Microsporidia cause opportunistic infections in AIDS patients and commonly infect laboratory animals, as well. Euthymie C57B1/6 mice experimentally infected with intraperitoneal injections of lxlO6 Encephalitozoon cuniculi Levaditi, Nicolau et Schoen, 1923, Encephalitozoon hellem Didier et al., 1991, or Nosema comeum Shadduck et al., 1990 displayed no clinical signs of disease. Athymic mice, however, developed ascites and died 8-16 days after inoculation with N. comeum, 21-25 days after inoculation with E. cuniculi, and 34-37 days after inoculation with E. hellem. All athymic mice displayed hepatomegaly, dilated intestine and accumulation of ascites fluid. Granulomatous lesions were primarily located in the liver, lung, pancreas, spleen, and on serosal surfaces of abdominal organs.
The development of the swimbladder nematode Anguillicola crassus Kuwahara, Niimi et Itagaki, 1974 in the definitive host (eels) was studied under experimental conditions. Small eels, Anguilla anguilla (L.) with body length 8-16 cm were infected by feeding them intermediate host copepods (Cyclops strenuus Fischer) harbouring third-stage larvae of this parasite. These experiments showed that, at 20-22° C, the development from the third-to the fourth-stage larvae lasted approximately three weeks, but some retarding third-stage larvae occurred in the wall of the host’s swimbladder or hyperparasitizing in the cuticle of adult nematodes as late as three months p.i. Young adults developed in the lumen of the swimbladder within approximately one month and noneinbryonated eggs first appeared in females 6-7 weeks p.i. The prepatent period was about three months and the patent period could be estimated to last no more than a month. Females degenerated soon after oviposition. The experiments confirmed that the size of mature A. crassus depends on the body size of its definitive host (eel).
The swimbladder parasite Anguillicola crassus Kuwahara, Niimi et Itagaki, 1974 (Nematoda: Dracunculoidea) is a well-known pathogenic parasite of the Japanese and European eels. Numerous studies on the life cycle of the parasite have revealed the involvement of a copepod or an ostracod intermediate host and a fish paratenic host, in which the third-stage larvae (Lj) infective to the eel develop. The present study comprised infection experiments with the larvae of A. crassus. These experiments can be divided into three groups: (1) experimental reproduction of the parasite's life cycle via copepod intermediate hosts and fish paratenic hosts, (2) infection of another potential paratenic host with third-stage larvae of A. crassus collected from a paratenic host; (3) study of the ability of larvae damaged by paratenic hosts to infect the final host, the eel. Infection experiments have revealed that larvae which are still viable but have become encapsulated as a result of the host reaction mounted against them by cyprinid paratenic hosts (bleak, Alhumus alhumus) have lost their ability to infect the final host, the eel. At the same time, experimental infection of the eel with larvae derived from other paratenic fish hosts (river goby, Neogobius fluviati-lis: ruffe, Gymnocephalus cemua) showing no or only weak host reaction proved to be successful.
The effect of host variables such as size and density, on the transmission of cercariae of Diplostomum spathaceum (Rudolphi, 1819) into a second intermediate fish host, rainbow trout, Oncorhynchus mykiss (Walbaum), was studied quantitatively in laboratory experiments under varying exposure conditions. Differences in the number of established metacercariae were noted in differently sized fish exposed singly to the same number of cercariae and in water volumes related to the body surface area of the host. When exposed (1) singly in an equal water volume or, (2) simultaneously in the same tank, no differences in recovery of metacercariae per fish were found between “small” and “large" hosts. The latter observation is valid for three water volumes tested using the same number of cercariae per host. No significant difference in metacercarial infection was revealed in similar sized fish exposed at different host densities. It appears that transmission is more influenced by cercarial density (number of cercariae per water volume) and fish size than by fish density. These experimental findings support the view that cercarial infection offish occurs by chance, presumably mainly in the gill region. Accordingly, in the field, individual fish size and cercarial density rather than fish population density, prevail in parasite transmission from snail to fish. This is of interest in coastal areas heated by cooling water, where fish growth and fish population density are enhanced.
An extrainlestinal coccidian parasite was identified in Schneider’s skinks Eumeces schneideri Daudin, 1802. Numerous tissue cysts were found in melanomacrophage aggregations in the liver of six of ten examined skinks. No tissue cysts were found in other tissues. Tissue cysts were 22-26 x 9-13 pm and contained a single sporozoite. Sporozoitcs were 10-13 x 2-4 pm, and contained a single nucleus, homogeneous inclusion and PAS positive granules, and were surrounded by PAS negative, 1.5-3.0 pm thick cyst wall. Transmission electron microscopy revealed that the tissue cyst wall was composed of granular material and the sporozoites contained crystalloid body with regular arrangements of units. Appearance of tissue cyst and structure of crystalloid body indicate that Schneider's skinks represent a paratenic host for non-determined Isospora species.