When chronic diseases meet infectious diseases, a proposal toward healthy aging: lessons from COVID-19 outbreak

As the novel COVID-19 disease spreads around the world, the most affected population are those who suffer from the most common chronic diseases, such as obesity, hypertension, and type 2 diabetes, which are quite associated with the so-called age-related diseases. On the other hand, since the Spanish influenza outbreak, humanity has not experienced an infectious disease that synergizes so quickly with chronic diseases, making it mortal for those individuals with comorbidities. In this context, COVID-19 is challenging for health systems all around the world due to the high prevalence of chronic diseases. Nowadays, we are facing the beginning of a new era in which health infectious and chronic diseases meet. Therefore, epidemiologic and biomedical researchers must work together to solve further contingencies, and politicians should direct science-centered decisions on public health. In the present paper, we make an urgent call to learn from the COVID-19 lessons in order to mitigate the chronic diseases prevalence and to address the influence of the infectious diseases on the aging process; since we are about to begin the Decade of Healthy Aging.


The rise of chronic and viral diseases
In the last 30 years, there have been several viral outbreaks that impact human health and influence our way of living since its acquisition depends on sexual practices (HIV, HPV, Herpes virus, HAV), food intake (SARS-CoV, MERS, Ebola), seasonal climate (Influenza, rhinoviruses, metapneumovirus, mainly), travel or living in tropical areas (Zika, Dengue, Chikungunya), to poor water and sanitation (HAV, Ebola, Dengue, Zika, among others), and more recently to anti-vaccine practices (Measles). Among the most representative viral outbreaks stand out those that have been extraordinarily contagious or lethal. For instance, since HIV emerged in the 1980s, it has accumulated 32 million deaths and 75 million infections worldwide (WHO 2019). Moreover, according to the Center CDC data from 2017-2018, influenza infected 9,3 -45 million people, causing 810,000 hospitalizations and 61,000 of deaths in the USA alone (CDC 2020).

Chronic diseases become the individual vulnerable to infectious diseases.
Chronic diseases, also known as noncommunicable diseases have been defined by Centers for Disease Control and Prevention (CDC) as "conditions that last one year or more and require ongoing medical attention or limit activities of daily living or both". Additionally, this cluster of diseases experienced a severe increase of its prevalence over the last years, due to the poor nutrition (high-fat and carbohydrate enriched diets), the sedentary lifestyle and to the increase of life expectancy and increased longevity over the last years (aging) (Black et al. 2012).
The World Health Organization (WHO) reports five chronic diseases (cardiovascular diseases, diabetes, cancer, obesity, and chronic respiratory disease) which represent the primary concern in public health worldwide, since they are partially responsible of both disability and early death ('WHO | Integrated chronic disease prevention and control', 2010). Additionally, as Table 1 describes, chronic diseases impaired the immune system due to the sustained chronic inflammation representative of this cluster of diseases. On the other hand, the prevalence of chronic diseases is quite common during aging, an in several cases they are closely related to the development of the so-called age-related diseases and the enhanced immunosenescence (Barzilai et al. 2018;Tchkonia and Kirkland 2018).  As mentioned above, most of the chronic diseases are related to aging, highlighting the relevance of immunosenescence and the molecular pillars of aging. Therefore, it is crucial to reconsider opening a new epidemiological panorama where infectious diseases meet chronic conditions, in order to develop effective approaches to address its impact on the elderly population. Otherwise, the evil triad will increase mortality abruptly as occurs in frailty HIV positive individuals due to the immune exhaustion, accelerated aging and precipitated immunosenescence (Álvarez et al. 2020); or as occurs nowadays in the novel COVID-19 outbreak in which the main victims are those with hypertension, obesity, and diabetes.

Conclusions
COVID-19 is giving us painful lessons at different levels about healthcare and science systems performance around the world. In this context, the consequences of sustaining both sedentary and poor nutritional lifestyles (for many years) lead to the development of chronic diseases that later impact negatively on the immunological system, and in the impaired immune response during aging. The first lesson should be considered for the politicians, and the health professionals since our public health care systems need to be improved, to guarantee access to medical services for the population. To achieve this goal is necessary to strengthen the public health systems and to avoid budget reductions; this will help be prepared to attend any contingency. Another lesson is that we urgently need scientists, physicians, and public health professionals to work together with both pharmaceutical and food-processing industries to develop new strategies which target the etiological agents responsible for chronic diseases, efficiently. Finally, we encourage the government and politicians to follow scientific evidence and establish interdisciplinary networks of specialists to lead and find alternatives to counteract against COVID-19 or further contingencies; we urgently need science-centered policies for public health. Since it will certainly not be the last pandemic and we could face similar outbreaks such as Dengue, Measles, or antibiotic resistant bacteria that could re-emerge.

Conflict of Interest
None