Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (516 page)

   Laboratory Findings

   See Microsporidia Examination in Chapter
17
, Infectious Disease Assays.

   
Direct detection
: EM is the gold standard for confirming infection and speciation, if needed. Several modified trichrome stains have been described for detection of microsporidia in stool. Stool smears should be very thin to help avoid artifacts. Optical brightening agents, like calcofluor, stain microsporidia in stool but are nonspecific.

   
Histology
: Microsporidia may be identified by a number of histologic stains, like H&E, periodic acid–Schiff, and silver stains. Staining may be inconsistent. Detection may be improved by examination of stained touch preparations.

PINWORM INFECTION (
ENTEROBIUS VERMICULARIS
)

   Definition

Enterobius vermicularis
is a small roundworm with global distribution. Enterobiasis may be more common in temperate climates. Female worms migrate through the anus at night to deposit embryonated eggs on perianal skin. The worms develop into infective stage 3 larvae within the egg. The worms and eggs cause intense pruritus ani. The host fingers are contaminated during scratching, facilitating fecal– oral transmission. Once ingested, the eggs hatch and then mature to adult worms in the large intestine. Female worms can produce over 10,000 eggs per day.

   Who Should Be Suspected?

Poor hygiene and crowding are predisposing factors. Most infections are asymptomatic. Perianal itching is the most common symptom.

   Laboratory Findings

Pinworm Examination: See Chapter
17
, Infectious Disease Assays.

Direct detection
: Detection of adult female worms or eggs is the usual method of diagnosis. Because release into stool is relatively uncommon, collection of specimens from perianal skin using cellophane tape or “pinworm paddles” is recommended. Collection of multiple night or first-morning specimens is recommended. Three tests detect 90% of cases, and five tests detect 95% of cases.

Core laboratory
: Pinworm infection is not associated with eosinophilia.

SCHISTOSOMIASIS

   Definition

Schistosomiasis is caused by infection by species in the
Schistosoma
genus. The major pathogens are
Schistosoma mansoni
,
Schistosoma japonicum,
and
Schistosoma haematobium
. There is a very wide geographic distribution of schistosomiasis in tropical and subtropical areas.

Humans acquire infection when cercaria penetrates through skin while wading or swimming in an infected water source. Most disease manifestations are due to the host immune reaction to the worms and their eggs.

   Who Should Be Suspected?

   Cercarial dermatitis, a pruritic, papular rash of skin exposed to contaminated water, is a frequent manifestation of acute infection. Dermatitis is usually associated with
S. mansoni
and
S. haematobium
. Symptoms of acute infection develop 2–4 weeks after exposure and are most commonly seen with
S. japonicum
and
S. mansoni
infections. Symptoms include fever (Katayama fever), with chills and sweats, abdominal pain, diarrhea, headache, and cough. Hepatosplenomegaly and lymphadenopathy may be seen. Eosinophilia is typical. Biopsy or serologic testing is used for diagnosis of acute infection.

   
Schistosoma japonicum
infection, also known as Oriental blood fluke, is seen in Japan, China, Indonesia, and the Philippines. Clinical symptoms are similar to those of
S. mansoni
infection but may be more severe because of the higher egg production by female–male pairs. Hepatocellular and colorectal carcinomas have been associated with
S. japonicum
infection. Severe disease in the large intestine is typical. This may be associated with lower abdominal pain and cycles of diarrhea and constipation. Hepatosplenic disease, similar to
S. mansoni
but more severe, is common. CNS disease, manifested by a wide variety of symptoms, occurs in <5% of patients.