Mirror carp (Cyprinus carpi0 L.) infected with sublethal doses of Zchthyophthirius rnultifliis, were free of parasites 21 days after infection. Fish remained free of parasites for at least 8 months when maintained in an infective environment. Such fish were refractory to reinfection with numbers of parasites that killed all normal, previously unexposed fish. Serum from fish recovered from previous infections with sublethal doses of parasites, immobilized free-swimming stages of I. multifiliis to a dilution of up to 1 : 1024. The rise in serum-immobilization titre occurred between the 10th and 22nd days of infection, the period during which parasites disappeared from the body surface of the fish. Infective stages of the parasite were unable to penetrate the mucus body covering of resistant fish.

Human erythrocytes contain only trace amounts of polyamines and lack active polyamine biosynthetic enzymes. A remarkable increase in polyamine content, and in the activity of ornithine and S-adenosyl-L-methionine decarboxylases, is noted in synchronous cultures of the malarial parasite, Plasmodium falciparum. Polyamine biosynthesis reached peak values during the early trophozoite stage, whereas nucleic acid and protein synthesis occurred later in mature trophozoites. DL-alpha-Difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, did not interfere with merozoite invasion and with ring-form development, but prevented the transformation of trophozoites to schizonts. Concomitantly, the synthesis of proteins and nucleic acids was significantly inhibited. These inhibitory effects could be readily reversed by the diamine putrescine. Macromolecular synthesis and schizogony were normal when 5-10 mM-DL-alpha-difluoromethylornithine and 0.1 mM-putrescine were added to the cultures simultaneously.

Mirror carp were infected with Ichthyophthirius mullifliis (Fouquet) under standardized conditions, The size and number of parasites at selected sites on the body were recorded during the course of the infection. Initial exposure to 40 mature parasites resulted ina mild infection with 100 % recovery after 18 days. Recovered fish did not appear to be carriers of the parasite. Exposure to 400 parasites resulted in 100% mortality between 22-25 days. The growth rate of the parasite was linear. Parasites were more numerous in the dorsal surface of the fish than in the lateral or ventral surface. The increase in parasite numbers during the disease was greater in the gills than in the skin.

No abstract

Abstract. The relative role of transmission of Toxoplasma gondii infection from cats to humans appears to have recently increased in certain areas. Large-scale screening of oocyst shedding in cats cannot rely on microscopy because oocyst identification lacks sensitivity and specificity, or on bioassays, which require test animals and weeks before examination. We compared a sensitive and species-specific coprologic-polymerase chain reaction (copro-PCR) for detection of T. gondii infected cats with microscopy and a bioassay. In experimentally infected cats followed over time, microscopy was positive occasionally, and positive copro-PCR and bioassay results were obtained continuously from days 2 to 24 postinfection. The copro-PCR is at least as sensitive and specific as the bioassay and is capable of detecting infective oocysts during cat infection. Therefore, this procedure can be used as the new gold standard for determining potential cat infectivity. Its technologic advantages over the bioassay make it superior for large-scale screening of cats.

DL-alpha-difluoromethylornithine (DFMO) inhibited ornithine decarboxylase (ODC) activity and arrested the growth of Plasmodium falciparum at the early trophozoite stage. The inhibition of ODC activity did not result in the formation of an alternative diamine such as cadaverine. When putrescine or spermidine were added to the parasites grown in culture, the arrest was reversed, and normal schizogony was completed even in the presence of DFMO. Some reversal of the inhibition was achieved with cadaverine at high concentrations, while 1,3-diaminopropane and spermine failed to restore the development. Resumption of growth could be detected when putrescine was added even after 67 h of DFMO treatment. Electron microscopy did not reveal any changes in the morphology of parasites treated for 47 h, while 73 h of treatment with DFMO induced massive accumulation of pigment. Death was observed a few hours later. These results suggest that DFMO acts as a cytostatic rather than as a cytocidal agent. The four carbon diamine restored cell growth while the shorter or the longer homologous compounds showed little activity.

No abstract

Some structural properties of the DNA of Plasmodium falciparum were studied thoroughly using several techniques. Its G+C content was found to be extremely low (17-19%), the lowest reported for a living organism. The DNA seems to be composed only of the four major bases as no methylated bases were detected. This DNA had a Tm value of 62.5 degrees C and its denaturation profile showed no marked intramolecular heterogeneity.