Characterizing the malaria rural-to-urban transmission interface: The importance of reactive case detection

• Published in: PLoS neglected tropical diseases 2017-07, Vol.11 (7), p.e0005780-e0005780
• Main Authors: Molina Gómez, Karen, Caicedo, M Alejandra, Gaitán, Alexandra, Herrera-Varela, Manuela, Arce, María Isabel, Vallejo, Andrés F, Padilla, Julio, Chaparro, Pablo, Pacheco, M Andreína, Escalante, Ananias A, Arevalo-Herrera, Myriam, Herrera, Sócrates
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Adults; Animals; Anopheles; Anopheles - classification; Anopheles - growth & development; Anopheles - parasitology; Biology and Life Sciences; Breeding; Breeding sites; Child; Colombia - epidemiology; Cross-Sectional Studies; Detection; Diagnostic Tests, Routine; Disease transmission; Disease Transmission, Infectious; Earth Sciences; ELISA; Enzyme-linked immunosorbent assay; Enzymes; Epidemiology; Female; Funding; Genetic Variation; Genomics; Genotype; Genotyping; Households; Housing; Human diseases; Humans; Infections; Interviews as Topic; Malaria; Malaria - diagnosis; Malaria - epidemiology; Malaria - parasitology; Malaria - transmission; Male; Medicine and Health Sciences; Methods; Microscopy; Middle Aged; Molecular Epidemiology; Mosquito Vectors - classification; Mosquito Vectors - growth & development; Mosquito Vectors - parasitology; Mosquitoes; Neighborhoods; Nucleotide sequence; Parasites; PCR; Plasmodium - classification; Plasmodium - genetics; Plasmodium - isolation & purification; Plasmodium falciparum; Polymerase Chain Reaction; Prevalence; Prevalence studies (Epidemiology); Research and Analysis Methods; Residential areas; Risk analysis; Risk Factors; Rural areas; Rural Population; Social Sciences; Studies; Surveys; Transmission; Tropical diseases; Urban areas; Urban environments; Urban Population; Vaccines; Vector-borne diseases; Vectors; Wildland-urban interface; Young Adult
• ISSN: 1935-2735; 1935-2727; 1935-2735
• DOI: 10.1371/journal.pntd.0005780

Reported urban malaria cases are increasing in Latin America, however, evidence of such trend remains insufficient. Here, we propose an integrated approach that allows characterizing malaria transmission at the rural-to-urban interface by combining epidemiological, entomological, and parasite genotyping methods. A descriptive study that combines active (ACD), passive (PCD), and reactive (RCD) case detection was performed in urban and peri-urban neighborhoods of Quibdó, Colombia. Heads of households were interviewed and epidemiological surveys were conducted to assess malaria prevalence and identify potential risk factors. Sixteen primary cases, eight by ACD and eight by PCD were recruited for RCD. Using the RCD strategy, prevalence of 1% by microscopy (6/604) and 9% by quantitative polymerase chain reaction (qPCR) (52/604) were found. A total of 73 houses and 289 volunteers were screened leading to 41 secondary cases, all of them in peri-urban settings (14% prevalence). Most secondary cases were genetically distinct from primary cases indicating that there were independent occurrences. Plasmodium vivax was the predominant species (76.3%, 71/93), most of them being asymptomatic (46/71). Urban and peri-urban neighborhoods had significant sociodemographic differences. Twenty-four potential breeding sites were identified, all in peri-urban areas. The predominant vectors for 1,305 adults were Anopheles nuneztovari (56,2%) and An. Darlingi (42,5%). One An. nuneztovari specimen was confirmed naturally infected with P. falciparum by ELISA. This study found no evidence supporting the existence of urban malaria transmission in Quibdó. RCD strategy was more efficient for identifying malaria cases than ACD alone in areas where malaria transmission is variable and unstable. Incorporating parasite genotyping allows discovering hidden patterns of malaria transmission that cannot be detected otherwise. We propose to use the term "focal case" for those primary cases that lead to discovery of secondary but genetically unrelated malaria cases indicating undetected malaria transmission.