Vector control intervention towards interruption of transmission of Chagas disease by Rhodnius prolixus, main vector in Guatemala

In Guatemala, the Ministry of Health (MoH) began a vector control project with Japanese cooperation in 2000 to reduce the risk of Chagas disease infection. Rhodnius prolixus is one of the principal vectors and is targeted for elimination. The control method consisted of extensive residual insecticide spraying campaigns, followed by community-based surveillance with selective respraying. Interventions in nine endemic departments identified 317 villages with R. prolixus of 4,417 villages surveyed. Two cycles of residual insecticide spraying covered over 98% of the houses in the identified villages. Fourteen villages reinfestated were all resprayed. Between 2000-2003 and 2008, the number of infested villages decreased from 317 to two and the house infestation rate reduced from 0.86% to 0.0036%. Seroprevalence rates in 2004-2005, when compared with an earlier study in 1998, showed a significant decline from 5.3% to 1.3% among schoolchildren in endemic areas. The total operational cost was US$ 921,815, where the cost ratio between preparatory, attack and surveillance phases was approximately 2:12:1. In 2008, Guatemala was certified for interruption of Chagas disease transmission by R. prolixus. What facilitated the process was existing knowledge in vector control and notable commitment by the MoH, as well as political, managerial and technical support by external stakeholders.

On an acute case of Chagas disease in a region under vector control in the state of São Paulo, Brazil

Desde a década de 1970 não se notificavam casos autóctones de doença de Chagas aguda em São Paulo. em março de 2006 a Vigilância Epidemiológica registrou óbito por doença de Chagas aguda, em Itaporanga, de paciente de seis anos de idade. Exame histopatológico post mortem realizado no Hospital das Clínicas da Faculdade de Medicina de Botucatu confirmou o diagnóstico. Consultamos prontuários de hospitais e entrevistamos profissionais de saúde envolvidos além de familiares do paciente. Descrevemos medidas adotadas in loco para identificar a via de transmissão, reservatórios e vetores. Discutimos as possíveis fontes de infecção. Na região não foram identificados outros casos humanos, vetores ou reservatórios vertebrados infectados por Trypanosoma cruzi. Salientamos a importância de manter a vigilância, mesmo em áreas onde a transmissão de doença de Chagas está interrompida e naquelas ainda infestadas por triatomíneos. Deve-se admitir a hipótese diagnóstica de doença de Chagas quando observados: edema palpebral (uni ou bilateral), insuficiência cardíaca, miocardite, pericardite, anasarca, quadros similares aos de síndrome nefrótica ou glomerulonefrite sem causas outras aparentes, em pacientes com dados epidemiológicos positivos. Encontro, mesmo em raras ocasiões, de triatomíneos na região ou ainda contato com alimento contaminável com formas infectantes de T. cruzi.

The anticancer drug tamoxifen is active against Trypanosoma cruzi in vitro but ineffective in the treatment of the acute phase of Chagas disease in mice

The activity of the antineoplastic drug tamoxifen was evaluated against Trypanosoma cruzi. In vitro activity was determined against epimastigote, trypomastigote and amastigote forms of CL14, Y and Y benznidazole resistant T. cruzi strains. Regardless of the strain used, the drug was active against all life-cycle stages of the parasite with a half maximal effective concentration ranging from 0.7-17.9 µM. Two experimental models of acute Chagas disease were used to evaluate the in vivo efficacy of treatment with tamoxifen. No differences in parasitemia and mortality were observed between control mock-treated and tamoxifen-treated mice.

Challenges and opportunities for primary, secondary, and tertiary prevention of Chagas' disease

A century after its discovery, Chagas' disease still represents a major public health challenge in Latin America. Moreover, because of growing population movements, an increasing number of cases of imported Chagas' disease have now been detected in non-endemic areas, such as North America and some European countries. This parasitic zoonosis, caused by Trypanosoma cruzi, is transmitted to humans by infected Triatominae insects, or occasionally by non-vectorial mechanisms, such as blood transfusion, mother to fetus, or oral ingestion of materials contaminated with parasites. Following the acute phase of the infection, untreated individuals enter a chronic phase that is initially asymptomatic or clinically unapparent. Usually, a few decades later, 40-50% of patients develop progressive cardiomyopathy and/or motility disturbances of the oesophagus and colon. In the last decades several interventions targeting primary, secondary and tertiary prevention of Chagas' disease have been attempted. While control of both vectorial and blood transfusion transmission of T cruzi (primary prevention) has been successful in many regions of Latin America, early detection and aetiological treatment of asymptomatic subjects with Chagas' disease (secondary prevention) have been largely underutilised. At the same time, in patients with established chronic disease, several pharmacological and non-pharmacological interventions are currently available and have been increasingly used with the intention of preventing or delaying complications of the disease (tertiary prevention). In this review we discuss in detail each of these issues.

Modelling congenital transmission of Chagas` disease

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. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

Lethality of triatomines (Hemiptera: Reduviiae), vectors of Chagas' disease, feeding on blood baits containing synthetic insecticides, under laboratory conditions

A laboratory study was conducted to test the toxicity of synthetic insecticides added to defibrinated sheep blood kept at room temperature and offered as food to the following triatomine species: Triatoma infestans, Panstrongylus megistus, Triatoma vitticeps, Triatoma pseudomaculata, Triatoma brasiliensis and Rhodnius prolixus. The insecticides used, at a concentration of 1g/l, were: HCH, DDT, Malathion and Trichlorfon, and the lethalithy observed at the end of a 7-day period varied according to the active principle of each. HCH was the most effective by the oral route, killing 100% of the insects, except P. megistus (95.7%) and T. pseudomaculata (94.1%). Trichlorfon killed the insects at rates ranging from 71.8% (T. vitticeps) to 98% (R. prolixus). Malathion was slightly less efficient, killing the insects at rates from 56.8% (T. vitticeps) to 97% (T.brasiliensis). DDT was the least effective, with a killing rate of 10% (T. vitticeps) to 75% (T.brasiliensis). Since the tests were performed at room temperature, we suggest that baits of this type should be tried for the control of triatomines in the field.

Lethal effect of a bait for Rhodnius prolixus (Hemiptera: Reduviidae), the vector of Chagas' disease, containing hexachlorocyclohexane (HCH), under laboratory conditions

The lethal effect of a bait containing an aqueous hexachlorocyclohexane (HCH) suspension at the concentration of 1g/l and maintained at room temperature was studied in the laboratory over a period of 12 weeks. The suspension was placed in a latex bag hanging inside a 1000-ml beaker tightly covered with nylon netting, and left there with no changes for 85 days. Sixteen groups of R. prolixas bugs, consisting on average of 30 specimens each, were successively exposed to the bait and observed at different intervals for one week each. The mortality rate was 100% for all groups, except for the 16th, whose mortality rate was 96.7%. As the groups succeeded one another, mortality started to occur more rapidly and was more marked at the 6- and 24-h intervals. Later tests respectively started at 6:00 a.m. and 6:00 p.m. showed that diurnal and nocturnal periodicity in the offer of food had no effect on mortality. First- and 2nd- instar nymphs and adults male were more sensitive and 5th- instar nymphs were more resistant to the active principle of the bait.

Seroepidemiological and clinical study of Chagas' disease in Nicaragua

With the aim of determining the prevalence, immunological profile, and knowing the electrocardiographic alterations, a clinical and Seroepidemiological study of Chagas' disease was performed in three rural settlements located at the North, East and West of Nicaragua. Anti T. cruzi antibodies were searched by indirect immunofluorescence (IFI) and hemagglutination (IHA) in a total of 803 subjects. Seropositives and the same number of seronegatives, matched by age and sex, were included in a case-control design for the electrocardiographic assessment. Antibody prevalence was 13.1, 4.3 and 3.2% in the respective settlements. In the first two the immunological profile corresponds to that of an endemic zone of long standing, were transmission has decreased, and in the third the pattern is of a zone under control. Electrocardiographic changes compatible with Chagas' disease were found in seropositive individuals, but difference with control group was not statistically significant. It is concluded that the disease is endemic in the three settlements and the clinical aspect requires further evaluation, including additional cardiologic techniques.

Oral transmission of Chagas disease: importance of Trypanosoma cruzi biodeme in the intragastric experimental infection

Oral transmission of Trypanosoma cruzi has been suspected when epidemic episodes of acute infection were observed in areas devoid of domiciled insect vectors. Considering that the distribution of T. cruzi biodemes differs in sylvatic and domestic cycles, results of studies on biodemes can be of interest regarding oral transmission. The infectivity of T. cruzi strains of different biodemes was tested in mice subjected to infection by the digestive route (gavage). Swiss mice were infected either with the Peruvian strain (Biodeme Type I, Z2b) or the Colombian strain (Biodeme Type III, Z1, or T. cruzi I); for control, intraperitoneal inoculation was performed in a group of mice. The Colombian strain revealed a similar high infectivity and pathogenicity when either route of infection was used. However, the Peruvian strain showed contrasting levels of infectivity and pathogenicity, being high by intraperitoneal inoculation and low when the gastric route was used. The higher infectivity of the Colombian strain (Biodeme Type III) by gastric inoculation is in keeping with its role in the epidemic episodes of acute Chagas disease registered in the literature, since strains belonging to Biodeme III are most often found in sylvatic hosts.