The tapeworm Ligula intestinalis occurs in the body cavity of its cyprinid second intermediate host, in this study the roach Rutilus rutilus, and inhibits host gonadal development. The mechanism by which infected fish are prevented from reproducing is unknown. Comparison of parameters, such as body length and weight, and condition factor and age, between infected and uninfected individuals, indicated only minor effects of parasitism on growth and condition. In contrast, seasonal gonadal development, as observed in uninfected fish, did not occur in infected fish, and gonads remained small and blocked at the primary oocyte stage in female roach. As immature ovaries and testes are still present, the parasite is presumed to act upon the brain -pituitary -gonadal axis of the fish to inhibit further development of reproductive organs. We investigated the Ligula/fish interaction at the level of the pituitary gland by determination of gonadotrophin (LH) content using a heterologous RIA for carp (Cyprinus carpio) LHb subunit. The results indicated that the pituitary glands of infected roach contained approximately 50% less LH than non-infected fish. After the cloning and sequencing of roach LHb subunit, we measured roach LHb mRNA levels by real-time RT-PCR. A corresponding 50% reduction in LHb mRNA pituitary levels was determined. These results reflect a significant and measurable effect of parasitism on the pituitary gland, and lend support to the hypothesis that excretory/secretory products released from the parasite interact with the brain -pituitary -gonadal axis of the fish host and thus inhibit gonadal development. Reproduction (2005) 130 939-945 IntroductionPrevious studies have revealed that several parasitic infections can affect host reproduction. For example, Joose & van Elk (1986) noted that Trichobilharzia ocellata induces gigantism and the cessation of egg production in its molluscan host, a snail Lymnea stagnalis, and Crews & Yoshino (1989) observed that Schistosoma mansoni similarly suppresses reproduction and gonadal growth in another snail species, Biomphalaria glabrata. Furthermore, in vertebrate hosts, Taenia taeniaeformis appears to directly affect the testis in the rat (Lin et al. 1990) and Taenia crassiceps induces feminisation in infected mice (Larralde et al. 1995).Ligula intestinalis, which is found in the body cavity of certain cyprinid fish, inhibits reproduction in both male and female fish. The gonads, however, are present but remain in an immature state, irrespective of fish age or season. Although this phenomenon has been reported several times (e.g. Arme & Owen 1968, Mahon 1976, Sweeting 1977, Bean & Winfield 1989, the mechanism of the action of this parasite remains unknown. Previous studies have indicated effects of infection at the pituitary gland level. Kerr (1948) and Arme (1968) noted that in ligulosed roach, Rutilus rutilus, the putative gonadotrophs are much reduced in number, compared with non-ligulosed individuals, are only lightly granulated, and have an irregular nucle...

Background:Two of the problems of malaria parasite vector control in Nigeria are the diversity of Anopheline vectors and large size of the country. Anopheline distribution and transmission dynamics of malaria were therefore compared between four ecotypes in Nigeria during the rainy season. Methods: Polymerase chain reaction (PCR) was used in molecular identification after morphological identification microscopically. Enzyme linked immunorsorbent assay (ELISA) was used for the blood meal analysis and sporozoite detection. Results: Five species were identified out of 16,410 anophelines collected. An. gambiae s.s made up approximately 29.2%-36.6% of the population in each zone. All five species acted as vectors for P. falciparum. An. gambiae s.s had the highest sporozoite rate. The most infected mosquitoes were found in the rain forest. More blood meals were taken from bovids, except the savannah forest, where 73.3% were on humans and Human Blood index (HBI) was 57.3%. The Entomological inoculation rate (EIR) was a mean of 13.6 ib/p but was highest in the rainforest zone. Conclusions and limitations:This study demonstrates the complex distribution of anophelines and the considerable variations in the intensity of malaria transmission in Nigeria. We highlight the need to consider diverse epidemiological situations when planning countrywide control programmes. Key words: Malaria; vectors; Plasmodium falciparum; transmission dynamics; ecotypes RésuméFond: Deux des problèmes de la commande de vecteur de parasite de malaria au Nigéria sont la diversité des vecteurs d'Anopheline et grande taille du pays. La distribution d'Anopheline et la dynamique de transmission de la malaria ont été donc comparées entre quatre ecotypes au Nigéria pendant la saison des pluies. Méthodes: La réaction en chaîne de polymérase (PCR) a été employée dans l'identification moléculaire après identification morphologique au microscope. L'analyse immunorsorbent liée par enzyme (ELISA) a été employée pour la détection d'analyse et de sporozoite de repas de sang. Résultats: Cinq espèces ont été identifiées sur 16.410 anophelines rassemblés. gambiae s.s composés approximativement 29.2-36.6% de la population dans chaque zone. Chacune des cinq espèces a agi en tant que vecteurs pour P. falciparum. gambiae s.s a eu le taux de sporozoite le plus élevé. Les moustiques les plus infectés ont été trouvés dans la forêt tropicale . Plus de repas de sang ont été pris des bovids, excepté la forêt de la savane, où 73.3% étaient sur des humains et l'index humain de sang (HBI) était 57.3%. Le taux entomologique d'inoculation (EIR) était un moyen de 13.6 ib/p mais était le plus haut dans la zone de forêt tropicale.

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