Ultrastructural Study of the Early Development and Localization of Loma Salmonae in the Gills of Experimentally Infected Rainbow Trout

Abstract

The early ultrastructural stages of Loma salmonae were studied in the gills of experimentally infected rainbow trout. No parasitic stages were identified during the first 2 wk of the infection. By week 3 postexposure (PE), uninucleate and binucleate meronts were recognized within host cells (no xenomas) associated with the capillary channels of secondary lamellae and lamellar arteries. An inflammatory reaction was absent. In secondary lamellae, infected cells were isolated from the capillary lumen, and some were recognized as pillar cells. In lamellar arteries, infected cells were localized beneath the endothelium and not in the lumen. Inflammatory reaction and destruction of parasites inside blood cells in the lumen of secondary lamellae were observed by week 4 PE. Three hypotheses, i.e., isolation, internalization, and evasion, are proposed to explain the localization of the infected cells in the gills. It is concluded that meronts are the earliest parasitic stage observed by week 3 PE, pillar cells are secondarily infected by phagocytosis of infected cells in the blood, endothelial cells of gills are not infected, and inflammatory response to the parasite starts by week 4 PE.

Strong effect of long-term Sparicotyle chrysophrii infection on the cellular and innate immune responses of gilthead sea bream, Sparus aurata

“…They include parasite migration (Buchmann et al, 2001) and exploitation of the host immune system (Buchmann, 2000). Other parasites have shown evasion mechanisms based on antigen variation or mimicry, modification of the host's immune system, resistance to host's cellular (Rodriguez-Tovar et al, 2002) or humoral factors through, for example, the development of a thick parasite tegument containing inhibitors of the complement cascade (Buchmann and Lindenstrøm, 2002).…”

Fish microsporidia: Immune response, immunomodulation and vaccination

“…For instance, in a series of studies aiming to elucidate the tissue reaction in rainbow trout, Oncorhynchus mykiss, experimentally exposed to infective spores of Loma salmonae, it was observed that infected cells were identified as blood cells. These cells were probably retained in lamellar capillaries due to their enlargement, as well as pillar cells and possibly leukocytes lying between the endothelium and the basement membrane of lamellar arteries [38]. In the same research, an early weak inflammatory response characterized by spore destruction within xenomas was observed at week four after exposure.…”

Ontogeny and disease responses of Langerhans-like cells in lymphoid tissues of salmonid fish

“…This might be explained by differences in the cell responses between the early stages of infection (1-4 weeks PE), which are more subtle than the cell responses during later stages of infection (5-10 weeks PE), which are associated with disease. In MGD, little host response is seen to the development of xenomas during the early stages of xenoma maturation (Rodriguez-Tovar et al 2002). Beginning at 5 weeks PE and continuing into 10 weeks PE, the rupture of xenomas is associated with a heavy inflammatory response, and during this time, clinical disease is apparent (Lovy et al 2007;Rodriguez-Tovar et al 2003).…”

“…During MGD, infection with L. salmonae occurs across the gastrointestinal tract, and at 2 weeks postexposure (PE), the parasite arrives in the gills and forms parasitic cysts called xenomas (Rodriguez-Tovar et al 2002;Sanchez et al 2001). Xenomas expand in size as the parasites replicate until around 6-9 weeks PE when the xenomas rupture liberating spores into the gill tissue leading to a severe inflammatory response (Lovy et al 2007).…”