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Our understanding of the life cycle of the malaria parasites did not proceed in the logical order just outlined but more like a jigsaw in which the various pieces were painstakingly put into place and, like a jigsaw, often involved mistakes and false starts. The story begins with the discovery of the stages in the blood. Many textbooks merely state that 'in 1880 Laveran discovered the malaria parasite' words that do not give this discovery the credit it deserves. In order to understand the background of this discovery it is necessary to go back to the 1870s. The discoveries of Pasteur and Koch had precipitated a search for a bacterial cause for many diseases including malaria. By 1879 the miasma theory was going out of favour and the two theories vying for contention were whether the microorganisms responsible were transmitted (1) by air and inhalation or (2) by water and ingestion. The leading theory was that proposed by the Italian Corrado Tommasi-Crudeli and the German, Theodor Albrecht Edwin Klebs, an eminent microbiologist who had been the first person to see the bacteria responsible for typhoid and diphtheria. Tommasi-Crudeli and Klebs claimed that they had isolated from the waters of the Pontine Marshes, where malaria was prevalent, a bacterium, Bacillus malariae, which when isolated in culture and injected into rabbits caused febrile infections accompanied by enlarged spleens reminiscent of malaria [14]. It was against this background that Charles Louis Alphonse Laveran, an unknown French army officer working in Algeria, challenged the perceived wisdom and began in his own words 'to follow the pigment'. Beginning with the known fact that the spleens of malaria patients contained pigment he began to look for pigment in the fresh unstained blood of patients and observed it first in leucocytes and then in or on red blood cells. Looking more carefully, he observed several different forms of erythrocytic organism including crescents, spherical motionless bodies with pigment, spherical moving bodies with pigment and bodies that extruded flagella-like structures all of which he thought were on the outside of the red cells. These observations are particularly interesting because Laveran not only used fresh blood but also a dry objective with a maximum magnification of 400 diameters. He also suggested a course of events that began with clear spots that grew, acquired pigment and filled the corpuscle which then burst coinciding with the fevers associated with malaria. Laveran meticulously examined the blood of 200 patients and in 148 observed the crescentic bodies in all cases of malaria but never in those without malaria. He also noted that quinine removed these stages from the blood. Laveran quickly realised that he had found a parasitic protozoan which he called Oscillaria malariae. He presented his findings to the French Academy of Medical Sciences in December 1880 [15] but failed to persuade any of the eminent microbiologists, zoologists or malariologists of the day that he was seeing anything other than disintegrating red blood cells. Nevertheless he persevered and by 1884 had convinced the leading Italian malariologists including Bignami, Golgi and Marchiafava that malaria was caused by a protozoan and not a bacterium [16]. His biggest triumph came in the same year when he also convinced the more cynical microbiologists Louis Pasteur, Charles Edouard Chamberland and Pierre Paul Émile Roux. Robert Koch, one of the most influential microbiologists of his time, however, remained sceptical until 1887. Nevertheless in some quarters the miasma theory persisted and as late as 1895 the American R. C. Newton, a supporter of Tommasi-Crudeli, wrote that 'Aerial and aquatic transportation of malaria has been proved' [17]. (This paper is worth reading in full because, although based on what we now know to be false premises, it contains a mass of interesting information about the prevention of malaria such as the use of screens or mosquito nets to exclude insects, closing doors at night and lighting fires out of doors). Laveran was awarded the Nobel Prize for Medicine in 1907 and his discoveries are described in some detail by the Sergent brothers [18] and Bruce-Chwatt [19] as well as in the various histories of malaria listed above.
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Manson, who had access to malaria patients in London, had observed that it was only when blood taken from such patients began to cool that the flagellated forms and subsequent fertilization, as described by MacCallum, appeared and concluded that further development must occur outside the human body in another host, probably a mosquito. Ross, having returned to India, examined several thousand mosquitoes from endemic areas without any success but, remembering Laveran's dictum 'follow the pigment' and Manson's advice to 'follow the flagellum', a reference to the flagella of the male gamete, he eventually found pigmented bodies, which he called spores, on the stomach wall of a mosquito experimentally fed on an infected patient. Ross was no entomologist (in fact the only book he had on entomology was one written for anglers) so he classified the mosquitoes he was studying as grey or barred-back (A), brindled (B), and dappled-winged (C). We now know that the grey mosquitoes were culicines and that the dappled-winged mosquitoes were anophelines. Grey mosquitoes were very common but never contained the pigmented spores. On the other hand the rarer 'dapple-winged' mosquitoes, after being fed on a malaria patient, were found to contain pigmented bodies that ruptured releasing 'rods' that invaded the mosquito's salivary glands. Ross had now made the crucial break-through and had found developmental stages of human malaria parasites in anopheline mosquitoes and, in his letters, he calls August 20th 1897 'Mosquito day' [31, 32]. Ross was on the brink of demonstrating that anopheline mosquitoes could transmit human malaria but unfortunately he was not able to complete his studies because at this crucial stage he was posted to Calcutta where there was very little malaria [31]. He did, however, have access to laboratory facilities and, remembering that in 1894 Manson had mentioned the possibility of using malaria parasites of birds in his investigations, he turned his attention to an avian malaria parasite, Proteosoma relictum (now called Plasmodium relictum), common in many species of birds including crows and sparrows. This parasite, he discovered, was transmitted by his 'grey' (culicine) mosquitoes, probably Culex fatigans. Of 242 'grey' mosquitoes fed on infected birds, 178 developed pigmented spores. Ross concluded that mosquitoes fed on infected birds took up male and female gametocytes which fertilized in the mosquito gut and developed into spores on the surface of the mosquito's gut within which rod-like structures were produced that invaded the mosquito's salivary glands and were injected into a new host when the infected mosquito fed. His results were made public in 1898 [35, 36]. Ross surmised correctly that human malaria was probably transmitted in the same way and later wrote that 'The triumph of 20 August was now completed and crowned by that of 9 July 1898' [31]. These experiments finally convinced Manson, that malaria was transmitted through the bite of a mosquito contrary to his earlier opinion that the infective stages were discharged into water. He nevertheless still thought that discharge of infective stages into water was the way that filiarial worms were transmitted until it was shown that they too were transmitted via the bite of a mosquito by George Carmichael Low in 1900 [37].
By this time the bulk of the army had reached Antioch, today just inside the southern Turkish border with Syria. This huge city had been a Roman settlement; to Christians it was significant as the place where saints Peter and Paul had lived and it was one of the five patriarchal seats of the Christian Church. It was also important to the Byzantines, having been a major city in their empire as recently as 1084. The site was too big to surround properly but the crusaders did their best to squeeze the place into submission. Over the winter of 1097 conditions became extremely harsh, although the arrival of a Genoese fleet in the spring of 1098 provided some useful support. The stalemate was only ended when Bohemond persuaded a local Christian to betray one of the towers and on June 3rd, 1098 the crusaders broke into the city and captured it. Their victory was not complete, however, because the citadel, towering over the site, remained in Muslim hands, a problem compounded by the news that a large Muslim relief army was approaching from Mosul. Lack of food and the loss of most of their horses (essential for the knights, of course) meant that morale was at rock bottom. Count Stephen of Blois, one of the most senior figures on the crusade, along with a few other men, had recently deserted, believing the expedition doomed. They met Emperor Alexios, who was bringing long-awaited reinforcements, and told him that the crusade was a hopeless cause. Thus, in good faith, the Greek ruler turned back. In Antioch, meanwhile, the crusaders had been inspired by the 'discovery' of a relic of the Holy Lance, the spear that had pierced Christ's side as he was on the cross. A vision told a cleric in Raymond of St Gilles' army where to dig and, sure enough, there the object was found. Some regarded this as a touch convenient and too easy a boost to the standing of the Provençal contingent, but to the masses it acted as a vital inspiration. A couple of weeks later, on June 28th, 1098, the crusaders gathered their last few hundred horses together, drew themselves into their now familiar battle lines and charged the Muslim forces. With writers reporting the aid of warrior saints in the sky, the crusaders triumphed and the citadel duly surrendered leaving them in full control of Antioch before the Muslim relief army arrived.
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