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SECTION I - INFECTIOUS AGENT
NAME: Dwarf Tapeworm
SYNONYM OR CROSS REFERENCE: Hymenolepis nana
CHARACTERISTICS: Intestinal cestode, 20-30mm, maximum width 500 um, scolex with armed tetrad suckers; eggs,
40-50 um.
SECTION II - HEALTH HAZARD
PATHOGENICITY: Vague abdominal pain, nausea, vomiting, weight loss, nervousness, diarrhea, headaches
all common in mild infections. Severe infections exhibit generalized enteritis, anemia, eosinophilia, possible
nervous system complications in children.
EPIDEMIOLOGY: Fecal-oral (direct transmission); ingestion of eggs in fecal material, contaminated water.
Accidental parasite in man, occurs worldwide but most common in tropics and subtropics. Common parasite in children
under 8 yrs of age.
May be transmitted directly by ingestion of infected insect vector (flea or flour beetle) and eggs may exhibit
auto-infection in infected hosts.
Hymenolepis nana is the only Cestode that can be transmitted directly from host to host. Eggs hatch in small
intestine, penetrate intestinal villi to develop into cystocercoid larvae and reenter the intestinal lumen to develop
to mature worms.
HOST RANGE: Rats, mice, humans (accidental host).
INFECTIOUS DOSE: Unknown
MODE OF TRANSMISSION:
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Direct - |
Fecal-Oral; ingestion of eggs. |
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Indirect - |
Ingestion of developed larvae through infected flea or flour beetles. |
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Auto-infection - |
Eggs hatch & develop within infected host. |
INCUBATION PERIOD: Approximately 15 days (direct transmission) from entry of egg into host to the development
of the mature worm. A further week is needed for these worms to generate infective eggs. Indirect transmission
exhibits a longer and very variable (approx. 30 days) incubation period.
COMMUNICABILITY: Person to person spread common though contact with infectious individuals;
associated with poor sanitary conditions.
SECTION III - DISSEMINATION
RESERVOIR: Rats, mice.
ZOONOSIS: Yes, feces of rats, mice (direct transmission).
VECTORS: Yes; flea, flour beetle (indirect transmission).
SECTION IV - VIABILITY
DRUG SUSCEPTIBILITY: Praziquantel (Biltride) and Niclosamide (Yomesan).
SUSCEPTIBILITY TO DISINFECTANTS: Susceptible to disinfectants - 1% sodium hypochlorite (20% commercial bleach),
2% glutaraldehyde, formaldehyde.
PHYSICAL INACTIVATION: Larvae sensitive to freezing and desiccation.
SURVIVAL OUTSIDE HOST: Larvae and eggs viable for short periods of time outside of host.
SECTION V - MEDICAL
SURVEILLANCE: Monitor for symptoms; confirmation of diagnosis by finding eggs in stool.
FIRST AID/TREATMENT: Treatment with Praziquantel or Niclosamide. Iron supplements in cases of severe anemia.
IMMUNIZATION: None available.
PROPHYLAXIS: None available.
SECTION VI - LABORATORY HAZARDS
LABORATORY-ACQUIRED INFECTIONS: Uncommon; although a high percentage of laboratory rodents are infected
with Hymenolepis nana.
SOURCES/SPECIMENS: Feces.
PRIMARY HAZARDS: Ingestion of eggs, droplet exposure on mucus membranes, accidental inoculation.
SPECIAL HAZARDS: None
SECTION VIII - RECOMMENDED PRECAUTIONS
CONTAINMENT REQUIREMENTS: Biosafety level 2 practices and containment equipment for all activities involving
infective stages of the parasite, infectious or potentially infectious body fluids or tissues.
PROTECTIVE CLOTHING: Laboratory coat; gloves when skin contact with infectious material is unavoidable.
OTHER PRECAUTIONS: None
SECTION VIII - HANDLING INFORMATION
SPILLS: Allow aerosols to settle; wearing protective clothing, gently cover the spill with absorbent
paper towel and apply 1% sodium hypochlorite (20% commercial bleach), starting at the perimeter and working towards
the center; allow sufficient contact time (30 min.) before clean up.
DISPOSAL: Decontaminate all wastes before disposal; steam sterilization, chemical disinfection, incineration.
STORAGE: In sealed containers that are appropriately labeled.
Information provided by the Colorado State University Office of Biosafety- June 16, 1998,
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