Environmental Health & Safety

Safety Precautions for Working with Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular protozoan parasite that can infect a wide range of tissues in many animal species. Although T. gondii requires a cat host to complete its sexual cycle, asexual forms of the parasite are capable of infecting humans. There are three main routes of potential exposure:

  1. Ingestion of sporulated oocysts from materials contaminated with cat feces.
  2. Ingestion of bradyzoites (tissue cysts) through undercooked or raw meat from infected animals.
  3. Direct introduction of tachyzoites via accidental needle stick or eye exposure from splashes.

Toxoplasma gondii infection develops over days, not minutes. Incase of suspected laboratory exposure, do not panic, but immediately contact ehsocchealth@ucr.edu and begin seeking medical care (see First Aid and Emergencies section)

Health Risks

In healthy individuals, infection is often asymptomatic due to effective immune response. Up to one-third of Americans may become infected during their lifetime—commonly via gardening, changing litter boxes, or consuming undercooked meat—without knowing it. 

However, certain populations are at significantly greater risk:

  • Pregnant individuals: While not more susceptible to infection, transplacental transmission can lead to miscarriage or severe congenital defects.
  • Individuals with HIV/AIDS: Reactivation of latent cysts may cause toxoplasmic encephalitis, a major cause of mortality.
  • Immunocompromised individuals: Including those undergoing chemotherapy, organ transplants, or treatment for autoimmune conditions.

Even healthy individuals may experience severe disease from high-dose or virulent strains, particularly in laboratory exposure.

Laboratory Safety Protocols

To prevent exposure in the lab environment, the following precautions must be observed:

  • Approval Required: Extra caution must be used when working with pyrimethamine-resistant strains.
  • Restrictions: The following individuals should not work with live Toxoplasma:
    • Immunosuppressed
    • HIV-positive
    • Pregnant or planning pregnancy
    • Those uncomfortable with potential pregnancy termination in the event of infection
  • Medical Consultations: Individuals with weakened immune systems—including those who are pregnant, immunocompromised, or have pre-existing medical conditions—are strongly encouraged to consult their personal physician and/or Occupational Health before working with Toxoplasma gondii or potentially contaminated materials (e.g. cat feces, raw meat, or infected animals). To request a consultation or access Occupational Health services, please contact ehsocchealth@ucr.edu. 
  • Containment: Work with live parasites is restricted to the tissue culture (TC) room. Only authorized individuals may enter.
  • Use of Biosafety Cabinets: All manipulations must occur in BL-2 biosafety cabinets within the tissue culture room.
  • Personal Protective Equipment (PPE):
    • Gloves must be worn at all times.
    • Gloves shall be discarded into autoclave bags or disinfected with 70% ethanol before exiting the TC room.
    • Eye protection is required at all times, whether during manipulation or transport of parasites.
  • Decontamination:
    • Toxoplasma is inactivated by either 70% ethanol or Vesphene.
    • All contaminated materials must be disinfected (alcohol, bleach) or autoclaved after use.
    • Filter assemblies should be soaked in distilled water for 20 minutes to lyse residual parasites.
  • Sharps Safety:
    • Use blunt needles when harvesting parasites.
    • Discard all needles in designated sharps containers without recapping.

In Case of Suspected Laboratory Exposure

  • Do not panic: Infection develops over days, not minutes.
  • Immediately notify: Occupational Health at ehsocchealth@ucr.edu.   
  • Seek medical evaluation and treatment:
    • Contact appropriate healthcare personnel.
    • Draw blood for CBC and Toxoplasma antibody titers.
    • Monitor CBC twice weekly for chemotherapy toxicity.
    • Retest antibody titers after 1–2 months.

Prophylactic Treatment (Standard Infection)

Start as soon as possible under physician guidance:

  • 25 mg pyrimethamine (Diaprim) once daily
  • 1 g sulfadiazine (Lilly) four times daily
    • Do not take if allergic to sulfonamides
  • 5 mg folinic acid (Ca-Leukovorin) once daily
  • Duration:
    • 1 week if patient is initially seropositive
    • 2 weeks if seronegative

Note: Sun sensitivity and allergic reactions are possible with sulfonamides. Discontinue and consult a physician if symptoms such as rash or breathing difficulties appear.

Steps to Get Baseline Testing for Toxoplasma:

  1. Request an Antibody Titer Test
  • The test you’re looking for is usually called a Toxoplasma gondii IgG and IgM antibody test. This will check: 
    • IgG antibodies: Indicate past exposure/infection.
    • IgM antibodies: Indicate recent or active infection.
  1.  Order the Test Through:
  • Your institution’s occupational health services at ehsocchealth@ucr.edu. 
  • Primary care physician (if you're handling it independently).
  1. Blood Draw & Lab Processing 
  • A healthcare provider will draw a small sample of your blood and send it to a clinical lab for analysis.
  1. Results & Documentation
  • If IgG positive, you’ve been exposed before and likely have immunity.
  • If IgM positive, further evaluation is needed to rule out active infection.
  • Both negative? You are considered seronegative (no prior exposure), and special precautions should be taken if you’re working with live Toxoplasma.

Key References:

  1. Centers for Disease Control and Prevention (CDC)

The CDC provides an overview of Toxoplasma gondii, routes of transmission, and testing methods:

  • CDC – Toxoplasmosis
  • "Toxoplasma antibody testing (IgG and IgM) is used to determine prior exposure or active infection."
  1. NIH Biosafety in Microbiological and Biomedical Laboratories (BMBL) – 6th Edition
  • Toxoplasma gondii is considered a Biosafety Level 2 (BSL-2) agent.
  • Recommends serologic testing for individuals working with organisms of concern, particularly those who are immunocompromised or pregnant.
  • BMBL 6th Edition PDF (NIH)

3. Naomi Morrissette, PhD