An appraisal of the epidemiology of Trypanosoma cruzi serology in Brazil

A large bibliographic survey provided data on Trypanosoma cruzi serology covering the period l948-l984. Epidemiological-demographic methods provided an estimate of 11% for the prevalenceof positive serology in Brazil, by 1984. Significant temporal trends were observed for most of the Brazilian geographical regions as well as for Brazil, as a whole. The parabolic curve that fit best for the entire country, indicates that by 1991, the incidence of new positive serology would be close to zero. This conclusion needs further fine-adjustment, since the forecast point is somewhat distant from the measured period.

Epidemiology and control of malaria and other arthropod born diseases

Malaria and other arthropod born diseases remain a serious public health problem affecting the lives and health of certain social groups when the two basic strategies to control fail due to : (1) the lack of effective chemoprophylaxis/chemotherapy or the rapid development of drug resistance of the infectious agents and (2) the ineffectiveness of pesticides or the arthropod vectors develop resistance to them. These situations enhances the need for the design and implementation of other alternatives for sustainable health programmes. The application of the epidemiological methods is essential not only for analyzing the relevant data for the understanding of the biological characteristics of the infectious agents, their reservoirs and vectors and the methods for their control, but also for the assessment of the human behaviour, the environmental, social and economic factors involved in disease transmission and the capacity of the health systems to implement interventions for both changes in human behaviour and environmental management to purpose guaranteed prevention and control of malaria and other arthropod born diseases with efficiency, efficacy and equity. This paper discuss the evolution of the malaria arthropod diseases programmes in the American Region and the perspectives for their integration into health promotion programs and emphasis is made in the need to establish solid basis in the decision-making process for the selection of intervention strategies to remove the risk factors determining the probability to get sick or die from ABDs. The implications of the general planning and the polices to be adopted in an area should be analyzed in the light of programme feasibility at the local level, in the multisectoral context specific social groups and taking in consideration the principles of stratification and equity

Transmission factors in malaria epidemiology and control in Africa

Genetic and environmental components of factors contributing in malaria transmission are reviewed. Particular attention is given to density dependent regulation of vector populations in relation to the survival rate anophelines. The expectation of vector activities are different according to the epidemiological characteristics of malaria, mainly its stability. In areas with perennial and high transmission (stable malaria) vector control could reduce malaria related morbidity and mortality, whithout any effect on the endemicity. However this need further investigations. In areas where the transmission period is very short (unstable malaria), vector control will have an important impact on the disease and the endemicity. Control projects using indoor spraying with insecticide and impregnated bed nets are discussed.

Recent advances and prospective researches on molecular epidemiology of dengue viruses

The determination of amino acid changes in the envelop protein by direct sequencing of either genomic RNA or PCR-amplified cDNA fragments provides useful informations for assessing the genetic variability and the geographic distribution of the actually most widespread dengue-2 serotype. The possible link of variations in the envelope protein-gene and virus virulence is discussed.

The dermal leishmaniases of Brazil, with special reference to the eco-epidemiology of the disease in Amazonia

Six species of Leishmania are at present known to cause cutaneous and/or mucocutaneous leishamniasis in Brazil, and they are all to be found in the Amazon region of this country. The eco-epidemiology of each is discussed, with the observation that the Amazonian leishmaniases are all zoonoses, with their source in silvatic mammals and phlebotomine sandfly vectors. With man's destruction of the natural forest in southern Brazil, some sandfly species have survived by adapting to a peridomestic or domiciliary habitat in rural areas. Some domestic animals, such as dogs and equines are seemingly now involved in the epidemiology of the disease. No such process has yet been reported in the Amazon region, but may well take place with the continuing devastation of its forest.

Immuno-epidemiology of Schistosoma mansoni infections in a recently exposed community in Senegal

The levels of IgE and IgG4 increased strongly between cohorts, indicating a dynamic immunological situation, but no immediate impact on infection levels. Morbidity was little specific abdominal discomfort was reported by 61%, diarrhoea by 33% of the subjects; mild hepatomegaly was found in 16%, splenomegaly in 0.5%. No relation to egg counts was observed for any symptom. This mild morbidity may be due to the recent nature of the focus. In the first cohort, the percentage of people with negative egg counts ten weeks after treatment was only 18%, though egg counts declined strongly. Antigen detection confirmed these results. Praziquantel treatment provoked transient but impressive side effects (colics, vomiting, urticaria, aedema), the occurrence of which correlated with intensity of infection. Cure rates in subsequent cohorts were followed up shorter after treatment but remained low. Reinfection nevertheless oppears limited. This lower drug efficacy may be due to very rapid reinfection and/or to the lack of immunity in the population, but also reduced susceptibility of the local parasite strain must be considered and studied.

A possible correlation between the host genetic background in the epidemiology of Hepatitis B virus in the Amazon region of Brazil

The Amazon region of Brazil is an area of great interest because of the large distribution of hepatitis B virus in specific Western areas. Seven urban communities and 24 Indian groups were visited in a total of 4,244 persons. Each individual was interviewed in order to obtain demographic and familial information. Whole blood was collected for serology and genetic determinations. Eleven genetic markers and three HBV markers were tested. Among the most relevant results it was possible to show that (i) there was a large variation of previous exposure to HBV in both urban and non-urban groups ranging from 0 to 59.2%; (ii) there was a different pattern of epidemiological distribution of HBV that was present even among a same linguistic Indian group, with mixed patterns of correlation between HBsAg and anti-HBs and (iii) the prevalence of HBV markers (HBsAg and anti-HBs) were significantly higher (P=0.0001) among the Indian population (18.8%) than the urban groups (12.5%). Its possible that the host genetic background could influence and modulate the replication of the virus in order to generate HB carrier state.

Schistosomiasis in a low prevalence area: incomplete urbanization increasing risk of infection in Paracambi, RJ, Brazil

The risk of schistosomiais infection and heavy infection in the locality of Sabugo was evaluated in relation to housing in areas with different urbanization development and to residential supply with snail-infested water. Critical sanitary conditions were found in areas of incomplete urbanization, where healthy water supply sources were scarce, and draining of sewage, without previous treatment, was made directly to the water-bodies used for domestic and leisure activities, despite being Biomphalaria tenagophila snail breeding-places. Stool examinations (Kato-Katz and Lutz methods) showed prevalence of 2.9%, mean intensity of 79 eggs per gram of stool and 47% of positive cases presenting intense infection. The use of snail-contaminated water for domestic purposes was considered a risk factor for infection. It is concluded that incomplete urbanization would facilitate transmission, probably enhancing the intensity of infection and that a low prevalence could hide a highly focal transmission. The relevance of these facts upon the efficiency of epidemiologic study methods and disease control planning are then discussed.

The use and mis-use of some ecological terms and concepts in epidemiology

The article discusses the current use and mis-use of ecological terms and concepts in epidemiological literature, and in special, in works dealing with zoonotic diseases. A selection of examples was taken from papers recently published on the transmission of Chagas' disease by Triatoma sordida. Proper definitions are listed, with the intent of helping non-ecologists to use those terms and concepts correctly.

The epidemiology of malaria in Prábis, Guinea-Bissau

This article reports upon a community survey of malaria in Prábis, Guinea-Bissau. A house to house census of the population was initially carried out from August to December 1991(rainy season). After completing the census of each village, the population was invited to come, a week later, to a central point, where they were medically examined and finger-prick blood samples were collected for epidemiological characterization of the malaria situation in the area. The blood films of the one single village were used to compare the sensitivity and specificity of Polymerase Chain Reaction (PCR) with optical microscopy detection of parasites. In another village, the occurrence of parasitaemia was compared in children with and without fever. During the dry season, from March to June 1992, the population in each village was again invited to come to a central point. Some of the field procedures were repeated. The study revealed Prábis as an administrative Sector of Guinea-Bissau with endemic malaria, mostly due to Plasmodium falciparum, but with a significant rate of mixed infections. Active transmission occurred throughout the year, but it was more intensive during the rainy season and in the northwestern quadrant of the Sector. The level of endemicity of the villages varied from hypo to holoendemic. The factors associated with the differences among villages included village size and predominant economic activity (closeness to rice fields). The transmission paradigm was, most likely, a mixture of malaria of the African wet Savannah and malaria associated with irrigated paddy fields. PCR proved to be a sensitive method with low specificity during the dry season. Pyraexia of 37.4ºC or higher in children aged 2-9 years is not a sensitive indicator of parasitaemia but, it is highly specific and it has a clinically useful predictive value.

Detection of Rotavirus in Sewage and Creek Water: Efficiency of the Concentration Method

Simian rotavirus SA-11, experimentally seeded, was recovered from raw domestic sewage by a two-step concentration procedure, using filtration through a positively charged microporous filter (Zeta Plus 60 S) followed by ultracentrifugation, effecting an 8,000-fold concentration. By this method, a mean recovery of 81% ± 7.5 of the SA-11 virus, was achieved