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Dynamics of positional warfare malaria: Finland and Korea compared.

Huldén L, Huldén L - Malar. J. (2008)

Bottom Line: The significance of the mosquito induced relapses is emphasized by two benefits for the Plasmodium.There is a synchronous increase of gametocytes when new mosquitoes emerge.It also enables meiotic recombination between different strains of the Plasmodium.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Forest Ecology, Faculty of Agriculture and Forestry, University of Helsinki, Finland. lena.hulden@helsinki.fi

ABSTRACT

Background: A sudden outbreak of vivax malaria among Finnish troops in SE-Finland and along the front line in Hanko peninsula in the southwest occurred in 1941 during World War II. The common explanation has been an invasion of infective Anopheles mosquitoes from the Russian troops crossing the front line between Finland and Soviet Union. A revised explanation is presented based on recent studies of Finnish malaria.

Methods: The exact start of the epidemic and the phenology of malaria cases among the Finnish soldiers were reanalyzed. The results were compared with the declining malaria in Finland. A comparison with a corresponding situation starting in the 1990's in Korea was performed.

Results and discussion: The malaria cases occurred in July in 1941 when it was by far too early for infective mosquitoes to be present. The first Anopheles mosquitoes hatched at about the same time as the first malaria cases were observed among the Finnish soldiers. It takes about 3-6 weeks for the completion of the sporogony in Finland. The new explanation is that soldiers in war conditions were suddenly exposed to uninfected mosquitoes and those who still were carriers of hypnozoites developed relapses triggered by these mosquitoes. It is estimated that about 0.5% of the Finnish population still were carriers of hypnozoites in the 1940's. A corresponding outbreak of vivax malaria in Korea in the 1990's is similarly interpreted as relapses from activated hypnozoites among Korean soldiers. The significance of the mosquito induced relapses is emphasized by two benefits for the Plasmodium. There is a synchronous increase of gametocytes when new mosquitoes emerge. It also enables meiotic recombination between different strains of the Plasmodium.

Conclusion: The malaria peak during the positional warfare in the 1940's was a short outbreak during the last phase of declining indigenous malaria in Finland. The activation of hypnozoites among a large number of soldiers and subsequent medication contributed to diminishing the reservoir of malaria and speeded up the eradication of the Finnish malaria. A corresponding evolution of Korean malaria is anticipated with relaxed tensions and decreasing troop concentrations along the border between South and North Korea.

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Scheme of re-emerging malaria during the Continuation War. In crowded conditions with mosquitoes the malaria epidemic starts with mosquito triggered relapses in hypnozoite carriers. In the next step mosquitoes become infective and gradually spread sporozoites into healthy humans. After the war hypnozoite carriers got relapses if Anopheles mosquitoes were present.
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Figure 8: Scheme of re-emerging malaria during the Continuation War. In crowded conditions with mosquitoes the malaria epidemic starts with mosquito triggered relapses in hypnozoite carriers. In the next step mosquitoes become infective and gradually spread sporozoites into healthy humans. After the war hypnozoite carriers got relapses if Anopheles mosquitoes were present.

Mentions: According to Hernberg [6] there were about 3000 cases of malaria among the Finns during 1941–1945. Because he did not know the true dynamics of relapses his judgement about separating primary infections from relapses cannot be relied on. A crude estimate of 1500 primary infections and 1500 relapses is accepted in this study. About 310,000 men were concentrated along the front line and exposed to mosquitoes. It can therefore be estimated that about 0.5% of the Finnish population still had hidden dormant hypnozoites in their liver in the 1940's. In 1945 after the war 1551 cases of malaria were reported all over Finland from February to October peaking in May and June. 299 patients had malaria two or several times so the remaining 1252 cases represent the true number of malaria infected persons. A detailed study on 868 patients revealed only 12 women. Practically all of them represented repatriated soldiers. Probably nearly all of the cases were relapses. They originated from primary infections that must have taken place during the war in the spring 1944 when many soldiers lived together in primitive conditions. The mosquitoes were then able to transmit malaria between infected and uninfected soldiers during the transmission season from December to May inside the dugouts and barracks. When the infected soldiers were repatriated after the war only those soldiers returning to conditions where they were locally exposed to mosquitoes got relapses. Those soldiers that returned to housing conditions without mosquitoes could still have hidden dormant stages of malaria in their liver a long time after the war. The schema in Figure 8 presents the principal mechanism of the outbreak of malaria in positional warfare conditions.


Dynamics of positional warfare malaria: Finland and Korea compared.

Huldén L, Huldén L - Malar. J. (2008)

Scheme of re-emerging malaria during the Continuation War. In crowded conditions with mosquitoes the malaria epidemic starts with mosquito triggered relapses in hypnozoite carriers. In the next step mosquitoes become infective and gradually spread sporozoites into healthy humans. After the war hypnozoite carriers got relapses if Anopheles mosquitoes were present.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2543043&req=5

Figure 8: Scheme of re-emerging malaria during the Continuation War. In crowded conditions with mosquitoes the malaria epidemic starts with mosquito triggered relapses in hypnozoite carriers. In the next step mosquitoes become infective and gradually spread sporozoites into healthy humans. After the war hypnozoite carriers got relapses if Anopheles mosquitoes were present.
Mentions: According to Hernberg [6] there were about 3000 cases of malaria among the Finns during 1941–1945. Because he did not know the true dynamics of relapses his judgement about separating primary infections from relapses cannot be relied on. A crude estimate of 1500 primary infections and 1500 relapses is accepted in this study. About 310,000 men were concentrated along the front line and exposed to mosquitoes. It can therefore be estimated that about 0.5% of the Finnish population still had hidden dormant hypnozoites in their liver in the 1940's. In 1945 after the war 1551 cases of malaria were reported all over Finland from February to October peaking in May and June. 299 patients had malaria two or several times so the remaining 1252 cases represent the true number of malaria infected persons. A detailed study on 868 patients revealed only 12 women. Practically all of them represented repatriated soldiers. Probably nearly all of the cases were relapses. They originated from primary infections that must have taken place during the war in the spring 1944 when many soldiers lived together in primitive conditions. The mosquitoes were then able to transmit malaria between infected and uninfected soldiers during the transmission season from December to May inside the dugouts and barracks. When the infected soldiers were repatriated after the war only those soldiers returning to conditions where they were locally exposed to mosquitoes got relapses. Those soldiers that returned to housing conditions without mosquitoes could still have hidden dormant stages of malaria in their liver a long time after the war. The schema in Figure 8 presents the principal mechanism of the outbreak of malaria in positional warfare conditions.

Bottom Line: The significance of the mosquito induced relapses is emphasized by two benefits for the Plasmodium.There is a synchronous increase of gametocytes when new mosquitoes emerge.It also enables meiotic recombination between different strains of the Plasmodium.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Forest Ecology, Faculty of Agriculture and Forestry, University of Helsinki, Finland. lena.hulden@helsinki.fi

ABSTRACT

Background: A sudden outbreak of vivax malaria among Finnish troops in SE-Finland and along the front line in Hanko peninsula in the southwest occurred in 1941 during World War II. The common explanation has been an invasion of infective Anopheles mosquitoes from the Russian troops crossing the front line between Finland and Soviet Union. A revised explanation is presented based on recent studies of Finnish malaria.

Methods: The exact start of the epidemic and the phenology of malaria cases among the Finnish soldiers were reanalyzed. The results were compared with the declining malaria in Finland. A comparison with a corresponding situation starting in the 1990's in Korea was performed.

Results and discussion: The malaria cases occurred in July in 1941 when it was by far too early for infective mosquitoes to be present. The first Anopheles mosquitoes hatched at about the same time as the first malaria cases were observed among the Finnish soldiers. It takes about 3-6 weeks for the completion of the sporogony in Finland. The new explanation is that soldiers in war conditions were suddenly exposed to uninfected mosquitoes and those who still were carriers of hypnozoites developed relapses triggered by these mosquitoes. It is estimated that about 0.5% of the Finnish population still were carriers of hypnozoites in the 1940's. A corresponding outbreak of vivax malaria in Korea in the 1990's is similarly interpreted as relapses from activated hypnozoites among Korean soldiers. The significance of the mosquito induced relapses is emphasized by two benefits for the Plasmodium. There is a synchronous increase of gametocytes when new mosquitoes emerge. It also enables meiotic recombination between different strains of the Plasmodium.

Conclusion: The malaria peak during the positional warfare in the 1940's was a short outbreak during the last phase of declining indigenous malaria in Finland. The activation of hypnozoites among a large number of soldiers and subsequent medication contributed to diminishing the reservoir of malaria and speeded up the eradication of the Finnish malaria. A corresponding evolution of Korean malaria is anticipated with relaxed tensions and decreasing troop concentrations along the border between South and North Korea.

Show MeSH
Related in: MedlinePlus