Population Biology of Rhodnius domesticus Neiva & Pinto, 1923 (Hemiptera: Reduviidae) under Laboratory Conditions

The entire life cycle of Rhodnius domesticus, fed weekly on mice, was studied under controlled conditions. Aspects related to hatching, life time, mortality, feeding behaviour and fecundity for each stage of the insect life-cycle were evaluated. The hatching rate observed in 100 eggs was 57% and the mean time of hatching was 15.6 days. Forty-six nymphs (80.7%) completed the cycle and the mean time from NI to adult was 93.8 days. The average span in days for each stage was 12.4 for NI, 9.8 for NII, 14.2 for NIII, 16.8 for NIV and 25.0 for NV. The number of bloodmeals in each nymphal stage varied from 1 to 3. The mortality rate was 12.3% for NI, 3.5% for NII and 1.7% for NIII and NV nymphs. The mean number of eggs laid per female in a 9-month period was 333.1. Average adult survival rates were 287.6 +133 and 328 +73 days for males and females respectively.

Basic Surface Properties of Mononuclear Cells from Didelphis marsupialis

The electrostatic surface charge and surface tension of mononuclear cells/monocytes obtained from young and adult marsupials (Didelphis marsupialis) were investigated by using cationized ferritin and colloidal iron hydroxyde, whole cell electrophoresis, and measurements of contact angles. Anionic sites were found distributed throughout the entire investigated cell surfaces. The results revealed that the anionic character of the cells is given by electrostatic charges corresponding to -18.8 mV (cells from young animals) and -29.3 mV (cells from adult animals). The surface electrostatic charge decreased from 10 to 65.2% after treatment of the cells with each one of trypsin, neuraminidase and phospholipase C. The hydrophobic nature of the mononuclear cell surfaces studied by using the contact angle method revealed that both young and adult cells possess cell surfaces of high hidrofilicity since the angles formed with drops of saline water were 42.5°and 40.8°, respectively. Treatment of the cells with trypsin or neuraminidase rendered their surfaces more hydrophobic, suggesting that sialic acid-containing glycoproteins are responsible for most of the hydrophilicity observed in the mononuclear cell surfaces from D. marsupialis.

Humoral Immune Response Kinetics in Philander opossum and Didelphis marsupialis Infected and Immunized by Trypanosoma cruzi Employing an Immunofluorescence Antibody Test

Philander opossum and Didelphis marsupialis considered the most ancient mammals and an evolutionary success, maintain parasitism by Trypanosoma cruzi without developing any apparent disease or important tissue lesion. In order to elucidate this well-balanced interaction, we decided to compare the humoral immune response kinetics of the two didelphids naturally and experimentally infected with T. cruzi and immunized by different schedules of parasite antigens, employing an indirect fluorescence antibody test (IFAT). Both didelphids responded with high serological titers to different immunization routes, while the earliest response occurred with the intradermic route. Serological titers of naturally infected P. opossum showed a significant individual variation, while those of D. marsupialis remained stable during the entire follow-up period. The serological titers of the experimentally infected animals varied according to the inoculated strain. Our data suggest that (1) IFAT was sensitive for follow-up of P. opossum in natural and experimental T. cruzi infections; (2) both P. opossum and D. marsupialis are able to mount an efficient humoral immune response as compared to placental mammals; (3) experimentally infected P. opossum and D. marsupialis present distinct patterns of infection, depending on the subpopulation of T. cruzi, (4) the differences observed in the humoral immune responses between P. opossum and D. marsupialis, probably, reflect distinct strategies selected by these animals during their coevolution with T. cruzi.

A New Method for Fixing Biomphalaria glabrata for Histologic Studies, Using Shell Perforation

A new technique for fixation of Biomphalaria glabrata for histologic studies is described. It consists in performing several external holes in the shell, before placing the entire snail into the fixative. It is a very practical and quick procedure that showed excellent results when compared to the usual techniques.

Complete nucleotide sequence analysis of a Brazilian dengue virus type 2 strain

In the last decade, dengue fever (DF) in Brazil has been recognized as an important public health problem, and an increasing number of dengue haemorrhagic fever (DHF) cases have been reported since the introduction of dengue virus type 2 (DEN-2) into the country in 1990. In order to analyze the complete genome sequence of a DEN-2 Brazilian strain (BR64022/98), we designed primers to amplify contiguous segments of approximately 500 base pairs across the entire sequence of the viral genome. Twenty fragments amplified by reverse transcriptase-PCR were cloned, and the complete nucleotide and the deduced amino acid sequences were determined. This constitutes the first complete genetic characterization of a DEN-2 strain from Brazil. All amino acid changes differentiating strains related to the Asian/American-Asian genotype were observed in BR64022/98, indicating the Asiatic origin of the strain.

Dominant character of the molecular marker of a Biomphalaria tenagophila strain (Mollusca: Planorbidae) resistant to Schistosoma mansoni

Biomphalaria tenagophila population from Taim (state of Rio Grande do Sul, Brazil) is totally resistant toSchistosoma mansoni, and presents a molecular marker of 350 bp by polymerase chain reaction and restriction fragment length polymorphism of the entire rDNA internal transcriber spacer. The scope of this work was to determine the heritage pattern of this marker. A series of cross-breedings between B. tenagophila from Taim (resistant) and B. tenagophila from Joinville, state of Santa Catarina (susceptible) was carried out, and their descendants F1 and F2 were submitted to this technique. It was possible to demonstrate that the specific fragment from Taim is endowed with dominant character, since the obtained segregation was typically mendelian.