Exploiting the life cycle of Strongyloides ratii.

The nematode Strongyloides ratti has a remarkable life cycle, which has both a parasitic and a free-living phase. The free-living phase includes a choice between two developmental routes. Here, Mark Viney discusses recent advances in understanding the biology of this developmental switch and shows how the life cycle of this nematode can be used to explore the lifestyle transitions common to all parasitic nematodes, as well as to address other basic biological questions.

Developmental switching in the parasitic nematode Strongyloides ratti.

Strongyloides ratti is a nematode parasite of rats. It is able to undergo two types of development outside the host: heterogonic (free-living adults and sexual reproduction) and homogonic (direct larval development). Homogonic development has a number of similarities with the development of the dauer stage of free-living nematodes, including Caenorhabditis elegans. Using isofemale lines of the parasite, factors that control this developmental choice have been investigated. Isofemale lines can be selected for both heterogonic and homogonic development, but are still able to respond to environmental conditions. By using temperature shift experiments it has been possible to determine when larvae become developmentally committed. All larvae are developmentally committed after 24 h at 19 degrees C.

Strongyloides ratti: mitochondrial enzyme activities of the classical electron transport pathway in the infective (L3) larvae.

Submitochondrial particles prepared from S. ratti L3 larvae exhibited NADH-oxidase (NOX), NADH-ferricyanide reductase (NFR), NADH-cytochrome-c-reductase (NCR), succinate-cytochrome-c-reductase (SCR), and cytochrome-aa3-oxidase activities of 2.1 +/- 0.3, 8.9 +/- 1.3, 0.6 +/- 0.1., 1.0 +/- 0.2 and 1.2 +/- 0.3 nm min-1 mg protein-1 respectively, at 37 degrees C. The NCR and NOX activities were 39.3% and 23.5% of the NFR activity, suggesting the occurrence of a rate-limiting step or bifurcation of the respiratory electron transport (RET) pathway on the oxygen-side of RET-Complex I. The NCR activity was 50% that of cytochrome-aa3-oxidase activity which suggests partitioning of electron flow at the level of RET-Complex III and/or the quinone-function. Antimycin A and rotenone but not 2-thenoyl trifluoroacetone (TTFA) inhibited NCR activity, the EC50 values were 3.6 x 10(-6) M, 3.7 x 10(-7) M, respectively. SCR activity was inhibited by antimycin A (EC50 = 3.8 x 10(-6) M) and TTFA (EC50 = 2.8 x 10(-5) M) but not by rotenone. The results suggest that presence of classical and alternate RET-pathways in S. ratti L3 larvae.

Contribuição para estudo da reação intradérmica com antígeno de Strongyloides ratti (Sandground, 1925) no diagnóstico da Estrongiloidose humana

1) Foi estudado o comportamento da reação intradérmica para o diagnóstico da estrongiloidose humana, utilizando-se larvas filarióides de Strongyloides ratti no preparo de antígeno. 2) As reações intradérmicas foram feitas na parte média da face flexora do antebraço e na parte superior do dorso, injetando-se 0,05 ml de antígeno, contendo 40 microgramas de azôto por ml, fazendo-se a leitura 15 minutos após a injeção intradérmica. Ficou evidenciado neste trabalho que o dorso é o melhor local para a reação intradérmica no diagnóstico da estrongiloidose. 3) O registro e a leitura das reações foram feitos pelos métodos recomendados por Vianna Martins (1949) e por Pellegrino e Macedo (1956). 4) Na seleção dos indivíduos infectados, com Strongyloides stercoralis utilizando-nos do método de Baermann (1917) adaptado por Gomes de Moraes (1948) para o diagnóstico da estrongiloidose humana, o qual foi superior aos métodos de M.I.F.C. (modificado por Coutinho, 1956) e ao método de Hoffman, Pons e Janer (1934).[...]