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Experimental human infections with Giardia lamblia
T E Nash1, D A Herrington, G A Losonsky
1Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892.
Abstract:
Fifteen healthy volunteers were inoculated enterally with trophozoites of two distinct human isolates of Giardia lamblia, GS/M and Isr. Each of two groups of five volunteers were inoculated with 50,000 (GS/M or Isr) trophozoites. All of the volunteers inoculated with GS/M and none of the volunteers inoculated with Isr became infected. Three of five volunteers infected with GS/M became ill, including two who had diarrhea and typical symptoms of giardiasis. In the second study, three patients who were previously infected with GS/M and treated were rechallenged 12 weeks after the first inoculation, together with five new control volunteers. All of the latter group became infected, and two developed loose stools; two rechallenged volunteers became reinfected but were asymptomatic, and a third was retrospectively found to be infected at the time of challenge. Serum IgM, IgG, and IgA antibody responses to Giardia and intestinal fluid IgA antibody responses to Giardia occurred in 100%, 70%, 60%, and 50%, respectively, of infected volunteers. These studies fulfill Koch's postulates and demonstrate strain variation in the pathogenicity of Giardia infections in humans.
Insights
Two Giardia lamblia strains showed varied pathogenicity in humans. The GS/M strain caused infection and illness, while the Isr strain did not, demonstrating strain-specific Giardia infection outcomes.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Parasitology
Background:
- Giardia lamblia is a common cause of parasitic intestinal disease.
- Understanding strain variation in pathogenicity is crucial for disease management.
Purpose of the Study:
- To investigate the pathogenicity of two distinct human Giardia lamblia isolates (GS/M and Isr).
- To fulfill Koch's postulates for Giardia lamblia in human volunteers.
Main Methods:
- Enteral inoculation of healthy volunteers with specific doses of Giardia lamblia trophozoites.
- Clinical observation and serological testing (IgM, IgG, IgA) for infection and immune response.
- Rechallenge study to assess immunity and reinfection in previously infected individuals.
Main Results:
- The GS/M strain caused infection and symptoms of giardiasis in volunteers, while the Isr strain did not.
- Rechallenge studies indicated partial immunity, with reinfection occurring asymptomatically in some previously infected individuals.
- Humoral immune responses, including serum and intestinal IgA, were observed in infected volunteers.
Conclusions:
- Demonstrates significant strain-specific variation in the pathogenicity of Giardia lamblia in humans.
- Supports the role of specific Giardia strains in causing symptomatic giardiasis.
- Highlights the complexity of Giardia immunity and the potential for asymptomatic reinfection.