From Hell’s Battlefield: The Australians in New Guinea in World War II, by Phillip Bradley (Allen & Unwin, 2012), Kindle Loc. 4885-4905:
From the moment the Australians flew into Nadzab, they were under insidious assault. Carried by the fragile mosquito, malaria could fell and even kill the strongest of men, and the Ramu Valley, the valley of death in the local dialect, had one of the highest incidences in the country.
The traditional treatment was with quinine, but 90 per cent of the world’s supply came from cinchona-tree plantations in Java, which was now under Japanese occupation. After the 252 Lark Force escapees ran out of quinine on New Britain in early 1942, fifty died within five weeks and most of the remainder needed hospitalisation. An alternative malaria suppressant had to be found or it would be impossible to maintain troops in northern Australia, let alone New Guinea. Atebrin, a synthetic version of quinine that had been developed in Germany before the war, became the Australian Army’s official antimalarial drug, and what quinine remained was reserved for treatment. Australian scientists helped develop practical methods of synthesising Atebrin and pinpointed the dosage that most effectively suppressed malaria among deployed troops. In New Guinea, wearing protective clothing, using mosquito nets, spraying, improving drainage and of course taking the bittertasting Atebrin pills became as important as any combat discipline.
Malaria is not found above elevations of about 1000 metres, but most of the fighting in New Guinea took place along the coast or in the lowlands of the Markham and Ramu Valleys. High rainfall increased the opportunities for mosquitoes to breed, so the relatively dry area around Port Moresby was less dangerous than Milne Bay and the Papuan beachheads, where malaria was rampant. From October 1942 to April 1943, malaria caused almost five times more casualties than combat did. Even that was not the full story, as most affected men had recurrences of the disease after returning to Australia. The highly malarial environment of the Ramu Valley almost crippled the Australian campaign. Almost 1 in 10 of the operational troops were falling ill with malaria each week, meaning that within eleven weeks almost all would be infected. There were other diseases, some—such as scrub typhus—much deadlier, but malaria accounted for 90 per cent of losses due to disease. As a result of the scientists’ studies, the daily Atebrin dose was doubled, and the infection rate fell by about two-thirds. For Japanese troops in New Guinea, malaria was also a serious problem. Though they had stocks of quinine, the progressive breakdown of their supply system meant that almost all frontline troops were infected with malaria, and deaths from it increased as the war went on.