The host specificity of Moniliformis dubius (Acanthocephala), a parasite of cockroaches

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

The results of 4 different assays for haemocytic immune responsiveness in the cockroach,Periplaneta americana, have shown that the presence of larvae ofMoniliformis moniliformiswithin the haemocoele depresses the insect's immune reactivity. Thus, the proportion of haemocytes that phagocytose fluorescent latex beadsin vivo, the proportion of haemocytes that can be stimulatedin vitroby theβ1,3-glucan, laminarin, to produce phenoloxidase, and the number of haemocytic aggregates producedin vivoin response to zymosan stimulation, are significantly depressed compared with control, unparasitized cockroaches. Also, when cockroaches are injected intra-haemocoelically with hatched oncospheres of the tapeworm,Hymenolepis diminuta, a higher prevalence and intensity of tapeworm larvae are found in insects already parasitized byM. moniliformis. All of these assays show that depression rather than total suppression of the immune response occurs; in the wild, this may be sufficient to ensure that the cockroach does not succumb to unrelated infections during the long developmental period of the parasite.

The ultrastructure of the surface of Diplocystis schneideri Kunstler (Sporozoa: Eugregarinida) a parasite of Periplaneta americana

Ultrastructural observations of the surface of Diplocystis schneideri reveal a folded, multilaminate membrane, similar to that found in other eugregarines, covered with a layer of fibrous material. It is suggested that this fibrous material is a product of the haemocytes of the host, Periplaneta americana.

A quantitative study of the susceptibility of cockroach species to Moniliformis moniliformis (Acanthocephala)

We exposed 19 species of cockroaches to Moniliformis moniliformis by administering shelled acanthors orally and by injecting hatched acanthors directly into the body cavity. The exposure method had little influence on susceptibility: with one exception, species that were susceptible to oral exposure were also susceptible to injected acanthors and, in no case, did acanthors develop in injected animals when they did not develop in orally exposed conspecifics. We found no support for the hypothesis that the intestine may be a barrier to M. moniliformis establishment in cockroaches. There is, however, clear interspecific variation in susceptibility to M. moniliformis infection.

Factors affecting the development of Dipylidium caninum in Ctenocephalides felis felis (Bouché, 1835)

Ctenocephalides felis felis larvae were infected with Dipylidium caninum at a range of temperatures from 20 degrees - 35 degrees C at 3 mm Hg saturation deficit (SD) and 30 degrees C at 8 mm Hg SD. Hosts were subsequently dissected at 6, 9 and 12 days after infection. Four replicate experiments were performed and results of development, and host reactions analysed by the Genstat computer programme. These were found to depend on the temperature and saturation deficit of the environment. Unlike previous findings, parasite development and host reaction were found to be independent of host development. Host reaction was more marked and prolonged at 20 degrees - 25 degrees C than at higher temperatures. No perceptible growth of the parasite occurred at 20 degrees C. The development patterns of growth at the higher temperatures were similar but shifted in time so that faster growth occurred at higher temperatures. Rate of growth was fastest at 35 degrees C, despite the fact that this temperature was unfavourable to the hosts, all of which died at the time of pupation.

Evasion of the insect immune response by Moniliformis dubius (Acanthocephala): further observations on the origin of the envelope

The envelope around larvae of Moniliformis dubius appears to protect the parasite against immune recognition and encapsulation by the insect host's haemocytes. The origin of this envelope has been the subject of controversy although most evidence suggests it is parasite-derived. If host-derived, the envelope would be expected to share surface properties with host tissue. Thus, experiments were undertaken, transplanting parasites and host tissue to other insects and using haemocytic encapsulation as an assay for immune recognition, in order to compare the response to host tissue and to the parasite's envelope. Parasites without their envelopes, and pieces of tissue (ventral nerve cord) from the experimental host (the locust Schistocerca gregaria) were recognized as foreign and encapsulated in the cockroach, Periplaneta americana. The majority of parasites with their envelopes were unencapsulated or only partially encapsulated on transfer to their normal host, P. americana, indicating that the envelope does not have surface similarity to locust tissue. Cockroach-derived parasites with or without envelopes were not encapsulated in S. gregaria, suggesting that the larva itself can evade or inhibit the locust's recognition mechanism. However, since larvae which develop in S. gregaria are enclosed in an envelope, the formation of the envelope would seem to be an inherent feature of the parasite's development.

The cystacanth of Moniliformis moniliformis (Bremser, 1811) and its relationship with the haemocytes of the intermediate host (Periplaneta americana)

The nature of the capsule of the cystacanth of Moniliformis moniliformis was studied. Fat body, tracheal system, Malpighian tubules and haemocytes of the host are intimately associated with the cystacanth. The capsule of the cystacanth is cellular. The cells encapsulating the middle and late acanthellae are granular haemocytes of the host, whereas those encapsulating the cystacanth are agranular. Degranulation of haemocytes after encapsulation of the cystacanth recalls the common method for encapsulation of parasites of insect haemocytes, but a difference between the two kinds of encapsulation is that the capsule around the cystacanth does not bring about melanization nor destroys the parasite. It is suggested that the surface of the parasite may have inhibitors against enzyme systems causing melanization. Host haemocytes are also found in the capsular fluid. The infiltration of haemocytes into the capsule may be in response to the release of metabolites by the parasites. It is also suggested that the haemocytes may detoxify the parasitic metabolities. Rarely, capsules containing two parasites were observed. In one of the cases, one of the two cystacanths already possessed its own capsule. This finding, together with the cellular nature of the capsule, suggests that the capsule is of host origin.

Evasion of the haemocytic defence reaction of certain insects by larvae of Hymenolepis diminuta (Cestoda)

Larvae of Hymenolepis diminuta develop in the haemocoele of the beetles Tribolium and Tenebrio, and of the locust Schistocerca gregaria, without being encapsulated by haemocytes. The mechanism of this evasion of the haemocytic defence reaction has been examined using various techniques. Larvae grown in culture and injected into S. gregaria have a few or no haemocytes adherent even after 8h, although latex beads injected at the same time have been thickly encapsulated. This, and results of transplanting cysticercoids and host tissue between different insect species, suggests that the surface of the larvae may bear an inherent similarity to the surface of host tissues and thus escape recognition as 'not-self' by the host's haemocytes.