: clinical findings
Infection is often asymptomatic, but eosinophilia may be marked
In symptomatic cases, manifestations include epigastric pain and diarrhea
Uncommon findings:
-Other gastrointestinal symptoms
-Ileus
-Edema
-Ascites
Intestinal flukes: diagnosis
Depends on finding characteristic eggs in stool
Occasionally, adult flukes in the stools
Moderate eosinophilia is common (hallmark!)
Illness >6 months after travel to endemic area is unlikely
Intestinal flukes: treatment
Praziquantel
(Drug of choice!!)
Triclabendazole and niclosamide are alternatives (for most species)
Noninvasive Cestode Infections aka “Tapeworms”
6 tapeworms infect humans frequently:
Large tapeworms:
Taenia saginata (the beef tapeworm, up to 25 m in length)
Taenia solium (the pork tapeworm, 7 m)
Diphyllobothrium latum (the fish tapeworm, 10 m)
The small tapeworms are:
Hymenolepis nana (the dwarf tapeworm, 25–40 mm)
Hymenolepis diminuta (the rodent tapeworm, 20–60 cm)
Dipylidium caninum (the dog tapeworm, 10–70 cm)
Tapeworms
Humans are the only definitive host of T saginata (beef) and T solium (pork)
Humans are infected by eating raw or undercooked infected meat
An adult tapeworm consists of a head (scolex), a neck, and a chain of individual segments (proglottids) in which eggs form in mature segments
Tapeworms: demographics
Infection most common in cattle breeding area
Gravid segments of T saginata are passed in human feces to soil, where they are ingested by grazing animals, especially cattle
The eggs then hatch to release embryos that encyst in muscle as cysticerci
Tapeworms: signs and symptoms, lab tests, diagnostic procedures
signs/symptoms:
-Most infected persons are asymptomatic
-Abdominal pain and other gastrointestinal symptoms may be present
Laboratory Tests:
-Complete blood count; eosinophilia is common
Diagnostic Procedures
-Infection is often discovered by finding passage of proglottids in stool
Tapeworms: Treatment
Praziquantel (single dose)
(Drug of choice!!)
Side effects include: headache, malaise, dizziness, abdominal pain, nausea
Niclosamide (Alternative therapy)
Side effects include nausea, malaise, abdominal pain
Tapeworms: prevention
Cysticercus bovis is killed by cooking at 133°F (56°C) or freezing at –10°C for 5 days
Pickling is not adequate
Prognosis is excellent with therapy
Ascariasis
Ascaris lumbricoides is the most common intestinal helminth
Infection follows ingestion of eggs in contaminated food
Larvae hatch in the small intestine
Penetrate the bloodstream
Migrate to lungs, then back to the gastrointestinal tract where they develop into adult worms (pearl!!)
Adult worms can be up to 40 cm long and live for 1–2 years
Ascaris: Demographics
Causes about 800 million infections, with 12 million acute cases and 10,000 or more deaths annually
Prevalence is high wherever there is poor hygiene and sanitation or where human feces are used as fertilizer
Heavy infections are most common in children
Ascaris: signs and symptoms
Most infected persons are asymptomatic
The following symptoms develop in a small number of patients during migration of worms through the lungs(PEARL):
Fever
Nonproductive cough
Chest pain
Dyspnea
Eosinophilia
Eosinophilic pneumonia (occasionally)
Ascaris: sign/symptoms cont. (respiratory most important to recall)
Rarely, larvae lodge ectopically in the brain, kidney, eye, spinal cord, and other sites and may cause local symptoms
With heavy infection, abdominal discomfort may be seen
Adult worms may migrate and be coughed up, vomited, or may emerge through the nose or anus
Ascaris: Lab tests
Diagnosis is made after adult worms emerge from the mouth, nose, or anus or by identifying characteristic eggs in the feces, usually with the Kato-Katz technique (breaking down stool sample then smear and look under microscope)
Eosinophilia is marked during worm migration but may be absent during intestinal infection
Ascaris: imaging studies
Chest radiographs may show pulmonary infiltrates
Plain abdominal films and ultrasonography can demonstrate worms, with filling defects in contrast studies and at times evidence of intestinal or biliary obstruction
Ascaris: treatment
All infections should be treated
Treatments of choice (-azole):
Albendazole (400 mg single dose)
Mebendazole (500 mg single dose or 100 mg twice daily for 3 days)
Pyrantel pamoate (11 mg/kg single dose, maximum 1 g)
All three of these drugs are well tolerated but may cause mild gastrointestinal toxicity
Ascaris: treatment
Albendazole considered safe for children older than 1 year and in pregnancy, although use in the first trimester is best avoided
Intestinal obstruction usually responds to conservative management and anthelminthic therapy
Surgery for appendicitis and other gastrointestinal complications
Trichuriasis aka “Whipworms”
Infects about 500 million persons throughout the world, particularly in humid tropical and subtropical environments
Infection is heaviest and most frequent in children.
Infections are acquired by ingestion of eggs.
The larvae hatch in the small intestine and mature in the large bowel to adult worms of about 4 cm in length
The worms do not migrate through tissues (not in muscles, lungs, etc.)
Whipworm: signs & symptoms
Most infected persons are asymptomatic
Heavy infections may be accompanied by:
abdominal cramps
tenesmus (diarrhea dry heaves)
diarrhea
distention
nausea
vomiting
Whipworms: Trichuris dysentery
The Trichuris dysentery syndrome may develop…
-Particularly in malnourished young children
-findings resembling IBD including bloody diarrhea and rectal prolapse.
-Chronic infections in children can lead to iron deficiency anemia and growth retardation
Whipworms: lab tests
Diagnosed by identification of characteristic eggs and sometimes adult worms in stools
Eosinophilia is common
Treatment is typically with:
albendazole (400 mg/day orally) or mebendazole (200 mg/day orally)
Hookworm disease
Infection with Ancylostoma duodenale and Necator americanus is very common, especially in most tropical and subtropical regions
When eggs are deposited on warm moist SOIL they hatch, releasing larvae that remain infective for up to a week
With contact, the larvae penetrate skin and migrate in the bloodstream to the pulmonary capillaries
In the lungs, larvae penetrate into alveoli and then are carried by ciliary action upward to the bronchi, trachea, and mouth
Hookworms:
After being swallowed, they reach and attach to the mucosa of the upper small bowel, where they mature to adult worms
Worms suck blood at attachment site
Blood loss is proportionate to worm burden
Hookworms: Signs & symptoms
Most infected persons are asymptomatic
A pruritic maculopapular rash (ground itch) may occur at the site of larval penetration (hallmark rash)
Pulmonary symptoms may be seen during larval migration through the lungs
-Dry cough
-Wheezing
-Low-grade fever
Signs & Symptoms cont.
Eosinophilia is common, especially during the phase of worm migration
About 1 month after infection, gastrointestinal symptoms may develop
Epigastric pain
Anorexia
Diarrhea
Signs & Symptoms cont.
Persons chronically infected with large worm burdens may have:
-Abdominal pain
-Anorexia
-Diarrhea
-Pallor, weakness, dyspnea, HEART FAILURE due to marked iron deficiency ANEMIA
-Hypoalbuminemia, edema, and ascites due to protein malnutrition
-May have impairment in growth and cognitive development in children
Signs & Symptoms cont.
Persons chronically infected with large worm burdens may have:
-Abdominal pain
-Anorexia
-Diarrhea
-Pallor, weakness, dyspnea, heart failure due to marked iron deficiency anemia
-Hypoalbuminemia, edema, and ascites due to protein malnutrition
-May have impairment in growth and cognitive development in children
Signs and symptoms cont.
Infection with the dog hookworm Ancylostoma caninum can uncommonly lead to
Abdominal pain
Diarrhea
Eosinophilia
Intestinal ulcerations and regional lymphadenitis
Hookworms
have the itchy rash that is weird and unique, and no other worm is so bad it will drain your blood (itchy dracula worms)
Hookworms: Diagnosis
Based on the demonstration of characteristic eggs in feces
Concentration techniques are usually not needed
Microcytic anemia, occult blood in the stool, and hypoalbuminemia are common
Eosinophilia is common, especially during worm migration
Hookworms: Diagnosis
Based on the demonstration of characteristic eggs in feces
Concentration techniques are usually not needed
Microcytic anemia, occult blood in the stool, and hypoalbuminemia are common
Eosinophilia is common, especially during worm migration
Hookworms: Treatment
Albendazole (single 400 mg orally dose) or mebendazole
Anemia should be managed with iron replacement and, for severe symptomatic anemia, blood transfusion
Mass treatment of children with single doses of albendazole or mebendazole at regular intervals limits worm burdens and the extent of disease and is advocated by the World Health Organization
Trichinella
Transmission occurs:
By ingestion of undercooked meat, most commonly pork in areas where pigs eat garbage
By ingestion of game and other animals, including bear and walrus in North America and wild boar and horse in Europe
Trichinella
When infected raw meat is ingested, Trichinella larvae are freed from cyst walls by gastric acid and pass into the small intestine
Larvae then invade intestinal epithelial cells, develop into adults, and the adults release infective larvae (which may be viable for years)
Parasites travel via the bloodstream to skeletal muscle where they invade muscle cells, enlarge, and form cysts (PEARL)
Trichinella: Signs & symptoms
Most infections are asymptomatic
In symptomatic cases, gastrointestinal symptoms (eg, diarrhea, vomiting, abdominal pain)
-Develop within 1 week after ingestion of contaminated meat
-Usually last for < 1 week but can persist for much longer
Tichinella: S&S cont.
During the following week, migrating larvae may produce:
Fever, myalgias, periorbital edema, and eosinophilia (most notably)
Headache
Cough
Dyspnea
Hoarseness, dysphagia
Macular or petechial rash
Subconjunctival and retinal hemorrhages
(note: as eosinophils travel around in bloodstream, they cause systemic immune response)
Trichinella: S&S cont.
Usually peak within 2–3 weeks
Commonly persist for about 2 months
In severe cases, generally with large parasite burdens, muscle involvement can be pronounced, with severe muscle pain, edema, and weakness, especially in the head and neck
Muscle pain may persist for months
Trichinosis: Lab tests
Elevated serum muscle enzymes (creatine kinase, lactate dehydrogenase, aspartate aminotransferase)
Erythrocyte sedimentation rate usually normal
A commercial ELISA is available in the United States
Serologic tests become positive 2 or more weeks after infection, but cross-reactivity can be seen with other parasites
Rising antibody titers are highly suggestive of the diagnosis
Trichinella: Diagnostic procedures
Muscle biopsy (invasive)
Can usually be avoided
If diagnosis is uncertain, biopsy of a tender, swollen muscle may identify Trichinella larvae
For maximal yield, specimen should be examined histologically, and a portion enzymatically digested to release larvae
However, larvae may not be seen in muscle until 3 weeks after infection
Trichinosis: Meds
No effective specific therapy for full-blown trichinosis
However, mebendazole (2.5 mg/kg orally twice daily) or albendazole (5–7.5 mg/kg orally twice daily) will kill intestinal worms and may limit progression to tissue invasion
Therapeutic Procedures
Supportive therapy for systemic disease consists of:
Analgesics (pain killer)
Antipyretics
Bed rest
Corticosteroids for severe illness (anti-inflamm)
Malaria (protozoal)
Systemic infection by plasmodia protozoa transmitted through bites of mosquitoes
90% of the cases are reported from AFRICA
Malaria: Risk Factors
Traveling to endemic regions
Pregnancy
Age < 5 years
HIV infection
Malaria: Pathogenesis
Sporozoites in infected mosquito saliva enter human bloodstream during bite
Sporozoites travel to liver for incubation. They rupture and release merozoites into the blood
Malaria: Pathogenesis
Sporozoites in infected mosquito saliva enter human bloodstream during bite
Sporozoites travel to liver for incubation. They rupture and release merozoites into the blood
Malaria: signs & symptoms
Fever
Vomiting
Headache
Cough
Chills
Body aches
Anorexia
Diarrhea
If not treated:
anemia
jaundice
respiratory distress syndrome
cerebral malaria
Malaria: diagnosis & managment
Peripheral blood smear:
Giemsa smear (exclusion should be based on 3 negative smears within 48 hours)
3-day treatment with artemisinin combination therapy (ACT)
Malaria: Prevention
mosquito netting, repellent, use screens, stay inside at night, wear long sleeves, etc.
Malaria: Prevention cont.
Drug choices (taking before a trip):
Chloroquine (TEST: really only used as anti-malarial med, easily tolerated)
Atovaquone-proguanil
Mefloquine
Doxycycline
Primaquine
Toxoplasmosis
Protozoan parasite Toxoplasma gondii
Transmission: ingestion of tissue cysts in infected meat, ingestion of soil, food, or water contaminated by oocysts or directly from FELINE FECES (PEARL)
Toxoplasmosis
Found worldwide
Estimated 1/3 of human population is infected worldwide
United States:
2nd leading cause of death and fourth leading cause of hospitalization from foodborne illness
Toxoplasmosis: clinical manifestations
Immunocompetent:
-Primary infection may be asymptomatic or cause mononucleosis like syndrome
-Retinochoroiditis
Immunocompromised:
-Encephalitis (brain inflammation)
-Retinochoroiditis
-Myocarditis
-Pneumonitis
-Acute respiratory failure
Toxoplasmosis: Diagnosis
ELISA for serum IgM and IgG antibodies
Detection of parasites:
-Microscopy
-PCR
-Culture
Toxoplasmosis: Management
Acute primary infection usually self-limiting
Treatment not usually needed in non-pregnant, immunocompetent persons
pyrimethamine plus either sulfadiazine or clindamycin
< 18 weeks of pregnancy and low suspicion of fetal infection, spiramycin
≥ 18 weeks of pregnancy or if fetal infection suspected combination therapy with pyrimethamine plus sulfadiazine and folinic acid for duration of pregnancy
Toxoplasmosis: Complications
Reactivation may occur and cause encephalitis, retinochoroiditis, myocarditis, pneumonitis
most infected neonates are asymptomatic at birth
manifestations may develop if untreated, such as:
retinochoroiditis
hydrocephaly
intellectual disability
seizure
delayed growth
Infection of back of the eye (chorioretinitis)=toxoplasmosis!!!
ring-enhancing lesions aka calcification in brain = toxoplasmosis!!
