DISEASES TRANSMISSIBLE BY INSECTS MALARIA 1. Infective Agents.—(a) Plasmodium vivax, causing simple tertian fever.
(b) Plasmodium malaria causing quartan fever.
(c) Plasmodium falciparum, causing malignant tertian or estivo-autumnal fever.
2. Source of Infection.—Human beings whose blood contains tne gametes or sexual forms of the parasites, either those having acute or chronic malaria, or merely carriers.
3. Portal of Exit.—Blood abstracted by anopheline mosquitoes.
4. Route of Transmission.—Through the agency of anophe line mosquitoes which have bitten persons whose blood contains gametes. The sexual cycle of the parasite requires about 12 days for completion in the mosquito, at the end of which period the infecting forms (sporozoites) have made their appearance in the salivary glands (extrinsic period of incubation). In the United States there are three species of anopheline mosquitoes which can serve as vectors namely Anopheles quadrirnaculatus (maculipennis, syn.) (Fig. 69, 73), Anopheles punctipennis and Anopheles crucians. Their ova, (Fig. 70) are most com monly deposited in open collections of water distant from dwellings, although they may be found in rain barrels, cisterns, etc., near homes. The adults are nocturnal in their habits. Only the females are blood suckers and hence only the females transmit malarial parasites. External temperatures below i5 to 16 degrees C. will inhibit the development of the parasite in the mosquito. Of the three species the quartan can develope at the lowest temperature, while the mstivo-autumnal requires the highest. Adult mosquitoes that successfully hibernate are rendered sterile. Infection is maintained by human gamete carriers. So far as is certainly known mosquitoes are not hereditarily infected.
5. Portal of Entrance.—Sporozoites are liberated in the sub cutaneous tissues or capillaries by the discharge of the salivary secretions of infected mosquitoes when biting.
6. Incubation Period (Intrinsic).—The duration of this period is influenced by the external temperature, being shorter during high temperatures. It is usually about two weeks with
modium vivax. The length of time following the onset before gametes appear varies with the different species. Thus, in Tertian, from 8 to 20 days; Quartan, ii days (for one observa tion); Malignant tertian, from io to 35 days.
In temperate climates infection is maintained not by the survival of the infected mosquitoes through the winter, but by the reinfection of the mosquitoes from human gamete carriers in the spring.
7. Period of Communicability.—As long as gametes are present in the circulation. This may be indefinitely.
8. Methods of Control. The Infected Individual (Active Malaria).--(a) Diagnosis: Clinical manifestations, always con firmed by detection of the parasites in the blood.
(b) Isolation: Protection of the patient from mosquitoes until his blood is free from parasites, especially gametes, by the use of screens or bars.
(c) Immunization: None.
(d) Quarantine: None.
(e) Concurrent Disinfection: None as such. Destroy by capture or swatting all mosquitoes in the sick room.
(j) Terminal Disinfection: Same as before.
General Heasures.—(a) Search for gamete carriers by the exam ination of blood smears. Intensively treat such persons with quinine until sterilized. For adults Bass recommends ro grains of quinine sulphate every night before retiring, continued for 8 weeks This treatment will destroy the parasites in eo per cent. of the carriers. The remaining io per cent. should receive 3, ten grain doses a day for three or four days and later io grains a day for eight weeks. Infants and children should be dosed as follows: Under r year o 5 grain .
I year r.o grain 2 years 2.o grain 3 to 4 years... 3.o grain 5, 6 and 7 years 4.0 grain 8, g and ro years 6.o grain I1-14 years 8.o grain 15 years io.o grain (b) Prophylactic administration of quinine: The daily admin istration of 3 grains of quinine will prevent infection from de veloping. Where employed on a large scale provision must either be made for its distribution gratis or at a very low charge.