The in vitro leishmanicidal activity of a series of imidazole-containing phthalazine derivatives 1–4 was tested on Leishmania infantum, Leishmania braziliensis and Leishmania donovani parasites, and their cytotoxicity on J774·2 macrophage cells was also measured. All compounds tested showed selectivity indexes higher than that of the reference drug glucantime for the three Leishmania species, and the less bulky monoalkylamino substituted derivatives 2 and 4 were clearly more effective than their bisalkylamino substituted counterparts 1 and 3. Both infection rate measures and ultrastructural alterations studies confirmed that 2 and 4 were highly leishmanicidal and induced extensive parasite cell damage. Modifications to the excretion products of parasites treated with 2 and 4 were also consistent with substantial cytoplasmic alterations. On the other hand, the most active compounds 2 and 4 were potent inhibitors of iron superoxide dismutase enzyme (Fe-SOD) in the three species considered, whereas their impact on human CuZn-SOD was low. Molecular modelling suggests that 2 and 4 could deactivate Fe-SOD due to a sterically favoured enhanced ability to interact with the H-bonding net that supports the antioxidant features of the enzyme.

Host specificity is a fundamental component of a parasite's life history. However, accurate assessments of host specificity, and the factors influencing it, can be obscured by parasite cryptic species complexes. We surveyed two congeneric species of intertidal snail intermediate hosts, Zeacumantus subcarinatus and Zeacumantus lutulentus, throughout New Zealand to identify the number of genetically distinct echinostome trematodes infecting them and determine the levels of snail host specificity among echinostomes. Two major echinostome clades were identified: a clade consisting of an unidentified species of the subfamily Himasthlinae and a clade consisting of five species of the genus Acanthoparyphium. All five Acanthoparyphium species were only found in a single snail species, four in Z. subcarinatus and one in Z. lutulentus. In contrast, the Himasthlinae gen. sp. was found in both hosts, but was more prevalent in Z. lutulentus (97 infections) than Z. subcarinatus (10 infections). At least two of the Acanthoparyphium spp. and the Himasthlinae gen. sp. are widespread throughout New Zealand, and can therefore encounter both snail species. Our results suggest that host specificity is determined by host–parasite incompatibilities, not geographic separation, and that it can evolve in different ways in closely related parasite lineages.

Aquaculture, including both freshwater and marine production, has on a world scale exhibited one of the highest growth rates within animal protein production during recent decades and is expected to expand further at the same rate within the next 10 years. Control of diseases is one of the most prominent challenges if this production goal is to be reached. Apart from viral, bacterial, fungal and metazoan infections it has been documented that protozoan parasites affect health and welfare and thereby production of fish in marine aquaculture. Representatives within the main protozoan groups such as amoebae, dinoflagellates, kinetoplastid flagellates, diplomonadid flagellates, apicomplexans, microsporidians and ciliates have been shown to cause severe morbidity and mortality among farmed fish. Well studied examples are Neoparamoeba perurans, Amyloodinium ocellatum, Spironucleus salmonicida, Ichthyobodo necator, Cryptobia salmositica, Loma salmonae, Cryptocaryon irritans, Miamiensis avidus and Trichodina jadranica. The present report provides details on the parasites’ biology and impact on productivity and evaluates tools for diagnosis, control and management. Special emphasis is placed on antiprotozoan immune responses in fish and a strategy for development of vaccines is presented.

Trypanosoma cruzi is the causative agent of Chagas’ disease, a parasitic disease that remains a serious health concern with unsatisfactory treatment. Drugs that are currently used to treat Chagas’ disease are partially effective in the acute phase but ineffective in the chronic phase of the disease. The aim of the present study was to evaluate the antitrypanosomal activity and morphological, ultrastructural and biochemical alterations induced by a new molecule, 4-nitrobenzaldehyde thiosemicarbazone (BZTS), derived from S-(-)-limonene against epimastigote, trypomastigote and intracellular amastigote forms of T. cruzi. BZTS inhibited the growth of epimastigotes (IC50 = 9·2 μm), intracellular amastigotes (IC50 = 3·23 μm) and inhibited the viability of trypomastigotes (EC50 = 1·43 μm). BZTS had a CC50 of 37·45 μm in LLCMK2 cells. BZTS induced rounding and distortion of the cell body and severely damaged parasite mitochondria, reflected by extensive swelling and disorganization in the inner mitochondrial membrane and the presence of concentric membrane structures inside the organelle. Cytoplasmic vacuolization, endoplasmic reticulum that surrounded organelles, the loss of mitochondrial membrane potential, and increased mitochondrial O2•ˉ production were also observed. Our results suggest that BZTS alters the ultrastructure and physiology of mitochondria, which could be closely related to parasite death.

Eight strains of mice, of contrasting genotypes, infected with Heligmosomoides bakeri were studied to determine whether the anthelmintic efficacy of papaya latex varied between inbred mouse strains and therefore whether there is an underlying genetic influence on the effectiveness of removing the intestinal nematode. Infected mice were treated with 330 nmol of crude papaya latex or with 240 nmol of papaya latex supernatant (PLS). Wide variation of response between different mouse strains was detected. Treatment was most effective in C3H (90·5–99·3% reduction in worm counts) and least effective in CD1 and BALB/c strains (36·0 and 40·5%, respectively). Cimetidine treatment did not improve anthelmintic efficacy of PLS in a poor drug responder mouse strain. Trypsin activity, pH and PLS activity did not differ significantly along the length of the gastro-intestinal (GI) tract between poor (BALB/c) and high (C3H) drug responder mouse strains. Our data indicate that there is a genetic component explaining between-mouse variation in the efficacy of a standard dose of PLS in removing worms, and therefore warrant some caution in developing this therapy for wider scale use in the livestock industry, and even in human medicine.

Parasitic castration is a strategy used by parasites to minimize damage to the host by consuming its reproductive system, which results in the morphological alteration of the host. We determined that the forewing shape and density of the antennal sensilla of field-collected adult male mantids (Hierodula formosana), infected by horsehair worms (Chordodes formosanus) was partially feminized (intersexuality), and both male and female mantids infected by horsehair worms exhibited allometric changes in their wings and walking legs. In addition, the testes of most infected male adults disappeared or reduced in size, whereas the number of ovarioles in infected female adults was unaffected. The infection mainly influenced the structures related to host reproduction and locomotion, suggesting unbalanced energy exploitation and the reduction of parasitic virulence. In addition, the intersexuality of infected male adults indicated that sexual differentiation in insects, which researchers have considered to be an autonomous process, was influenced by the infection. The similarity of the antennae of infected male adults with those of last-instar female nymphs suggested that parasitic juvenilization may cause such feminization, but the mechanism of parasitic influence on insect sex characteristics should be studied further.

Mariculture is a rapidly developing industrial sector. Generally, fish are maintained in net cages with high density. Cage culture systems allow uncontrolled flow of sea water containing potentially infectious stages of fish parasites. In such culture conditions, prevention of such parasitic infections is difficult for parasites with life cycles that complete within culture sites, among which monogeneans and blood flukes are the most important platyhelminthes. Intense monogenean infections induce respiratory and osmo-regulatory dysfunctions. A variety of control measures have been developed, including freshwater bath treatment and chemotherapy. The potential to control monogenean infections through selective breeding, modified culture techniques to avoid infection, and general fish health management are discussed. It should be noted that mariculture conditions have provided some host-specific monogeneans with a chance to expand their host ranges. Blood flukes sometimes induce mass mortality among farmed fish. In-feed administration of praziquantel is the best solution to treat infected fish. Some cases are described that show how international trade in marine fish has resulted in the spread of hitherto unknown parasites into indigenous farmed and wild fish.