Impacts of Environmental Parameters on the Infectivity of Freshwater Snail

The successful transmission of the infective stage of the parasite (miracidia) depends on different factors. These free-living stages miracidia rely on their own stored energy and are directly exposed to environmental factors including disturbance resulting from pollution and human activities. There are different environmental factors that affect the cercarial infection of the snail. These include pH, temperature, salinity, dissolved oxygen, water hardness, habitat conditions, presence of predators and competitors, etc. Each of these factors may increase or decrease the freshwater snail’s infectivity. The more hydrogen ion concentration in the aquatic habitat could have an effect on the maturation and physiology of the parasitic stage (miracidia), leading to impaired survival and reduced infectivity. In contrast, high temperature increases snail infectivity. While low dissolved oxygen in the aquatic environment results in low snail infectivity. Regarding the presence of predators can result in low snail infectivity by consuming the schistosome egg and the snails themselves. Total hardness also had a negative impact on the prevalence of snail infection. The hardness of the water results in the shell hardening of snails subsequently leads to low infection of snail by miracidia.

Karyotype and reproduction mode of the rodent parasite Strongyloides venezuelensis

SUMMARYStrongyloides venezuelensis is a parasitic nematode that infects rodents. Although Strongyloides species described to date are known to exhibit parthenogenetic reproduction in the parasitic stage of their life cycle and sexual reproduction in the free-living stage, we did not observe any free-living males in S. venezuelensis in our strain, suggesting that the nematode is likely to depend on parthenogenetic reproduction. We confirmed by cytological analysis that S. venezuelensis produces eggs by parthenogenesis during the parasitic stage of its life cycle. Phylogenetic analysis using nearly the full length of 18S and D3 region of 28S ribosomal RNA gene suggested that S. venezuelensis is distantly related to another rodent parasite, namely Strongyloides ratti, but more closely related to a ruminant parasite, Strongyloides papillosus. Karyotype analysis revealed S. venezuelensis reproduces with mitotic parthenogenesis, and has the same number of chromosomes as S. papillosus (2n = 4), but differs from S. ratti (2n = 6) in this regard. These results, taken together, suggest that S. venezuelensis evolved its parasitism for rodents independently from S. ratti and, therefore, is likely to have a different reproductive strategy.

The hidden coloniality at the parasitic stage in Peltogaster reticulatus (Crustacea: Rhizocephala)

Upon infesting the hermit crab Pagurus proximus the parasitic barnacle Peltogaster reticulatus typically forms a single externa on each host. In vivo, histological and histochemical study revealed that most P. reticulatus with a single mature externa also exhibited three or four primordial externae and several buds of earlier developmental stages. It is shown that stolon buds and primordial externae in P. reticulatus internae intensively express alkaline phosphatase activity, the classical histochemical marker for mammalian embryonic stem and primary germ cells. Ovaries of the most developed primordial externae were filled with growing oocytes, so the process of oogenesis begins in the externa rudiments of P. reticulatus before the externae appear on the surface of the host body. Since the interna, which is connected to the mature externa, also integrated three or four additional primordial externae and several earlier buds, P. reticulatus, a non-colonial species based on the common presence of a single externa in each host, appears to have a hidden colonial organization at the parasitic stage of its life cycle.

Changes in the pre-parasitic developmental stage of Globodera rostochiensis in response to green manures

The sequence of events during the pre-parasitic and parasitic stages of the life cycle of Globodera rostochiensis, starting from hatching until host invasion and infection, is of major importance. Many of the physiological changes are initiated in the pre-parasitic stage in response to the influences exerted by the root diffusates of the host plant. The objectives of this study were to investigate whether root diffusates and extracts of green manures from Brassicaceae, in particular yellow mustard, fodder radish and rapeseed, have a direct effect on the pre-parasitic stage of G. rostochiensis. Unhatched second-stage juveniles (J2) were exposed to root diffusates and extracts from roots or above-ground parts of the green manures to assess: i) changes in eggshell permeability; ii) changes in diameter of the dorsal gland nucleolus; and iii) the activation of transcription in the dorsal and subventral pharyngeal glands. The 24 h exposure of unhatched J2 to the green manures did not indicate an alteration in eggshell permeability. The diameter of the dorsal gland nucleolus increased significantly after exposure to diffusates but not to extracts of the green manures, although the size in that case still did not exceed the measurements in J2 exposed to tomato root diffusates. The expression of the gene IVg9 in the dorsal gland was not detected after any treatment. However, transcriptional activation in the subventral pharyngeal glands was observed. Although the maximum expression of the cellulase gene was found in J2 exposed to tomato root diffusates, the expression in J2 exposed to root extracts of green manures was higher than in J2 exposed to root diffusates and extracts of above-ground plant parts. The potential of the investigated brassicaceous green manures to influence the pre-parasitic stage of G. rostochiensis is discussed.