Nanophyetus Salmincola - Detailed Information Regarding The Life Cycle Stages

Detailed Information Regarding The Life Cycle Stages

Eggs and miracidia: The eggs passed in the feces are unembryonated. Experimental studies demonstrate that eggs collected in room water temperature require 75 days to 200 days to hatch., The hatching rate of miracidia from eggs increases with decreasing temperatures, and egg mortality increases with increasing temperatures. Fully developed miracidia within the eggs contract and elongate repeatedly, and newly emerged miracidia swim in “characteristic, long graceful curves.” Interestingly, the miracidia seem to have no attraction to host snails, bumping into the snails without attempting to penetrate and infect them.

Rediae: The rediae are the second larval stage of the trematode life cycle, that develops from the miracidum and contains germ cells that develop into cercariae. The rediae are found in the second intermediate host, the snail. Rediae can range from 0.45 mm to 3 mm, and the larger rediae can contain up to 76 cercariae. Rediae and cercariae are found in all tissues of the host snail, but primarily in the gonads and the digestive gland., Rediae destroy the gonads, invade the hepatopancreas, damage it by 1) increased pressure from rapid growth, 2) active ingestion by the parasites, and 3) the disposition of parasitic wastes. Furthermore, parasites take up glycogen and lipids from the hepatopancreas.

Cercariae: The cercariae measure 0.31 mm to 0.47 mm by 0.03 mm to 0.15 mm and live up to 48 hours in water. They have a tendency to infect snails that are at least 2.5 cm in length, though smaller snails have also been observed to shed cercariae. Cercariae shed intermittently by the thousands, entering the mantle cavity of the snail, and drifting out with the “exhalent water current on the right side of the snail’s head.”, Cercariae from snails in brackish water of a low salinity were found to survive longer than snails in freshwater.20

Once cercariae are shed from the snail, it contracts repeatedly until it contacts a fish and penetrates under its skin within 30 seconds to 2 minutes. The cercariae penetrate further into the renal portal blood system, into the kidney and deeper tissues into the base of the tail. Penetrations sights are easily visible, as the skin, fins, and tails of the fish appear to be heavily eroded and damaged. Cercariae can also indirectly infect the fish, if the fish eat the cercariae orally.

Metacercariae: The cercariae lose their tails in the act of penetration and encyst as metacercariae in almost any tissue of the salmonid fish. The new cyst wall is thin, transparent, and easily ruptured. If the cyst wall breaks, the metacercariae crawl out and re-encyst a few hours later in a tougher, larger cyst wall. While cysts can be found in all tissues of the fish, most encystment occurs in the kidneys and body muscles of the salmonid fish, and in the gills and fins of the non-salmonid fish. Cercariae penetrate less deeply in non-salmonid fish than in salmonid fish. Infected fish experience a decrease in their swimming activity and loss of equilibrium, and it is not uncommon for fish to have as many as 1000 to 2000 metacercariae in its tissues.,

Importantly, metacercariae can be destroyed either by cooking or freezing infected fish.

Snail: The Oxytrema silicula host snail is prevalent in coast streams and prefers large rocks, bridges, old planks, and debris on stream bed bottoms. It rarely migrates into shallow water. The infection of snails is high in comparison to the number of cercariae it sheds, since larval development continues slowly over a long period of time. Evidence of mixed infection varied between studies, but snails with large numbers of N. salmincola were not parasitized by other trematodes. It was also found that monthly incidences of infection in snails ranged from 9–52% after examining over 3000 snails every month for 10 months, and that mature cercariae infected snails in a seasonal manner. Mature cercariae were more likely to infect snails in late April to November.

Neorickettsia helmintheoca Neorickettsia helmintheoca is the etiological agent for salmon poisoning disease, found to be present in all stages of the trematode. It is 0.3 micrometers in size and a purple Giemsa stain indicates that it is Gram negative. Thus far, only canids are susceptible to disease by rickettsia and it is still uncertain how the rickettsia leave the trematode vector and reaches the host tissues. Experiments do show that the bacteria lead to necrosis of lymph follicles, ulceration, and severe hemorrhage in its host.