To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure no-reply@cambridge.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Prior observational studies have reported conflicting results regarding whether antidepressant treatment reduces long-term dementia risk, likely due to confounding by indication and reverse causation. We aimed to investigate the association between baseline antidepressant use and incident dementia, incorporating cognitive and neuroimaging outcomes.
Methods
We conducted a prospective cohort study using UK Biobank participants free of dementia at baseline. Antidepressant use was self-reported at baseline (2006–2010). Incident dementia was identified through linked electronic health records until December 19, 2022. Cox proportional hazards models estimated hazard ratios (HRs) for all-cause dementia, Alzheimer’s disease (AD), and vascular dementia (VD), adjusting for sociodemographic, lifestyle, health-related, antidepressant indication factors, and co-medication of other anticholinergics. In subsamples, cognitive performance (n = 57,330) and structural brain imaging (n = 42,276) were examined as intermediate outcomes.
Results
Among 461,464 participants, 33,721 (7.3%) reported baseline antidepressant use. Over a mean follow-up of 13.4 years, 7,922 (1.7%) developed incident dementia. Baseline antidepressant use was associated with higher risks of all-cause dementia (adjusted HR: 1.47, 95% CI 1.36–1.60), AD (1.53, 1.36–1.73), and VD (1.44, 1.23–1.70). Users performed worse on fluid intelligence and prospective memory tasks and showed lower total and gray matter volume, regional reductions in the hippocampal gray matter and basal nucleus, and greater white matter hyperintensity volume.
Conclusions
Baseline antidepressant use was linked to a higher risk of dementia, poorer cognitive performance, and adverse brain structural changes. These findings underscore the importance of judicious prescribing, regular cognitive monitoring, and consideration of non-pharmacological approaches in clinical care.
In intensive livestock and poultry production systems, animals are often exposed to environmental and physiological stressors that impair intestinal barrier function and growth performance. Akkermansia muciniphila (AKK) has gained attention as a next-generation probiotic. However, its practical application is often hindered by its strict anaerobic nature and sensitivity to feed processing conditions. In this review, the AKK secretome is defined as the total collection of bioactive factors released or shed into the extracellular space, encompassing functional proteins, extracellular vesicles, metabolic by-products, and cell envelope-derived fragments, which collectively constitute the cell-free supernatant. This review summarizes current knowledge on the molecular components of AKK secretome and discusses its potential application as a functional feed additive. At the mechanistic level, AKK secretome supports intestinal epithelial integrity by regulating tight junctions through TLR2 signaling and promoting mucosal repair via Wnt/β-catenin-dependent stem cell activity. Individual components of the secretome, including branched-chain phospholipids, the AmTARS protein, and Amuc_1100, contribute to immune homeostasis and Nrf2-mediated redox regulation, respectively, thereby increasing host tolerance to oxidative stress. For animal production applications, AKK secretome has several practical advantages over live bacterial preparations, such as improved thermal stability during processing and reduced biosafety concerns related to bacterial translocation and antibiotic resistance gene transfer. In conclusion, the AKK secretome represents a promising and practical strategy for translating mechanistic insights into effective interventions for stress mitigation in modern animal production systems.
Although children with cochlear implants (CIs) have limited access to pitch information due to the suboptimal device transmission, durational cues are relatively well preserved, allowing for the acquisition of prosodic cues needed for communication. Recent findings show that Mandarin-speaking preschoolers with CIs can produce prosodic cues (e.g., duration and pitch) to disambiguate noun-noun compounds (e.g., xiong-mao “panda”) and lists (e.g., xiong, mao “bear, cat”), with those implanted early (before age 2) demonstrating production patterns similar to their typical hearing (TH) peers. This then raises questions about these children’s ability to perceive prosodic cues, and if early implantation again enhances their performance. These questions were investigated using a two-alternative forced-choice task with 57 Mandarin-speaking preschoolers with CIs and 66 TH peers. The results show that all preschoolers can perceive the prosodic cues needed to identify compounds but not lists, suggesting that, like English, the mapping between prosodic cues and postlexical meaning is also acquired late in children learning a tonal language. In terms of the effect of CIs, those implanted before age 2 performed as well as their TH peers. These findings suggest that preschoolers may rely more on other linguistic information rather than prosodic cues when comprehending compounds and lists, offering cross-linguistic evidence for this tendency. Furthermore, interventions for preschoolers with CIs should support the mapping of prosodic cues to discourse functions rather than just vocabulary training, improving daily communicative abilities.
Increasing evidences show that inflammation might be involved in bipolar disorder (BD), but the association between abnormal brain function and inflammation in BD is still unclear. In this study, we tried to explore the disrupted brain functional network topology, peripheral inflammatory cytokine levels, and their correlations in unmedicated bipolar II depression (BDII-D).
Methods
In this study, 65 individuals with unmedicated BDII-D and 50 healthy controls (HCs) underwent resting-state magnetic resonance imaging scans. Graph theory analysis was performed to investigate the topological properties of the whole-brain functional connectome at both global and nodal levels. Besides, serum levels of 17 inflammatory cytokines were measured in both BDII-D and HCs. Correlations between topological properties, clinical variables, and peripheral inflammatory cytokine levels in BDII-D were calculated.
Results
Compared with HCs, at the global level, BDII-D showed significantly higher $ \lambda $, decreased $ \gamma $, $ \sigma $, Eglo, and Eloc; at the nodal level, BDII-D showed decreased Enodal in the right olfactory cortex, left pallidum, and vermis. Besides, BDII-D showed higher levels of interleukin-8 (IL-8), interleukin-10 (IL-10), and granulocyte colony-stimulating factor (G-CSF) compared with the HCs. In BDII-D, $ \gamma $ and $ \sigma $ were significantly negatively correlated with the Hamilton Depression Rating Scale (HDRS) scores and number of episodes. Also, IL-8 level showed significant negative correlation with $ \gamma $, $ \sigma $, and Enodal of the left pallidum in BDII-D.
Conclusions
Reduced information segregation and integration, and lower nodal efficiency in the left pallidum were associated with proinflammatory cytokine IL-8 level and might contribute to severe depressive symptoms in unmedicated BDII-D.
This study explored the effects of different preparations of Akkermansia muciniphila (AKK) on the gut microbiota and jejunal transcriptome of lipopolysaccharide (LPS) challenged yellow-feathered broilers. A total of 100 one-day-old broilers were divided into five groups, including control group (Control), LPS injection (LPS), gavage of AKK broth culture plus LPS injection (AKK), gavage of viable AKK suspension plus LPS injection (Active) and gavage of heat-inactivated AKK suspension plus LPS injection (Inactive). Growth performance results showed that LPS significantly reduced the body weight of broilers. Alpha diversity showed no significant group differences. At the phylum level, Firmicutes was significantly lower in groups with AKK gavage. At the genus level, Bacteroides was relatively more abundant, whereas Streptococcus was numerically less abundant in AKK-treated groups. The Active group had the highest abundance of Akkermansia. Transcriptome analysis revealed the Inactive group had significantly lower Occludin. Combined KEGG and GO analyses revealed that the LPS challenge suppressed innate immunity by downregulating the Retinoic acid-inducible gene (RIG)-I-like receptor signaling pathway. In response, different interventions distinctly modulated the transcriptome. The AKK group counteracted this suppression by upregulating innate immune and antiviral defense responses. The Active group primarily influenced metabolism, downregulating pathways for drug and glutathione metabolism and xenobiotic responses while upregulating retinol metabolism. In addition, the Inactive group demonstrated an upregulation of ribosome biogenesis, and energy metabolism, suggesting a restoration of core cellular functions. In summary, all gavaged AKK preparations maintained broiler gut microbiome stability, while AKK broth culture demonstrated superior efficacy in alleviating LPS-induced jejunal stress.
To determine values for the digestible indispensable amino acid score (DIAAS), it is recommended that ileal amino acid (AA) digestibility values obtained in growing pigs are used to characterise protein quality in different foods. Therefore, an experiment was conducted to determine the standardised ileal digestibility (SID) of AA in eight energy ingredients (barley, sorghum, wheat, brown rice, rice bran, wheat bran, cassava and paddy rice) fed to pigs, where SID values in pigs can be used to calculate approximate DIAAS values in humans. Among the data obtained for all energy ingredients, significant variations (P < 0·01) in CP and AA composition were observed. Rice bran and wheat bran had the highest CP (16·43 % and 18·16 %, respectively) and DIAAS scores of 81–88 for adult, qualifying as ‘good’ protein sources (> 75). Cassava, with the lowest CP (2·74 %), was limited by sulphur amino acid (54). Lysine (Lys) was the first-limiting AA in barley (74), sorghum (51) and wheat (49), with SID values lowest in wheat (71·04 %). Brown rice and paddy rice showed higher SIDLys (87·51 % and 78·13 %, respectively). These findings highlight the potential of bran-based ingredients and Lys fortification to improve protein quality in grain-dependent diets, providing the scientific basis to combat protein malnutrition.
Solidification of droplets is of great importance to various technological applications, drawing considerable attention from scientists aiming to unravel the fundamental physical mechanisms. In the case of multicomponent droplets undergoing solidification, the emergence of concentration gradients may trigger significant interfacial flows that dominate the freezing dynamics. Here, we experimentally investigate the fascinating interfacial freezing dynamics of supercooled ethanol–water droplets, accompanied with the migration and growth of massive ice particles. We reveal that this unique freezing dynamics is driven by solidification-induced solutal Marangoni flow within the droplets. Our model, which incorporates the temperature- and concentration-dependent properties of the ethanol–water mixture, quantitatively predicts both the migration velocity and the growth rate of the ice particles. The former is determined by the solutal Marangoni flow velocity, while the latter is governed by a balance between the latent heat release and the enhanced thermal dissipation by the Marangoni flow. Moreover, we show that the final wrapping state of droplets can be modulated by the concentration of ethanol. Our findings may pave the way for novel insights into the physicochemical hydrodynamics of multicomponent liquids undergoing phase transitions.
African swine fever (ASF) is a highly contagious animal disease caused by African swine fever virus (ASFV). It is listed by the World Organization for Animal Health (WOAH) as an animal disease subject to statutory reporting. ASFV, a large, enveloped double-stranded DNA virus with high genomic complexity, exhibits a case fatality rate of up to 100%, posing a significant threat to the global pig industry and food safety. To date, the absence of a safe commercial ASFV vaccine primarily stems from challenges in identifying immunogenic viral antigens, insufficient characterization of ASFV pathogenesis, and limited understanding of the virus’s immune evasion mechanisms. Here, we review the pathogenic characteristics (morphological structure, clinical symptoms, and epidemiological characteristics), molecular biological characteristics, and infection mechanism of ASFV, as well as the immune response mechanism, vaccine research, and the latest information on ASFV in other areas. This review will be in favour of understanding the current state of knowledge of ASF and developing effective vaccines to control this disease.
This article shows that when a compensation peer firm experiences a significant failure in its say-on-pay (SOP) voting, the focal firm’s stock price is adversely affected, resulting in reduced CEO pay in the subsequent period. This pay-reduction effect is amplified when the board is more powerful, when proxy advisors express concerns about CEO pay, and when the compensation consultant lacks quality. Directors who react to the price drop and cut the CEO’s pay receive higher votes in future director elections, implying a market feedback effect for directors of the focal firm triggered by their peers’ SOP voting failure.
Turbulence amplification is crucial in shock-wave/turbulent boundary layer interaction (SWTBLI). To examine the impact of interaction intensity on turbulence amplification and inter-component energy transfer, direct numerical simulations of impinging oblique shock reflections at strong ($37^\circ$) and weak ($33.2^\circ$) incident angles are conducted. The results indicate that strong interaction generates a larger permanent separation zone, featuring the unique ‘oblique platform’ in Reynolds stress peaks and ‘secondary turbulence amplification’ downstream. Reynolds stress budget and spanwise spectral analyses reveal that $\widetilde {u^{\prime \prime}u^{\prime \prime}}$ and $-\!\widetilde{\ u^{\prime\prime}v^{\prime\prime}}$ amplify primarily by production terms. $u''$, $v''$ and $w''$ represent the streamwise, wall-normal and spanwise velocity fluctuations. At the investigated Reynolds number, deceleration effect dominates the initial amplification of $\widetilde {u^{\prime \prime}u^{\prime \prime}}$, influencing multi-scale wall-bounded turbulence structures, while shear effect remains active along the shear layer and may primarily affects streaky structures. The initial amplification of $-\!\widetilde{\ u^{\prime\prime}v^{\prime\prime}}$ is driven by the adverse pressure gradient, which reshapes the velocity profile and affects the wall-normal velocity. The primary energy for $\!\widetilde{\ v^{\prime\prime}v^{\prime\prime}}$ and $\widetilde {w^{\prime \prime}w^{\prime \prime}}$ amplification originates from $\widetilde{ u^{\prime \prime}u^{\prime \prime}}$ via the pressure-strain term. The delayed amplification of $\!\widetilde{\ v^{\prime\prime}v^{\prime\prime}}$ is influenced by its production term and energy redistribution, with $\widetilde {w^{\prime \prime}w^{\prime \prime}}$ exhibiting higher spectral consistency with $\widetilde {u^{\prime \prime}u^{\prime \prime}}$ and receiving more energy. In strong interaction, the ‘oblique platform’ serves as a stable dissipation region, formed by increased separation–incident shock distance, characterised by progressively concentrated stress spectra and the transition to large-scale streaks. The downstream ‘secondary amplification’ process resembles the initial amplification near the separation shock foot, driven by intermittent compression waves that strengthen shear instabilities and the deceleration effect. These findings detail the streamwise stress evolution, providing a more comprehensive turbulence amplification mechanism in SWTBLI.
Depression is closely associated with abnormalities in brain function. Traditional static functional connectivity analyses offer limited insight into the temporal variability of brain activity. Recent advances in dynamic analyses enable a deeper understanding of how depression relates to temporal fluctuations in brain activity.
Methods
This study utilized a large resting-state functional magnetic resonance imaging dataset (N = 696) to examine the association between brain dynamics and depression. Two complementary approaches were employed. Hidden Markov modeling (HMM) was used to identify discrete brain states and quantify their temporal switching patterns; temporal variability was computed within and between large-scale functional networks to capture time-varying fluctuations in functional connectivity.
Results
Depression scores were positively associated with switching rate and negatively associated with maximum fractional occupancy. Furthermore, depression scores were significantly associated with greater temporal variability both within and between networks, with particularly strong effects observed in the default mode network, ventral attention network, and frontoparietal network. Together, these findings suggest that individuals with higher depression scores exhibit more unstable brain dynamics.
Conclusion
Our findings reveal that individuals with higher depression levels exhibit greater instability in brain state transitions and increased temporal variability in functional connectivity across large-scale networks. This instability in brain dynamics may contribute to difficulties in emotion regulation and cognitive control. By capturing whole-brain temporal patterns, this study offers a novel perspective on the neural basis of depression.
Cavitation bubble pulsation and liquid jet loads are the main causes of hydraulic machinery erosion. Methods to weaken the load influences have always been hot topics of related research. In this work, a method of attaching a viscous layer to a rigid wall is investigated in order to reduce cavitation pulsations and liquid jet loads, using both numerical simulations and experiments. A multiphase flow model incorporating viscous effects has been developed using the Eulerian finite element method (EFEM), and experimental methods of a laser-induced bubble near the viscous layer attached on a rigid wall have been carefully designed. The effects of the initial bubble–wall distance, the thickness of the viscous layer, and the viscosity on bubble pulsation, migration and wall pressure load are investigated. The results show that the bubble migration distance, the normalised thickness of the oil layer and the wall load generally decrease with the initial bubble–wall distance or the oil-layer parameters. Quantitative analysis reveals that when the initial bubble–wall distance remains unchanged, there exists a demarcation line for the comparison of the bubble period and the reference period (the bubble period without viscous layer under the same initial bubble–wall distance), and a logarithmic relationship is observed that $\delta \propto \log_{10} \mu ^*$, where $\delta =h/R_{max}$ is the thickness of the viscous layer h normalised by the maximum bubble radius $R_{max}$, $\mu ^* = \mu /({R_{max }}\sqrt {{\rho }{{\mathop {P}\nolimits } _{{atm}}}})$ is the dynamic viscosity $\mu$ normalised by water density $ \rho $ and atmospheric pressure $P_{atm}$. The results of this paper can provide technical support for related studies of hydraulic cavitation erosion.
Compounds (e.g., jellybeans) and list forms (e.g., jelly, beans) can be distinguished by the presence or absence of boundaries, marked by durational and pitch cues. Studies have shown that 5-year-olds learning English have acquired both cues for distinguishing compounds and lists. However, it is not clear how and when this ability is acquired by children speaking tonal languages, such as Mandarin. This study examined whether Mandarin-speaking preschoolers can use durational and pitch cues to distinguish compounds and lists and whether their productions are adult-like. Thirty-one 4-year-olds, 34 5-year-olds, 29 6-year-olds, and 43 adults participated in an elicited production experiment. Results showed that similar to English-speaking preschoolers, Mandarin-speaking preschoolers can use durational cues to mark boundaries, triggering appropriate pitch changes for distinguishing compounds and lists, though these were not fully adult-like, even in the oldest age group.
The effect of the polarizations of two counter-propagating relativistic laser pulses interacting with subwavelength thin solid-density foil is investigated. Three-dimensional particle-in-cell simulations and analytical modelling show that the interaction and resulting transverse instability depend strongly on the polarization directions as well as the intensity distribution of the resultant light field in the foil. The left- and right-handed circularly polarized laser pair with the same phase at the common focal spot in the ultrathin foil leads to the strongest distortion of the foil. The fastest growing mode and maximum growth rate depend mainly on the laser intensity. For all polarization and phase-difference combinations, the instability is weakest when the two laser pulses are exactly out of phase at the common focusing point in the foil.
The spatio-temporal scales, as well as a comprehensive self-sustained mechanism of the reattachment unsteadiness in shock wave/boundary layer interaction, are investigated in this study. Direct numerical simulations reveal that the reattachment unsteadiness of a Mach 7.7 laminar inflow causes over $26\,\%$ variation in wall friction and up to $20\,\%$ fluctuation in heat flux at the reattachment of the separation bubble. A statistical approach, based on the local reattachment upstream movement, is proposed to identify the spanwise and temporal scales of reattachment unsteadiness. It is found that two different types, i.e. self-induced and random processes, dominate different regions of reattachment. A self-sustained mechanism is proposed to comprehend the reattachment unsteadiness in the self-induced region. The intrinsic instability of the separation bubble transports vorticity downstream, resulting in an inhomogeneous reattachment line, which gives rise to baroclinic production of quasi-streamwise vortices. The pairing of these vortices initiates high-speed streaks and shifts the reattachment line upstream. Ultimately, viscosity dissipates the vortices, triggering instability and a new cycle of reattachment unsteadiness. The temporal scale and maximum vorticity are estimated with the self-sustained mechanism via order-of-magnitude analysis of the enstrophy. The advection speed of friction, derived from the assumption of coherent structures advecting with a Blasius-type boundary layer, aligns with the numerical findings.
Pebrine disease, caused by Nosema bombycis (Nb) infection in silkworms, is a severe and long-standing disease that threatens sericulture. As parasitic pathogens, a complex relationship exists between microsporidia and their hosts at the mitochondrial level. Previous studies have found that the translocator protein (TSPO) is involved in various biological functions, such as membrane potential regulation, mitochondrial autophagy, immune responses, calcium ion channel regulation, and cell apoptosis. In the present study, we found that TSPO expression in silkworms (BmTSPO) was upregulated following Nb infection, leading to an increase in cytoplasmic calcium, adenosine triphosphate, and reactive oxygen species levels. Knockdown and overexpression of BmTSPO resulted in the promotion and inhibition of Nb proliferation, respectively. We also demonstrated that the overexpression of BmTSPO promotes host cell apoptosis and significantly increases the expression of genes involved in the immune deficiency and Janus kinase-signal transducer and the activator of the transcription pathways. These findings suggest that BmTSPO activates the innate immune signalling pathway in silkworms to regulate Nb proliferation. Targeting TSPO represents a promising approach for the development of new treatments for microsporidian infections.
As a promising machine learning method for active flow control (AFC), deep reinforcement learning (DRL) has been successfully applied in various scenarios, such as the drag reduction for stationary cylinders under both laminar and weakly turbulent conditions. However, current applications of DRL in AFC still suffer from drawbacks including excessive sensor usage, unclear search paths and insufficient robustness tests. In this study, we aim to tackle these issues by applying DRL-guided self-rotation to suppress the vortex-induced vibration (VIV) of a circular cylinder under the lock-in condition. With a state space consisting only of the acceleration, velocity and displacement of the cylinder, the DRL agent learns an effective control strategy that successfully suppresses the VIV amplitude by $99.6\,\%$. Through systematic comparisons between different combinations of sensory-motor cues as well as sensitivity analysis, we identify three distinct stages of the search path related to the flow physics, in which the DRL agent adjusts the amplitude, frequency and phase lag of the actions. Under the deterministic control, only a little forcing is required to maintain the control performance, and the VIV frequency is only slightly affected, showing that the present control strategy is distinct from those utilizing the lock-on effect. Through dynamic mode decomposition analysis, we observe that the growth rates of the dominant modes in the controlled case all become negative, indicating that DRL remarkably enhances the system stability. Furthermore, tests involving various Reynolds numbers and upstream perturbations confirm that the learned control strategy is robust. Finally, the present study shows that DRL is capable of controlling VIV with a very small number of sensors, making it effective, efficient, interpretable and robust. We anticipate that DRL could provide a general framework for AFC and a deeper understanding of the underlying physics.
Aphis spiraecola Patch is one of the most economically important tree fruit pests worldwide. The pyrethroid insecticide lambda-cyhalothrin is commonly used to control A. spiraecola. In this 2-year study, we quantified the resistance level of A. spiraecola to lambda-cyhalothrin in different regions of the Shaanxi province, China. The results showed that A. spiraecola had reached extremely high resistance levels with a 174-fold resistance ratio (RR) found in the Xunyi region. In addition, we compared the enzymatic activity and expression level of P450 genes among eight A. spiraecola populations. The P450 activity of A. spiraecola was significantly increased in five regions (Xunyi, Liquan, Fengxiang, Luochuan, and Xinping) compared to susceptible strain (SS). The expression levels of CYP6CY7, CYP6CY14, CYP6CY22, P4504C1-like, P4506a13, CYP4CZ1, CYP380C47, and CYP4CJ2 genes were significantly increased under lambda-cyhalothrin treatment and in the resistant field populations. A L1014F mutation in the sodium channel gene was found and the mutation rate was positively correlated with the LC50 of lambda-cyhalothrin. In conclusion, the levels of lambda-cyhalothrin resistance of A. spiraecola field populations were associated with P450s and L1014F mutations. Our combined findings provide evidence on the resistance mechanism of A. spiraecola to lambda-cyhalothrin and give a theoretical basis for rational and effective control of this pest species.
As frontline workers, pharmacists often face significant work stress, especially in psychiatric settings. A multicenter cross-sectional design was conducted in 41 psychiatric hospitals. The Depression, Anxiety and Stress Scale–21 (DASS-21) was used to measure the mental health of 636 pharmacists. We also collected demographic data and work-related variables. The prevalence of depression, anxiety and stress was 20.60%, 22.96% and 8.96%, respectively. Multivariate logistic regression showed that several common factors were associated with depression, anxiety and stress, including professional identity (odds ratio [OR] = 0.132, 0.381 and 0.352) and verbal violence (OR = 2.068, 2.615 and 2.490). Those who were satisfied with their job were less likely to develop depression (OR = 0.234) or anxiety (OR = 0.328). We found specific factors associated with mental health. Older age (OR = 1.038) and perceived negative impact (OR = 2.398) of COVID-19 on medical work were associated with anxiety, and those with frontline experience with COVID-19 patients (OR = 2.306) were more likely to experience stress. More than one-fifth of pharmacists in psychiatric hospitals experienced symptoms of depression or anxiety during the pandemic, highlighting the need for policy change to improve workplace conditions and psychological well-being for this professional group.
This paper is concerned with a nonlocal reaction–diffusion system with double free boundaries and two time delays. The free boundary problem describes the evolution of faecally–orally transmitted diseases. We first show the well-posedness of global solution, and then establish the monotonicity and asymptotic property of basic reproduction number for the epidemic model without delays, which is defined by spectral radius of the next infection operator. By introducing the generalized principal eigenvalue defined in general domain, we obtain an upper bound of the limit value of basic reproduction number. We discuss the spreading and vanishing phenomena in terms of the basic production number. By employing the perturbed approximation method and monotone iteration method, we establish the existence, uniqueness and monotonicity of solution to semi-wave problem. When spreading occurs, we determine the asymptotic spreading speeds of free boundaries by constructing suitable upper and lower solutions from the semi-wave solutions. Moreover, spreading speeds for partially degenerate diffusion case are provided in a similar way.