Immunosuppression by larvae of Moniliformis moniliformis (Acanthocephala) in their cockroach host ( Periplaneta Americana )

Encapsulation of the Acanthocephalan Corynosoma strumosum (Rudolphi, 1802) LÜHE, 1904, in the Intermediate Host Spinulogammarus ochotensis

We describe the thin and ultra-thin structures of the envelopes surrounding the cystacanth of Corynosoma strumosum (Rudolphi, 1802) Lühe, 1904, in its intermediate host. A total of 4,357 amphipods from 2 species were examined: Locustogammarus locustoides (Brandt, 1851) and Spinulogammarus ochotensis (Brandt, 1851). Eleven corynosome cystacanths were found in 6 S. ochotensis specimens. Three were enclosed in acellular cysts originating from the parasite. Three other cystacanths were also encysted and were surrounded by a lighter capsule consisting of the host's hemocytes. Five cystacanths were enclosed in a cyst and a darker capsule, in which both the acanthocephalans and their surrounding envelopes were destroyed. We suggest that the cystacanth's cyst is a protective barrier against the host's cellular response, while the lighter and darker capsules represent different stages of parasite degeneration.

A parasitological evaluation of edible insects and their role in the transmission of parasitic diseases to humans and animals

From 1 January 2018 came into force Regulation (EU) 2015/2238 of the European Parliament and of the Council of 25 November 2015, introducing the concept of "novel foods", including insects and their parts. One of the most commonly used species of insects are: mealworms (Tenebrio molitor), house crickets (Acheta domesticus), cockroaches (Blattodea) and migratory locusts (Locusta migrans). In this context, the unfathomable issue is the role of edible insects in transmitting parasitic diseases that can cause significant losses in their breeding and may pose a threat to humans and animals. The aim of this study was to identify and evaluate the developmental forms of parasites colonizing edible insects in household farms and pet stores in Central Europe and to determine the potential risk of parasitic infections for humans and animals. The experimental material comprised samples of live insects (imagines) from 300 household farms and pet stores, including 75 mealworm farms, 75 house cricket farms, 75 Madagascar hissing cockroach farms and 75 migrating locust farms. Parasites were detected in 244 (81.33%) out of 300 (100%) examined insect farms. In 206 (68.67%) of the cases, the identified parasites were pathogenic for insects only; in 106 (35.33%) cases, parasites were potentially parasitic for animals; and in 91 (30.33%) cases, parasites were potentially pathogenic for humans. Edible insects are an underestimated reservoir of human and animal parasites. Our research indicates the important role of these insects in the epidemiology of parasites pathogenic to vertebrates. Conducted parasitological examination suggests that edible insects may be the most important parasite vector for domestic insectivorous animals. According to our studies the future research should focus on the need for constant monitoring of studied insect farms for pathogens, thus increasing food and feed safety.

The life cycle ofSclerocollum saudiiAl-Jahdali, 2010 (Acanthocephala: Palaeacanthocephala: Rhadinorhynchidae) in amphipod and fish hosts from the Red Sea

The rhadinorhynchidSclerocollum saudiiAl-Jahdali, 2010 was found in the intestine of its type host,SiganusrivulatusForsskål & Niebuhr, 1775, a siganid fish permanently resident in a lagoon within the mangrove swamps found on the Egyptian coast of the Gulf of Aqaba (between 28°7′N and 28°18′N). Larval forms of this acanthocephalan (acanthors, acanthellae and cystacanths) were only found inMegaluropus agilisHoek, 1889 (Crustacea: Gammaridae), a benthic amphipod abundant on algae and seagrasses in the lagoon. So, this life cycle ofS. saudiiwas elucidated under semi-natural conditions: embryonated eggs ofS. saudiiwere directly ingested by the amphipod and hatched in its intestine; the released acanthor penetrated the intestinal epithelium in 12–18 h to reach the connective tissue serosa, where it remained for about 3 days, then penetrated the intestinal wall and remained attached to its outer surface for 4 days. It then detached and dropped free in the amphipod haemocoel and transformed into an oval acanthella, growing for 16 days to reach the cystacanth stage. The cystacanth at 46 days post-infection was infective to fish (excysted in its intestine as an active juvenile). Male and female juveniles reached maturity 17 and 23 days post-infection. Recently copulated females first appeared 26 days post-infection and all females seemed to be copulated at 28 days post-infection; partially and fully gravid females first appeared 31 and 35 days post-infection. Mature males and fully gravid females started to die off naturally 31 and 43 days post-infection and were totally expelled from the fish intestine by 42 and 52 days post-infection. The cycle was completed in 89 days and is similar to other known palaeacanthocephalan life cycles, but has its own characteristics.

Differences in parasite susceptibility and costs of resistance between naturally exposed and unexposed host populations

It is generally assumed that resistance to parasitism entails costs. Consequently, hosts evolving in the absence of parasites are predicted to invest less in costly resistance mechanisms than hosts consistently exposed to parasites. This prediction has, however, rarely been tested in natural populations. We studied the susceptibility of three naïve, three parasitized and one recently isolated Asellus aquaticus isopod populations to an acanthocephalan parasite. We found that parasitized populations, with the exception of the isopod population sympatric with the parasite strain used, were less susceptible to the parasite than the naïve populations. Exposed but uninfected (resistant) isopods from naïve populations, but not from parasitized populations, exhibited greater mortality than controls, implying that resistance entails survival costs primarily for naïve isopods. These results suggest that parasites can drive the evolution of host resistance in the wild, and that co-existence with parasites may increase the cost-effectiveness of defence mechanisms.

Pomphorhynchus laevisin its intermediate hostEchinogammarus stammeriin the River Brenta, Italy

Infection rates of larvalPomphorhynchus laevisMu¨ller, 1776 (Acanthocephala) were studied in its intermediate hostEchinogammarus stammeriS. Karaman, 1931 (Amphipoda). Crustaceans were collected monthly, from July 1990 to July 1997, at two sites on the River Brenta (northern Italy). Of over 50,000E. stammeriexamined, more than 24% were parasitized withP. laevislarvae. The differences in the prevalence of infection between the two stations were significant. The intensity of infection varied from one to 15 acanthocephalans per host. Amphipods with multiple infections constituted 28–32% of each monthly sample. During the 7 years of investigation, the prevalence of infection typically reached its highest and lowest levels in the summer and spring months, respectively. Acanthocephalan larvae showed no preference for host sex. Infected ovigerous females ofE. stammeriwere found carrying eggs or juveniles in their brood pouches, but had fewer and smaller eggs.Pomphorhynchus laevislarvae co-occurred withAcanthocephalus clavula(Dujardin, 1845) and also with the tapewormCyathocephalus truncatus(Pallas, 1781) in the same host.

Localization of phenoloxidase in the midgut of Periplaneta americana parasitized by larvae of Moniliformis moniliformis (Acanthocephala)

In cockroaches infected with Moniliformis moniliformis, the melanogenic enzyme phenoloxidase (PO) was histochemically localized in the posterior midgut and in haemocytes. Midguts were incubated with either 3-hydroxytyramine-HCl (dopamine) or 3-(3,4-dihydroxyphenyl)-L-alanine (dopa), and the resulting electron-dense reaction products of PO activity were found to be homogeneously distributed in the cytoplasm of both midgut cells and haemocytes. Following experimental infection, the first acanthors that reached the outer surface of the gut elicited a haemocyte response similar to that observed during wound healing. Larvae that remained attached to the gut became melanized or developed successfully. PO activity gradually decreased as the course of infection proceeded (10-50 days post-infection) but was apparently not inhibited in either midgut cells or haemocytes that were closely associated with the parasites. PO was lacking in the midgut cells of uninfected cockroaches. The results of the present study are discussed with respect to the defence reactions of the host and the survival mechanisms of the parasite.