Malaria parasite

“ It is at that stage in the development of the parasite in the human body when it multiplies by dividing that the chills and fever in malaria appear. What causes the malarial attack at this point is unknown, unless it be that the parasites give rise to a poison at the time of their division. Between the attacks of chills and fever in malaria there is usually an interval of freedom of a few hours, which corresponds to the period intervening in the life of the parasite in the human body, between the birth of the young parasites and their growth and final division, in turn, into new individuals. ”

“ Abstract Since the 1970's, the diversity of Plasmodium parasites in African great apes has been neglected. Surprisingly, P. reichenowi, a chimpanzee parasite, is the only such parasite to have been molecularly characterized. This parasite is closely phylogenetically related to P. falciparum, the principal cause of the greatest malaria burden in humans. Studies of malaria parasites from anthropoid primates may provide relevant phylogenetic information, improving our understanding of the origin and evolutionary history of human malaria species. ”

“ Many had the suspicion that gnats may play some part in the inoculation of malaria: the Italian peasants always thought so, and in the medical literature an American doctor, Mr. King, had advocated the same idea. But the complete life-history of the malaria parasite being not yet known fifteen years ago, the necessity of the mosquito or of some other living being serving as a host for the completion of the reproduction-cycle was not understood. ”

“ The malaria-parasite undergoes, in its passage through the body of the Anopheles, many and varied phases of its life-history. As the Frenchman said of the pork, which goes into one end of the machine in the Chicago meat factories as live pig, and comes out at the other in the form of sausages, ‘Il est diablement changé en route.’ The mosquito is as truly a host of the malarial parasite as man, and is as necessary for its full development as is man. ”

“ Most observers are now of opinion that the malaria parasite, under natural conditions, can be acquired by man only through the bite of the mosquito; that the mosquito can acquire the parasite only by ingesting the blood of a malaria-infected man or, possibly, other mammal ”

“ In accordance with this definition malaria is not a contagious disease in the sense that it is acquired by contact with the sick, which is not the case, but it is derived from contact with certain kinds of mosquitoes, and can be contracted in no other way, despite the many popular notions to the contrary. Mosquitoes, in their turn, acquire the malarial parasite by biting human beings suffering from malaria. It thus becomes possible for one malarial patient, coming to a region hitherto free from the disease, to infect the whole [Pg 248] district with malaria through the medium of mosquitoes. ”

“ That it lies on a substratum of fact there can be no doubt; nor can there be much doubt that it has in many particulars a general application to malarial disease as found all over the world. Still, judging from clinical facts, there seems ground for believing that there are other species or varieties of the malaria parasite besides those described by the Italians, and that the list here given will have to be enlarged or recast in the future. ”

“ Sambon ingeniously suggests that there may be special local conditions that favour hyperparasitism, that is, the attack and destruction of the malaria parasite by some other kind of parasite. Similar occurrences are common enough in nature. ”

“ He has shown, and his statements have been abundantly confirmed, that the natives of such districts acquire their immunity from repeated and persistent infection in childhood. In such places the blood of practically every child up to three or four years of age contains malaria parasites. The proportion of infected children gradually becomes smaller with each additional year, until adolescence is approached, when the blood becomes practically parasite-free, and immunity is established. ”

“ As far as we know, the parasite of malaria exists only in infected man and in infected mosquito. Perpetuation of the disease is due to the perpetuation of the cycle, man to mosquito, mosquito to man. If the parasite is destroyed in man or the Anopheles is not allowed to breed, the disease disappears. ”

“ Malaria is one of the world's most deadly diseases. Even though it is highly preventable and treatable, it causes approximately 881,000 deaths every year [1] , with nine out of ten deaths occurring in sub-Saharan Africa, and 85% of malaria-related deaths in children under five years of age. This is the equivalent of a child dying of malaria in Africa every 30 seconds [ [2] . The most serious forms of the disease are caused by the parasite Plasmodium falciparum ”

“ Malaria is a disease produced by a parasite belonging to the very lowest order of animal life—the Plasmodium malaria, which is conveyed from man to man by that genus of mosquitoes called the Anopheles. The parasite attacks and destroys the red cells of the blood, and produces a poison that causes the symptoms characteristic of malaria. ”

“ The “deadly” climates, to which so much dread attaches, generally mean malaria, and the mastery of this disease would be equivalent to the addition of vast and valuable areas to the empire. The problem, therefore, is eminently one for the statesman and administrator. A solution may be sought in several directions, suggested by the facts already explained. The existence of the parasite is maintained by a vicious interchange between its alternate hosts, mosquitoes and man, each infecting the other. ”

“ This increase in the parasitic burden causes malaria's characteristic symptoms—debilitating and recurring fevers and chills. Infected red blood cells also release gametocytes, which infect mosquitoes when they take a blood meal. In the mosquito, the gametocytes multiply and develop into sporozoites, thus completing the parasite's life cycle. Malaria can be prevented by controlling the mosquitoes that spread the parasite and by avoiding mosquito bites. Effective treatment with antimalarial drugs also helps to reduce malaria transmission. ”

“ In the year 1900, however, English scientists, working in the Roman Campagna, demonstrated conclusively that which had been vaguely suggested before, namely, that the cause of malaria is a parasite composed of little more than an unformed mass of protoplasm, not floating in the air at all, but transmitted only by the bite of a mosquito. ”

“ The infections were in non-immune adults whereas the burden of vivax disease in endemic areas was in children. Adults in the malaria endemic areas have usually developed significant immunity to a broad range of local parasites which controls symptoms and reduces parasite densities. The artificial infections in the majority of volunteer studies and in malaria therapy followed the bites of 5-10 infected anopheline mosquitoes selected for maximal infectivity based on salivary gland sporozoite loads in sibling mosquitoes. ”

“ In the short space at our disposal, we are not concerning ourselves with the micro-organism, first discovered in Algiers by Dr. Laveran, and considered to be the parasite of malaria. Without in the least committing oneself to a general belief in the germ-theory of disease, there may, here and there, be maladies produced by parasites. Yet, apparently, fever, bearing all the clinical symptoms of malaria, may occur without the presence in the blood of such organisms, no matter whether parasitic or inbred. ”

“ MALARIA WORK AND THE HOSPITAL SYSTEM In the early years of our construction malaria was very common and gave a great deal of trouble. As I have explained before, malaria is caused by a small animal parasite which lives in the blood of man and feeds upon the red globules. The excretions of this parasite poison man and cause the fever and other symptoms which we know as malarial fever. This parasite is transferred from the sick man to the well man by the bite of the mosquito. ”

“ In malaria, recrudescence is necessary for onward transmission of a de-novo resistant mutant parasites' progeny [ [143] . In P. vivax malaria the de-novo recrudescent infection is effectively in a race with the relapse-either of heterologous or drug sensitive homologous (sibling) parasites. Resistant parasites will only be transmitted if their progeny reach transmissible parasite densities before the relapse does. If the de-novo resistance is high grade then the resistant parasites may expand in numbers rapidly and may not be impeded by the relapse. ”

“ It is during this time that parasites sequentially invade and egress from their host RBCs and cause the signs and symptoms of malaria. While developing within the RBC, the parasite traffics proteins to the RBC surface that mediate binding to extracellular host receptors and enable the parasite to sequester in the placenta, brain, and virtually every other organ. The attenuation of malaria by repeated, sub-lethal P. falciparum infections suggests a significant role for adaptive immunity, but the targets of this attenuating immune response remain largely obscure. ”

“ This and the proposed future studies will substantially improve our understanding of malaria transmission in Djibouti, but without a carefully defined plan, staff or funding elimination of malaria in Djibouti remains only a biological possibility. The threshold of parasite prevalence seen as the benchmark for deciding whether to move on to malaria elimination or sustain low endemic control is seen as 1% parasite prevalence [3] , [11] . But to detect this level of prevalence requires large and expensive survey samples. ”

“ It is worth reiterating that if the international community wishes to demonstrate progress in malaria control, then the quantity and timeliness of prevalence information and parasite-specific surveillance records must dramatically improve. This is true for all countries but is particularly important in India, Nigeria, DRC, and Myanmar because of the large populations at risk and the paucity of existing malariometric information. ”

“ This was near the end of the dry season. When the rains commence a greater number of mosquitoes must be expected.
Natives of the Isthmus and the West Indies are not immune from malaria, and in [Pg 137] 1904-5 about one-half of the inhabitants who were examined proved to have the parasite of malaria in their blood. As the anopheles becomes infectious through biting a malarious man, it is evident that such a dissemination of the parasite throughout the blood of the human population renders mosquitoes especially dangerous. ”

“ We can consider later how the disease can be averted by keeping down the number of gnats and by preventing their access to infected patients.
We now pass to the second of the diseases carried by gnats, that of malaria.
The parasite which causes malaria is a much more lowly organized animal than the Filaria. It is named Hæmamœba, and it, too, is conveyed by an insect, and, so far as we know, by one genus of mosquito only, the Anopheles. Hence, from the point of view of malaria, it is important to know whether a district is infected with Culex or Anopheles. ”

“ Once the parasite begins to divide, the trophozoites are called schizonts, consisting of many daughter merozoites (blood schizogony) . Eventually, the infected erythrocytes are lysed by the merozoites, which subsequently invade other erythrocytes, starting a new cycle of schizogony. The duration of each cycle in P. falciparum is about 48 hours. In non-immune humans, the infection is amplified about 20-fold each cycle. After several cycles, some of the merozoites develop into gametocytes, the sexual stage of malaria, which cause no symptoms, but are infective for mosquitoes [5] . ”

“ Globally, this is likely to be of particular utility in those areas of low and unstable transmission where surveillance capabilities are often more robust and correspondingly where prevalence data are often rare as the number of people needed to be sampled to find infections is prohibitive [5] .
The malaria clinical burden estimates presented in this paper are driven by the underlying model of global prevalence [22] . This global malaria map is, to our knowledge, the first evidence-based attempt to define populations at risk of different levels of parasite transmission. ”

“ The problem in Africa is more complex, owing to the fact that the native population is thoroughly permeated with the parasite. Mr. Christophers and Dr. Stephens, in their ‘Further Reports to the Malaria Committee,’ have shown that the children of natives are in the great majority of cases infected with malaria. In one village where the Anopheles was found in ‘considerable numbers,’ 90 per cent. of the babies suffered, 57 per cent. of the children up to eight years, 28 per cent. ”

“ Less than half (22/49) of the malaria endemic countries (MECs) in Africa provided information for the most recent reporting year, 2003; the rest were older. These data are neither reconciled at sub-national scales, nor against populations at risk of any standard definition of the intensity of malaria transmission.
Recent work has also involved the assemblage of historical and contemporary evidence on the distributions of malaria risk and Anopheles vector species into a compendium of maps and geographic descriptions of various malaria indicators by region and country [19] . ”