8 DISEASES DUE TO PROTOZOA 



(i) The malarial parasites, P. vivax, P. malariie and P. falciparum 

 have their reservoir in convalescents from primary attacks and for 

 weeks after such attacks; the parasites leave the host, man, by blood 

 drawn up by blood-sucking insects; the sexual stages or external 

 development of the parasite takes place in some species or anophelines ; 

 it re-enters man with the saliva of the biting mosquito. 



(2) In Yellow fever the parasite is not known, but the reservoir 

 is the blood in the early stages of the disease; it leaves the host like 

 the above; passes its external phase in a mosquito, Stegomyia calopus; 

 and re-enters man by mosquito bites about ten days after feeding on 

 infected persons, after which period the mosquitoes have become 

 infective. 



(3) In Dengue fever the parasite is not known ; its reservoir is 

 human blood, and is carried away with the blood by the Stegomyia 

 calopus or Culex fatigans ; re-infecting man by the mosquito. 



(4) In Trypanosomiasis the parasite, Trypanosome gambiense or 

 T. rhodesiense, has its reservoir usually in man in the former instance 

 and usually in wild game in the latter case; it leaves the host with the 

 blood; passes its external life in the Glossina palpalis or G. morsitans ; 

 and re-enters man eighteen days or more after the fly has fed on an 

 infected person by biting and sucking blood in the ordinary way. 



(5) In Kala-azar the parasites, Leishman-Donovan bodies, prob- 

 ably have their reservoir in man ; leave the host in the leucocytes with 

 the blood ; pass their extra-corporal life in bed bugs, Cimex rotundatus, 

 and re-infect man by the bites of these bugs. 



(6) In Relapsing fever the parasite, Spiroch^ete recurrentis, has its 

 reservoir usually in man ; leaves the host by the blood plasma ; passes 

 its external life probably in the Pediculus, and re-infects man by its 

 bites. 



(7) In African Tick fever the parasite, S. duttoni, has its reservoir 

 in man or a progeny of infected ticks ; leaves man in the blood and 

 saliva; passes its external life in the Ornithodorus moubata and re- 

 enters man by its bites. 



(8) In SpirochcBtal diseases, Yaws, S^philis and some ulcers, the 

 parasites, S. pertenuis and S. pallida, have their reservoir in man; 

 leave the host by the discharges; have no external development, and 

 re-infect man by contact usually with an abraded surface. 



(9) In Amoebic dysentery the parasite. Entamoeba tetragena, has 

 its reservoir in convalescents from the disease, leaving the host in the 

 fasces in an encysted form ; further developing while encysted, in earth, 

 water or dust; re-infecting man by the mouth in water, milk, food, &c., 

 contaminated by the parasite. 



