Malaria in Highlands of Ecuador since 1900 - Vol. 18 No. 4 - April 2012 - Emerging Infectious Disease journal - CDC
Table of Contents
Volume 18, Number 4–April 2012
Volume 18, Number 4—April 2012
Malaria in Highlands of Ecuador since 1900
Some authors have speculated that Anopheles mosquitoes may begin transmitting malaria parasites (Plasmodium spp.) at higher altitudes in the South American Andes because of climate change (1,2). In contrast, highland malaria in Africa has more often been attributed to land use alterations, malaria treatment resistance, changes in vector control measures, and human migration into foothill and mountainous regions (3). Before 2004, a short-lived epidemic of P. vivax malaria was recorded in a village in Bolivia at an altitude of 2,300 m that was transmitted by Anopheles pseudopunctipennis Theobald mosquitoes (4). Multiple anopheline malaria vectors have also become established in the highlands of Ecuador (5).
AbstractA recent epidemic of malaria in the highlands of Bolivia and establishment of multiple Anopheles species mosquitoes in the highlands of Ecuador highlights the reemergence of malaria in the Andes Mountains in South America. Because malaria was endemic to many highland valleys at the beginning of the 20th century, this review outlines the 20th century history of malaria in the highlands of Ecuador, and focuses on its incidence (e.g., geographic distribution) and elimination from the northern highland valleys of Pichincha and Imbabura and the role of the Guayaquil to Quito railway in creating highland larval habitat and inadvertently promoting transportation of the vector and parasite. Involvement of control organizations in combating malaria in Ecuador is also outlined in a historical context.
In this review, we summarize documented cases of highland malaria that occurred in Ecuador during the early 20th century. We define the term highland malaria to mean all malaria that occurs in regions with steep topography. Using geographic information systems (ArcGIS version 10; ESRI, Redlands, CA, USA) and tabulated data from historical sources, we reconstruct the geographic extent of malaria incidence during several periods of interest. We also outline malaria control efforts and attempts at malaria elimination for Ecuador during the 20th century and at the beginning of the 21st century.
Although malaria was prevalent on the coast of Ecuador at the beginning of the 20th century, it was considered by public health officials to be a minor problem (6). Until 1908, Guayaquil on the coast of Ecuador was affected by the constant menace of mosquitoes transmitting yellow fever, and flea-borne bubonic plague reoccurred regularly in all areas of the city and surrounding countryside (6–8). Because Guayaquil had an image of being an unhealthy major port city, officials in Ecuador signed an international sanitation convention in 1906 to combat outbreaks of yellow fever, bubonic plague, and cholera (9). Under terms of the convention, officials were to take measures to prevent ongoing transmission of these diseases, including the use of mosquito screens on windows and doors of hospitals (9). During that time, officials also experimented with the use of mosquito larvae–eating fish as a biocontrol method in an attempt to control yellow fever (8).
Malaria in Ecuador at the Beginning of the 20th Century
In 1908, the public health movement became active in Ecuador, and a special sanitary commission was formed in Guayaquil (7,8). At that time, malaria was still considered a minor health problem and many residents allowed mosquitoes to bite them to provide them with long-term immunity to malaria (10). Malaria prevention measures included bed nets, window and door screens, and anopheline larval habitat destruction (8,10). Several medical entomologists became active during this period in Ecuador. These entomologists included the French entomologist Paul Rivet, and the Ecuadorian entomologists F.R. Campos, Luis León, and J. Rodríguez (11).
In 1919, many physicians in Ecuador began to receive training in foreign countries, particularly in the United States through grants from the Rockefeller Foundation, in an attempt to eliminate yellow fever and malaria from Ecuador (6,8,12). With the elimination of yellow fever in 1920, attention inevitably turned to malaria, which still accounted for a large percentage of deaths on the coast of Ecuador (13). By 1940, malaria still remained a priority and was the second leading cause of death in Ecuador after whooping cough (7). At the time, it was recommended that a campaign against malaria should be initiated throughout the entire country (7).
In 1886, construction began on the railway that was to link some of the low-altitude regions of the country near Guayaquil to highland regions and eventually Quito (altitude 2,800 m) (14). The railway was constructed on a route that began in Guayaquil (at sea level), passed through Milagro, and followed the valley bottom up toward Huigra, in Chimborazo (altitude 1,250 m). After Huigra, the railway continued higher toward Alausí, Chimborazo (altitude 2,340 m), after climbing the infamous Devil’s Nose switchbacks (14) (Figure 1).
Highland Malaria during Construction of Guayaquil to Quito Railway (1890–1945)
When construction of the railway reached an elevation of 200 m, workers reported bites from an unidentified bush-dwelling, flying insect and many subsequently died of high fevers (15). At higher altitudes, workers began to report fevers attributed to malaria (14). In 1906, the Guayaquil newspaper Grito del Pueblo reported that railway workers affected by fevers were removed from the construction site and brought to the highland village of Chasqui, Pichincha, for recovery (16). The following quotation from Daniel Barragán, one of the engineers for the railway, provides strong evidence that mosquitoes (Culicidae) were present at worksites: “The mosquitoes were our eternal companions, during all of the night, their melodious and incessant humming many times did not let us find sleep” (translated into English by L.L.P.) (14).
Meitzner described treating many of the railway workers for malaria during 1911 (10). In the winter of that year, the incidence of malaria was so great among workers that construction halted completely (10). Patients were usually brought to higher altitude towns such as Huigra for treatment because there were insufficient medical facilities at lower altitudes (10). Patients with malaria among the railway workers were treated by Meitzner by using a combination of castor oil and quinine and a diet that excluded meat (10). Before operation of the railway, transportation between the coast and highland regions was limited. Therefore, during the early operation of the railway to Quito, the malaria parasite could have been repeatedly introduced by infected passengers and workers to higher altitude regions, including the valleys around the city of Quito (10).
The presence of malaria rather than other similar febrile illnesses in railway workers is further supported by multiple collections of An. pseudopunctipennis larvae (the highland malaria vector) in the Chiripungo Valley, near Alausí, Chimborazo (altitude <2,400 m) (17). As early as 1911, Meitzner made recommendations to railway engineers to construct drainage ditches along the sides of the tracks to prevent establishment of additional larval habitats in the pools that formed there (10). Despite the efforts of Meitzner, An. pseudopunctipennis mosquitoes remained in highland valleys of Chimborazo along the railway at least into the mid 1940s. In 1943, Levi Castillo collected An. pseudopunctipennis larvae along railway tracks up to an altitude of 1,250 m, and in 1944, he collected larvae in pools associated with rivers in the towns of Huigra and Sibambe, Chimborazo (17). These entomologic collections are consistent with the epidemiology of continued malaria transmission; in 1944, a total of 154 cases of malaria among 864 residents were documented in Huigra (18). Aside from habitats associated with the railway line, as shown in Figure 2, partial blockage of the river below the newly built tracks along Devil’s Nose would probably have produced suitable pools for An. pseudopunctipennis larval habitat.
Trains were a likely carrier for continued introduction of anopheline mosquitoes into highland regions from the coast (17,19). At Milagro station, adult mosquitoes were observed to fill train cars bound for higher elevations (19). Levi Castillo found pools of water in ceiling portions of trains, which served as mobile larval habitats for anopheline mosquitoes (17). At higher elevations (>1,100 m), An. pseudopunctipennis mosquitoes were documented as the sole vector, although An. albimanus Wiedemann larvae were collected at lower altitudes along the railway (18). Trains likely served to introduce anopheline mosquitoes to highland regions until the 1960s and 1970s, when the railway fell into disuse (15).