Novel bacterium infecting an African snail

Diseases of Gastropoda

Gastropods (class Gastropoda) form the largest of the classes in the phylum Mollusca and inhabit terrestrial, fresh water and marine environments. A large number of these species are of major conservation importance and are an essential component of ecosystems. Gastropods may be deemed as pests, having a negative impact in horticulture and agriculture, whereas others may be used as a food source for human consumption and therefore are beneficial. Gastropods are susceptible to primary diseases and also act as intermediate hosts for diseases which affect other animals, including humans. The diseases described include two that are notifiable to the World Organisation for Animal Health (OIE): Xenohaliotis californiensis and Abalone viral ganglioneuritis caused by Haliotid herpesvirus-1 (HaHV-1). Research into the diseases of gastropods has often focused on those species that act as intermediate disease hosts, those that are used in research or those cultured for food. In this paper we review the viral, bacterial, fungal, parasitic and miscellaneous conditions that have been reported in gastropods and mention some of the factors that appear to predispose them to disease. The pathogenicity of a number of these conditions has not been fully ascertained and more research is needed into specifying both the etiological agent and significance in some of the diseases reported.

New Nodule Type Found in the Lungs of Pomacea canaliculata, an Intermediate Host of Angiostrongylus cantonensis

BACKGROUND

Pomacea canaliculata (P.canaliculata) lung nodules, were commonly caused by Angiostrongylus cantonensis infection. Here, we found a new nodule type without any parasites.

METHODS

Overall, 447 P. canaliculata snails were collected in Ning Bo, Zhe Jiang, China in 2018. In order to exhibit the similarities and differences between two nodules types (2018, Huzhou Zhejiang, China), both types were collected in formalin for tissue pathological sectioning. Besides, to obtain the microbial community of the new nodule, the 18S ribosomal RNA (rRNA) gene of it was amplified and analyzed using the Illumina second-generation sequencing platform.

RESULTS

Although two nodules were found in the lungs of P. canaliculata, they were different in shape and pathology. Illumina sequencing indicated Poterioochromonas sp., a species of golden algae, might be the causing agent of the new nodule.

CONCLUSION

We firstly found a new pathological nodule type in the lungs of P. canaliculata, and this nodule might be induced by golden algae infection, however, the direct link between the golden algae and the new nodules, as well as the nodules' impact on the snails' physiology and A. cantonensis infection require further study.

A novel bacterial pathogen of Biomphalaria glabrata: a potential weapon for schistosomiasis control?

BACKGROUND

Schistosomiasis is the second-most widespread tropical parasitic disease after malaria. Various research strategies and treatment programs for achieving the objective of eradicating schistosomiasis within a decade have been recommended and supported by the World Health Organization. One of these approaches is based on the control of snail vectors in endemic areas. Previous field studies have shown that competitor or predator introduction can reduce snail numbers, but no systematic investigation has ever been conducted to identify snail microbial pathogens and evaluate their molluscicidal effects.

METHODOLOGY/PRINCIPAL FINDINGS

In populations of Biomphalaria glabrata snails experiencing high mortalities, white nodules were visible on snail bodies. Infectious agents were isolated from such nodules. Only one type of bacteria, identified as a new species of Paenibacillus named Candidatus Paenibacillus glabratella, was found, and was shown to be closely related to P. alvei through 16S and Rpob DNA analysis. Histopathological examination showed extensive bacterial infiltration leading to overall tissue disorganization. Exposure of healthy snails to Paenibacillus-infected snails caused massive mortality. Moreover, eggs laid by infected snails were also infected, decreasing hatching but without apparent effects on spawning. Embryonic lethality was correlated with the presence of pathogenic bacteria in eggs.

CONCLUSIONS/SIGNIFICANCE

This is the first account of a novel Paenibacillus strain, Ca. Paenibacillus glabratella, as a snail microbial pathogen. Since this strain affects both adult and embryonic stages and causes significant mortality, it may hold promise as a biocontrol agent to limit schistosomiasis transmission in the field.

Biological methods for the control of freshwater snails

As a result of the advent of new drugs and diagnostic techniques, the emphasis in the control of schistosomiasis has changed from snail control to chemotherapy for infected individuals. However, chemotherapy does not prevent reinfection and there remains a need to reduce snail densities in human water supplies. In the past, treatment with molluscicides has proved ineffective, expensive and has had environmental drawbacks. Here, Henry Madsen describes research into alternative methods of snail control. As yet, little is known of the predators and parasites of schistosome intermediate hosts, but such agents could be suitable as biocontrol agents. To date, the most promising results have been obtained from experimental introductions of competitive snail species, but this strategy still has its drawbacks under many environmental conditions and the development of a universal method of biological control for the intermediate hosts of schistosomes is still a long way off.

Fever in snails, reflection on a negative result

1. Groups of aquatic snails (Limnaea auricularia) were placed in a temperature gradient and their thermopreferendum measured. 2. Injected with various amounts of killed Escherichia coli, bacterial endotoxin, human interleukin, and prostaglandin E1, E2 and F2 alpha, they did not develop a fever. 3. High doses of prostaglandins were toxic. 4. These results suggest that fever appeared in the course of evolution after the emergence of molluscs and before that of arthropods.

Ecology of bacterial communities in the schistosomiasis vector snailBiomphalaria glabrata

The internal colony-forming bacterial flora of the schistosome intermediate host snailBiomphalaria glabrata (Say) has been characterized in ca. 500 individual snails from Puerto Rico, Guadeloupe, and St. Lucia, and from laboratory aquaria. Freshly captured wild snails harbor 2-40×10(6) CFU·g(-1), and healthy aquarium snails harbor 4-16×10(7) CFU·g(-1), whereas moribund individuals have 4-10 times as many bacteria as healthy individuals from the same habitats.Pseudomonas spp. are the most common predominant bacteria in normal snails, whereasAcinetobacter, Aeromonas, andMoraxella spp. predominate in moribund snails. External bacterial populations in water appear to have little effect on the composition and size of the flora in any snail. In addition to normal (healthy) and moribund snails, a third group of snails has been distinguished on the basis of internal bacterial density and predominating genera. These "high-density" snails may have undergone stresses and may harbor opportunistic pathogens. The microfloras of wild and laboratory-reared snails can be altered and stimulated to increase in density by crowding the snails or treating them with antibiotics.

Human infection from an unidentified erythrocyte-associated bacterium

A 49-year-old splenectomized man had an infection from an unidentified, gram-positive, rod-shaped bacterium that adhered to the majority of his peripheral-blood erythrocytes. On transmission electron microscopy, the bacterium was seen to be extra-erythrocytic and was 0.2 micrometer wide by 1.0 to 1.7 micrometer long. It possessed a thick, granular cell wall, a trilamellar membrane external to the cell wall and prominent mesosomes. Attempts to cultivate the organism in vitro or to duplicate the patient's disease in splenectomized animals were unsuccessful. The patient's response suggested that the bacterium was susceptible to cell-wall-active antibiotics and to chloramphenicol but not to tetracycline. This bacterium may be the cause of other chronic, fever-producing, multisystem diseases of unknown origin.

Bacterial flora of the schistosome vector snail Biomphalaria glabrata

The aerobic heterotrophic bacterial flora in over 200 individuals from 10 wild populations and 3 laboratory colonies of the schistosome vector snail Biomphalaria glabrata was examined. Internal bacterial densities were inversely proportional to snail size and were higher in stressed and laboratory-reared snails. The numerically predominant bacterial genera in individual snails included Pseudomonas, Acinetobacter, Aeromonas, Vibrio, and several members of the Enterobacteriaceae. Enterobacteriaceae seldom predominated in laboratory colonies. Our data suggest that Vibrio extorquens and a Pasteurella sp. tend to predominate in high-bacterial-density snails. These snails may be compromised and may harbor opportunistic snail pathogens.