Causes Of Resurgence Research Articles

Factor Influencing the Resurgence of Brown Planthopper in Bangladesh

Possible causes of brown plant hopper resurgence were determined at the net-house of Entomology Division of Bangladesh Rice Research Institute (BRRI) during 2015. Causes of resurgence in the form of resurgence ratios were higher with acetamiprid, acephate, chlorpyrifos, cypermethrin, deltamethrin, fenvalerate, lambda cyhalothrin, thiamethoxam insecticides compared to imidacloprid, cartap, dinotefuran, isoprocarb /MIPC, phenthoate, pymetrozine when even applied at recommended dose. However, thiamethoxam, imidacloprid, isoprocarb / MIPC and cartap applied at sub-lethal dose produced higher resurgence ratio of BPH than others. Isoprocarb / MIPC, a commonly used recommended insecticide was found to have a higher resurgence ratio with the insecticide treatment at the egg stage (1.71) and combination of all stages (0.82). These insecticides influenced on the growth and reproductive physiology of rice brown planthopper and consequently resurgence ratio ranged increased.
 SAARC J. Agri., 18(1): 117-128 (2020)

Combating pertussis resurgence: One booster vaccination schedule does not fit all

Pertussis has reemerged as a major public health concern in many countries where it was once considered well controlled. Although the mechanisms responsible for continued pertussis circulation and resurgence remain elusive and contentious, many countries have nevertheless recommended booster vaccinations, the timing and number of which vary widely. Here, using a stochastic, age-stratified transmission model, we searched for cost-effective booster vaccination strategies using a genetic algorithm. We did so assuming four hypothesized mechanisms underpinning contemporary pertussis epidemiology: (I) insufficient coverage, (II) frequent primary vaccine failure, (III) waning of vaccine-derived protection, and (IV) vaccine "leakiness." For scenarios I-IV, successful booster strategies were identified and varied considerably by mechanism. Especially notable is the inability of booster schedules to alleviate resurgence when vaccines are leaky. Critically, our findings argue that the ultimate effectiveness of vaccine booster schedules will likely depend on correctly pinpointing the causes of resurgence, with misdiagnosis of the problem epidemiologically ineffective and economically costly.

Modelling the effect of changes in vaccine effectiveness and transmission contact rates on pertussis epidemiology

The incidence of the highly infectious respiratory disease named pertussis or whooping cough has been increasing for the past two decades in different countries, as in much of the highly vaccinated world. A decrease in vaccine effectiveness over time, especially when acellular vaccines were used for primary doses and boosters, and pathogen adaptation to the immunity conferred by vaccines have been proposed as possible causes of the resurgence. The contributions of these factors are not expected to be the same in different communities, and this could lead to different epidemiological trends. In fact, differences in the magnitude and dynamics of pertussis outbreaks as well as in the distribution of notified cases by age have been reported in various regions.Using an age-structured mathematical model designed by us, we evaluated how the changes in some of the parameters that could be related to the above proposed causes of disease resurgence – vaccine effectiveness and effective transmission rates – may impact on pertussis transmission.When a linear decrease in vaccine effectiveness (VE) was assayed, a sustained increase in pertussis incidence was detected mainly in infants and children. On the other hand, when changes in effective transmission rates (βij) were made, a dynamic effect evidenced by the presence of large peaks followed by deep valleys was detected. In this case, greater incidence in adolescents than in children was observed. These different trends in the disease dynamics due to modifications in VE or βij were verified in 18 possible scenarios that represent different epidemiological situations. Interestingly we found that both incidence trends produced by the model and their age distribution resemble the profiles obtained from data reported in several regions. The implications of these correlations are discussed.

The Unexpected Impact of aChlamydia trachomatisInfection Control Program on Susceptibility to Reinfection

After the introduction of a program to control Chlamydia trachomatis infection in British Columbia, Canada, case rates fell from 216 cases/100,000 population in 1991 to 104 cases/100,000 population in 1997. Since 1998, rates have increased, and case counts now exceed those recorded before the intervention. We used Cox proportional-hazards survival analysis and developed a compartmental mathematical model to investigate the cause of resurgence in chlamydia cases. Cox proportional-hazards survival analysis showed that the relative risk of C. trachomatis reinfection has increased 4.6% per year since 1989, with the increased risk greatest among the young and greater among women than men. A compartmental mathematical model of C. trachomatis transmission showed that a control strategy based on shortening the average duration of infection results in an early reduction in prevalence followed by a rebound in prevalence, reproducing the observed trends. We speculate that a C. trachomatis infection control program based on early case identification and treatment interferes with the effects of immunity on population susceptibility to infection and that, in the absence of strategies to alter sexual networks, a vaccine will be needed to halt the spread of infection at the population level.

殺虫剤削減による土着天敵の働きを活かした北海道でのジャガイモのアブラムシ類防除

The possibility of reducing insecticide use for controlling direct sucking damage to potatoes by Aphis gossypii was investigated under field conditions. A laboratory experiment was also conducted to determine the possible cause of resurgence in A. gossypii treated with acephate. The susceptibility of A. gossypii to this insecticide was much lower than that of two other inhabiting aphids (Myzus persicae and Aulacorthum solani) and predators (Harmonia axyridis and Orius minutus), indicating that the resurgence of A. gossypii was probably caused by the elimination of natural enemies and competitors by this insecticide. In the field plot without insecticide application, there was no outbreak of A. gossypii (or other aphid species) observed due to suppression by indigenous predators (ex. ladybirds, lacewings, Orius bugs); e.g., the density of A. gossypii did not exceed 10 insects per compound leaf, and no other insect pests were conspicuous. Consequently, both the tuber yield and the starch value were comparable to those in the insecticide-treated plot. The indigenous predators inhabited the environment around the field over a wide area during the potato-growing season. These findings suggested that there is a possibility of realizing potato cultivation without the application of insecticides.