Infection is the invasion of disease-causing organisms into the body tissues of the host organism and their multiplication, and the response of the host body tissues to these organisms and the toxins they produce. Infections are caused by microorganisms such as viruses, prions, bacteria, and virus-like organisms as well as larger microorganisms such as microparasites and fungi. Hosts can use their immune systems to fight off infections. Mammalian hosts have an innate response to infection, characterized by inflammation and the adaptive response that immediately follows. Medicines help fight infection.
One branch of medicine, infectious diseases, is devoted to the medicine of infections and pathogens.
Classification classifies infections according to the pathogens and the signs and symptoms they produce. Infections that are active but have no obvious symptoms can be referred to as inactive, static, subclinical infections, while infections that are inactive and dormant are referred to as latent infections.
A short-term infection is an acute infection and a long-term infection is a chronic infection primary and secondary infections primary and secondary infections can refer to successive infections or different stages of an infection, the same infection, such as an acute herpes infection of the mouth and lips, is an acute infection, and if present in an acute AIDS infection, is a secondary infection in terms of acute AIDS infection.
Occult infection Occult infection or asymptomatic infection is the medical term for a “hidden infection” that can be detected by a doctor. The term “occult infection” was coined.
Diagnosis of infection is difficult when specific signs and symptoms are rare. If an infection is suspected, the first step is usually to check blood, urine and sputum cultures. Chest x-rays and stool analysis can help with the diagnosis. Tests of spinal fluid are performed to ensure that there is no brain infection.
In children, cyanosis, shortness of breath, peripheral malperfusion (lack of blood to peripheral tissues and organs), or a petechial rash of petechiae increase the risk of serious infection by more than five times. Other important indicators include parental concern, clinical intuition, and temperatures greater than 40°C.
Signs and symptoms of infection depend on the type of disease. Some signs of infection affect the entire body, such as weakness, loss of appetite, weight loss, fever, night sweats, chills, pain and suffering. Other signs and symptoms are specific to various parts of the body, such as rash, cough, and runny nose.
Bacterial or viral Bacterial and viral infections can cause the same symptoms and distinguishing a definite cause of the infection can be difficult. However, it is important to differentiate because viral infections cannot be treated with antibiotics.
Comparative characteristics of viral and bacterial infections Viral infections Bacterial infections Typical symptoms In general, viral infections are systemic. This means that the viral infection involves different parts of the body or more than one body system at the same time, i.e. runny nose, nasal congestion, cough, generalized aches and pains, etc. Sometimes it can be localized, such as viral conjunctivitis or “pinkeye” and herpes. Some viral infections are painful, like herpes. The pain of a viral infection is often described as itchy or burning.
The typical symptoms of a bacterial infection are localized redness, heat, swelling and pain. One of the signs of a bacterial infection is localized pain, which is pain in a specific part of the body. For example, if a cut is followed by a bacterial infection, the pain occurs at the site of the infection. Bacterial throat pain is often characterized by more pain on one side of the throat. If the pain occurs in only one ear, the ear infection is more likely to be diagnosed as bacterial. A potentially infected wound that produces pus and milky fluid is likely to be infected.
Etiology Causative viruses Causative bacteria Pathophysiology There is a universal chain of links that applies to infections. Once an infection occurs, there must be a chain of links that occur . A chain of links involves several steps, including pathogens, their massive accumulation, entry into a susceptible host, exit from the host and transmission to a new host. Each link must occur in a chronological order for infection to arise. Understanding these steps helps health care workers fight infection and prevent it from occurring in the first place.
Colonization Infection begins when an organism enters the body, grows, multiplies, and successfully colonizes the organism. Most people are not susceptible to infection. Those who are weak, sick, malnourished, have cancer or diabetes are more likely to develop chronic or persistent infections. People with suppressed immune systems are particularly susceptible to opportunistic infections. The entry points into the host are generally mucosal tissues such as the oral cavity, nose, eyes, genitalia, anus, or open wounds. Although a few organisms grow at the initial entry point, a large number migrate causing systemic infection of different organs. Some pathogens grow in host cells (intracellular), while others grow freely in body fluids.
Wound colonization is in terms of non-replicating microorganisms within the wound, while in infected wounds, replicating organisms are present and tissues are injured. To some extent, foreign organisms colonize all multicellular organisms, the vast majority of which survive by mutualistic or symbiotic relationships with their hosts. An example of mutualism is anaerobic species that colonize mammalian colon, and an example of symbiosis is the different species of staphylococci present in human skin. None of these two colonizations are considered infections. The difference between infection and colonization usually lies only in the environment. Non-pathogenic microorganisms given a specific environment can become pathogenic, in the same way that even the most lethal organisms require a certain environment to cause an infection to which they are not immune. Certain colonizing bacteria, such as bacillus species and Streptococcus griseus, prevent the adhesion and colonization of pathogenic bacteria and thus have a symbiotic relationship with the host, preventing infection and accelerating wound healing.
The variables involved in the outcome and final result of pathogen inoculation of the host include.
§ The pathway of entry of the pathogen and the access to the host area it can reach § The intrinsic virulence of the particular organism § The amount or load of the initial immune enhancer § The immune status of the colonized host For example, Staphylococcus species are harmless to the skin, but when present in a normally sterile space, such as in the joint cavity or abdominal cavity, can multiply unimpeded and place a heavy burden on the host.
Seeing the large number of wounds in clinical practice, it may be difficult to know which chronic wounds become infected. There is limited quality data to assess signs and symptoms. A review of chronic wounds in the American Medical Association’s “Rational Clinical Testing Series” journal quantified the importance of aggravated pain as an indicator of infection. The review showed that the most useful finding was that increased pain was positively associated with infection [odds ratio (LR) range, 11-20], but that the absence of pain (negative LR range, 0.64-0.88) did not exclude infection. (Summary LR 0.64-0.88 ) disease may occur if the host’s protective immune mechanisms are compromised and the organism inflicts harm on the host. Microorganisms release a variety of toxins or destructive enzymes that cause tissue damage. For example, tetanus bacilli release a toxin that paralyzes muscles, and staphylococci release a toxin that causes shock and sepsis. Not all pathogens cause disease in all hosts. For example, less than 5% of people infected with poliomyelitis develop the disease. On the other hand, some pathogens are highly virulent. Prions cause mad cow disease, and Creutzfeldt-Jakob disease kills almost all infected animals and humans.
Persistent infections occur because the body is unable to clear the pathogens after the initial infection. Persistent infection, characterized by the presence of latent infection in the infected organism and occasional recurrence of active infection, recurs in a cycle. There are certain viruses that pass through the different cells of the infected body to maintain a persistent infection. Some viruses, once acquired, never leave the body. A classic example is the herpes viruses, which tend to hide in nerves and recur when the time is right.
Persistent infections cause millions of deaths worldwide each year. In many less developed countries, chronic parasitic infections have high morbidity and mortality rates.
For the infecting organism to survive and repeat its infection cycle in other hosts, they (or their offspring) must leave their existing colonies to cause infection elsewhere. Infection can be spread through many potential pathways. Infected organisms can be transmitted through direct or indirect contact. Direct contact infection occurs when an individual comes into contact with the “source site”. This may mean contact with infected body fluids or drinking contaminated water or deer tick bites. Direct contact infection can also result from inhaling infectious microbial aerosol particles, which are spread out of sneezing or coughing. Another common route of direct contact transmission involves sexual activity – oral, vaginal or anal intercourse.
Indirect contact infection occurs when an organism is able to withstand a hostile environment other than that of the host for a long period of time, remaining infectious when specific conditions arise. Often contaminated inanimate objects, including toys, furniture, doorknobs, hand towel wipes or personal care products of infected patients. Contact with food and drink items used by infected organisms is another situation where indirect contact transmission of disease is a common mode of transmission in less developed countries, fecal-oral route transmission. In such cases, sewage is used for washing food or drinking. This leads to food poisoning. Common fecal-oral transmission pathogens include Vibrio cholerae sporozoites, Giardia species, rotavirus, lysoameba, Escherichia coli, and tapeworms. Most of these pathogens cause gastroenteritis.
All of the above patterns are examples of horizontal transmission, as the infected organisms are transmitted from person to person in the same generation. There are also various types of vertically transmitted infections – this is transmitted from mother to child during delivery or fetal development. Common diseases with this mode of transmission include AIDS, hepatitis, herpes, and cytomegalovirus.
Treatment and prevention feasible treatment and prevention strategies are to disrupt the cycle of infection. For example, adequate hygiene can reduce direct transmission, maintain environmental sanitation, and health education.
When the body is attacked by an infection, anti-infective drugs can suppress the infection. There are four types of anti-infectives or drugs: antimicrobials (antibiotics), antivirals, antituberculosis, and antifungals. Depending on the severity and type of infection, antibiotics can be given orally, by injection, or can be applied topically. Intravenous antibiotics are given to treat severe brain infections. Sometimes, multiple antibiotics are used to reduce the risk of resistance and increase efficacy. Antibiotics are for bacteria only and do not affect viruses. Antibiotics work by slowing down the reproduction of bacteria or by killing them. The most common antibiotics used in medicine include penicillin, cephalosporins, aminoglycosides, macrolides, quinolones, and tetracyclines. Washing hands, wearing a coat, and wearing a mask are techniques that can prevent the spread of infection from doctor to patient and vice versa. Frequent hand washing remains the most important line of defense against the spread of unwanted organisms. Nutrition must improve and lifestyle changes must be made – avoid illicit drugs, use condoms, join an exercise program. Cooking food and avoiding food that has been left out for a long time is also important. Do not take antibiotics for long periods of time in excess of the therapeutic amount. Long-term use of antibiotics can lead to drug resistance and the development of opportunistic infections, such as Clostridium difficile enteritis. Another way to prevent infections is vaccination, which promotes the development of immune resistance in the vaccinated host.
The fossil record is an interesting topic for ancient pathologists, scientists studying injury and disease events in extinct life forms, and the evidence of infection in fossil remains. The bones of carnivorous dinosaurs have been found to show signs of infection. When infections do occur, they seem to be more likely to be confined to just a small area of the body. The surface of the skull of the early carnivorous dinosaur Arenosaurus exhibits pit-like wounds with swelling and porous bone around the wounds. The unusual texture of the bone around the wounds suggests that they suffered a short-term, non-lethal infection. Scientists studying the skulls speculate that the bite marks came from an attack by another conspecific. Documented evidence of infection in other carnivorous dinosaurs includes Highspinosaurus, Allosaurus, Tyrannosaurus, and Cortland Formosaurus. Tyrannosaurus rex attacked each other and caused infection, as did the Irellosaurus skull specimen.