Interactions between the parasitic protozoa of small mammals

In the wild, small mammals are frequently infected with more than one parasite. Laboratory studies have revealed complex interactions between parasites and also between parasitic protozoa and viruses or bacteria. In general, infection with many parasites is accompanied by a period of immunodepression during which superimposed infections are favoured, giving rise to more intense and prolonged secondary infections while the original infection is unaffected. On the other hand, organisms that activate macrophages may protect die host against a subsequent infection. These kinds of interactions have been investigated in the laboratory using Trypanosoma musculi, T. lewisi, Giardia muris, Spironucleus muris, Babesia microti and Heligmosomoides polygyrus , all of which occur in British small mammals, suggesting that such interactions occur in the field, are worth investigating and should be considered in epidemiological studies.