Notable changes in the endemo-epidemicity of malaria have been observed in Greece during the course of recent studies. Measurements, made in 1930, showed a general condition of low endemicity in the country which had been subjected to severe malaria in past years. In 1931 a severe epidemic occurred and in the following year the intensity declined to one of moderate to high endemicity. A low stage of endemicity was again reached in 1933.
A review of the published reports of malaria in Greece since 1905 indicates that epidemics of malaria are a recurring feature of the disease, which appears at irregular intervals. According to the official statistics 5.6 per cent of the total deaths in Greece since 1921 have been attributed to malaria. It has been conservatively estimated that there are from one to two million malaria cases each year among the six and one-quarter million inhabitants. Quinine importations have varied from 20 to 50 tons annually in recent years. Morbidity reports from 1905 to 1924 have shown a general distribution of malaria which affected all parts of the country, even before the arrival of the million and a quarter Greek refugees in 1923 and 1924.
Intensive surveys of malaria were made in certain regions of the Peloponnesus, Attica, Macedonia, and Thrace from 1930 to 1933. Spleen indices were generally high and this group measure increased or decreased very slowly under changed conditions of transmission. Blood indices changed more rapidly and showed a marked increase during the epidemic year of 1931. There has been a progressive decline in blood indices during 1932 and 1933. Evidence is available to show that in Greece more than one year of reduced transmission may be required to change appreciably the crude blood index. Falciparum is the prevalent species under epidemic conditions, while vivax and malariae become the predominant types under endemic conditions. The percentage of falciparum reflects rapidly a changed condition, whereas vivax and malariae are persistent species which usually show a relative increase following a decline in transmission.
A study of a group of school children on whom monthly examinations were made throughout the year rarely showed a double infection on one examination, but 45 per cent of them showed both vivax and falciparum at some time during the year.
In view of the malaria conditions of the country the blood examination of infants born during a particular year is believed to be the most valuable comparative measure of new infections.
A country-wide survey made in 1933 showed definitely that malaria is widespread throughout Greece. No major area is free of the disease. The Ionian and Aegean Islands appear to have less malaria, while Crete and continental Greece showed a general uniformity of average spleen and blood indices among the major divisions of the country. In general the blood indices were about one half the spleen indices; 8184 spleen examinations showed an index of 35.6 per cent, while 7662 blood examinations gave 17.4 per cent positives. Among the 1330 positive bloods, the relative percentage of the three species were vivax, 34.5 per cent; falciparum, 38 per cent; and malariae, 26.5 per cent. The average rates of the rural villages of less than 1000 inhabitants were approximately double the corresponding rates in the towns and cities having more than 1000 population. The towns and cities above 250 meters altitude had, in general, lower average spleen and blood indices than the communities below this altitude.
On the analysis of spleen and blood findings according to age, the highest spleen rates and greatest average spleen measures have been observed in the five to fourteen year group, while the highest blood indices were usually found in the group from one to four years.
The monthly distribution of malaria, as recorded by the composite malaria picture of three dispensaries during the three years, 1931 to 1933, showed that the principal malaria wave extended from the end of July to October. The seasonal wave was on the average longer and continued later in the year than is the case in Italy and other European countries. It is believed that the explanation lies in the greater prevalence in Greece of A. superpictus, which has its greatest density in August and September. The seasonal distribution of the species of plasmodia showed clearly that P. vivax predominated in spring and early summer, while P. falciparum was the most important species in connection with the extended autumnal wave. The morbidity picture may vary considerably from year to year with locality and according to the densities of the different anopheline vectors.