Development of Dipetalonema gracile and D. caudispina to the infective stage in Culicoides hollensis

The microfilariae of 2 species of Dipetalonema (i.e., D. gracile and D. caudispina), common parasites of South American monkeys, develop to the third (infective) stage in the biting midge, Culicoides hollensis. Development of both species occurs in the abdominal fat body; D. gracile requires 13 days and D. caudispina 9 days. Despite similarities in the patterns of development of both species, the third-stage larvae of each is morphologically distinct.

Development of Dipetalonema viteae third-stage larvae (Nematoda: Filarioidea) in micropore chambers implanted into jirds, hamsters, normal and immunized mice

Development of third-stage larvae of Dipetalonema viteae within subcutaneously implanted micropore chambers proceeded in all hosts tested up to the fourth-stage larvae and occasionally to adolescent worms. In the jird the timing of development was comparable to a natural infection. Although the mouse is an insusceptible host, larval development could take place, but was very slow. Two intraperitoneal inoculations of living third-stage larvae into mice induced the production of antibodies against the larval cuticle and against common antigens. In such immune mice the development of third- and fourth-stage larvae within micropore chambers was significantly inhibited, larval mortality was increased, and the larval motility was impaired.

[Dipetalonema dessetae--Aedes aegypti: study of the infected adipose tissue (author's transl)]

Histological and ultrastructural study of the adipose tissue of Aedes aegypti has shown that infection with the filaria Dipetalonema dessetae locally induces a highly active synthesis of proteins (formation of ribosomes, endoplasmic reticulum and Golgi complexes, multiplication of mitochondria). This phenomenon appears similar to the effect of beta-ecdysone after the up-take of blood. Mosquitoes let to starve during the development of the filaria show a quick disappearance of storage substances (lipids and glycogen) and involution forms of the induced ergastoplasma (after seventh days only), so that the infected tissue degenerates and the development of the filaria is arrested.

Studies on Dipetalonema viteae (Filarioidea) I. Microfilaraemia in hamsters in relation to worm burden and humoral immune response

The course of a primary infection with Dipetalonema viteae was studied in one randomly bred and in one inbred strain of hamster. Worm recovery and the duration and intensity of the microfilaraemia were analyzed and related to the humoral immune response of the host by using the indirect immunofluorescent antibody test on frozen sections of female worms, on eggs and on intact microfilariae. The inbred strain showed a greater susceptibility to the parasite. This was evidenced by high worm recovery and prolonged microfilaraemia. The duration of microfilaraemia did not depend on the number of recovered female worms. Most of the randomly bred hamsters suppressed microfilaraemia by week 30 post infection whereas some hamsters of the inbred strain were still microfilaraemic. Splenectomy prior to infection did not affect the duration of microfilaraemia. Antibodies to the cuticle of microfilariae always appeared in the sera after immunity to circulating microfilariae had been built up.

Studies on Dipetalonema vitae (Filarioidea). II. Antibody dependent adhesion of peritoneal exudate cells to microfilariae in vitro

Peritoneal exudate cells from normal uninfected hamsters adhered in vitro to microfilariae in the presence of 19S antibody fractions from hamsters which had suppressed or were going to suppress their microfilaremia. The adhering cells were predominantly mononuclear, although eosinophils were occasionally found. Experiments with sensitized microfilariae and peritoneal exudate cells indicated that the macrophage probably recognizes the microfilariae/antibody complex. Macrophage cytophilic antibodies did not seem to be involved. This adhesion reaction may initiate the trapping of microfilariae in vivo, thus contributing to the observed acquired immunity to circulating microfilariae in the hamster.

Intrauterine development of the microfilariae of Dipetalonema viteae

The egg shell of Dipetalonema viteae separated from the oolemma and became highly convoluted at an early stage of development. No second oolemma or trilaminate membrane was seen. Channels containing electron dense material (thought to be nutrient material from the uterine wall) were formed between adjacent embryos. Many developing embryos died. Microvilli were formed by the uterine wall and developing embryos were closely apposed to these (again presumably to obtain nutrient). Embryos emerged from the egg in the uterus and were born as unsheathed microfilariae.

Studies on naturally occurring filarial infections in dogs in Lebanon. I. Dipetalonema reconditum

A survey for filarial parasites was carried out on dogs in Lebanon. The peripheral blood was examined for microfilariae and the skins and carcasses for adult worms. Three methods were used for blood examination: (a) thick blood films stained with Giemsa; (b) a modified Knott's technique (Methylene Blue stained); (c) sodium citrate technique. Two species of filarial worm were found, Dipetalonema reconditum and another species of Dipetalonema which will be described in a later paper. The morphology of microfilariae and adults of D. reconditum is described. The microfilariae of D. reconditum showed a nocturnal sub-periodicity. Attempts were made to find vectors by feeding Aedes aegypti, Aedes phoeniciae, Culex pipiens molestus and Clenocephalides felis on an infected dog. Developing and infective stages were recovered only from C. felis.

Dipetalonema viteae infection in hamsters: enhancement and suppression of microfilaraemia

Mature male Dipetalonema viteae released a substance(s) which caused enhanced microfilaraemia in infected hamsters. In hamsters implanted with female D. viteae, the microfilaraemia of a subsequent infection was suppressed. The microfilaraemia of female worms implanted in hamsters was depressed within 5 days when the animals were given a further infection with infective larvae.

Dipetalonema viteae in hamsters: effect of antiserum or immunization with parasite extracts on production of microfilariae

After hamsters have been infected with Dipetalonema viteae for about 4 months, microfilariae disappear from the circulation but the adult worms remain alive and active. Such hamsters are said to harbour a ‘latent’ infection. Additional adult worms implanted into such hamsters produce no microfilariae, but adult worms recovered from hamsters with latent infections resume microfilariae production when surgically transplanted into new hosts. In vitro, worms from hamsters with latent infections renewed microfilariae production in the presence of serum from uninfected but not infected hamsters. Serum from infected animals had a marked suppressive effect on the microfilariae production of adult worms implanted into passively immunized hamsters. This suggests that microfilarial release is regulated by a serum factor. Microfilarial production in in vitro and in vivo experiments was more strongly inhibited by serum taken from hamsters with latent infections and hamsters infected for only 30 days (pre-patent) than by serum taken 90 days after infection (whilst microfilariae were in the circulation of the serum donors). A cytotoxic effect of sera from infected hamsters on the microfilariae could not be demonstrated.

In animals immunized by extracts of adult worms or microfilariae, microfilaraemia was considerably reduced. In contrast, animals immunized repeatedly with the extract from small numbers of microfilariae during the pre-patent phase of an infection had an enhanced microfilaraemia. Adult worm numbers were not affected by immunization except in animals given extract from a single female worm which harboured fewer worms than controls.

Development of D. (A.) weissi, a macroscelid's filaria, in Ornithodoros erraticus (author's transl)

The microfilariae of D. (A.) weissi parasite of Elephantulus rozeti in North Africa evolved in Ornithodoros erraticus (Vellozo strain from Casablanca) where they reach the infective stage. The Filaria D. (A.) viteae, parasite of Gerbillid Rodents, is closely related to D. (A.) weissi but has some clear differential characters; on the contrary the infective stages seem to be undistinguishable.

[Deviation of the life cycle of Dipetalonema viteae (Filarioidea)]

Dipetalonema viteae is a filarial that can evoluate among hosts zoologically broadly apart (Ixodides and Argasides), but always gathered from meriones burrows. Its evolution is, on the contrary, blocked among most of the other ticks, particularly among Ornithodoros erraticus morphologically very similar to the normal vector. Our work concerns the experimental deviation of the cycle of Dipetalonema viteae, with its possible adaptability in the bosom of an intermediate of fowl tropism and a permanent host, different from a gnawing.

Transmission of microfilariae and infective larvae of Dipetalonema viteae (Filarioidea) among vector ticks, Ornithodoros tartakowskyi (Argasidae), and loss of microfilariae in coxal fluid

During studies on the acquisition and transmission of infection with the filaria Dipetalonema viteae by Ornithodoros tartakowskyi, it was found that young nymphs and starved medium-sized ticks feed on recently engorged larger ticks. In this manner young ticks acquired the infection with microfilariae, and the microfilariae thus taken developed normally and after 30 days of development were transmitted to a jird. Ticks harboring infective larvae were able to transfer them to other engorged ticks when attempting to feed on them. Although it is not known whether this occurs in nature, it could be a supplementary mechanism in the natural maintenance of this species of filaria. Ticks eliminated microfilariae in the coxal fluid in small numbers during the 1st hr after the infective meal and in increasing numbers with time, reaching a peak between 3 and 5 hr. This mechanism may prevent some ticks from becoming hyperinfected.

Life cycle of Dipetalonema sprenti Anderson (Nematoda: Filarioidea) of beaver (Castor canadensis)

Adult Dipetalonema sprenti Anderson occur mainly in the peritoneal cavity of beaver (Castor canadensis Kuhl). Microfilariae were taken up with blood and developed to the infective stage in the fat body of the abdomen and thorax of Aedes intrudens Dyar and A. abserratus (Felt and Young). At 27C the first molt occurred 4 to 6 days and the second molt 7 to 9 days after ingestion by the mosquito. Infective larvae were first seen in the head on the eighth day. A "sausage-stage" was present during development to the first molt at 27C but not at 23C. Microfilariae appeared in the blood of six previously uninfected beaver 116–135 days after each was injected with about 125 infective larvae. Aedes intrudens and A. abserratus fed on beaver in Algonquin Park, Ontario, from the first week of June until about the middle of July during 1970 and 1971. Transmission of D. sprenti may occur principally within beaver lodges or dens.