Schistosoma spp.

Characteristics

Morphology Trematode, flatworm. There are 2 sexual forms. Adult worms are 12-16 mm in length and 0.3-0.6 mm in width and male worms are shorter and thicker than the females. Eggs are round or oval. Cercariae (infective larva) are 400-600 µm in length and contain a pear-shaped head and a forked tail.
Growth Conditions
  • Schistosoma eggs hatch
  • Schistosoma develops in snails present
  • Cercariae leave snails; enter water
  • Cercariae live for 48 hours
  • Cercariae infect people swimming
  • Infected people urinate/deficate in the water

Cycle continues

Health Hazards

Host Range

S. heamatobium and S. mansoni: humans

S. japonicum: humans, dogs, cats, pigs, water buffalo, horses and rodents

Modes of Transmission

Skin contact with fresh water contaminated with cercariae (infective larval forms of Schistosoma).

Signs and Symptoms

Rash/itchy skin appears within days of initial infection. After 1-2 months, fever, chills, cough, and muscle aches develop. When Schistosoma eggs travel to the liver or intestine/bladder inflammation and scaring appears. Years of infection can cause damage to the liver, intestines, lungs, and bladder. Occasionally, damage occurs in the spinal cord/brain leading to seizures and paralysis.

Infectious Dose Unknown
Incubation Period 2-6 weeks

Medical Precautions/Treatment

Prophylaxis None available
Vaccines None available
Treatment

Administer appropriate drug therapy:

  • All are sensitive to praziquantel.
  • S. mansoni is sensitive to oxamniquine.
  • S. japonicum is sensitive to metrifonate
Surveillance

Monitor for symptoms and confirm by testing stool, urine, or blood using microscopy or antibody detection

Emory Requirements Report all exposures

Laboratory Hazards

Laboratory Acquired Infections (LAIs) In 1987, there was one documented LAI.
Sources Feces, biopsy specimens, urine, contact with infected freshwater.

Supplemental References

Containment

BSL-2 Required for all work with infective stages of Schistosoma and potentially infected body tissues, fluids, and freshwater.

Spill Procedures

Small Notify others working in the lab. Allow aerosols to settle. Don appropriate PPE. Cover area of the spill with paper towels and apply a freshly made solution of 10% sodium hypochlorite, working from the perimeter towards the center. Allow 30 minutes of contact time before disposal and cleanup of spill materials.
Large

Contact Emory’s Biosafety Officer (404-727-8863),
the EHSO Office (404-727-5922), or
The Spill Response Team (404-727-2888).

Exposure Procedures

Mucous membrane Flush eyes, mouth or nose for 15 minutes at eyewash station.
Other Exposures Wash area with soap and water for 15 minutes; rinse with ethanol. Cercariae require 1-2 minutes to penetrate skin.
Reporting Immediately report incident to supervisor, complete an employee incident report in PeopleSoft.
Medical Followup 

7am-4pm (OIM): EUH (404-686-7941) EUHM (404-686-7106) WW (404-728-6431)

After Hours: OIM NP On Call 404-686-5500 PIC# 50464

Needle Stick (OIM): EUH (404-686-8587) EUHM (404-686-2352)

Yerkes: Maureen Thompson Office (404-727-8012) Cell (404-275-0963)

Viability

Disinfection

All infective stages are susceptible to 2% gluteraldehyde, 10% sodium hypochlorite. Surface cercariae are susceptible to 70% ethanol.

Inactivation Sensitive to freezing.
Survival Outside Host Unknown

Personal Protective Equipment (PPE)

Minimum PPE Requirements At minimum, personnel are required to don gloves, closed toed shoes, lab coat, and appropriate face and eye protection prior to working with Schistosoma. Additional PPE may be required depending on lab specific SOPs.
Additional Precautions Wash hands and change gloves frequently.

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