Effects of urban development and habitat alterations on the distribution and abundance of native and exotic freshwater fish in the Brisbane region,Queensland

The distribution of freshwater fish in creeks throughout the Brisbane region was determined by a survey carried out in 1977–78. Seventeen native and six exotic species were recorded in 55 creeks. Sixteen native and four exotic species were collected in a more restricted survey of central Brisbane in 1981. Urban development and the establishment of exotic plants have resulted in substantial changes to the aquatic environment in many of the creeks surveyed. Exotic grasses, especially para grass (Brachiaria mutica) have reduced the extent of free water by growing partly into stream channels. Floating exotic plants blanketed some stream reaches. Native aquatic macrophytes have declined, apparently due to dredging, siltation and other disturbances. These changes have affected the distribution and abundance of native and exotic fish. Native species with a preference for open water and beds of aquatic plants have declined in creeks overgrown by para grass and floating plants. Melanotaenia fluviatilis, Retropinna semoni, Pseudomugil signifer, Craterocephalus stercusmuscarum and Ambassis nigripinnis have been affected. Para grass and floating plants have not affected the range or abundance of Hypseleotris galii, H. compressus and Mogurnda adspersa. Gambusia affinis and Xiphophorus helleri have been advantaged by expansion of their preferred habitat type - the edges of pools where exotic grasses have grown partly into the water. The effect of exotic fish on native species is unclear. There was a correlation between large numbers of G. affinis and small numbers of H. galii and M. fluviatilis. Correlations could result from predatory or competitive interactions between species. Alternatively, correlations could be due entirely to the effects of habitat alterations on exotic and native species. However, H. galii was evidently not disadvantaged by the habitat alterations studied. Thus there may be a complex interaction between this species and G. affinis. There was no evidence that X. helleri had affected the range or abundance of native species.     

Monospecific helminth and arthropod infections in an urban population of brown rats from Doha, Qatar

Parasitic infections were studied for the first time in an urban population of brown rats (Rattus norvegicus) from Doha. Only one species of helminth was found, the cestode Hymenolepis diminuta, and one ectoparasite, the flea Xenopsylla astia, from a sample size of 136 rats (52 males and 84 females). The prevalence of H. diminuta was 17.6%, increasing with host age but not in relation to host sex nor season of capture. Host age was a key factor in influencing abundance of infection, although there was a significant three-way interaction with season and host sex arising through heavy infections in juvenile male rats in the summer. The prevalence of X. astia was 45.6%, although both prevalence and abundance of infestations were season and host age dependent. In the winter prevalence and abundance were similar in both host age and sex groups, but in the summer both parameters of infestation were markedly higher among juveniles compared with adults. We found evidence for some association between these two species: H. diminuta was more prevalent among rats with fleas than among those without, although this association was season-, and independently sex- and age-dependent. There were no quantitative interactions and reasons for this are discussed in relation to the foraging and breeding behaviour of the brown rat in Qatar.     

Rodent zoonoses in North Queensland: the occurrence and distribution of zoonotic infections in North Queensland rodents

A study of potentially zoonotic infections was carried out on 351 rodents trapped in north-eastern Queensland. Their ecosystems included towns, agricultural and livestock areas, wookland and rainforest. Nine serotypes of salmonellae were obtained from asymptomatic carries in predominantly settled locations. Two strains of Ps. pseudomallei occurred in rainforest near Innisfail and one on a cattle property adjacent to Townsville. Ps. aeruginosa caused bronchopneumonia in one animal from Townsville harbour. Ifection by leptospirae of six serogroups and seven serovars were identified by serological or cultural examinations. Enzootic foci occurred on the Mount Spec rainforest where celledoni and australis were being excreted by rats adjacent to the Paluma dam system. In addition to the scrub typhus locations at Rocky Creek, Atherton Tableland and Bullocky Creek, near Ingham, which were confirmed, a new focus of infection by R. tsutsugamushi was identified at El Arish near Tully. Water rat (H. chrysogaster) at Townsville harbour constituted a reservoir of toxoplasmosis. In addition to the known human pathogenic helminths H. nana and H. diminuta, localized foci of hookworms (Ancylostoma spp.) were found. Histological evidence of cytomegalic disease of the salivary glands or kidneys was a common finding.     

Immunity to systemic Salmonella infections

Salmonella infections are a serious public health problem in developing countries and represent a constant concern for the food industry. The severity and the outcome of a systemic Salmonella infection depends on the "virulence" of the bacteria, on the infectious dose as well as on the genetic makeup and immunological status of the host. The control of bacterial growth in the reticuloendothelial system (RES) in the early phases of a Salmonella infection relies on the NADPH oxidase-dependent anti-microbial functions of resident phagocytes and is controlled by the innate resistance gene Nramp1. This early phase is followed by the suppression of Salmonella growth in the RES due to the onset of an adaptive host response. This response relies on the concerted action of a number of cytokines (TNFalpha, IFNgamma, IL12, IL18, and IL15), on the recruitment of inflammatory phagocytes in the tissues and on the activation of the recruited cells. Phagocytes control bacterial growth in this phase of the infection by producing reactive nitrogen intermediates (RNI) generated via the inducible nitric oxide synthase (iNOS). Clearance of the bacteria from the RES at a later stage of the infection requires the CD28-dependent activation of CD4+ TCR-alphabeta T-cells and is controlled by MHC class II genes. Resistance to re-infection with virulent Salmonella micro-organisms requires the presence of Th1 type immunological memory and anti-Salmonella antibodies. Thus, the development of protective immunity to Salmonella infections relies on the cross-talk between the humoral and cellular branches of the immune system.     

Protagonists of innate immunity during in Salmonella infections

Salmonella are facultative intracellular Gram-negative bacteria that are found ubiquitously in nature and have the ability to infect a wide range of hosts including humans, domesticated, wild mammals, and birds. The principal clinical manifestations associated with Salmonella infection in humans are enteric fever (typhoid and paratyphoid) and a self-limiting gastroenteritis (salmonellosis). Additionally, silent carriage of this bacterium is frequent and contributes to disease dissemination. Typhoid fever still represents a major public health problem in many developing countries. On the other hand, industrialized countries experience an increased incidence of nontyphoidal Salmonella infections with most cases tracing back to food contamination. Studies using mouse model of infection with a highly virulent Salmonella typhimurium serotype have provided important insight into the complexity of the innate immune response to infection. The players are numerous but emphasis was placed on the genes that were discovered using genetic approaches and in vivo assay with live pathogen and include positional cloning of mouse mutations and manipulation of genes in the context of whole animal either by transgenesis or knockout technologies. Some of the critical genes include those known to play a role in the detection of the bacteria (Cd14, Lbp, Tlr4 and Tlr5) and in microbicidal activity (Slc11a1, Nos2, NADPH oxidase and cryptdins). These discoveries have already initiated the search for the contribution of particular genetic pathways in the innate immune response of humans to infection with Salmonella and other intracellular microorganisms.     

Salmonella andArizona infections in reptiles in the Netherlands

Summary A survey is given ofArizona andSalmonella types isolated from reptiles in Dutch zoological gardens. The importance of these findings with respect to public health are discussed.