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Exposure Response Plan for Laboratory Handling of Schistosoma mansoni

Background Information

Schistosoma mansoni is a human parasite (trematode) and one of the major agents of the disease schistosomiasis. Schistosoma mansoni is the most widespread of the human-infecting schistosome species. It is present in a number of tropical countries.

Exposure Incident: Free-swimming larval stage forms (cercariae) penetrate directly through the skin. In research labs both temperature and light can be used to fuel hatching from snails. Laboratory workers that handle only the eggs are not at risk.

Reporting Exposure Incidents: All exposure incidents must be reported immediately to the supervisor. This agent infrequently causes laboratory acquired infections. Asymptomatic cases have been detected serologically.

Pre-exposure Health Screening:

Employees must be given a copy of this information at the initiation of work in laboratories in which S. mansoni is present in the cercarial free-swimming larval forms (snails are the vector).

Workers with concerns about pre-existing medical conditions should make an appointment with Employee Health (TMC) or the Occupational Medical Clinics (Grafton, Medford) to discuss with physician.

Before an Exposure Incident Occurs:

Workers are encouraged to obtain pre-employment Schistosome antibody titres, especially if he/she was born in, has resided in, has worked in, or has traveled in a country in which schistosomiasis caused by any species is endemic.

After an Exposure Incident Occurs: Immediate Action by Route of Exposure

  • Needle stick or laceration: Wash the area with soap and running water.

  • Mucous membranes (eye, mouth): If contaminated material is ingested, rinse mouth out with clean water. If contaminated material is splashed or sprayed into the eyes, flush the eyes for 10-15 minutes.

  • Inhalation: If contaminated materials are aerosolized outside of a biological safety cabinet and the cloud inhaled, rinse mouth twice expelling the rinsate. Do not swallow.

  • Contact with intact skin and clothing: Remove contaminated clothing using gloves and place objects in plastic bags. Wash skin with soap and water. Infective free-swimming larval forms (cercariae) penetrate directly through the skin.

After an Exposure Incident Occurs: Medical Evaluation and Follow-up:

Following immediate actions, contact the Tufts MC Employee Health Clinic (Boston),
TCSVM Occupational Medical Clinic (Grafton) or the Mt. Auburn Occupational Health Services (Medford) and arrange for medical diagnosis and treatment.

Signs and Symptoms of Disease:

Within hours an individual may note a tingling sensation or light rash due to irritation at the point of entrance. An initial fever with tiredness and a pale itchy rash may indicate primary disease.

If one develops chronic or intermittent abdominal pain, diarrhea, anorexia, or rectal itching, or neurologic symptoms such as lower limb pain, leg weakness, bowel/bladder dysfunction, focal neurologic deficits, chronic headaches, change in mental status, or seizures following a known exposure, s/he must inform the Principal Investigator. This will be treated as possible laboratory-acquired schistosomiasis and the individual will be referred to Employee Health or the Occupational Medical Clinic (Grafton, Medford) for evaluation. The above symptoms require a minimum 2-6 weeks to develop following a known exposure.

If a laboratory worker develops signs/symptoms that are otherwise unexplained that could be consistent with S. mansoni infection, in the absence of known exposure, s/he should only be tested for S. mansoni if s/he works in a laboratory in which the infective form is used. Pre-employment S. mansoni screening may be very helpful in this case.

If S. mansoni infection is suspected or identified through laboratory procedures from laboratory workers, this will be treated as a potential failure of biosafety measures. The PI must be informed immediately. The PI must inform the Biosafety Officer within 72 hours of diagnosis. The BSO will complete a formal re-evaluation of laboratory safety procedures to determine the possible event that may have lead to this exposure.

Post-exposure Prophylaxis:

The individual may be started on preventative treatment in the case of an exposure event, based on the judgment of the attending physician. The individual will be instructed to watch for symptoms, and will be followed longitudinally from the time of the exposure for development of asymptomatic infection.   

To download a copy, click here.



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