a handbook of the mosquitoes of north america - Systematic Catalog ...

50 MOSQUITOES OF NORTH AMERICA
(No. 18). The sporozoites escape by the bursting of the oocyst
and are now in the body cavity. As insects have no closed
circulatory system, the blood bathes all the tis,sues so the
sporozoites are now free to wander with the blood. They are
said to bore into almost all the tissues and organs of the host
but great numbers of them invade the salivary glands (No.
19). The sporozoites are now ready to be passed with the
saliva into a new host when the mos,quito bites (No. 21). The
entire cycle within the mosquito occupies from 8 to 14 days,
depending on the temperature and other factors. It will thus
be seen that the presence of anopheline mosquitoes is essential
for the beginning of a new infection in man and furthermore
that man with gametocytes in his blood is essential before
mosquitoes can become infected. This interdependence is well
illustrated in figure 16, the so called etiological chain of
malaria. If it can be broken at any one point, a reduction or
even a complete elimination of the disease can be accomplished.
The cycles of the other two types of malarial organisms
correspond very closely to that of P. &ax. The time of spor-
ulation differs-that of P. quartavt taking place at the end of
three days and the rise in temperature occuring on the fourth
day ; that of P. fallcipa~rzw~ taking place irregularly in from
24 to 48 hours so that the rise in temperature of the patient
is irregular. Of course people suffering from malaria may
have two species present or a double infection of any one
and this complicates the clinical picture of the disease.
Fortunately, all anopheline mosquitoes are not vectors of
malaria. Some are known to be good vectors-that is they
are readily infected by feeding them blood containing the
male and female organisms; others are refractory and are not
easily infected; while others cannot, apparently, be infected.
Furthermore, even good vectors do not all become infected when
they feed on blood containing the male and female gameto-
cytes. Again some are infected by one parasite and refractory
to the other species of the parasites ; and again a mosquito may
be a good vector in one part of the world and the same species,