A comparison of Aedes vigilax larval population densities and associated vegetation categories in a coastal wetland, Northern Territory, Australia.

Darwin's northern suburbs border an extensive coastal reed and upper mangrove wetland recognized as an important larval habitat for Aedes vigilax (Skuse), the northern salt marsh mosquito, an established vector for Ross River and Barmah Forest viruses and an appreciable pest species. We sought to identify the most important vegetation categories associated with Ae. vigilax breeding to maximize the efficiency of mosquito control efforts. Using a generalized linear model with negative binominal distribution and log link, this study compares larval densities, determined by focused dipping, between 13 discernable vegetation categories. The incidence rate ratios (RR) generated can be used to compare the magnitude of larval densities for each vegetation category, compared with the reference category. Aedes vigilax larval densities were almost ten times greater in artificial drainage areas (RR=9.82), followed by tide-affected reticulate (Sporobolus/Xerochloa) areas (RR=8.15), then Schoenoplectus/mangroves (RR=2.29), compared with the reference vegetation category "lower mangroves." Furthermore, larval densities were highest in May, due to tidal inundation, for drainage areas and tide-affected reticulates (RR=12.2, 11.7, respectively) compared with March, the reference month. Thus, to maximize the efficiency of aerial salt marsh mosquito control operations in this wetland, larval control is best accomplished by concentrating on drains, Schoenoplectus/mangroves, and tide-affected reticulate areas, commencing early after the wet season. These results should apply to other areas of salt marsh mosquito breeding across northern Australia.

A geospatial evaluation of Aedes vigilax larval control efforts across a coastal wetland, Northern Territory, Australia.

Adjacent to the northern suburbs of Darwin is a coastal wetland that contains important larval habitats for Aedes vigilax (Skuse), the northern salt marsh mosquito. This species is a vector for Ross River virus and Barmah Forest virus, as well as an appreciable human pest. In order to improve aerial larval control efforts, we sought to identify the most important vegetation categories and climatic/seasonal aspects associated with control operations in these wetlands. By using a generalized linear model to compare aerial control for each vegetation category, we found that Schoenoplectus/mangrove areas require the greatest amount of control for tide-only events (30.1%), and also extensive control for tide and rain events coinciding (18.2%). Our results further indicate that tide-affected reticulate vegetation indicated by the marsh grasses Sporobolus virginicus and Xerochloa imberbis require extensive control for Ae. vigilax larvae after rain-only events (44.7%), and tide and rain events coinciding (38.0%). The analyses of vector control efforts by month indicated that September to January, with a peak in November and December, required the most control. A companion paper identifies the vegetation categories most associated with Aedes vigilax larvae population densities in the coastal wetland. To maximize the efficiency of aerial salt marsh mosquito control operations in northern Australia, aerial control efforts should concentrate on the vegetation categories with high larval densities between September and January.

Health effects of kava use in an eastern Arnhem Land Aboriginal community.

BACKGROUND: Heavy kava use in Aboriginal communities has been linked to various health effects, including anecdotes of sudden cardiac deaths. AIMS: To examine associations between kava use and potential health effects. METHODS: A cross-sectional study was carried out within a kava-using east Arnhem Land Aboriginal community in tropical northern Australia. One-hundred-and-one adults who were current, recent or non-users of kava were enrolled in March 2000. Main outcome measures were physical, anthropometric, biochemical, haematological, immunological and neurocognitive assessments. RESULTS: Kava users more frequently showed a characteristic dermopathy (P<0.001). They had increased levels of gamma-glutamyl transferase and alkaline phosphatase (P<0.001). Lymphocyte counts were significantly lower in kava users (P<0.001). Fibrinogen, plasminogen activator inhibitor-1 and neurocognitive tests were not different between kava use categories. IgE and IgG antibodies were elevated across the whole group, as were C-reactive protein and homocysteine. CONCLUSIONS: Kava use was associated with dermopathy, liver function abnormalities and decreased lymphocytes. If kava continues to be used by Aboriginal populations, monitoring should focus on the health consequences of these findings, including a possible increase in serious infections. The interaction between kava, alcohol and other substances requires further study. Although markers of cardiovascular risk are increased across the population, these were not higher in kava users, and this increase may be linked to the large infectious pathogen burden reflective of the socioeconomic disadvantage seen in many remote Aboriginal communities.

Endemic melioidosis in tropical northern Australia: a 10-year prospective study and review of the literature.

In a prospective study of melioidosis in northern Australia, 252 cases were found over 10 years. Of these, 46% were bacteremic, and 49 (19%) patients died. Despite administration of ceftazidime or carbapenems, mortality was 86% (43 of 50 patients) among those with septic shock. Pneumonia accounted for 127 presentations (50%) and genitourinary infections for 37 (15%), with 35 men (18%) having prostatic abscesses. Other presentations included skin abscesses (32 patients; 13%), osteomyelitis and/or septic arthritis (9; 4%), soft tissue abscesses (10; 4%), and encephalomyelitis (10; 4%). Risk factors included diabetes (37%), excessive alcohol intake (39%), chronic lung disease (27%), chronic renal disease (10%), and consumption of kava (8%). Only 1 death occurred among the 51 patients (20%) with no risk factors (relative risk, 0.08; 95% confidence interval, 0.01-0.58). Intensive therapy with ceftazidime or carbapenems, followed by at least 3 months of eradication therapy with trimethoprim-sulfamethoxazole, was associated with decreased mortality. Strategies are needed to decrease the high mortality with melioidosis septic shock. Preliminary data on granulocyte colony-stimulating factor therapy are very encouraging.

Melioidosis: acute and chronic disease, relapse and re-activation.

In melioidosis-endemic regions the importance of re-activation of Burkholderia pseudomallei from latent foci remains unclear. This topic was assessed in a 10-year prospective study (1989-99) of melioidosis in the tropical north of the Northern Territory of Australia, together with other aspects of the nature of melioidosis. Incubation period from defined inoculating events was previously ascertained as 1-21 (mean 9) days. Of 252 total cases 244 (97%) were considered to be from recent acquisition of B. pseudomallei infection and 8 (3%) were considered to be re-activation from a latent focus. Acute illness occurred in 222 (88%) cases; 30 (12%) cases had chronic illness (symptomatic for > 2 months). Of the 207 patients surviving the initial illness, 27 (13%) had a confirmed relapse (mean time from initial diagnosis of 8 months), with 5 relapsing twice. Of these 32 relapses, 15 (3 fatal) were associated with poor adherence to the eradication therapy antibiotics and 10 (none fatal) were failures of eradication with doxycycline monotherapy. Following initial intensive therapy with ceftazidime or meropenem for at least 14 days, eradication therapy with trimethoprim-sulphamethoxazole monotherapy for at least 3 months had been more successful.