Pathogenesis of an experimental mycobacteriosis in an apple snail

CRUZ FLORES, CESAR; RODRIGUEZ CRISTIAN; CONSTANZA GIAI; VEGA, ISRAEL A.; CASTRO VAZQUEZ, ALFREDO

Frontiers in Immunology

Frontiers Media SA

Año: 2023 vol. 14 p. 1 - 13

In this work, we aimed at investigating cell and tissue responses of the apple snailPomacea canaliculata, following the inoculation of the zoonotic pathogenMycobacterium marinum. Different doses were tested (10, 20, 65, and 100 MCFU) and the mortality rate was negligible. The histopathogenesis was followedat 4, 9, and 28 days after inoculation. Overt histopathological lesions wereconsistently observed after the two largest doses only. In the lung, markedhemocyte aggregations, including intravascular nodule formation, wereobserved within the large blood veins that run along the floor and roof of thisorgan. Hemocyte aggregations were found occluding many of the radial sinusessupplying the respiratory lamina. Acid-fast bacilli were contained in the differenthemocyte aggregations. In addition, hemocytes were observed infiltrating thestorage tissue, which makes up most of the lung wall, and the connective tissueof the mantle edge. Additionally, signs of degradation in the storage tissue wereobserved in the lung wall on day 28. In the kidney, nodules were formedassociated with the constitutive hemocyte islets and with the subpallialhemocoelic space, in whose hemocytes the acid-fast structures were found.Electron microscopy analysis revealed the presence of bacteria-containingphagosomes within hemocytes located in the surface zone of the islets.Additionally, electron-dense spheroidal structures, which are likely remnants ofdigested mycobacteria, were observed in close proximity to the hemocytes’nuclei. The size attained by the hemocyte nodules varied during the observationperiod, but there was no clear dependence on dose or time after inoculation.Nodules were also formed subpallially. Some of these nodules showed 2–3layers with different cellular composition, suggesting they may also form throughsuccessive waves of circulating cells reaching them. Nodular cores, includingthose formed intravascularly in the lung, would exhibit signs of hemocytededifferentiation, possibly proliferation, and death. Hemocyte congestion wasobserved in the hemocoelic spaces surrounding the pallial ends of the renalcrypts, and the renal crypts themselves showed de-epithelization, particularly onday 28. The diverse cellular responses of P. canaliculata to M. marinuminoculation and the high resilience of this snail to the pathogen make it asuitable species for studying mycobacterial infections and their effects oncellular and physiological processes.