Effects of Climate Change and Heterogeneity of Local Climates on the Development of Malaria Parasite (Plasmodium Vivax) in Moscow Megacity Region
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International Journal of Environmental Research and Public Health Article Effects of Climate Change and Heterogeneity of Local Climates on the Development of Malaria Parasite (Plasmodium vivax) in Moscow Megacity Region Varvara Mironova 1, Natalia Shartova 1,*, Andrei Beljaev 2, Mikhail Varentsov 1,3,4 and Mikhail Grishchenko 1 1 Faculty of Geography, Lomonosov Moscow State University, Moscow 119991, Russia; [email protected] (V.M.); [email protected] (M.V.); [email protected] (M.G.) 2 WHO Consultant on Malaria, Former WHO Advisor on malaria, WHO EMRO, Cairo 11371, Egypt; [email protected] 3 A.M. Obukhov Institute of Atmospheric Physics, 3 Pyzhyovskiy Pereulok, Moscow 119017, Russia 4 Research Computing Center, Lomonosov Moscow State University, Moscow 119991, Russia * Correspondence: [email protected]; Tel.: +7-(495)-939-2140 Received: 28 January 2019; Accepted: 23 February 2019; Published: 26 February 2019 Abstract: The article presents the results of a spatio-temporal analysis of the changes of the favorability of climatic conditions for the transmission of vivax malaria in the Moscow megacity and its surroundings during the period from 1977 to 2016. Using the historical temperature records at urban and rural weather stations, we calculated the key indicators of climate favorability for malaria transmission, viz. the sum of effective temperatures, the duration of the season of effective infectiveness, and a new integral index of climate favorability. We demonstrated a dramatic increase of all three indicators, which accelerated after 1984, and a high spatial heterogeneity among them. Due to the urban heat island effect, the degree of climatic favorability is especially high in the densely urbanized areas of Moscow megacity compared with the suburban and rural areas. Climatic conditions for vivax malaria in Moscow are better now than before. The season of effective infectiveness continues in the central part of the city for 25 days longer, and the integral index of climate favorability is 85% higher in comparison to mean values over the rural surroundings. The study contains an alert regarding the risk of malaria resurgence in the Moscow region in the case of the sufficient importation of cases from abroad. Keywords: vivax malaria; urban heat island; climate change; malaria season; Plasmodium vivax; Russia; Moscow 1. Introduction Human malaria is a group of four infections caused by protozoan parasites of the genus Plasmodium and transmitted by anopheline mosquitoes. On a global scale, practically all cases of malaria are caused by either P. falciparum or P. vivax. The former is the predominant of the two (ca 90%). The share of infections caused by human parasites P. malariae and P. ovale is negligible. Humans occasionally become infected with Plasmodium species that normally infect animals, such as P. knowlesi. As of yet, there are no reports of human–mosquito–human transmission of such zoonotic species of malaria [1]. Particular parasite species have their specific strategies for survival [2], as well as their own features of pathology, epidemiology, public health significance, and amenability to control. Malaria reintroduction in the territories that had been freed from it is one of the critical issues of malaria control in the 21st century [3]. In the pre-elimination era, malaria was endemic in most of the European countries, including a considerable part of Russia. In Europe, all of the species of malaria Int. J. Environ. Res. Public Health 2019, 16, 694; doi:10.3390/ijerph16050694 www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2019, 16, 694 2 of 18 Int. J. Environ. Res. Public Health 2019, 16, x 2 of 18 ever present (that is P. malariae, P. falciparum, and P. vivax) had been eliminated in the mid-20th century, and vivaxvivax malaria malaria was was the lastthe onelast to one disappear. to disappear Since then,. Since short-living then, short-living episodes of theepisodes autochthonous of the autochthonoustransmission of transmissionP. vivax have beenof P.vivax documented have been in a documented number of European in a number countries, of European and, among countries, them, and,Russia among was thethem, most Russia affected. was the most affected. Between 1979 and 1990, episodes of local transmission of P.vivaxP. vivax inin Russia Russia occurred occurred mostly mostly due due toto importation importation from Afghanistan by the returning Soviet soldiers [4]. [4]. Importation Importation of of malaria malaria became became a problem again after the dissolution of the Union of the Soviet Socialist republics (USSR), which triggeredtriggered epidemics epidemics of of vivax vivax malaria malaria in in a a number number of of former former member member states, states, including including Tajikistan Tajikistan and and Azerbaijan in particular. During During the the post-Soviet ep epoch,och, the local transmission of malaria in Russia followedfollowed ups and and downs downs of of malaria malaria in in Asiatic Asiatic ex-members ex-members of of USSR, USSR, with with a a lag lag of of about about two two years years [5]. [5]. Since the dissolution of of the USSR in 1991, there we werere no autochthonous cases of malaria in Russia until 1996. An An upsurge of malaria in post-Soviet st statesates provoked secondary transmission transmission in in Russia, Russia, which happened due to the importation of malaria by migrants migrants and often often coincided coincided with with hot hot summer summer weather. FromFrom 19961996 to to 2009, 2009, there there was was a wavea wave of transmissionof transmission with with more more than than 700 autochthonous 700 autochthonous cases. cases.After that,After only that, five only episodic five episodic autochthonous autochthonous casesoccurred cases occurred within within Russia Russia (Figure (Figure1). 1). Figure 1. Malaria cases in Russia. Source: Russian Federal Service for Surveillance on Consumer Rights Figure 1. Malaria cases in Russia. Source: Russian Federal Service for Surveillance on Consumer Protection and Human Wellbeing (Rospotrebnadzor). * CIS—Commonwealth of Independent States, Rights Protection and Human Wellbeing (Rospotrebnadzor). * CIS—Commonwealth of Independent consisting of a part of former Soviet Republics. States, consisting of a part of former Soviet Republics. The reintroduction of vivax malaria remains possible in temperate regions; this is why the The reintroduction of vivax malaria remains possible in temperate regions; this is why the question of determinants and drivers of malaria re-emergence does not lose its relevance and requires question of determinants and drivers of malaria re-emergence does not lose its relevance and requires new approaches. new approaches. Malaria is often referred to as a climate-dependent disease, which is primarily because a certain Malaria is often referred to as a climate-dependent disease, which is primarily because a certain sum of temperatures is needed for the complete maturation of sporozoites in mosquitoes. Plasmodium sum of temperatures is needed for the complete maturation of sporozoites in mosquitoes. Plasmodium vivax requires lower temperatures for its development in the vector than other human malaria vivax requires lower temperatures for its development in the vector than other human malaria species. At temperatures between 16 ◦C and 18 ◦C, P. vivax would develop, albeit slowly, whereas the species. At temperatures between 16 °С and 18 °С, P.vivax would develop, albeit slowly, whereas the development of P. falciparum is possible only at 18 ◦C and above. P. falciparum used to be widespread in development of P.falciparum is possible only at 18 °С and above. P.falciparum used to be widespread Europe, including the southernmost areas of Russia. In warm years, it could spread in Russia even up in Europe, including the southernmost areas of Russia. In warm years, it could spread in Russia even to 61◦ N[6]. However, the Palaearctic variety of P. falciparum had been probably eliminated throughout up to 61° N [6]. However, the Palaearctic variety of P.falciparum had been probably eliminated Europe by the end of the 1950s. The importation of P. falciparum from elsewhere is arguably impossible, throughout Europe by the end of the 1950s. The importation of P.falciparum from elsewhere is arguably impossible, because the mosquitoes of the Palaearctic region are insusceptible to P.falciparum varieties from the Afrotropical and Oriental regions [7–9]. Therefore, we discuss here the Int. J. Environ. Res. Public Health 2019, 16, 694 3 of 18 because the mosquitoes of the Palaearctic region are insusceptible to P. falciparum varieties from the Afrotropical and Oriental regions [7–9]. Therefore, we discuss here the climatic conditions favoring the possible reintroduction of P. vivax only, and leave the question of P. falciparum beyond the scope of this work. Malaria vectors are much more resistant to low temperatures than malaria parasites. Temperature affects the bionomics of Anopheles mosquitoes, such as the speed of development of the aquatic stages (which depends on the temperature of the place of breeding), the speed of blood digestion (which depends on the temperature of the resting place), and their survival in general [10]. However, the minimum temperature requirements of malaria parasites during the extrinsic part of the cycle are significantly higher than those of the mosquitoes. For example, aquatic stages of the principal malaria vector in the Palaearctic region, A. maculipennis s.l, require no less than +10 ◦C, and adults actively feed at this temperature, whereas stages of P. vivax in mosquitoes die out at temperatures below 16 ◦C. This was the explanation of the phenomenon of “anophelism without malaria” that puzzled European malariologists in the 1920s and 1930s [11,12]. Hence, in temperate regions, by the time of the year when the temperatures become suitable for the development of the parasite in the mosquito, active vectors are already present in ample quantities. Therefore, we focus on the temperature requirements of parasites, not the vectors, as only the former present the limiting factor.