Malaria 615 



falciparum. In unusual cases symptoms may appear after much longer 

 periods. For example, mosquito inoculation of P. vivax has produced a 

 primary attack after 10 months (21). Likewise, under natural conditions, 

 autumnal mosquito inoculations sometimes do not lead to primary attacks 

 of vivax malaria until the following spring (101). A more unusual case, 

 involving an apparent "incubation" period of 19 years, has been re- 

 ported for P. maJariae (78). Such cases may be considered latent infections 

 and presumably involve an unusually prolonged pre-erythrocytic phase. 

 Somewhat similar to these latent infections, occasional cases show very 

 mild symptoms; unless treated, these may develop into typical cases. 



Mixed infections may introduce complications. In experimental mix- 

 tures of P. vivax and P. falciparum (19), the latter was the first to populate 

 the blood and the early symptoms were those of falciparum malaria. P. 

 vivax later increased in number, while the population of P. falciparum 

 decreased rapidly, and a typical attack of benign tertian occurred next. 



Prodromal symptoms 



In a typical primary attack of vivax malaria, mild symptoms ap- 

 pear a day or so before the patent period. These include nausea, loss of 

 appetite, constipation, apathy, and sometimes insomnia. The mouth often 

 feels dry and the tongue may be thickly coated. Headache, muscular 

 pains, and aches in the joints soon develop, and there may be sensations 

 of chilliness. Comparable early symptoms may appear in quartan malaria, 

 but usually not before parasites are detectable. Such prodromal symptoms 

 are sometimes seen in falciparum cases but are often so insignificant 

 that the attack shows a sudden onset, particularly in partially resistant 

 individuals. 



The paroxysm 



Prodromal symptoms are followed by a series of paroxysms, the 

 length of the series varying with the patient and the type of malaria. A 

 clinical reaction may occur in naturally induced vivax malaria when the 

 parasite density approximates lO/mm^ (8), whereas recognizable symp- 

 toms may accompany the first appearance of parasites in the peripheral 

 blood in falciparum malaria (23). The complete paroxysm includes the 

 rigor (cold stage, chill), the fever stage, and the sweating stage. 



The rigor usually begins with a chilly sensation, in the hands and feet 

 at first and more general later on. Acute shivering may follow, with 

 cyanosis of the lips and fingers tips. Rapid pulse and respiration, and 

 sometimes severe headaches, may be expected. Nausea and vomiting also 

 are fairly common. A rigor rarely initiates the first paroxysm in vivax 

 malaria, may not occur until after several days of intermittent fever, and 

 seldom precedes a peak temperature of less than 102° F. Appearance of 

 a rigor in the first paroxysm suggests previous experience with malaria 



