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Published on: May 30, 2019

Sudden increase in virulence in a strain of Plasmodium berghei yoelii

M Yoeli, B Hargreaves, R Carter

    Annals of Tropical Medicine and Parasitology
    |June 1, 1975
    PubMed

    Insights

    A Plasmodium berghei yoelii strain (17X) unexpectedly increased virulence after cryopreservation, causing high parasite levels and 100% mouse mortality. This enhanced virulence was stable and not due to viral co-infection.

    Area of Science:

    • Malariology
    • Parasitology
    • Molecular Biology

    Background:

    • The 17X strain of Plasmodium berghei yoelii is typically mild and chronic.
    • Cryopreservation is a common method for preserving biological samples, including Plasmodium strains.
    • Understanding factors influencing parasite virulence is crucial for malaria research.

    Purpose of the Study:

    • To investigate the sudden increase in virulence of the 17X strain of Plasmodium berghei yoelii after prolonged cryopreservation.
    • To characterize the virulence phenotype and rule out confounding factors like viral co-infection.
    • To explore the potential of virulence as a genetic marker in rodent malaria.

    Main Methods:

    • Cryopreservation of Plasmodium berghei yoelii strain 17X for 110 days.
    • Infection of mice to assess virulence (parasitemia, mortality).
    • Blood transfers and cyclical transmission through Anopheles stephensi to evaluate virulence stability.
    • Enzyme typing (GPI-1, 6 PGD-4) to characterize the strain.
    • Viral screening in infected mice.

    Main Results:

    • The cryopreserved 17X strain exhibited significantly enhanced virulence, characterized by high and early parasitemia and 100% mouse mortality.
    • The enhanced virulence phenotype remained stable after serial blood passages and cyclical transmission.
    • Enzyme typing confirmed the strain as characteristic of 17X, with GPI-1 and 6 PGD-4 enzyme types.
    • No detectable viral co-infection was found in the infected mice.

    Conclusions:

    • Cryopreservation can induce a stable increase in Plasmodium berghei yoelii virulence.
    • Virulence in rodent malaria parasites may serve as a useful genetic marker.
    • Virulence markers could be valuable in conjunction with enzyme and drug resistance markers for genetic studies.

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