The development of resistance in three stages throughout an active infection (pre-ovular, acute and initial chronic stages) was studied, comparing the total number of adult worms recovered from the reinfected group and the control groups. It was shown that Nectomys squamipes was unable to develop resistance in the tested conditions and, on the other hand, reinfection in the pre-ovular period of the parasite led the rodent to present the phenomenonacilitation, with reduction of natural resistance and an increase in the parasite load. These results suggest the existence of other forms of immunity diverse from the concomitant immunity in the host-parasite relationship, according to the employed model.

Twenty specimens of Nectomys squamipes born in captivity, were infected with 500 cercariae by the transcutaneous route. Coprologic examinations were carried out from the 5th to 23rd week after infection. On the 7th, 8th, 12th, 16th, and 23rd weeks the animals were sacrificed and perfused. The oogram was performed in segments of the small intestine (proximal, medial and distal portions) and the large intestine. The average pre-patent period was of 42 days. The average number of eggs varied from 350 on the 6th week, to 800 on the 13th. From the 14th week on, the average number of eggs eliminated was lower than 50 per gram of feces. The recovery of worms kept steady on the 7th, 8th and 12th week (16.85%; 15.45% and 11.95%), decreasing to 7.70% on the 16th week and 8.45% on the 23rd week. The proportion of male/female worms was about the same on the first two weeks, but from the 12th week on, the proportion was: 1.4/1 on the 12th week; 2.5/1 on the 16th week and 1.8/1 on the 23rd week. These observations suggest that N. squamipes may be used as an experimental model for schistosomiasis mansoni, to which it develops resistance mechanism, useful for immunity studies.

A infecção experimental do A. arviculoides através de diferentes vias de penetração das cercárias de Schistosoma mansoni (transcutânea e subeutânea) foi estudada pela cinética de eliminação de ovos nas fezes, pela recuperação dos vermes adultos (no sistema porta e nos vasos mesentéricos) e pelo oograma quantitativo. Demonstrou-se que a infecção do A. arviculoides assemelha-se à dos camundongos albinos que serviram de controle, quanto a eficácia das vias de penetração, ao habitat dos vermes adultos e ao oograma. Esses resultados sugerem que se avaliem outros aspectos da relação parasito-hospedeiro para que o A. arviculoides possa ser indicado como modelo experimental alternativo, nos estudos sobre a esquistossomose.

The evaluation of the role of rodents as natural hosts of Schistosoma mansoni was studied at the Pamparrão Valley, Sumidouro, RJ, with monthly captures and examination of the animals. Twenty-three Nectomys squamipes and 9 Akodom arviculoides with a shistosomal infection rate of 56.5% and 22.2% respectively eliminated a great majority of viable eggs. With a strain isolated from one of the naturally infected N. squamipes, we infected 75% of simpatric Biomphalaria glabrata and 100% of albino Mus musculus mice. The adult worms, isolated from N. squamipes after perfusion were located mainly in the liver (91.5%) and the mesenteric veins (8.5%). The male/female proportion was 2:1. The eggs were distributed on small intestine segments (proximal, medial and distal portions) and the large intestine without any significant differences in egg concentration of these segments. In A. arviculoides, the few eggs eliminated by the stools were viable and there was litlle egg retention on intestinal segments. Considering the ease to complete S. mansoni biological cycle in the Nectomys/Biomphalaria/Nectomys system under laboratory conditions, probably the same is likely to occur in natural conditions. In support to this hypotesis there are also the facts that human mansonic shistosomiasis has a very low prevalence in Sumidouro and endemicity among the rodents has not changed even after repetead treatments of the local patients. Based on our experiments, we conclude that N. squamipes has become a natural host of S. mansoni and possibly may participate in keeping the cycle of schistosomiasis transmission at Pamparrão Valley

The effect of anesthetic drugs on the localization of adult worms in albino mice was compared. The animals with 56 days of infection were anesthetized with pentobarbital sodium, ether or chlorophorm. Perfusion was carried out immediately after, recovering the worms and classifying them in relation to their localization on the liver or portal vein and the mesenteric veins. Our results showed that pentobarbital sodium produced a greater displacement of the worms to the liver (89%) than ether (76%) and chlorophorm (34%) did, when compared to the control group (22%). The difference between pentobarbital sodium and ether was significant (p < 0.05). We suggest that anesthetic drugs may not be used in studies on the distribution of adult worms in several hosts.

No abstract

Subsistence hunting is the main source of protein for forest reserve dwellers, contributing to the development of spurious infections by Calodium hepaticum, frequently associated with the consumption of the liver from wild mammals. The prevalence of infections by soil-transmitted helminths (STHs) and intestinal protozoa is considered an indicator of the social vulnerability of a country, besides providing information on habits, customs and quality of life of a given population. Intestinal parasites mostly affect poor rural communities with limited access to clean water and adequate sanitation. This study reports the results of a parasitological survey carried out in 2017 and 2019, in two municipalities (Xapuri and Sena Madureira) in Acre State. Stool samples were collected from 276 inhabitants. Upon receipt, each sample was divided into two aliquots. Fresh samples without preservative were processed and examined by the Kato-Katz technique. Samples fixed in 10% formalin were processed by the spontaneous sedimentation and the centrifugal sedimentation techniques. Calodium hepaticum eggs were found in three stool samples. The overall STH prevalence was 44.9%. The hookworm prevalence (19.2%) was higher than that of Ascaris lumbricoides (2.5%) and Trichuris trichiura (0.7%), an unexpected finding for municipalities belonging to the Western Brazilian Amazon. When considering parasites transmitted via the fecal-oral route, Endolimax nana and Entamoeba coli showed the highest positivity rates, of 13% and 10.9%, respectively. This study is the first report of spurious infection by C. hepaticum among forest reserve dwellers that consume undercooked liver of lowland pacas. Additionally, this is the first report of Blastocystis sp. in Acre State.

Los especímenes de museo representan un recurso valioso para la investigación helmintológica. Hemos examinado los hígados fijados en formalina conservados por períodos de más de 50 años a partir de cerdos infectados naturalmente en el material de archivo de la Colección Helmintológica del Instituto Oswaldo Cruz (CHIOC), Fundación Oswaldo Cruz (FIOCRUZ). El examen microscópico reveló evidencia de parásitos en estructuras quísticas uniloculares que contienen una vesícula de la membrana del parásito recubierto con una lámina delgada. La capa interna germinal contiene los restos del parásito y un líquido proteíco como hidatídico. El parénquima hepático mostró un denso infiltrado inflamatorio cerca del quiste, los vasos arteriales de paredes gruesas y necrosis de vez en cuando. El parénquima hepático adyacente mostró fibrosis delgada inter e intralobular, la infiltración de células inflamatorias y necrosis de vez en cuando. Otros cortes histológicos mostraron una estructura de pared gruesa laminada quística con cápsulas de cría en la capa germinal que contienen proyecciones pequeñas y redondas con el centro de las vesículas internas en la superficie interna, lo que sugiere la presencia de protoescólices. Teniendo en cuenta que Echinococcus multilocularis no ocurre en Brasil, nuestros hallazgos histológicos fueron identificados como Echinococcus granulosus de origen. En conclusión, el protocolo que se presenta en este estudio pone de relieve la posibilidad de lograr resultados histológicos de muy alta calidad en archivos fijados en formalina y parafina de tejidos embebidos recuperados de especímenes de museo que se han conservado durante muchos años.