Field evaluation of the establishment potential of wMelPop Wolbachia in Australia and Vietnam for dengue control

Background

Introduced Wolbachia bacteria can influence the susceptibility of Aedes aegypti mosquitoes to arboviral infections as well as having detrimental effects on host fitness. Previous field trials demonstrated that the wMel strain of Wolbachia effectively and durably invades Ae. aegypti populations. Here we report on trials of a second strain, wMelPop-PGYP Wolbachia, in field sites in northern Australia (Machans Beach and Babinda) and central Vietnam (Tri Nguyen, Hon Mieu Island), each with contrasting natural Ae. aegypti densities.

Methods

Mosquitoes were released at the adult or pupal stages for different lengths of time at the sites depending on changes in Wolbachia frequency as assessed through PCR assays of material collected through Biogents-Sentinel (BG-S) traps and ovitraps. Adult numbers were also monitored through BG-S traps. Changes in Wolbachia frequency were compared across hamlets or house blocks.

Results

Releases of adult wMelPop-Ae. aegypti resulted in the transient invasion of wMelPop in all three field sites. Invasion at the Australian sites was heterogeneous, reflecting a slower rate of invasion in locations where background mosquito numbers were high. In contrast, invasion across Tri Nguyen was relatively uniform. After cessation of releases, the frequency of wMelPop declined in all sites, most rapidly in Babinda and Tri Nguyen. Within Machans Beach the rate of decrease varied among areas, and wMelPop was detected for several months in an area with a relatively low mosquito density.

Conclusions

These findings highlight challenges associated with releasing Wolbachia-Ae. aegypti combinations with low fitness, albeit strong virus interference properties, as a means of sustainable control of dengue virus transmission.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1174-x) contains supplementary material, which is available to authorized users.

The imprinted gene and parent-of-origin effect database

The database of imprinted genes and parent-of-origin effects in animals (http://www.otago.ac.nz/IGC ) is a collation of genes and phenotypes for which parent-of-origin effects have been reported. The database currently includes over 220 entries, which describe over 40 imprinted genes in human, mouse and other animals. In addition a wide variety of other parent-of-origin effects, such as transmission of human disease phenotypes, transmission of QTLs, uniparental disomies and interspecies crosses are recorded. Data are accessed through a search engine and references are hyperlinked to PubMed.

Increasing the amount of leucaena on offer gives faster growth rates of grazing cattle in South East Queensland

We measured the effect of increased supply of leucaena (Leucaena leucocephala cv. Peru) on the growth of steers grazing native pasture in South East Queensland. Steers grazed paddocks of black speargrass (Heteropogon contortus) pasture in which either 0, 25 or 100% of the area was sown to 3 m-wide rows of leucaena. In the 25% leucaena treatment, the leucaena portion was ungrazed in summer. Mimosine toxicity was avoided by dosing cattle with mimosine-detoxifying rumen bacteria. The growth rate of steers increased with the proportion of the paddock covered by leucaena. Steers grazing paddocks with 0, 25, and 100% of the paddock covered by leucaena rows gained 90, 127 and 205 kg/steer.year, respectively. The amount of leucaena foliage on offer appeared to be the major factor increasing steer growth.

The pH dependent platelet utilization of arachidonic acid and a thromboxane A2 mimetic, in vitro

The effects of carbon dioxide (CO2) and pH on platelet aggregation in vitro have been studied to simulate pH changes observed in tissue fluid stasis and inflammation. Platelet aggregation induced by the 7-oxabicycloheptane mimetic of thromboxane A2 (TxA2) showed increased sensitivity in CO2-treated platelet-rich plasma (PRP). This effect is similar to that previously reported for arachidonate-induced aggregation. In contrast, aggregation of washed platelet suspensions (i.e. protein-free), in response to both arachidonate and TxA2 mimetic, was inhibited under acid conditions. These results confirm the importance of plasma proteins in the control of platelet function and support the hypothesis that the pH effects are dependent on these proteins.

Increased sensitivity of arachidonic acid-induced platelet aggregation in the presence of carbon dioxide

The effects of carbon dioxide on citrated human platelet-rich plasma (PRP) have been studied as a means of imitating the changes in pH and PCO2 observed in inflammation and tissue fluid stasis. Adenosine diphosphate (ADP)-induced platelet aggregation was inhibited in CO2-treated PRP. In contrast, CO2-treated platelets were rendered up to eight times more sensitive to sodium arachidonate and this effect could be imitated by the addition of exogenous calcium 1 min before the addition of arachidonate. The effects of CO2 on ADP-induced and arachidonate-induced aggregation were abolished if the CO2 was allowed to disperse from treated PRP subsequently exposed to air, suggesting no permanent alteration in platelet metabolism. The increased sensitivity of arachidonate-induced aggregation with lowered pH may be a significant factor in influencing platelet behaviour in haemostasis.

Standardization of prekallikrein activator (PKA): the 1st British reference preparation for PKA

A collaborative study on prekallikrein activator (PKA) has been carried out involving four laboratories for the purpose of establishing a British reference preparation for PKA. Samples of two plasma protein fractions (PPF) were assayed against participants' own supplies of the Bureau of Biologics Reference Preparation No. 2 (BoB 2). There was good agreement on the relative PKA activities of the two preparations. One of the preparations, coded 79/572, was established as the 1st British Reference Preparation for Prekallikrein Activator, with an assigned potency of 78.9 units/ml.