When you’re sick, your body produces antibodies to defend itself. The cells, that produce these antibodies, store this in their memory. When reinfected with the same disease, the cells can just reactivate that same defence. This is called adaptive immunity. You don’t need to get sick to develop immunity. Vaccines do the same thing. A vaccine is introduced into the body to trigger the production of antibodies as if it had been exposed to a disease naturally.
Infectious diseases are all caused by the same culprit: germs. Bacteria and viruses are germs. Though they are both extremely small, bacteria and viruses are very different. Bacteria are microscopic living organisms, smaller than the width of a strand of hair. Composed of one or more cells, without nuclei and surrounded by a wall, they are often shaped like a sphere or rod. While they can cause serious diseases, such as cholera or tuberculosis, not all bacteria are harmful and some can even be beneficial to humans. Antibiotics can prevent the growth of bad bacteria. Unfortunately, antibiotics are indiscriminate and they will also kill good bacteria.
Viruses are a completely different thing. Infectious agents of varying forms, they’re made of proteins and they contain their own genetic material. Twenty times smaller than a bacterium, a virus invades a cell and reproduces. It then acts as a parasite and multiplies within the cell before being released into the body and contaminating other cells. Unfortunately, antibiotics have no effect on viruses
Source: Merck Manual
Your immune system protects your body from potential invaders. It needs to be able to tell the difference between the organisms that belong in the body and those that are foreign or internal ones that have become unbalanced. These intruders can be micro-organisms (like bacteria or viruses), cancer cells, parasites and even transplanted organs. To defend your body, your immune system has to recognize dangerous antigens that will cause disease (like bacteria, viruses, other microorganisms, parasites or cancer cells).
Sometimes the immune system overreacts to a certain molecule, and you get an allergic reaction (like with food molecules or pollens). The immune system involves organs and cells from many molecules. Although it may seem like an abstract concept, your immune system is constantly protecting your body.
There are two types of immunity. Innate (or natural) immunity, present from birth, works by indiscriminately fighting off pathogens. Adaptive (or acquired) immunity, on the other hand, is an immune response specific to the germs causing the infection. Your immune system remembers the germs and is better able to target them the next time they attack.
Source : Le monde invisible du vivant, p. 118
Endemic or Pandemic
When an infectious disease starts rapidly progressing and spreading across the borders of a country or area, it becomes a pandemic rather than an epidemic. In a short period of time, millions of people are affected in large areas, if not around the world. However, all pandemics come to an end. An infection becomes endemic when the situation becomes more stable in terms of the number of cases and its impact on daily life and the healthcare system.
Is there a link between viruses and cancer? The answer to that question is yes, there is. Up to 18% of human cancers are believed to be linked to viral infections. One of the prime examples of this is that the leading cause of cervical cancer is HPV (human papillomavirus) infection. Along with HPV, hepatitis B and hepatitis C are the main viruses linked to cancer.
It’s not uncommon for viruses to make “mistakes” when they multiply. When these abnormalities multiply and the mutation reproduces and becomes more widespread, we see the emergence of what is called a new variant.
Many infectious diseases are viral in origin. Some trigger little or no symptoms. Others, if left untreated, can be fatal. Antiviral drugs work by blocking the infection process. They either prevent the virus from coming into contact with a healthy cell, prevent it from reproducing, or boost the immune system action. Some antiviral drugs are used in combination, disrupting the different stages of a viral infection and increasing the chances of recovery. While some diseases cannot be completely cured, the drugs can lead to substantial improvement.
Sources : Le monde invisible du vivant, p. 110 et Le Manuel Merck
Antibiotics vs Drugs
All antibiotics are drugs, but not all drugs are antibiotics. Antibiotics are very special drugs used to treat bacterial infections. In other words, they kill or prevent the spread of pathogens. So there’s no point in taking antibiotics to treat viral infections – it won’t do a thing! However, it’s not uncommon for bacterial infections to occur in parallel to, or after a viral infection. A weakened body makes it easier for opportunist pathogens to proliferate. That’s why it’s not uncommon to prescribe antibiotics to someone with a viral infection. However, the downside to this practice is that it increases antibiotic resistance.
Also, each antibiotic fights restricted types of bacteria. Taking antibiotics meant to target a different bacteria than the one causing your disease will have no effect whatsoever. In short, you need the right antibiotic for the right bacteria!
Thanks to the “species barrier,” viruses that target animals don’t usually spread to humans. But, of course, there are exceptions! It’s never that simple. These are zoonoses and diseases that jump the species barrier. These are viruses that are fairly mild in animals, but, once they jump to humans, tend to be particularly aggressive, especially at first. They eventually adapt to the new host and become less virulent. Remember SARS and the chikungunya virus? Over the years, modern humanity has experienced several zoonotic episodes, like SARS, which jumped from civets to humans, and chikungunya, which originated from great apes!
Source : Le monde invisible du vivant, p. 110
Oral drug vs Intramuscular vaccine
Many drugs are administered orally, meaning they get swallowed, chewed, or dissolved. It’s a convenient, and low-cost way to get drugs in your system. However, this method has its limitations. The digestive tract metabolizes and thus modifies the drugs, reducing the quantity of active product in the bloodstream.
Injecting drugs into a muscle is designed to solve this issue by allowing larger volumes of drugs to be administered without being digested. Obstacles with this approach are skin and fatty tissue, and a longer needle is all you need to get around those.
Source: Administration des médicaments
Pandemics have occurred since the beginning of time. They happen when several factors align. A pandemic is an outbreak of an infectious disease that affects a large part of the population in multiple countries and keeps spreading around the world. In short, a pandemic is a global epidemic. Pandemics occur when a highly contagious bacteria or virus appears. Pandemics often start abruptly, peak rapidly, and subside. However, they tend to recur in waves.
Most pandemic infectious diseases result from person-to-person contamination. However, some pandemic diseases are transmitted by animals. Plagues were caused by fleas that fed on diseased rodents. Cholera is transmitted through contaminated water or food. Bats are known to harbour coronaviruses, which can be transmitted from animals to humans.
Though they don’t have a brain, viruses seem to be pretty smart! Unable to reproduce on their own, they invade living organisms in order to multiply. In other words, although not living, they hijack the living to “steal” and destroy “lives” to continue their existence. Some types of viruses were found to communicate with each other, leaving short “posts” for kin and descendants. These messages help the viruses reading them to decide how to proceed with the process of infection. Who would have thought?
While we haven’t been able to prove the presence of intelligence in viruses, one thing is sure, viruses are capable of unexpected feats. They can adapt to the environment, overcome obstacles to attack uninfected cells, and mutate to survive.