Acanthocephalan infection levels in native and invasive amphipods were .. a bell-shaped relationship between parasite abundance and host body size, with. Acanthocephalan parasites and their amphipod . attention from scientists in relation to biological invasions. .. referred as Rotifera, see Fig. Acanthocephala and Rotifera specimen information and GenBank Bayesian consensus phylogram for Acanthocephala relationship based on the . using waterfowls as definitive hosts and amphipods as intermediate hosts.
In most cases, however, it is unknown whether differences in sites occupied result from differences in sites of activation, differential mortality or emigration by the parasites. Scanning electron micrograph of an egg from Leptorhynchoides thecatus showing unwrapping of embryonic membranes. Unwrapped membranes entangle aquatic vegetation and anchor egg in habitat of intermediate host feeding. Unpublished micrograph courtesy of M. Course of infection Shortly after infection, the proboscis is surrounded by necrotic tissue, which becomes haemorrhagic and inflamed after a few days.
During the second week after infection by species that penetrate deeply e. This chronic stage often results in a fibrous nodule visible on the outer surface of the intestine.
Species that do not penetrate deeply e. Copulation in the definitive host may occur within 24 h of infection Muzzall and Rabalais, In laboratory infections of green sunfish Lepomis cyanelluscopulation within a group of L.
For most species, egg production starts between 4 and 8 weeks after infection, and it continues for approximately 2 months.
Acanthocephalan infections of fish
The number of eggs produced daily by each female acanthocephalan is unknown for most species, but it appears to be related to the size of the worm.
At peak production, a female Macracanthorhynchus hirudinaceus large worms found in pigs may produce abouteggs per day Kates,a female Moniliformis moniliformis intermediate-sized worms in rats about Reyda and Nickol, and a female Polymorphus minutus small worms found in waterfowl about Crompton and Whitfield, Male worms have shorter lifespans than do females; death of males and subsequent loss from the host may begin shortly after copulation.
Although females of some species, especially those parasitic in mammals, may live longer than a year, most in poikilothermic hosts live about one season. There may be more than one generation each year.
Clinical signs and gross pathology Acanthocephalans in moribund or dead animals are frequently assumed to indicate deleterious effects; worms have been observed extending from the rectum Schmidt et al. There are, however, numerous instances of exceedingly heavy infections in animals that do not show any obvious disease.
Photograph of Acanthocephalus dirus attached to the prolapsed rectum of a mottled sculpin Cottus bairdii. From Schmidt et al. External view of intestine from a quillback Carpiodes cyprinus showing a parasite-induced nodule P and expansion of the intestine compared with the normal gut NG from a fish infected with Neoechinorhynchus carpiodi.
From Szalai and Dick, Bullock described trout of several species infected with Acanthocephalus dirus as having underdeveloped musculature, heads that were disproportionately large and a slightly concave dorsolateral surface.
He interpreted these as signs of malnutrition. Fibrotic nodules induced on the intestinal surface Fig. At times the viscera may be discoloured or the infected intestine enlarged and inflamed. Pyloric caeca of green sunfish L. Acanthocephalans occasionally perforate the intestinal wall and protrude into the coelom or attach their proboscides to another organ. Histopathology Acanthocephalans embed their spiny proboscis into the mucosal epithelium.
Attachment is frequently between villi. At the site of attachment, cells are destroyed and fibroblasts, lymphocytes and macrophages are mobilized below the lamina propria Dezfuli et al. In some species, fibroplasia extends to layers of themuscularis mucosa de Buron and Nickol, Transverse section through the region of the pyloric caeca of a green sunfish Lepomis cyanellus infected with Leptorhynchoides thecatus, showing unparasitized caecum top and enlarged parasitized caecum bottom.
Note the compressed and eroded villi along the trunk of the parasite a compared with normal villi in the unparasitized caecum. Unpublished micrograph, courtesy of I. Worms of the deeply penetrating species often possess very long necks and bulbous proboscides, which anchor them deep within the gut wall of their piscine hosts. The tunnel terminates in a capsule, covered by serosa and mesentery, which protrudes several millimetres into the coelomic cavity Fig.
Sometimes these capsules persist as conspicuous fibrinous nodules on the external surface of the alimentary canal, or the proboscis perforates the capsule to emerge free in the coelom or to penetrate the liver or another visceral organ.
Acanthocephalan infections of fish
Similar findings were reported for P. Section of chub Leuciscus cephalus intestine showing penetration of Pomphorhynchus laevis.
Note hyperplasia of the lamina propria arrows around the neck cou and bulbous proboscis P of the worm, forming a nodule in the coelom. An anterior portion of the trunk T of the worm shows in the intestinal lumen. Most studies of acanthocephalan-induced lesions reveal areas along the trunk of the worm where the mucosal surface is compressed or desquamated Fig. In these cases, mucosal folds and tips of villi may be absent and the paramucosal lumen contains large amounts of mucoid material originating from goblet-cell hyperplasia.
In green sunfish infected with L. This suggests a parasite-induced response that might lessen damage from the erosive nature of the worms. Taraschewski concluded that mucins from goblet cells also contribute to the expulsion of acanthocephalans from immunized hosts.
Acanthocephala - Wikipedia
Pathophysiology Chronic fibrosis, destruction of intestinal villi and necrotic and degenerative changes in mucosal epithelium adversely affect motility and the absorptive efficiency of the fish intestine.
This might affect the general health and growth of the host. According to Bristol et al. Trout infected with P. Seasonal factors, such as host spawning or reduced winter feeding, exacerbate the protein depletion. This phenomenon is not uncommon in fishes under stress.
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Further, the acanthocephalan Plagiorhynchus cylindraceus, considered of little pathological consequence, has a significant detrimental effect on the flow of food energy through the host and alters its basal metabolism Connors and Nickol, There are few field studies that relate acanthocephalan infections to the condition factor or survivorship of fishes.
Probably this is because less fit animals are sampled less frequently as a result of more efficient predation on sick and weak hosts. Nevertheless, Bakker and Mundwiler and Sasal et al.
Mechanism of disease Several biologists have suggested that acanthocephalans secrete toxic substances that paralyse or kill their hosts or that promote other patent pathological changes, such as emaciation, discoloured viscera and prolapse of the rectum Holloway, ; Fig. No such substance has been isolated, however, and Schmidt et al. Action of the spined proboscis results in destruction of mucosal cells and penetration of the intestinal wall, with an accompanying loss of absorptive capability, impaired gut motility and sometimes perforation of the intestinal wall.
Apparently this damage is exacerbated by biochemical reactions. Miller and Dunagan described a pore-like opening and groove on acanthocephalan hooks, and they postulated delivery of a secretion via the proboscis hooks. Taraschewski b demonstrated proteolytic enzymes incorporated within osmiophilic material associated with the proboscis of Paratenuisentis ambiguus in eels Anguilla anguilla and postulated that they are discharged from the worms through pores in the proboscis hooks.
Such enzymes with trypsin-like activity secreted by P. In addition to aggravating damage done to cells and tissues by the proboscis, biochemical reactions might also increase loss of gut motility caused by parasite-induced fibrosis in the intestinal wall. Most of these neuromodulators are known to control gut motility and digestive and absorptive processes.
Changes in these functions probably occur in infected fishes. Reproduction[ edit ] The Acanthocephala are dioecious an individual organism is either male or female.
There is a structure called the genital ligament which runs from the posterior end of the proboscis sheath to the posterior end of the body. In the male, two testes lie on either side of this. Each opens in a vas deferens which bears three diverticula or vesiculae seminales.
The male also possesses three pairs of cement glands, found behind the testes, which pour their secretions through a duct into the vasa deferentia. These unite and end in a penis which opens posteriorly. In the female, the ovaries are found, like the testes, as rounded bodies along the ligament. From the ovaries, masses of ova dehisce into the body cavity, floating in its fluids for fertilization by male's sperm. After fertilization, each egg contains a developing embryo. These embryos hatch into first stage larva.
The fertilized eggs are brought into the uterus by actions of the uterine bell, a funnel like opening continuous with the uterus. At the junction of the bell and the uterus there is a second, smaller opening situated dorsally. The bell "swallows" the matured eggs and passes them on into the uterus. Immature embryos are passed back into the body cavity through the dorsal opening. From the uterus, mature eggs leave the female's body via her oviductpass into the host's alimentary canal and are expelled from the host's body within feces.
Other features[ edit ] A curious feature shared by both larva and adult is the large size of many of the cells, e. Polyploidy is common, with up to n having been recorded in some species. The acanthocephalans lack an excretory system, although some species have been shown to possess flame cells protonephridia.
Gammarus lacustrisa small crustacean that feeds near ponds and rivers, is one invertebrate that the thorny-headed worm may occupy. This crustacean is preyed on by ducks and hides by avoiding light and staying away from the surface.
However, when infected by a thorny-headed worm it becomes attracted toward light and swims to the surface. Gammarus lacustris will even go so far as to find a rock or a plant on the surface, clamp its mouth down, and latch on, making it easy prey for the duck.
The duck is the definitive host for the acanthocephalan parasite. In order to be transmitted to the duck, the parasite's intermediate host the gammarid must be eaten by the duck. This modification of gammarid behavior by the acanthocephalan is thought to increase the rate of transmission of the parasite to its next host by increasing the susceptibility of the gammarid to predation. It is thought that when Gammarus lacustris is infected with a thorny-headed worm, the parasite causes serotonin to be massively expressed.
Serotonin is a neurotransmitter involved in emotions and mood. Researchers have found that during mating Gammarus lacustris expresses high levels of serotonin. Also during mating, the male Gammarus lacustris clamps down on the female and holds on for days.
Researchers have additionally found that blocking serotonin releases clamping. Another experiment found that serotonin also reduces the photophobic behavior in Gammarus lacustris.