The Course of the Blood-Induced Plasmodium Berghei Infection in the Meadow Mouse Microtus Pennsylvanicus Pennsylvanicus and Certain other Small Rodents

Teresa I. Mercado Laboratory of Tropical Diseases, National Microbiological Institute, National Institutes of Health, Bethesda, 14, Maryland

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G. Robert Coatney Laboratory of Tropical Diseases, National Microbiological Institute, National Institutes of Health, Bethesda, 14, Maryland

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Summary

Plasmodium berghei in the American meadow mouse (Microtus pennsylvanicus pennsylvanicus) was fatal to one-third of the 81 mice experimentally infected. Up to the time of death, the lethal cases showed few significant differences from those which recovered. The peak parasitemia was reached within 6 days, the average being about 3 days in both groups. Death occurred some 24 hours after the peak in all but a few of the lethal cases, but in the animals which recovered, parasitemia continued for three or four more days, when the smears became negative. Subinoculations showed however that in at least 9 of the recovered animals the infection was still present 19 to 51 days following the last positive smear.

The merozoite mean per segmenter increased in both groups during the course of infection from a low of 4 to 7.3 in the lethal cases just before death, and to as high as 8.1 in the animals which recovered, fluctuating to lower levels as the parasitemia disappeared.

The red blood cell count dropped from a normal of 9.5 million per cu. mm. to 3.1 m. in lethal cases, and to 3.9 m. in animals that recovered, but rose again in the latter to 8 m. by the tenth day.

P. berghei was found infective to the rice rat, Oryzomys palustris; pouch mice, Perognathus penicillatus, P. baileyi and P. intermedius; the kangaroo rats, Dipodomys spectabilis and D. merriami; the Egyptian mouse, Acomys cahirinus; and the cotton rat, Sigmodon hispidus hispidus, with varying courses of infection as described.

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