Investigating disease persistence in host vector systems: dengue as a case study

The investigation of pathogen persistence in vector-borne diseases is important in different ecological and epidemiological contexts. In this thesis, I have developed deterministic and stochastic models to help investigating the pathogen persistence in host-vector systems by using efficient modelling paradigms. A general introduction with aims and objectives of the studies conducted in the thesis are provided in Chapter 1. The mathematical treatment of models used in the thesis is provided in Chapter 2 where the models are found locally asymptotically stable. The models used in the rest of the thesis are based on either the same or similar mathematical structure studied in this chapter. After that, there are three different experiments that are conducted in this thesis to study the pathogen persistence. In Chapter 3, I characterize pathogen persistence in terms of the Critical Community Size (CCS) and find its relationship with the model parameters. In this study, the stochastic versions of two epidemiologically different host-vector models are used for estimating CCS. I note that the model parameters and their algebraic combination, in addition to the seroprevalence level of the host population, can be used to quantify CCS. The study undertaken in Chapter 4 is used to estimate pathogen persistence using both deterministic and stochastic versions of a model with seasonal birth rate of the vectors. Through stochastic simulations we investigate the pattern of epidemics after the introduction of an infectious individual at different times of the year. The results show that the disease dynamics are altered by the seasonal variation. The higher levels of pre-existing seroprevalence reduces the probability of invasion of dengue. In Chapter 5, I considered two alternate ways to represent the dynamics of a host-vector model. Both of the approximate models are investigated for the parameter regions where the approximation fails to hold. Moreover, three metrics are used to compare them with the Full model. In addition to the computational benefits, these approximations are used to investigate to what degree the inclusion of the vector population in the dynamics of the system is important. Finally, in Chapter 6, I present the summary of studies undertaken and possible extensions for the future work

The impact of disease control measures on the spread of COVID-19 in the province of Sindh, Pakistan

The province of Sindh reported the first COVID-19 case in Pakistan on 26(th) February 2020. The Government of Sindh has employed numerous control measures to limit its spread. However, for low-and middle-income countries such as Pakistan, the management protocols for controlling a pandemic are not always as definitive as they would be in other developed nations. Given the dire socio-economic conditions of Sindh, continuation of province-wise lockdowns may inadvertently cause a potential economic breakdown. By using a data driven SEIR modelling framework, this paper describes the evolution of the epidemic projections because of government control measures. The data from reported COVID-19 prevalence and google mobility is used to parameterize the model at different time points. These time points correspond to the government’s call for advice on the prerequisite actions required to curtail the spread of COVID-19 in Sindh. Our model predicted the epidemic peak to occur by 18(th) June 2020 with approximately 3500 reported cases at that peak, this projection correlated with the actual recorded peak during the first wave of the disease in Sindh. The impact of the governmental control actions and religious ceremonies on the epidemic profile during this first wave of COVID-19 are clearly reflected in the model outcomes through variations in the epidemic peaks. We also report these variations by displaying the trajectory of the epidemics had the control measures been guided differently; the epidemic peak may have occurred as early as the end of May 2020 with approximately 5000 reported cases per day had there been no control measures and as late as August 2020 with only around 2000 cases at the peak had the lockdown continued, nearly flattening the epidemic curve

The separate roles played by the two geographical poles of the NAO in influencing winter precipitation over Spain

In this article, the spatiotemporal relationship between winter (DJF) precipitation over Spain and sea level pressure fields is studied using the Center of Action (COA) approach. The COAs which make up the North Atlantic Oscillation (NAO), i.e., the Azores High (AH) and the Icelandic Low (IL), are considered separately, and we find that interannual variations in the strength and position of the AH explain a very high fraction of the variance of Spain winter precipitation. The correlation of AH properties with winter precipitation is strongest in the northwest of the country. A regression model was developed that explains 83 percent of the variance of the Spain precipitation over 1981-2011. We found that the positive extreme values of AH indices are related to droughts, and negative extremes to heavy rain. The westward and southward shifts of the AH encourage the presence of low pressure system over the Iberian Peninsula and high precipitation in Spain occurs due to the moisture transport off the North Atlantic impinging upon Peninsula Spain and France

The impact of disease control measures on the spread of covid-19 in the province of Sindh, Pakistan

The province of Sindh reported the first COVID-19 case in Pakistan on 26th February 2020. The Government of Sindh has employed numerous control measures to limit its spread. However, for low-and middle-income countries such as Pakistan, the management protocols for controlling a pandemic are not always as definitive as they would be in other developed nations. Given the dire socio-economic conditions of Sindh, continuation of province-wise lockdowns may inadvertently cause a potential economic breakdown. By using a data driven SEIR modelling framework, this paper describes the evolution of the epidemic projections because of government control measures. The data from reported COVID-19 prevalence and google mobility is used to parameterize the model at different time points. These time points correspond to the government\u27s call for advice on the prerequisite actions required to curtail the spread of COVID-19 in Sindh. Our model predicted the epidemic peak to occur by 18th June 2020 with approximately 3500 reported cases at that peak, this projection correlated with the actual recorded peak during the first wave of the disease in Sindh. The impact of the governmental control actions and religious ceremonies on the epidemic profile during this first wave of COVID-19 are clearly reflected in the model outcomes through variations in the epidemic peaks. We also report these variations by displaying the trajectory of the epidemics had the control measures been guided differently; the epidemic peak may have occurred as early as the end of May 2020 with approximately 5000 reported cases per day had there been no control measures and as late as August 2020 with only around 2000 cases at the peak had the lockdown continued, nearly flattening the epidemic curve

Association between maternal experiences of intimate partner violence and child stunting: a secondary analysis of the Demographic Health Surveys of four South Asian countries

Objectives To determine the association between maternal exposure to intimate partner violence (IPV) and child stunting using the Demographic Health Survey (DHS) data comparing four South Asian countries.Design A secondary analysis.Setting Data from the seventh round of the DHS data of four South Asian countries; Pakistan, Nepal, India and Maldives.Participants Married women of reproductive age (15–49 years) from each household were randomly selected, having at least one child less than 5 years of age for whom all anthropometric measures were available.Outcome measure The exposure variable was maternal IPV including, sexual violence, physical violence or both. The outcome variable was moderate or severe stunting, measured based on the height-for-age Z-score of children aged 6–59 months old . Multiple Cox proportional regression analyses were used separately on each country’s data to determine the association between maternal IPV and child stunting.Results The prevalence of IPV among women ranged from 10.17% in the Maldives to 31% in India. The burden of child stunting was the lowest in the Maldives at 14.04% and the highest in Pakistan at 35.86%. The number of severely stunted children was the highest in Pakistan (16.60%), followed by India (14.79%). In India, children whose mothers were exposed to IPV showed a 7% increase in the prevalence of moderate to severe child stunting (OR 1.07; 95% CI 1.01 to 1.14). Additionally, in Nepal, severe stunting was strongly associated with the prevalence of physical IPV (OR 1.66; 95% CI 1.01 to 2.87).Conclusion Our study findings suggest that maternal exposure to IPV is associated with child stunting. Further research investigating the relationship between IPV and child outcomes using improved and advanced statistical analyses can provide substantial evidence to enhance public awareness and potentially reduce the burden of child stunting in South Asian countries

Assessing medical students\u27 perception of cross-cultural competence at a private university in Karachi

Background: Cross-cultural competence is widely regarded to play an important role in being able to deliver appropriate and effective health care to patients with different backgrounds, race, gender orientation and cultural beliefs. This study aims to assess how medical students feel about their comfort, knowledge, and skill level in handling a diverse patient population using a validated questionnaire.Methods: This study was carried out over a period of three weeks from July 5th to July 26th of 2021, in the Aga Khan University Hospital, Karachi, Pakistan. All medical students who fulfilled the eligibility criteria and gave informed consent were included in the study. A modified version of the Harvard cross-cultural care survey was used to assess the medical students\u27 comfort, knowledge and skill level in a variety of circumstances related to patients with different backgrounds and cultures. Descriptive statistical analysis of the questionnaire items was carried out. We reported frequencies and percentages for gender and year of study. For the questionnaire items, we reported mean, assuming that our Likert scale had equivariant intervals. Furthermore, multivariate analysis between demographics and themes was carried out. A p-value of \u3c 0.05 was taken as statistically significant.Results: It was found that students of year 5 considered themselves more knowledgeable, comfortable and skilled in dealing with patients of different backgrounds, religions and beliefs compared to students of year 1 and had a higher average score in all of these categories which was statistically significant. Additionally, students who believed it is extremely important to practice medicine with a diverse patient population also had the highest averages in perceived knowledge, comfort and skills in dealing with patients of different sociocultural backgrounds compared to students who believed it wasn\u27t important at all.Conclusion: This is a first of its kind study in a private medical university in Pakistan and highlights the students\u27 self-assessment of their competence when caring for patients from different backgrounds. This study can be used as a reference study in the region to carry out further studies and to assess and improve the gaps in medical training being provided

Attitudes towards vaccines and intention to vaccinate against COVID-19: a cross-sectional analysis - implications for public health communications in Australia

Objective To examine SARS-CoV-2 vaccine confidence, attitudes and intentions in Australian adults as part of the iCARE Study. Design and setting Cross-sectional online survey conducted when free COVID-19 vaccinations first became available in Australia in February 2021. Participants Total of 1166 Australians from general population aged 18-90 years (mean 52, SD of 19). Main outcome measures Primary outcome: responses to question € If a vaccine for COVID-19 were available today, what is the likelihood that you would get vaccinated?'. Secondary outcome: analyses of putative drivers of uptake, including vaccine confidence, socioeconomic status and sources of trust, derived from multiple survey questions. Results Seventy-eight per cent reported being likely to receive a SARS-CoV-2 vaccine. Higher SARS-CoV-2 vaccine intentions were associated with: increasing age (OR: 2.01 (95% CI 1.77 to 2.77)), being male (1.37 (95% CI 1.08 to 1.72)), residing in least disadvantaged area quintile (2.27 (95% CI 1.53 to 3.37)) and a self-perceived high risk of getting COVID-19 (1.52 (95% CI 1.08 to 2.14)). However, 72% did not believe they were at a high risk of getting COVID-19. Findings regarding vaccines in general were similar except there were no sex differences. For both the SARS-CoV-2 vaccine and vaccines in general, there were no differences in intentions to vaccinate as a function of education level, perceived income level and rurality. Knowing that the vaccine is safe and effective and that getting vaccinated will protect others, trusting the company that made it and vaccination recommended by a doctor were reported to influence a large proportion of the study cohort to uptake the SARS-CoV-2 vaccine. Seventy-eight per cent reported the intent to continue engaging in virus-protecting behaviours (mask wearing, social distancing, etc) postvaccine. Conclusions Most Australians are likely to receive a SARS-CoV-2 vaccine. Key influencing factors identified (eg, knowing vaccine is safe and effective, and doctor's recommendation to get vaccinated) can inform public health messaging to enhance vaccination rates