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650.e2 Mesocestoides Infection

Mesocestoides Infection Client Education
Sheet
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intermediate host, the cysticercoid develops
BASIC INFORMATION
tissues of the cestodes) may be present.
into a tetrathyridium. round to oval structures that are remnant
Definition • The tetrathyridium is the second larval stage • Tetrathyridia are often found on aspiration
Infection with an adult cestode (tapeworm) and often occurs in the peritoneal cavity and of cystic lesions or of histopathologic exam
occurs in the small intestine of mammals musculature of the second intermediate host. of infected tissues.
(frequently dogs) and birds. The larval or • Dogs and cats are presumably infected by
metacestode stage of this tapeworm, the ingestion of the tetrathyridia in the second Advanced or Confirmatory Testing
tetrathyridium, may infect serous cavities of intermediate host (i.e., from capturing Recovery of organisms from peritoneal cavity,
many animals, particularly canines, causing infected birds, snakes, and small mammals with identification of cestode DNA with
ascites and pleural effusion. as prey). polymerase chain reaction (PCR)
• Dogs often serve as definitive hosts, harboring
Epidemiology the adult tapeworms.
SPECIES, AGE, SEX • Dogs may be infected by the larval stages of TREATMENT
There is a wide range of intermediate hosts the parasite, the tetrathyridia, by ingesting Treatment Overview
(reptile, avian, amphibian, and mammals), the first intermediate host or by ingesting The adult stage of this parasite in the canine
especially carnivores. Domestic and wild canids tetrathyridia in the second intermediate host. small intestine can be easily treated. The larval
may serve as definitive hosts and harbor the • Tetrathyridia develop into adult tapeworms tetrathyridium stage in serous cavities is almost
adult stages of the tapeworm. Cats may also (16-20 days in dogs, longer in cats) in the impossible to eliminate because of its ability to
serve as definitive hosts. intestine and rarely produce clinical disease. undergo uncontrolled asexual multiplication,
• Some tetrathyridia migrate through the intes- and the goal of ongoing treatment becomes
RISK FACTORS tinal wall into the subcutaneous tissues, liver, palliation of the infection.
Hunting, scavenging carrion, and exposure to lungs, retroperitoneal space, or abdominal
wildlife and thoracic cavities. These tetrathyridia are Acute General Treatment
capable of asexual multiplication by binary • Laparotomy and lavage of peritoneal cavity
CONTAGION AND ZOONOSIS fission; one tetrathyridium splits into two may be helpful to decrease larval tetrathyridia
Unknown; infections with adult tapeworms in tetrathyridia, two into four, and so on. The burdens, but the sheer numbers of tetrathy-
humans have been reported. tetrathyridia multiply to the point that they ridia may prevent complete removal.
completely fill and expand the peritoneal • Anthelmintics
GEOGRAPHY AND SEASONALITY and pleural cavities. ○ For adult organisms, praziquantel 5 mg/
• Many parts of the world, including Africa, • Tetrathyridia may incite a nonpurulent kg PO, repeat in 2 weeks
Asia, and throughout the United States granulomatous inflammatory response on ○ For larvae, fenbendazole 100 mg/kg PO
• There is no seasonal association for this serosal surfaces. q 24h for 28 days (off-label use). Side
cestode/metacestode. effects (bone marrow toxicosis, hypersen-
Clinical Presentation DIAGNOSIS sitivity reaction, gastrointestinal signs) are
possible.
HISTORY, CHIEF COMPLAINT Diagnostic Overview
• Small sesame seed–appearing tapeworm A patient with abdominal or pleural effusion Recommended Monitoring
segments may be noted on the perineum whose centesed fluid is grossly milky white Regular fecal exams
or in the feces by the owner. should be suspected of having Mesocestoides
• Complaints may include anorexia, weight infection, especially if the patient appears less PROGNOSIS & OUTCOME
loss, abdominal distension, depression, ill than would be expected if the fluid were
vomiting, diarrhea, abdominal pain, shallow chylous or septic. Confirmation is made by Guarded for infection with larval tetrathyridia
respirations, or respiratory distress. cytologic exam of aspirated fluid. because infection generally persists
• The most common clinical abnormality is
ascites, being seen in approximately 60% of Differential Diagnosis PEARLS & CONSIDERATIONS
affected dogs. Abdominal and pleural effusions: congestive
• 20% of affected dogs are subclinical. heart failure, portal hypertension, liver disease, Comments
hemorrhagic effusions, neoplastic effusions, The tetrathyridium is a single, solid-bodied
PHYSICAL EXAM FINDINGS hypoalbuminemia, septic effusions, chylous metacestode stage with a deeply invaginated
Signs of abdominal or pleural effusion effusions. The latter two would be most likely to acetabular scolex. Grossly, it resembles a grain
be confounded grossly with Mesocestoides-related of cooked grits, but it has a unique appearance
Etiology and Pathophysiology effusions (opaque, white fluid). when viewed under a compound microscope.
• Life cycle involves two intermediate hosts.
• First intermediate host may be a ground- Initial Database Prevention
dwelling coprophagous arthropod (oribatid • Thoracic and/or abdominal imaging to • Prevent dogs and cats from roaming and
mite, beetle) that becomes infected by ingest- confirm effusion. ingesting second intermediate hosts such as
ing eggs of Mesocestoides species. Eggs develop • Abdominocentesis (p. 1056) or thoracocen- birds, amphibians, reptiles, and rodents as
to the cysticercoid stage in the arthropod tesis (p. 1164) typically reveals a distinctive live prey or carrion.
intermediate host. thick, opaque, white fluid, which often con- • Regular anthelminthic therapy
• Second intermediate host (reptile, amphib- tains hundreds to thousands of tetrathyridia.
ian, bird, rodent, cat) becomes infected by • Cytologic evaluation of fluid may show a Technician Tips
ingestion of the larval forms (cysticercoids) mixed inflammatory exudate ± hemorrhage. During microscopic exams, look for the
in the first intermediate host. In this second Calcareous corpuscles (clear to yellow-gold, characteristic ovum on fecal flotation. After

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