BioSystems 99 (2010) 215–222 Contents lists available at ScienceDirect BioSystems journal homepage: www.elsevier.com/locate/biosystems Modelling congenital transmission of Chagas’ disease Silvia Martorano Raimundo a,∗ , Eduardo Massad a,b , Hyun Mo Yang c a School of Medicine, University of Sao Paulo and LIM 01-HCFMUSP, Rua Teodoro Sampaio, 115 CEP: 05405-000 - São Paulo, S.P., Brazil b London School of Hygiene and Tropical Diseases, UK c Universidade Estadual de Campinas, IMECC – Departamento de Matemática Aplicada, Brazil article info Article history: Received 28 September 2009 Received in revised form 26 November 2009 Accepted 26 November 2009 Keywords: Congenital transmission Chagas’ disease Control strategy Demography abstract The successful elimination of vectorial and transfusional transmission of Chagas’ disease from some countries is a result of the reduction of domestic density of the primary vector Triatoma infestans, of almost 100% of coverage in blood serological selection and to the fact that the basic reproductive number of Chagas’ disease is very close to one (1.25). Therefore, congenital transmission is currently the only way of acquiring Chagas’ Disease in such regions. In this paper we propose a model of congenital transmission of Chagas’ disease. Its aim is to provide an estimation of the time period it will take to eliminate this form of transmission in regions where vetorial transmission was reduced to close to zero, like in Brazil. © 2009 Elsevier Ireland Ltd. All rights reserved. 1. Introduction On June 9, 2006, the Pan American Health Organization (PAHO) presented the Minister of Health of Brazil with the Interna- tional Elimination of Transmission of Chagas’ Disease Certificate (Ministério de Saúde, 2007; PAHO, 2007). This act was the culmi- nation of an intensive process that begun in 1991 with the Southern Cone Initiative, a joint agreement between the governments of Argentina, Bolivia, Brazil, Chile, Paraguay, Uruguay and Peru, to con- trol Chagas’ disease by the elimination of the main vector, Triatoma infestans. This initiative has been highly successful and the preva- lence area of the vector plummeted in the last years (Esgolts, 1970). As a consequence, the current seroprevalence of children between 0 and 5 years in Brazil is of the order of 10 -5 , a clear indication that transmission, if it is occurring, is only accidental (Massad, 2008). The successful elimination of vectorial and transfusional trans- mission of Chagas’ disease from Brazil was a result of the reduction of domestic density of the primary vector T. infestans and of almost 100% of coverage in blood serological selection. As mentioned in Kirchhoff (2000), the basic reproductive number (R 0 ) of Chagas’ disease was very close to one (1.25) (Kirchhoff, 2000), that is, not far from the elimination threshold. So, an average reduction of 25% in the vector life expectancy (feasible thanks to the domestic habits of T. infestans) was enough to reduce R 0 below unit, and to achieve the elimination of this form of transmission. Therefore, congenital ∗ Corresponding author. E-mail address: silviamr@dim.fm.usp.br (S.M. Raimundo). transmission is currently the only way of acquiring Chagas’ Disease in Brazil. American trypanosomiasis (Chagas’ Disease) is a zoonosis caused by the protozoan parasite Trypanosoma cruzi [4]. The disease is characterized by two phases: acute and chronic. The principal mechanism of Chagas’ disease transmission in humans is through the bites of insect vectors called Triatoma sp bugs (CDC, 2007). These blood-sucking bugs, in turn, get infected by biting an infected animal or person. This vector belongs to the subfamily Triatominae (Hemiptera: Reduviidae) (Lent et al., 1994; Schofield, 1994, 2000) comprising 130 recognized species, of which about a dozen are commonly involved in transmission of the trypanosome to humans. Other forms of transmission include: consumption of uncooked food contaminated with faeces from infected bugs; congenital transmission (from a pregnant woman to her baby); blood transfusion; organ transplantation; and accidental laboratory exposure (CDC, 2007). Congenital transmission may occur at any time of pregnancy, in successive gestations and may affect twins. The infection may produce pathology in the growing foetus. The consequences on the newborn are variable, ranging from asymptomatic to severe clinical manifestations. Congenital transmission cannot be prevented, but early diagnosis of the newborn enables prompt treatment, achiev- ing cure rates close to 100% (the treatment regimen should include benznidazol between 5 and 10 mg/kg/d for 30–60 days or nifur- timox at 10–15 mg/kg/d for 60 days) and thus avoiding progression to chronic Chagas’ disease (Massad, 2008). It is a consensus that congenital Chagas disease will be a pressing public health concern until the pool of infected women of childbearing age decreases to 0303-2647/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.biosystems.2009.11.005