Laboratory evaluation on pathogenic potentialities of Vibrio furnissii

Sixteen strains of Vibrio furnissii recovered from 16 Brazilian patients with diarrhea were screened for virulence-associated factors. All strains were non-invasive, non-fimbriated, and did not produce either enterotoxins or cholera-like toxin. In contrast, most were hemolytic on blood agar and their broth-culture supernatants damaged HeLa cell monolayers. These cytolysins, as accepted for other enteropathogenic members of the family Vibrionaceae, might be determinants of pathogenicity in V. furnissii-mediated enteritis.

Helminth parasites of conventionally mantained laboratory mice

The spectrum of intestinal parasites present in the SwissWebster, C57B1/6 and DBA/2 mice strains from different animal houses was identified and prevalences compared. Three parasites were observed during the course ofthis study, namely the cestode. Vampirolepis nana (Siebold, 1852) Spasskii, 1954(=Hymenolepis nana) and the nematodes Aspiculuris tetraptera (Nitzsch, 1821) Schulz, 1924 and Syphacia obvelata (Rudolphi, 1802) Seurat, 1916. The scope of thisinvestigation has been widened to also include morphometric data on the parasites, to further simplify their identification, since the presence of helminths in laboratory animals is regarded as a restricting factor for the proper attainment of experimental protocols.

Trypanosoma cruzi: metacyclogenesis in vitro - I. Changes in the properties of metacyclic trypomastigotes maintained in the laboratory by different methods

In this work we have studied the modifications in the biological properties of Trypanosoma cruzi when the parasite is maintained for a long time in axenic culture. The studies were done with a clone from an avirulent strain (Dm30L) and a non-cloned virulent strain (EP) of T. cruzi. Both parasiteswere maintained, for at least three years, by successive triatomine/mouse alternate passage (control condition), or by serial passage in axenic medium (culture condition), or only in the mouse (mouse condition). The comparison between parasites of culture and control condition showed that metacyclogenesis capacity was reduced in the former and that the resulting metacyclics displayed an attenuatedvirulence. In order to compare the virulence of metacyclics from the urine of the insect vector, Rhodnius prolixus were infected by artificial feeding with parasites of the control or culture condition. After three triatomine/triatomine passages, there was observed an almost identical biological behavior for these parasites, hence indicating that the maintenance of T. cruzi for a long time in axenic culture affects the differentiation capacity and the virulence of the parasite. Additionally, it was demonstrated that it is possible to maintain T. cruzi exclusively through passages in the invertebrate host.

Possible absence of attraction to odor in Panstrongylus megistus (Hemiptera: Reduviidae) under laboratory conditions

We tested the attraction of Panstrongylus megistus odor under laboratory conditons, between males and females of this species and by individuals of each sex on recently fed virgin couples. We employed a system of choice boxes both with or without aeration over the stimuli in the tested situations. We also observed a clear trend among the insects to remain in the central box where they had been placed in the beginning of the tests.

Longevity of adults of Peckia chrysostoma and Adiscochaeta ingens (Diptera: Sarcophagidae) reared with and without protein

With access to a proteic source in the diet the mean longevity and lethal time (MLT) of Peckia chrysostoma was 52.6 ± 5.5 and 30.3 ± 5.9 days, respectively. With an isolated protein source, the mean longevity was 49.1 ± 2.6 days and the MLT was 28.5 ± 0.8 days. Without a proteic source the mean longevity and the MLT lowered to 37.4 ± 4.0 and 18.1 ± 1.3 days, respectively. For Adiscochaeta ingens the mean longevity with access to a proteic source in the diet was 29.0 ± 6.0 days and the MLT was 16.7 ± 2.7 days. The figures with an isolated proteic source were 26.9 ± 4.8 and 14.9 ± 2.0 days, and without a proteic source were 24.7 ± 4.2 and 13.3 ± 1.4 days, respectively. These results show that in P. chrysostoma the longevity is higher than in A. ingens and that the access to the proteic source increase the longevity in both species.

Some environmental and biological factors influencing the activity of entomopathogenic Bacillus on mosquito larvae in Brazil

The influence of environmental and biological factors on the efficacy of Bacillus thuringiensis serovar israelensis and B. sphaericus as mosquito larvicides are reviewed. The importance of strain dependence, cultivating media/methods, mosquito species/specificity, formulations and their relation to mosquito feeding habits, as well as temperature, solar exposure, larval density and concomitant presence of other aquatic organisms are addressed with reference to the present status of knowledge in Brazil.

Effect of Niclosamide (Bayluscide WP 70 (R)), Anacardium occidentale hexane extract and Euphorbia splendens latex on behavior of Biomphalaria glabrata (Say, 1818), under laboratory conditions

The repellent effect of the molluscicides Niclosamide (Bayluscide WP 70 (R)), Anacardium occidentale and the latex of Euphorbia splendens on Biomphalaria glabrata was observed through the investigation of the occurrence of escape behavior among molluscs that were exposed to dosages lower than the LD 50. The total number of individuals out of water among the surviving snails in the control group provided a "Natural Escape Index". The comparison between this total and the total number of surviving snails in each group exposed to the different dosages of the molluscicides after 24 hr provided the "Molluscicide Escape Index" and the detection of a "Repellency Range" to these snails. The escape indexes for Niclosamide, A. occidentale and E. splendens were 10, 6.22 and 6.44 respectively. Repellency occurred at the following concentration ranges: 0.01, 0.02 and 0.03 ppm Bayluscide, 0.1, 0.2 and 0.3 ppm A. occidentale and 0.05, 0.10, 0.15 and 0.20 ppm E. splendens. The Natural Escape Index obtained in the control group was zero.

Effects of three organophosphorus insecticides in the reproductive potential of Culex quinquefasciatus

A Culex quinquefasciatus Say 1823 strain with resistant genes to organophosphates was tested in the laboratory to know the reproductive potential after exposure, as larvae, at the LC30 and LC70 (mg/l) of three organophosphorus insecticides: malathion, chlorpyrifos and methyl-pirimiphos. Data showed that fecundity was decreased significantly by malathion at LC30 = 0.0025 and LC70 = 0.0075, whereas fertility has a no significant decrement by chlorpyrifos and methyl-pirimiphos at the LC70 (0.000016, 0.00043). The sexual index was affected by chlorpyrifos and methyl-pirimiphos showing a greater number of adult females.

The biology of Aedes (Ochlerotatus) albifasciatus Macquart, 1838 (Diptera: Culicidae) in Central Argentina

Aedes albifasciatus is a flood water mosquito ocurring in the southern countries of South America. It is a competent vector of the Western Equine Encephalitis (WEE) and causes important losses on milk and beef production in central Argentina. Field work was carried out from December 1990 to March 1993, on a monthly basis during the dry season and biweekly during the rainy season. Larvae were collected using the 'dipping' technique and females with CDC traps baited with CO2. Field collected larvae were used to build laboratory cohorts, from which basic population parameters were estimated. Eggs survived up to six months on dry soil, although there was a linear decrease of viability with time. At 23ºC, larval development time was around nine days, and all adults emerged within one week. The estimation of larval development in the laboratory seems to be very near the development on the field, as larvae have been collected on average eight days after a rainfall. Egg to adult survival was 83%, with the highest mortality on fourth larval instar (6%). In the laboratory studies, sex proportion among the adults was 1:1, females lived longer than males (median 13 and five days, respectively), and adult survival pattern showed a constant number of individuals dying per unit time. Field collected females layed an average of 84 eggs per batch, and completing up to five gonotrophic cycles, suggesting an estimated survival of up to 35-50 days.

The influence of sugars and amino acids on the blood-feeding behaviour, oviposition and longevity of laboratory colony of Lutzomyia longipalpis (Lutz & Neiva, 1912) (Diptera: Psychodidae, Phlebotominae)

Schneider's Drosophila medium, a complex amino acid rich medium was tested alone and with seven different sugars for some aspects of the biology of Lutzomyia longipalpis. Statistically significant results were obtained when sucrose was used alone, indicating that among the sugars tested, this is still the most suitable and practical one for the maintenance of L. longipalpis colonies. However, the addition of Schneider's medium to a pool of different sugars, was suggested to be related with the acceptance of the first and second blood meals and to longevity, these being, obviously, quite relevant aspects when tansmission experiments are contemplated.