Malaria

MALARIA. - The generic term malaria denotes a group of infections of humans and animals caused by protozoa of the genus Plasmodium.

I. HISTORICAL AND SOCIAL ASPECTS

Malaria, since the most remote epochs, has always constituted a serious obstacle to human progress, both with respect to population and with respect to the economy and agriculture.

In the 4th century B.C., the depopulation of Latium and Etruria, caused by malaria, had come to compromise greatly the military strength of Rome. Having abated during the imperial period, malaria later became the best ally of Rome against the barbarian invasions and the subsequent imperial encroachment. Ostrogoths and Huns were decimated by malaria at the gates of Rome, and a similar fate befell the Germanic armies between 964 and 1167. In modern times, certain Napoleonic wars were influenced by malaria. In the First World War, on the Piave front alone, from April to August 1918, 22,671 cases of malaria were confirmed, and the troops of other nations suffered greatly from the same cause, especially in the Balkan countries and in Africa. In the Second World War, malaria did not fail to disrupt military plans, as a cause of depression of the morale of the troops. In many zones, especially during the first phases of the war, there were more men annihilated by malaria than by enemy actions. The agricultural development of many regions was for a long time impeded by malaria. Italy may be said to be by now redeemed from this scourge, but little more than half a century ago conditions in this regard were such as to induce G. B. Grassi to write that the unity of Italy had been achieved materially, but that in reality there were still two Italies: the one prosperous, the non-malarial Italy, the other decadent, the malarial Italy. Colonial enterprises have always found in malaria one of the most serious obstacles. The opening of the Panama Canal found one of its greatest difficulties, besides in yellow fever, in malaria. At the time of the French colonization in Algeria, the mortality from malaria had reached such figures that in 1835 the abandonment of the colony was proposed.

Still in our own days, extensive areas of the African continent, of India, of tropical America and many islands of the Pacific cannot be exploited because of malaria, still prevailing in an endemic state, which annually mows down millions of human lives, keeps populations in a state of general organic impairment and psychic inertia, lowers the working output of individuals and hinders the penetration of the faith.

II. GEOGRAPHICAL DISTRIBUTION

The geographical distribution of human malaria is closely linked to that of mosquitoes of the genus Anopheles, which carry out its transmission. At present malaria extends from 32° south latitude (Argentina) to 60° north latitude (Russia). Extensive zones of endemic malaria are found between 45° north latitude and 30° south latitude, in Central America, in the northernmost part of South America, in Central Africa, in southeastern Europe, in Mesopotamia, in Persia, in India, in Ceylon, in China, in Indochina, in Siam, in Malaysia, in the Philippines and in many other islands of the Pacific. A vast zone free of malaria extends across the center and south of the Pacific Ocean, including the Caroline, Marshall, Ellice, Samoa, Fiji and Marquesas Islands, New Caledonia and New Zealand. It is noteworthy that the Fiji Islands and New Caledonia are free of malaria, while the nearby New Hebrides are intensely malarial. The spread of malaria in relation to altitude is linked to the influence exerted by this factor on the life of anophelines. The anopheline species that can live at considerable heights above sea level are relatively few. In general, malaria is found at considerable heights more in tropical regions than in temperate ones, but the limits of its spread from the standpoint of altitude are very wide. From the lowest area of the globe, represented by the valley of the Dead Sea, at 400 m. below sea level, one reaches high elevations such as El Tungo near Quito in Ecuador (2460 m.), and it seems that in Quito itself (2850 m.) cases of autochthonous malaria have occurred. In Bolivia endemic malaria is common at 2500-2600 m. of altitude and is found up to 2770 m. in the region of Cochabamba. In the Andes too malaria reaches considerable heights. In Africa malaria is present in the Atlas range up to 2500 m., in regions covered by snow for more than half the year. Autochthonous cases have been reported in Ethiopia, at Addis Ababa (2450 m.), at Londiani, in Kenya (2600 m.). In the Himalayas malaria reaches 2300 m. of altitude. In Europe it has rarely been found above 1000 m.

III. EPIDEMIOLOGY AND PATHOLOGY

The fight against malaria was for a long time a fight against an unknown enemy, until Laveran in 1880 first discovered the presence of protozoa of the genus Plasmodium in the blood of persons stricken with malaria and gave the parasite the name Oscillaria malariae. To Golgi, Marchiafava and Celli is owed the discovery of different species of malarial parasites causing different types of malarial infection (tertian, quartan, pernicious) and of their development in the red blood cells. In 1898 G. B. Grassi succeeded in proving, together with his collaborators Bignami and Bastianelli, that human malaria is transmitted exclusively by mosquitoes of the genus Anopheles and that the fight against the onset and spread of the disease had to be directed against them.

The parasites causing human malaria belong to the genus Plasmodium of the family Plasmodidae. Plasmodidae may be defined as parasites of the blood cells and of other cells of the organism, in whose life cycle there is an asexual phase (schizogony), which takes place in a vertebrate host, and a sexual phase (anfigony), which takes place in an insect vector. Some species of Plasmodidae cause, besides human malaria, that of monkeys, bats, birds, reptiles and also amphibians. Those specific to man are Plasmodium vivax, P. malariae, P. falciparum (immaculatum), causing respectively benign tertian, quartan and malignant or aestivo-autumnal tertian fever.

Malarial infection manifests itself in man with the various types of fever, with enlargement of the spleen and anemia. In the course of aestivo-autumnal fever, more rarely in tertian and quartan infection, hemoglobinuric attacks may occur with the emission of urine containing albumin and hemoglobin: this is frequent in tropical countries. In all species of malaria there occur relapses with the reappearance of the clinical symptoms and of the parasites that may have disappeared from the blood.

From relapses are distinguished recrudescences, a term often used for attacks that supervene within two months of the primary infection, while the term recurrences designates the attacks that supervene after an interval of 7-8 months. Following a greater or lesser number of relapses, but also as a result of repeated infections, the picture of chronic malaria takes shape, characterized by enlargement of the spleen, by alterations of the liver, the kidneys, the bone marrow, and culminating in cachexia accompanied by extreme decline of strength and intense anemia.

The epidemiology of malaria is linked to numerous and variable factors. In general terms the persistence of malaria in a given locality is necessarily connected to interdependent factors, namely: a) the presence of carriers of gametocytes exposed to the bite of anophelines susceptible to the malarial parasites; b) the presence of vector anophelines sufficiently numerous and associated with man to a sufficient degree; c) environmental conditions, particularly of temperature and humidity, suitable for the survival of the malarial parasite in the anopheline; d) the presence of healthy individuals exposed to the bite of infected anophelines. Consequently, malarial infection in a given locality may assume different aspects according to the variations that may occur in one or more of the aforesaid factors.

IV. ANTIMALARIAL STRUGGLE

For this campaign, of capital importance was the discovery that Anopheles maculipennis, the principal vector of malaria in Europe, was not a homogeneous species, but a group of species and races, namely: A. maculipennis maculipennis, the typical form of the group and which was designated by the simple name typicus, A. messeae, A. melanoon melanoon, A. melanoon subalpinus, A. labranchiae labranchiae; A. labranchiae var. atroparvus and A. elutus (syn. sacharovi). It was seen that these species and races were biologically distinct and therefore not equally capable of transmitting malaria. It thus became possible to explain the regression of malaria that had occurred in certain regions, the phenomenon, which had remained inexplicable for many years, of anophelism without malaria, and new bases for the antimalarial campaign were indicated. Where the typical A. maculipennis prevailed, which does not bite humans, along with A. messeae, A. melanoon melanoon, and A. labranchiae var. atroparvus, which can bite humans only under particular conditions, malaria was absent or did not persist in an intensive state or was mildly endemic. But where A. elutus (sacharovi) and A. labranchiae labranchiae prevailed, species closely associated with humans and which therefore fed repeatedly on human blood, malaria was always in a more or less serious endemic state. The prevalence of one or another species or race of the maculipennis group was linked above all to the characteristics of the water collections where larval life took place. A. elutus (sacharovi) and A. labranchiae labranchiae, tolerating a certain degree of salinity in the water, prevailed in regions rich in salt water where malaria consequently reached its greatest intensity.

Comprehensive land reclamation restored the malarial zones to health even without inducing a notable reduction in the number of anophelines, which could even increase, and this because in the drained lands returned to agriculture the percentage of chlorides in the water gradually diminished as a result of cultivation work and irrigation. The aquatic environments thus became favorable to the development of the species and races of the maculipennis group, poorly suited to transmitting malaria, which ended up gaining the upper hand over the two most dangerous ones, labranchiae and elutus. The regression of malaria in the Agro Romano and Pontino was therefore due, in addition to other factors (improved economic and hygienic conditions of the workers, prophylactic measures, new therapeutic means), to the gradual disappearance of the principal malarial vector, labranchiae, following comprehensive land reclamation. With such reclamation in the Agro Pontino, however, the malarial problem in Italy was not solved, especially for southern Italy and the islands where A. labranchiae prevailed over the other species of the maculipennis group, both in fresh water and in salt water. Moreover, the Second World War destroyed what human labor had accomplished in the reclaimed Agro. Because of the floods provoked for military purposes along the Tyrrhenian coast, many areas returned to a marshy state, the water of the flooded zones again presented a certain degree of salinity following the spread of sodium chloride from the underlying soil, the harmful A. labranchiae reappeared, reaching the suburbs of Rome, and malaria flared up again.

The discovery of D.D.T. (p-p²-dichlorodiphenyltrichloroethane) and of its long residual action made it possible to gain the upper hand over the malaria that was spreading menacingly in Italy. The antianopheline campaign conducted in the Agro Pontino between 1945 and 1947, which consisted in treating the inhabited areas with D.D.T., resulted in the disappearance of A. labranchiae and, in parallel, the disappearance of malaria. And together with the anophelines, other dangerous domestic insects also disappeared (flies, fleas, bedbugs, lice, etc.), insidious spreaders of pathogenic germs for humans. With D.D.T., the antimalarial campaign has entered a new phase because of its rapidity and its independence from other auxiliary means, such as comprehensive land reclamation, which are not always feasible.

Sardinia and other regions of Italy soon followed the Agro Pontino in the redemption from malaria, which will soon be, for Italy, a sad memory of the past.

Important successes in the antimalarial campaign by means of D.D.T. are reported from all parts of the world. In Greece, the region of Europe most affected by malaria, this disease no longer constitutes a serious problem for the health authorities. In Argentina, Bolivia, Brazil, Peru, Venezuela, and India the curve of malaria cases and of the related mortality is declining. The African continent too is on the right track.

Lidia La Face