Hydrobionts as reservoir hosts for infectious agents of bacterial sapronoses

Data on parasitism of the infectious agents of sapronoses in hydrobionts (protozoans, crustaceans, worms, mollusks, echinoderms, and fishes) are considered from the population-ecological viewpoint. The symbiotic relationships between populations of pathogenic bacteria and protozoans are of the host-parasite type. An ultrastructural analysis demonstrates that phagocytosis is incomplete both in planktonic forms and in biofilms formed by bacteria and protozoa. This provides for long-term survival of infectious agents in the environment. The migration of Yersinia pseudotuberculosis along trophic chains from the lowest to the highest level has been simulated experimentally. The long-term survival of pathogenic bacteria in aquatic animals and the ability of bacteria to migrate along trophic chains, reaching soil animals and humans, provide evidence that comprehensive studies on the routes of circulation of pathogens in natural ecosystems are highly relevant from the ecological and epidemiological viewpoints.     

Molecular trees of trypanosomes incongruent with fossil records of hosts

Molecular trees of trypanosomes have confirmed conventionally accepted genera, but often produce topologies that are incongruent with knowledge of the evolution, systematics, and biogeography of hosts and vectors. These distorted topologies result largely from incorrect assumptions about molecular clocks. A host-based phylogenetic tree could serve as a broad outline against which the reasonability of molecular phylogenies could be evaluated. The host-based tree of trypanosomes presented here supports the " invertebrate first " hypothesis of trypanosome evolution, supports the monophyly of Trypanosomatidae, and indicates the digenetic lifestyle arose three times. An area cladogram of Leishmania supports origination in the Palaearctic during the Palaeocene.     

Natural human immunity to trypanosomes

Complement-dependent destruction of invading micro-organisms is a crucial first-line defense against infection, yet both African and American trypanosomes are able to resist attack by complement. African trypanosomes resist non-specific complement attack by virtue of a thick glycoprotein surface coat, and the host range of certain African trypanosomes is believed to be defined by their susceptibility to a subclass of human high density lipoprotein (HDL) and/or a high molecular weight protein complex present in human serum. In the first part of this review, Stephen Tomlinson and Jayne Raper look at the properties and mechanisms of action of these trypanolytic factors on African trypanosomes, and discuss briefly the possible mechanisms whereby these human pathogens resist lysis by human serum. The mechanisms that enable the American trypanosome Trypanosoma cruzi to resist complement attack are reviewed in the second part of this article.     

Experimental evaluation of xenodiagnosis to detect trypanosomes at low parasitaemia levels in infected hosts

In Human African Trypanosomosis (HAT) endemic areas, there are a number of subjects that are positive to serological tests but in whom trypanosomes are difficult to detect with the available parasitological tests. In most cases and particularly in West Africa, these subjects remain untreated, thus posing a fundamental problem both at the individual level (because of a possible lethal evolution of the disease) and at the epidemiological level (since they are potential reservoirs of trypanosomes). Xenodiagnosis may constitute an alternative for this type of cases. The objective of this study was to update the use of xenodiagnosis to detect trypanosomes in infected host characterized by low parasitaemia levels. This was carried out experimentally by infecting cattle and pigs with Trypanosoma congolense and T. brucei gambiense respectively, and by feeding tsetse flies (Glossina morsitans submorsitans and G. palpalis gambiensis, from the CIRDES colonies) on these animals at a time when the observed blood parasitaemia were low or undetectable by the classical microscopic parasitological tests used for the monitoring of infected animals. Our results showed that: i) the G. p. gambiensis colony at CIRDES could not be infected with the T. b. gambiense stocks used; ii) midgut infections of G. m. submorsitans were observed with both T. congolense and T. b. gambiense; iii) xenodiagnosis remains positive even at very low blood parasitaemia for both T. congolense and T. b. gambiense; and iv) to implement T. b. gambiense xenodiagnosis, batches of 20 G. m. submorsitans should be dissected two days after the infective meal. These results constitute a first step toward a possible implementation of xenodiagnosis to better characterize the parasitological status of seropositive individuals and the modalities of parasite transmission in HAT foci.     

Rodents as reservoir hosts in the transmission of Schistosoma mansoni in Richard-Toll, Senegal, West Africa

More than 2000 animals belonging to six different rodent species and one insectivore species were examined for infection with schistosomes in the region of Richard-Toll, Senegal. Two murid rodents, Arvicanthis niloticus and Mastomys huberti, were found infected with Schistosoma mansoni. Prevalences were about 5% for both rodent species with a mean worm burden of about 20 worms per host. The sex-ratios of S. mansoni worms were always biased towards males. Prevalences and worm burdens, although similar in both male and female rodents, increased significantly with age. The highest prevalences and worm burdens were found near habitations and decreased significantly with the distance from the town of Richard-Toll. Eggs were also observed in the liver and faeces of the two naturally infected rodent species. The results suggest that rodents participate in the transmission of intestinal schistosomiasis in Richard-Toll but the human population is the main source of infection. The genetic resemblance between human and murine isolates of S. mansoni suggests that further epidemiological studies are needed in this region of Senegal.     

Patterns of co-evolution between trypanosomes and their hosts deduced from ribosomal RNA and protein-coding gene phylogenies

Trypanosomes (genus Trypanosoma) are widespread blood parasites of vertebrates, usually transmitted by arthropod or leech vectors. Most trypanosomes have lifecycles that alternate between a vertebrate host, where they exist in the bloodstream, and an invertebrate host, where they develop in the alimentary tract. This raises the question of whether one type of host has had greater influence on the evolution of the genus. Working from the generally accepted view that trypanosomes are monophyletic, here we examine relationships between trypanosomes using phylogenies based on the genes for the small subunit ribosomal RNA (SSU rRNA) and the glycosomal glyceraldehyde phosphate dehydrogenase (gGAPDH). New analysis of a combined dataset of both these genes provides strong support for many known clades of trypanosomes. It also resolves the deepest split within the genus between the Aquatic clade, which mainly contains trypanosomes of aquatic and amphibious vertebrates, and a clade of trypanosomes from terrestrial vertebrates. There is also strengthened support for two deep clades, one comprising a wide selection of mammalian trypanosomes and a tsetse fly-transmitted reptilian trypanosome, and the other combining two bird trypanosome subclades. Considering the vertebrate and invertebrate hosts of each clade, it is apparent that co-speciation played little role in trypanosome evolution. However most clades are associated with a type of vertebrate or invertebrate host, or both, indicating that 'host fitting' has been the principal mechanism for evolution of trypanosomes.     

Hematophagous insects as vectors for frog trypanosomes

Experimental infections of three hematophagous arthropods (Rhodnius prolixus, Aedes aegypti, and Culex pipiens) with a trypanosome of the Trypanosoma rotatorium complex found in the frogs Hyla crepitans and Leptodactylus insularum revealed that A. aegypti is a good host for the flagellate; the course of development in the intestinal tract of the mosquito is described from 15 minutes to 168 hours. C. pipiens showed only low intestinal infections and R. prolixus did not permit development of the parasite. It is postulated that, in addition to the transmission of T. rotatorium by leeches, batrachophilic mosquitoes may transmit the parasite to frogs of more terrestrial habits by being ingested by these anurans.     

Companion Animals as Selfobjects

ABSTRACT

This research examined whether self psychology could be systematically applied to human–animal relationships. Twenty-four semi-structured interviews were conducted, which consisted of 16 questions designed to illuminate selfobject needs. The interviews were intended to identify whether the horse/dog/cat/rabbit was a selfobject, that is, a provider of self-cohesion, self esteem, calmness, soothing, and acceptance, for the participant and, if so, whether the primary type(s) of selfobject was mirroring, idealizing, or twinship. Results revealed that self psychology could be applied successfully to human–animal relationships, that it could usually be determined whether the animal served a selfobject function, and that selfobject type was generally able to be established. In this sample, animals rivaled and even surpassed humans in their ability to provide important selfobject needs.     

Weeds as hosts of Mycocentrospora acerina

Weeds were collected from carrot fields and some other sites at 27 localities in seven counties in Norway during August and September of 1986 and 1987. Leaf and petiole lesions were microscopically examined for Mycocentrospora acerina. Viola arvensis and Viola tricolor were commonly observed with the pathogen. The fungus was also registered on Fumaria officinalis, Galium aparine, Matricaria inodora, Matricaria matricarioides, Ranunculus repens, Senecio vulgaris and Stachys palustris. In inoculation experiments in the greenhouse, M. acerina infected carrot leaves and 13 of 16 species of weeds. The symptoms on the various susceptible plants showed some variation, but were essentially of the same pattern. The investigation indicates that weeds are common hosts of M. acerina. A list of 23 host weed species is given.     

The rhizosphere as a reservoir for opportunistic human pathogenic bacteria

During the last years, the number of human infections caused by opportunistic pathogens has increased dramatically. One natural reservoir of opportunistic pathogens is the rhizosphere, the zone around roots that is influenced by the plant. Due to a high content of nutrients, this habitat is a 'microbial hot-spot', where bacterial abundances including those with strong antagonistic traits are enhanced. Various bacterial genera, including Burkholderia, Enterobacter, Herbaspirillum, Ochrobactrum, Pseudomonas, Ralstonia, Staphylococcus and Stenotrophomonas, contain root-associated strains that can encounter bivalent interactions with both plant and human hosts. Mechanisms responsible for colonization of the rhizosphere and antagonistic activity against plant pathogens are similar to those responsible for colonization of human organs and tissues, and pathogenicity. Multiple resistances against antibiotics are not only found with clinical strains but also with strains isolated from the rhizosphere. High competition, the occurrence of diverse antibiotics in the rhizosphere, and enhanced horizontal gene transfer rates in this microenvironment appear to contribute to the high levels of natural resistances. While opportunistic bacteria from the rhizosphere have some properties in common, each of these emerging pathogens has its own features, which are discussed in detail for Burkholderia, Ochrobactrum and Stenotrophomonas.     

Protein kinases as drug targets in trypanosomes and Leishmania

Protein kinases represent promising drug targets for a number of human and animal diseases. The recent completion of the sequenced genomes of three human-infective trypanosomatid protozoa, Leishmania major, Trypanosoma brucei and Trypanosoma cruzi, has allowed the kinome for each parasite to be defined as 179, 156 and 171 eukaryotic protein kinases respectively, that is about one third of the human complement. The analysis revealed that the trypanosomatids lack members of the receptor-linked or cytosolic tyrosine kinase families, but have an abundance of STE and CMGC family protein kinases likely to be involved in regulating cell cycle control, differentiation and response to stress during their complex life-cycles. In this review, we examine the prospects for exploiting differences between parasite and mammalian protein kinases to develop novel anti-parasitic chemotherapeutic agents.     

Plants as alternative hosts for Salmonella

Recent findings show that many human pathogenic bacteria can use multiple host organisms. For example, Salmonella Typhimurium can use plants as alternative hosts to humans and other animals. These bacteria are able to adhere to plant surfaces and actively infect the interior of plants. Similarly to the infection of animal cells, S. Typhimurium suppresses plant defense responses by a type III secretion mechanism, indicating that these bacteria possess a dedicated multi-kingdom infection strategy, raising the question of host specificity. In addition, evidence is accumulating that the interaction of Salmonella with plants is an active process with different levels of specificity, because different Salmonella serovars show variations in pathogenicity, and different plant species reveal various levels of resistance towards these bacteria.     

The human spleen as an erythrocyte reservoir in diving-related interventions.

Twelve subjects without and ten subjects with diving experience performed short diving-related interventions. After labeling of erythrocytes, scintigraphic measurements were continuously performed during these interventions. All interventions elicited a graduated and reproducible splenic contraction, depending on the type, severity, and duration of the interventions. The splenic contraction varied between approximately 10% for "apnea" (breath holding for 30 s) and "cold clothes" (cold and wet clothes applied on the face with no breath holding for 30 s) and approximately 30-40% for "simulated diving" (simulated breath-hold diving for 30 s), "maximal apnea" (breath holding for maximal duration), and "maximal simulated diving" (simulated breath-hold diving for maximal duration). The strongest interventions (simulated diving, maximal apnea, and maximal simulated diving) elicited modest but significant increases in hemoglobin concentration (0.1-0.3 mmol/l) and hematocrit (0.3-1%). By an indirect method, the splenic venous hematocrit was calculated to 79%. No major differences were observed between the two groups. The splenic contraction should, therefore, be included in the diving response on equal terms with bradycardia, decreased peripheral blood flow, and increased blood pressure.