Life Cycle Charts 
COMMON BLOOD AND TISSUE PARASITES OF MAN 
I. Introduction 
The blood and tissue parasites of man include representatives of 
two groups of helminths, nematodes and cestodes, and of two groups 
of protozoa, hemoflagellates and sporozoa. In general, the life cycles 
tend to be more complex than those of the intestinal parasites and, 
in the case of the blood parasites, involve an arthropod vector as 
well as a human host. Intermediate hosts are necessary for the trans- 
mission of most of the blood and tissue organisms and in several 
cases, reservoir hosts are important. With the exception of Toxocara 
canis , no external development takes place. 
Like those of the intestinal parasites,* the life cycle charts of 
the blood and tissue parasites are intended for use by students of 
parasitology, laboratory technicians, public health workers, and 
physicians. They are designed as simple, basic patterns that pur- 
posely omit details of epidemiology, incubation periods, patent 
periods, and exceptions to the usual pattern. The individual user can 
add any needed or desired details, obtaining this information from 
lectures or from the literature. Toxoplasma gondii has been excluded 
from this presentation since neither the correct classification nor 
the complete life history has been determined. 
The design of the charts conforms to the following general rules, 
insofar as possible: 
1. The diagnostic and infective stages are indicated and empha- 
sized. These stages are in proportion with regard to species 
within a given group but, because of size variations, the scale 
is not uniform between groups. The sizes of the nematode male 
and female adults are relative to each other and, within the 
filariae, are drawn to a single scale. 
♦Melvin, D. M., Brooke, M. M. and Sadun, E. H. 1965. Common Intestinal Helminths 
of Man - Life Cycle Charts. PHS Publication No. 1235. 
Brooke, M. M. and Melvin, D. M. 1964. Common Intestinal Protozoa of Man - Life 
Cycle Charts. PHS Publication No. 1140. 
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