Transmission intensity affects almost all aspects of malaria epidemiology and the impact of malaria on human populations. Maps of transmission intensity are necessary to identify populations at different levels of risk and to evaluate objectively options for disease control. To remain relevant operationally, such maps must be updated frequently. Following the first global effort to map Plasmodium falciparum malaria endemicity in 2007, this paper describes the generation of a new world map for the year 2010. This analysis is extended to provide the first global estimates of two other metrics of transmission intensity for P. falciparum that underpin contemporary questions in malaria control: the entomological inoculation rate (Pf EIR) and the basic reproductive number (PfR). Annual parasite incidence data for 13,449 administrative units in 43 endemic countries were sourced to define the spatial limits of P. falciparum transmission in 2010 and 22,212 P. falciparum parasite rate (Pf PR) surveys were used in a model-based geostatistical (MBG) prediction to create a continuous contemporary surface of malaria endemicity within these limits. A suite of transmission models were developed that link Pf PR to Pf EIR and PfR and these were fitted to field data. These models were combined with the Pf PR map to create new global predictions of Pf EIR and PfR. All output maps included measured uncertainty. An estimated 1.13 and 1.44 billion people worldwide were at risk of unstable and stable P. falciparum malaria, respectively. The majority of the endemic world was predicted with a median Pf EIR of less than one and a median PfRc of less than two. Values of either metric exceeding 10 were almost exclusive to Africa. The uncertainty described in both Pf EIR and PfR was substantial in regions of intense transmission. The year 2010 has a particular significance as an evaluation milestone for malaria global health policy. The maps presented here contribute to a rational basis for control and elimination decisions and can serve as a baseline assessment as the global health community looks ahead to the next series of milestones targeted at 2015.

/pdf/a-world-malaria-map-plasmodium-falciparum-endemicity-in-2007-2rjucpgi15.pdf

A world malaria map: Plasmodium falciparum endemicity in 2007

Many attempts have been made to quantify Africa's malaria burden but none has addressed how urbanization will affect disease transmission and outcome, and therefore mortality and morbidity estimates In 2003, 39% of Africa's 850 million people lived in urban settings; by 2030, 54% of Africans are expected to do so We present the results of a series of entomological, parasitological and behavioural meta-analyses of studies that have investigated the effect of urbanization on malaria in Africa We describe the effect of urbanization on both the impact of malaria transmission and the concomitant improvements in access to preventative and curative measures Using these data, we have recalculated estimates of populations at risk of malaria and the resulting mortality We find there were 1,068,505 malaria deaths in Africa in 2000 - a modest 67% reduction over previous iterations The public-health implications of these findings and revised estimates are discussed

Urbanization, malaria transmission and disease burden in Africa

Summary The world is becoming urban. The UN predicts that the world's urban population will almost double from 3·3 billion in 2007 to 6·3 billion in 2050. Most of this increase will be in developing countries. Exponential urban growth is having a profound effect on global health. Because of international travel and migration, cities are becoming important hubs for the transmission of infectious diseases, as shown by recent pandemics. Physicians in urban environments in developing and developed countries need to be aware of the changes in infectious diseases associated with urbanisation. Furthermore, health should be a major consideration in town planning to ensure urbanisation works to reduce the burden of infectious diseases in the future.

/pdf/urbanisation-and-infectious-diseases-in-a-globalised-world-3koh8nsg96.pdf

Urbanisation and infectious diseases in a globalised world

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(10)61270-6.pdf

Shrinking the malaria map: progress and prospects

Malaria not only remains a leading cause of morbidity and mortality, but it also impedes socioeconomic development, particularly in sub-Saharan Africa. Rapid and unprecedented urbanization, going hand-in-hand with often declining economies, might have profound implications for the epidemiology and control of malaria, as the relative disease burden increases among urban dwellers. Reviewing the literature and using a modeling approach, we find that entomologic inoculation rates in cities range from 0 to 54 per year, depending on the degree of urbanization, the spatial location within a city, and overall living conditions. Using the latest United Nations figures on urbanization prospects, nighttime light remotely sensed images, and the "Mapping Malaria Risk in Africa" results on climate suitability for stable malaria transmission, we estimate that 200 million people (24.6% of the total African population) currently live in urban settings where they are at risk of contracting the disease. Importantly, the estimated total surface area covered by these urban settings is only approximately 1.1-1.6% of the total African surface. Considering different plausible scenarios, we estimate an annual incidence of 24.8-103.2 million cases of clinical malaria attacks among urban dwellers in Africa. These figures translate to 6-28% of the estimated global annual disease incidence. Against this background, basic health care delivery systems providing early diagnosis and early treatment and preventive actions through mother and child health programs and the promotion of insecticide-treated bed nets for the rapidly growing numbers of the urban poor must be improved alongside well-tailored and integrated malaria control strategies. We propose environmental management and larviciding within well-specified productive sites as a main feature for such an integrated control approach. Mitigation of the current burden of malaria in urban African settings, in turn, is a necessity for stimulating environmentally and socially sustainable development.

Urbanization in sub-saharan africa and implication for malaria control

The rapid increase in the world's urban population has major implications for the epidemiology of malaria. A review of malaria transmission in sub-Saharan African cities shows the strong likelihood of transmission occurring within these sprawling cities, whatever the size or characteristics of their bioecologic environment. A meta-analysis of results from studies of malaria transmission in sub-Saharan Africa shows a loose linear negative relationship between mean annual entomologic inoculation rates (EIR) and the level of urbanicity. Few studies have failed to find entomologic evidence of some transmission. Our results show mean annual EIRs of 7.1 in the city centers, 45.8 in periurban areas, and 167.7 in rural areas. The impact of urbanization in reducing transmission is more marked in areas where the mean rainfall is low and seasonal. Considerable variation in the level of transmission exists among cities and within different districts in the same city. This article presents evidence from past literature to build a conceptual framework to begin to explain this heterogeneity. The potential for malaria epidemics owing to decreasing levels of natural immunity may be offset by negative impacts of urbanization on the larval ecology of anopheline mosquitoes. Malaria control in urban environments may be simpler as a result of urbanization; however, much of what we know about malaria transmission in rural environments might not hold in the urban context.

Malaria transmission in urban sub-Saharan Africa

Macaca fascicularis monkeys from Mauritius were shown to be susceptible via sporozoite inoculation to 7 species of Plasmodium (P. fragile, P. coatneyi, P. gonderi, P. inui, P. cynomolgi, P. knowlesi, and P. fieldi), indigenous to macaques in southeastern Asia. Four monkeys were sequentially infected with different species of Plasmodium to determine maximum and course of parasitemia. In 2 nonsplenectomized monkeys, P. fragile developed maximum parasite counts of only 134 and 155/microliters. For Plasmodium knowlesi, a parasite that is life-threatening to rhesus monkeys, maximum parasite counts were 4,278 and 7,440/microliters. Plasmodium coatneyi developed to what must be considered as moderate levels. After animals underwent splenectomy, parasite counts of P. coatneyi were 58,280, 89,094, 4,464, and 43,524/microliters. The maximum parasite counts for P. gonderi (13,508 and 21,576/microliters) and P. fieldi (1,767 and 17,836/microliters) were lower than would be expected in M. mulatta. In 2 monkeys that developed patent parasitemia with P. inui, the maximum parasite counts (95,046 and 728,748/microliters) indicated that this parasite may be the best adapted species for development in these animals once infection is established. Finally, the reinfection of 2 monkeys with P. cynomolgi suggested that some animals may be basically more resistant than others, whether splenectomized or not, to the production of high-density parasitemia.

Susceptibility of macaca fascicularis monkeys from mauritius to different species of plasmodium

Serologic studies for malaria using the indirect fluorescent antibody technique suggest that active transmission is either absent or very low in 6 villages on the Pacific side of Costa Rica. Positive titers (1:20 or higher) were seen in the under-15-year age group in three of the study localities, but only 5 such responses were encountered among 249 people examined in this age range. In the adults (15 years and over) from the same 3 villages there were 68 positive titers among 161 examined. There were 43 positive responses in 189 adults from the remaining 3 villages where none of 307 persons under 15 years of age showed a titer of 1:20 or higher to any of the 3 malaria antigens tested (Plasmodium falciparum, P. vivax and P. malariae). These data suggest that the positive responses in the latter villages are more likely to be associated with old or imported cases than with current local transmission. Serologic responses of 1:80 or higher to the P. falciparum antigen suggested the continued presence of this parasite in the population in spite of the paucity of positive blood smears with this species in recent years. Positive titers with the P. malariae antigen suggest that this parasite is probably still present in the area. Such serologic studies help to indicate areas where malaria transmission is active and provide information on parasite reservoirs in particular populations.

The seroepidemiology of malaria in Middle America. II. Studies on the Pacific coast of Costa Rica.

Entomologic surveys conducted in a small village in an area of known high malaria transmission in El Salvador yielded a high rate of infection in Anopheles albimanus collected inside houses in which cases of malaria had occurred. Of 324 specimens dissected, 12 were found to harbor sporozoites or oocysts. This is in contrast to prior reports of extremely low infection rates in collections of this species from malarious areas, and suggests that under some circumstances A. albimanus does meet the criteria of an effective malaria vector.

McWilson Warren

Papers

Malaria transmission in urban sub-Saharan Africa

Susceptibility of macaca fascicularis monkeys from mauritius to different species of plasmodium

The seroepidemiology of malaria in Middle America. II. Studies on the Pacific coast of Costa Rica.

Natural infections of Anopheles albimanus with Plasmodium in a small malaria focus.

Host effects on the lipid fraction of Hymenolepis diminuta.