Within-farm transmission characteristics of bluetongue virus serotype 8 in cattle and sheep in the Netherlands, 2007-2008.

In 2006 and 2007, sheep and cattle farms in the Netherlands were affected by an epidemic of bluetongue virus serotype 8 (BTV-8). In order to obtain insight into the within-farm spread of the virus, five affected cattle and five affected sheep farms were longitudinally monitored between early 2007 and mid or late 2008. The farms were visited between four and seven times to collect blood samples. During each visit, all animals present in the flock or herd were sampled. The samples were analysed for the presence of BTV-8 antibodies (ELISA) and BTV-8 antigen (rRT-PCR). The observed patterns of RT-PCR positives indicate a rapid within-farm virus spread during the vector season. During vector-free periods we observed a complete rRT-PCR positivity decline within a few months. During the vector season a lower bound estimate of the basic reproduction number (R0) ranges from 2.9-6.9 in the cattle herds (one herd not analysed), and from 1.3-3.2 in the sheep flocks in this study.

Feasibility of eliminating visceral leishmaniasis from the Indian subcontinent: explorations with a set of deterministic age-structured transmission models.

BACKGROUND: Visceral leishmaniasis (VL) is a neglected tropical disease transmitted by sandflies. On the Indian subcontinent (ISC), VL is targeted for elimination as a public health problem by 2017. In the context of VL, the elimination target is defined as an annual VL incidence of <1 per 10,000 capita at (sub-)district level. Interventions focus on vector control, surveillance and on diagnosing and treating VL cases. Many endemic areas have not yet achieved optimal control due to logistical, biological as well as technical challenges. We used mathematical modelling to quantify VL transmission dynamics and predict the feasibility of achieving the VL elimination target with current control strategies under varying assumptions about the reservoir of infection in humans. METHODS: We developed three deterministic age-structured transmission models with different main reservoirs of infection in humans: asymptomatic infections (model 1), reactivation of infection after initial infection (model 2), and post kala-azar dermal leishmaniasis (PKDL; model 3). For each model, we defined four sub-variants based on different assumptions about the duration of immunity and age-patterns in exposure to sandflies. All 12 model sub-variants were fitted to data from the KalaNet study in Bihar (India) and Nepal, and the best sub-variant was selected per model. Predictions were made for optimal and sub-optimal indoor residual spraying (IRS) effectiveness for three different levels of VL endemicity. RESULTS: Structurally different models explained the KalaNet data equally well. However, the predicted impact of IRS varied substantially between models, such that a conclusion about reaching the VL elimination targets for the ISC heavily depends on assumptions about the main reservoir of infection in humans: asymptomatic cases, recovered (immune) individuals that reactivate, or PKDL cases. CONCLUSIONS: Available data on the impact of IRS so far suggest one model is probably closest to reality (model 1). According to this model, elimination of VL (incidence of <1 per 10,000) by 2017 is only feasible in low and medium endemic settings with optimal IRS. In highly endemic settings and settings with sub-optimal IRS, additional interventions will be required.

Direct and indirect effects of pollutants on algae and algivorous ciliates in an aquatic indoor microcosm.

An aquatic indoor microcosm was used to study effects of the pesticides parathion-methyl and prometryn on phototrophic flagellates (Cryptomonas sp.) and predatory ciliates (Urotricha furcata). Parathion-methyl caused effects to flagellates and ciliates at the range of low mg L(-1), regardless of whether the organisms were exposed separately or combined in the multi-species test system. Prometryn caused effects on the flagellates at low microg L(-1) concentrations, resulting in a NOEC of 6.9 microg L(-1) in the single-species test and a NOEC of 15.2 microg L(-1) in the multi-species microcosm. For ciliates the NOEC decreased by factor 145 in the multi-species test compared to the NOEC of 2.2 mg L(-1) in the single-species test when exposed to prometryn. The lower NOEC for ciliates exposed to prometryn in the microcosm was most likely caused by an indirect effect due to reduced availability of flagellates as food. The measurement of nutrient concentrations in the test media and organisms facilitated the modelling of effects. The presented aquatic indoor microcosm is considered as a tool which could be standardised and applied as an instrument to provide data for higher tier risk assessment.