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
