26/07/2022
Mohiuddin Abdul Quader
[1][10][20][30][40]{a}{b}{c}{d} < / > ( )
Primary versus opportunistic
See also: Coinfection
Among the many varieties of microorganisms, relatively few cause disease in otherwise healthy individuals.[44] Infectious disease results from the interplay between those few pathogens and the defenses of the hosts they infect. The appearance and severity of disease resulting from any pathogen depend upon the ability of that pathogen to damage the host as well as the ability of the host to resist the pathogen. However, a host's immune system can also cause damage to the host itself in an attempt to control the infection. Clinicians, therefore, classify infectious microorganisms or microbes according to the status of host defenses – either as primary pathogens or as opportunistic pathogens.[45]
Primary pathogens
Primary pathogens cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic virulence (the severity of the disease they cause) is, in part, a necessary consequence of their need to reproduce and spread. Many of the most common primary pathogens of humans only infect humans, however, many serious diseases are caused by organisms acquired from the environment or that infect non-human hosts.[46]
Opportunistic pathogens
Main article: Opportunistic infection
Opportunistic pathogens can cause an infectious disease in a host with depressed resistance (immunodeficiency) or if they have unusual access to the inside of the body (for example, via trauma). Opportunistic infection may be caused by microbes ordinarily in contact with the host, such as pathogenic bacteria or fungi in the gastrointestinal or the upper respiratory tract, and they may also result from (otherwise innocuous) microbes acquired from other hosts (as in Clostridium difficile colitis) or from the environment as a result of traumatic introduction (as in surgical wound infections or compound fractures). An opportunistic disease requires impairment of host defenses, which may occur as a result of genetic defects (such as chronic granulomatous disease), exposure to antimicrobial drugs or immunosuppressive chemicals (as might occur following poisoning or cancer chemotherapy), exposure to ionizing radiation, or as a result of an infectious disease with immunosuppressive activity (such as with measles, malaria or HIV disease). Primary pathogens may also cause more severe disease in a host with depressed resistance than would normally occur in an immunosufficient host.[11]
Secondary infection
While a primary infection can practically be viewed as the root cause of an individual's current health problem, a secondary infection is a sequela or complication of that root cause. For example, an infection due to a burn or penetrating trauma (the root cause) is a secondary infection. Primary pathogens often cause primary infection and often cause secondary infection. Usually, opportunistic infections are viewed as secondary infections (because immunodeficiency or injury was the predisposing factor).[45]
Other types of infection
Other types of infection consist of mixed, iatrogenic, nosocomial, and community-acquired infection. A mixed infection is an infection that is caused by two or more pathogens. An example of this is appendicitis, which is caused by Bacteroides fragilis and Escherichia coli. The second is an iatrogenic infection. This type of infection is one that is transmitted from a health care worker to a patient. A nosocomial infection is also one that occurs in a health care setting. Nosocomial infections are those that are acquired during a hospital stay. Lastly, a community-acquired infection is one in which the infection is acquired from a whole community.[43]
Infectious or not
One manner of proving that a given disease is infectious, is to satisfy Koch's postulates (first proposed by Robert Koch), which require that first, the infectious agent be identifiable only in patients who have the disease, and not in healthy controls, and second, that patients who contract the infectious agent also develop the disease. These postulates were first used in the discovery that Mycobacteria species cause tuberculosis.[47]
However, Koch's postulates cannot usually be tested in modern practice for ethical reasons. Proving them would require experimental infection of a healthy individual with a pathogen produced as a pure culture. Conversely, even clearly infectious diseases do not always meet the infectious criteria; for example, Treponema pallidum, the causative spirochete of syphilis, cannot be cultured in vitro – however the organism can be cultured in rabbit te**es. It is less clear that a pure culture comes from an animal source serving as host than it is when derived from microbes derived from plate culture.[48]
Epidemiology, or the study and analysis of who, why and where disease occurs, and what determines whether various populations have a disease, is another important tool used to understand infectious disease. Epidemiologists may determine differences among groups within a population, such as whether certain age groups have a greater or lesser rate of infection; whether groups living in different neighborhoods are more likely to be infected; and by other factors, such as gender and race. Researchers also may assess whether a disease outbreak is sporadic, or just an occasional occurrence; endemic, with a steady level of regular cases occurring in a region; epidemic, with a fast arising, and unusually high number of cases in a region; or pandemic, which is a global epidemic. If the cause of the infectious disease is unknown, epidemiology can be used to assist with tracking down the sources of infection.[49]
Contagiousness
Infectious diseases are sometimes called contagious diseases when they are easily transmitted by contact with an ill person or their secretions (e.g., influenza). Thus, a contagious disease is a subset of infectious disease that is especially infective or easily transmitted. Other types of infectious, transmissible, or communicable diseases with more specialized routes of infection, such as vector transmission or sexual transmission, are usually not regarded as "contagious", and often do not require medical isolation (sometimes loosely called quarantine) of those affected. However, this specialized connotation of the word "contagious" and "contagious disease" (easy transmissibility) is not always respected in popular use. Infectious diseases are commonly transmitted from person to person through direct contact. The types of contact are through person to person and droplet spread. Indirect contact such as airborne transmission, contaminated objects, food and drinking water, animal person contact, animal reservoirs, insect bites, and environmental reservoirs are another way infectious diseases are transmitted.[50]
By anatomic location
Infections can be classified by the anatomic location or organ system infected, including:[citation needed]
Urinary tract infection
Skin infection
Respiratory tract infection
Odontogenic infection (an infection that originates within a tooth or in the closely surrounding tissues)
Vaginal infections
Intra-amniotic infection
In addition, locations of inflammation where infection is the most common cause include pneumonia, meningitis and salpingitis.[citation needed]
Prevention
Main articles: Public health and Infection control
Washing one's hands, a form of hygiene, is an effective way to prevent the spread of infectious disease.[51]
Techniques like hand washing, wearing gowns, and wearing face masks can help prevent infections from being passed from one person to another. Aseptic technique was introduced in medicine and surgery in the late 19th century and greatly reduced the incidence of infections caused by surgery. Frequent hand washing remains the most important defense against the spread of unwanted organisms.[52] There are other forms of prevention such as avoiding the use of illicit drugs, using a condom, wearing gloves, and having a healthy lifestyle with a balanced diet and regular exercise. Cooking foods well and avoiding foods that have been left outside for a long time is also important.
Antimicrobial substances used to prevent transmission of infections include:
antiseptics, which are applied to living tissue/skin
disinfectants, which destroy microorganisms found on non-living objects.
antibiotics, called prophylactic when given as prevention rather as treatment of infection. However, long term use of antibiotics leads to resistance of bacteria. While humans do not become immune to antibiotics, the bacteria does. Thus, avoiding using antibiotics longer than necessary helps preventing bacteria from forming mutations that aide in antibiotic resistance.
One of the ways to prevent or slow down the transmission of infectious diseases is to recognize the different characteristics of various diseases.[53] Some critical disease characteristics that should be evaluated include virulence, distance traveled by those affected, and level of contagiousness. The human strains of Ebola virus, for example, incapacitate those infected extremely quickly and kill them soon after. As a result, those affected by this disease do not have the opportunity to travel very far from the initial infection zone.[54] Also, this virus must spread through skin lesions or permeable membranes such as the eye. Thus, the initial stage of Ebola is not very contagious since its victims experience only internal hemorrhaging. As a result of the above features, the spread of Ebola is very rapid and usually stays within a relatively confined geographical area. In contrast, the human immunodeficiency virus (HIV) kills its victims very slowly by attacking their immune system.[11] As a result, many of its victims transmit the virus to other individuals before even realizing that they are carrying the disease. Also, the relatively low virulence allows its victims to travel long distances, increasing the likelihood of an epidemic.
Another effective way to decrease the transmission rate of infectious diseases is to recognize the effects of small-world networks.[53] In epidemics, there are often extensive interactions within hubs or groups of infected individuals and other interactions within discrete hubs of susceptible individuals. Despite the low interaction between discrete hubs, the disease can jump and spread in a susceptible hub via a single or few interactions with an infected hub. Thus, infection rates in small-world networks can be reduced somewhat if interactions between individuals within infected hubs are eliminated (Figure 1). However, infection rates can be drastically reduced if the main focus is on the prevention of transmission jumps between hubs. The use of needle exchange programs in areas with a high density of drug users with HIV is an example of the successful implementation of this treatment method.[citation needed] Another example is the use of ring culling or vaccination of potentially susceptible livestock in adjacent farms to prevent the spread of the foot-and-mouth virus in 2001.[55]
A general method to prevent transmission of vector-borne pathogens is pest control.
In cases where infection is merely suspected, individuals may be quarantined until the incubation period has passed and the disease manifests itself or the person remains healthy. Groups may undergo quarantine, or in the case of communities, a cordon sanitaire may be imposed to prevent infection from spreading beyond the community, or in the case of protective sequestration, into a community. Public health authorities may implement other forms of social distancing, such as school closings, to control an epidemic.
Immunity
Mary Mallon (a.k.a. Typhoid Mary) was an asymptomatic carrier of typhoid fever. Over the course of her career as a cook, she infected 53 people, three of whom died.
Infection with most pathogens does not result in death of the host and the offending organism is ultimately cleared after the symptoms of the disease have waned.[44] This process requires immune mechanisms to kill or inactivate the inoculum of the pathogen. Specific acquired immunity against infectious diseases may be mediated by antibodies and/or T lymphocytes. Immunity mediated by these two factors may be manifested by:
a direct effect upon a pathogen, such as antibody-initiated complement-dependent bacteriolysis, opsonoization, phagocytosis and killing, as occurs for some bacteria,
neutralization of viruses so that these organisms cannot enter cells,
or by T lymphocytes, which will kill a cell parasitized by a microorganism.
The immune system response to a microorganism often causes symptoms such as a high fever and inflammation, and has the potential to be more devastating than direct damage caused by a microbe.[11]
Resistance to infection (immunity) may be acquired following a disease, by asymptomatic carriage of the pathogen, by harboring an organism with a similar structure (crossreacting), or by vaccination. Knowledge of the protective antigens and specific acquired host immune factors is more complete for primary pathogens than for opportunistic pathogens. There is also the phenomenon of herd immunity which offers a measure of protection to those otherwise vulnerable people when a large enough proportion of the population has acquired immunity from certain infections.
Immune resistance to an infectious disease requires a critical level of either antigen-specific antibodies and/or T cells when the host encounters the pathogen. Some individuals develop natural serum antibodies to the surface polysaccharides of some agents although they have had little or no contact with the agent, these natural antibodies confer specific protection to adults and are passively transmitted to newborns.
Host genetic factors
The organism that is the target of an infecting action of a specific infectious agent is called the host. The host harbouring an agent that is in a mature or sexually active stage phase is called the definitive host. The intermediate host comes in contact during the larvae stage. A host can be anything living and can attain to asexual and sexual reproduction.[56] The clearance of the pathogens, either treatment-induced or spontaneous, it can be influenced by the genetic variants carried by the individual patients. For instance, for genotype 1 hepatitis C treated with Pegylated interferon-alpha-2a or Pegylated interferon-alpha-2b (brand names Pegasys or PEG-Intron) combined with ribavirin, it has been shown that genetic polymorphisms near the human IL28B gene, encoding interferon lambda 3, are associated with significant differences in the treatment-induced clearance of the virus. This finding, originally reported in Nature,[57] showed that genotype 1 hepatitis C patients carrying certain genetic variant alleles near the IL28B gene are more possibly to achieve sustained virological response after the treatment than others. Later report from Nature[58] demonstrated that the same genetic variants are also associated with the natural clearance of the genotype 1 hepatitis C virus.
Treatments
When infection attacks the body, anti-infective drugs can suppress the infection. Several broad types of anti-infective drugs exist, depending on the type of organism targeted; they include antibacterial (antibiotic; including antitubercular), antiviral, antifungal and antiparasitic (including antiprotozoal and antihelminthic) agents. Depending on the severity and the type of infection, the antibiotic may be given by mouth or by injection, or may be applied topically. Severe infections of the brain are usually treated with intravenous antibiotics. Sometimes, multiple antibiotics are used in case there is resistance to one antibiotic. Antibiotics only work for bacteria and do not affect viruses. Antibiotics work by slowing down the multiplication of bacteria or killing the bacteria. The most common classes of antibiotics used in medicine include penicillin, cephalosporins, aminoglycosides, macrolides, quinolones and tetracyclines.[59][60]
Not all infections require treatment, and for many self-limiting infections the treatment may cause more side-effects than benefits. Antimicrobial stewardship is the concept that healthcare providers should treat an infection with an antimicrobial that specifically works well for the target pathogen for the shortest amount of time and to only treat when there is a known or highly suspected pathogen that will respond to the medication.[61]
Epidemiology
Deaths due to infectious and parasitic diseases per million persons in 2012
28–81
82–114
115–171
172–212
213–283
284–516
517–1,193
1,194–2,476
2,477–3,954
3,955–6,812
See also: Epidemic and Pandemic
Disability-adjusted life year for infectious and parasitic diseases per 100,000 inhabitants in 2004.[62]
no data
≤250
250–500
500–1000
1000–2000
2000–3000
3000–4000
4000–5000
5000–6250
6250–12,500
12,500–25,000
25,000–50,000
≥50,000
In 2010, about 10 million people died of infectious diseases.[63]
The World Health Organization collects information on global deaths by International Classification of Disease (ICD) code categories. The following table lists the top infectious disease by number of deaths in 2002. 1993 data is included for comparison.
Worldwide mortality due to infectious diseases[64][65]
Rank Cause of death Deaths 2002
(in millions) Percentage of
all deaths Deaths 1993
(in millions) 1993 Rank
N/A All infectious diseases 14.7 25.9% 16.4 32.2%
1 Lower respiratory infections[66] 3.9 6.9% 4.1 1
2 HIV/AIDS 2.8 4.9% 0.7 7
3 Diarrheal diseases[67] 1.8 3.2% 3.0 2
4 Tuberculosis (TB) 1.6 2.7% 2.7 3
5 Malaria 1.3 2.2% 2.0 4
6 Measles 0.6 1.1% 1.1 5
7 Pertussis 0.29 0.5% 0.36 7
8 Tetanus 0.21 0.4% 0.15 12
9 Meningitis 0.17 0.3% 0.25 8
10 Syphilis 0.16 0.3% 0.19 11
11 Hepatitis B 0.10 0.2% 0.93 6
12–17 Tropical diseases (6)[68] 0.13 0.2% 0.53 9, 10, 16–18
Note: Other causes of death include maternal and perinatal conditions (5.2%), nutritional deficiencies (0.9%),
noncommunicable conditions (58.8%), and injuries (9.1%).
The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include pertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In 2012, approximately 3.1 million people have died due to lower respiratory infections, making it the number 4 leading cause of death in the world.[69]
Historic pandemics
Great Plague of Marseille in 1720 killed 100,000 people in the city and the surrounding provinces
With their potential for unpredictable and explosive impacts, infectious diseases have been major actors in human history.[70] A pandemic (or global epidemic) is a disease that affects people over an extensive geographical area. For example:
Plague of Justinian, from 541 to 542, killed between 50% and 60% of Europe's population.[71]
The Black Death of 1347 to 1352 killed 25 million in Europe over 5 years. The plague reduced the old world population from an estimated 450 million to between 350 and 375 million in the 14th century.
The introduction of smallpox, measles, and typhus to the areas of Central and South America by European explorers during the 15th and 16th centuries caused pandemics among the native inhabitants. Between 1518 and 1568 disease pandemics are said to have caused the population of Mexico to fall from 20 million to 3 million.[72]
The first European influenza epidemic occurred between 1556 and 1560, with an estimated mortality rate of 20%.[72]
Smallpox killed an estimated 60 million Europeans during the 18th century[73] (approximately 400,000 per year).[74] Up to 30% of those infected, including 80% of the children under 5 years of age, died from the disease, and one-third of the survivors went blind.[75]
In the 19th century, tuberculosis killed an estimated one-quarter of the adult population of Europe;[76] by 1918 one in six deaths in France were still caused by TB.
The Influenza Pandemic of 1918 (or the Spanish flu) killed 25–50 million people (about 2% of world population of 1.7 billion).[77] Today Influenza kills about 250,000 to 500,000 worldwide each year.
Emerging diseases
In most cases, microorganisms live in harmony with their hosts via mutual or commensal interactions. Diseases can emerge when existing parasites become pathogenic or when new pathogenic parasites enter a new host.
Coevolution between parasite and host can lead to hosts becoming resistant to the parasites or the parasites may evolve greater virulence, leading to immunopathological disease.
Human activity is involved with many emerging infectious diseases, such as environmental change enabling a parasite to occupy new niches. When that happens, a pathogen that had been confined to a remote habitat has a wider distribution and possibly a new host organism. Parasites jumping from nonhuman to human hosts are known as zoonoses. Under disease invasion, when a parasite invades a new host species, it may become pathogenic in the new host.[78]
Several human activities have led to the emergence of zoonotic human pathogens, including viruses, bacteria, protozoa, and rickettsia,[79] and spread of vector-borne diseases,[78] see also globalization and disease and wildlife disease:
Encroachment on wildlife habitats. The construction of new villages and housing developments in rural areas force animals to live in dense populations, creating opportunities for microbes to mutate and emerge.[80]
Changes in agriculture. The introduction of new crops attracts new crop pests and the microbes they carry to farming communities, exposing people to unfamiliar diseases.
The destruction of rain forests. As countries make use of their rain forests, by building roads through forests and clearing areas for settlement or commercial ventures, people encounter insects and other animals harboring previously unknown microorganisms.
Uncontrolled urbanization. The rapid growth of cities in many developing countries tends to concentrate large numbers of people into crowded areas with poor sanitation. These conditions foster transmission of contagious diseases.
Modern transport. Ships and other cargo carriers often harbor unintended "passengers", that can spread diseases to faraway destinations. While with international jet-airplane travel, people infected with a disease can carry it to distant lands, or home to their families, before their first symptoms appear.
Germ theory of disease
Main article: Germ theory of disease
East German postage stamps depicting four antique microscopes. Advancements in microscopy were essential to the early study of infectious diseases.
In Antiquity, the Greek historian Thucydides (c. 460 – c. 400 BCE) was the first person to write, in his account of the plague of Athens, that diseases could spread from an infected person to others.[81][82] In his On the Different Types of Fever (c. 175 AD), the Greco-Roman physician Galen speculated that plagues were spread by "certain seeds of plague", which were present in the air.[83] In the Sushruta Samhita, the ancient Indian physician Sushruta theorized: "Leprosy, fever, consumption, diseases of the eye, and other infectious diseases spread from one person to another by sexual union, physical contact, eating together, sleeping together, sitting together, and the use of same clothes, garlands and pastes."[84][85] This book has been dated to about the sixth century BC.[86]
A basic form of contagion theory was proposed by Persian physician Ibn Sina (known as Avicenna in Europe) in The Canon of Medicine (1025), which later became the most authoritative medical textbook in Europe up until the 16th century. In Book IV of the Canon, Ibn Sina discussed epidemics, outlining the classical miasma theory and attempting to blend it with his own early contagion theory. He mentioned that people can transmit disease to others by breath, noted contagion with tuberculosis, and discussed the transmission of disease through water and dirt.[87] The concept of invisible contagion was later discussed by several Islamic scholars in the Ayyubid Sultanate who referred to them as najasat ("impure substances"). The fiqh scholar Ibn al-Haj al-Abdari (c. 1250–1336), while discussing Islamic diet and hygiene, gave warnings about how contagion can contaminate water, food, and garments, and could spread through the water supply, and may have implied contagion to be unseen particles.[88]
When the Black Death bubonic plague reached Al-Andalus in the 14th century, the Arab physicians Ibn Khatima (c. 1369) and Ibn al-Khatib (1313–1374) hypothesised that infectious diseases were caused by "minute bodies" and described how they can be transmitted through garments, vessels and earrings.[89] Ideas of contagion became more popular in Europe during the Renaissance, particularly through the writing of the Italian physician Girolamo Fracastoro.[90] Anton van Leeuwenhoek (1632–1723) advanced the science of microscopy by being the first to observe microorganisms, allowing for easy visualization of bacteria.
In the mid-19th century John Snow and William Budd did important work demonstrating the contagiousness of typhoid and cholera through contaminated water. Both are credited with decreasing epidemics of cholera in their towns by implementing measures to prevent contamination of water.[91] Louis Pasteur proved beyond doubt that certain diseases are caused by infectious agents, and developed a vaccine for rabies. Robert Koch, provided the study of infectious diseases with a scientific basis known as Koch's postulates. Edward Jenner, Jonas Salk and Albert Sabin developed effective vaccines for smallpox and polio, which would later result in the eradication and near-eradication of these diseases, respectively. Alexander Fleming discovered the world's first antibiotic, Penicillin, which Florey and Chain then developed. Gerhard Domagk developed sulphonamides, the first broad spectrum synthetic antibacterial drugs.
Medical specialists
The medical treatment of infectious diseases falls into the medical field of Infectious Disease and in some cases the study of propagation pertains to the field of Epidemiology. Generally, infections are initially diagnosed by primary care physicians or internal medicine specialists. For example, an "uncomplicated" pneumonia will generally be treated by the internist or the pulmonologist (lung physician). The work of the infectious diseases specialist therefore entails working with both patients and general practitioners, as well as laboratory scientists, immunologists, bacteriologists and other specialists.
An infectious disease team may be alerted when:
The disease has not been definitively diagnosed after an initial workup
The patient is immunocompromised (for example, in AIDS or after chemotherapy);
The infectious agent is of an uncommon nature (e.g. tropical diseases);
The disease has not responded to first line antibiotics;
The disease might be dangerous to other patients, and the patient might have to be isolated
Society and culture
Several studies have reported associations between pathogen load in an area and human behavior. Higher pathogen load is associated with decreased size of ethnic and religious groups in an area. This may be due high pathogen load favoring avoidance of other groups, which may reduce pathogen transmission, or a high pathogen load preventing the creation of large settlements and armies that enforce a common culture. Higher pathogen load is also associated with more restricted sexual behavior, which may reduce pathogen transmission. It also associated with higher preferences for health and attractiveness in mates. Higher fertility rates and shorter or less parental care per child is another association that may be a compensation for the higher mortality rate. There is also an association with polygyny which may be due to higher pathogen load, making selecting males with a high genetic resistance increasingly important. Higher pathogen load is also associated with more collectivism and less individualism, which may limit contacts with outside groups and infections. There are alternative explanations for at least some of the associations although some of these explanations may in turn ultimately be due to pathogen load. Thus, polygyny may also be due to a lower male: female ratio in these areas but this may ultimately be due to male infants having increased mortality from infectious diseases. Another example is that poor socioeconomic factors may ultimately in part be due to high pathogen load preventing economic development.[92]
Fossil record
Main article: Paleopathology
Skull of dinosaur with long jaws and teeth.
Herrerasaurus skull.
Evidence of infection in fossil remains is a subject of interest for paleopathologists, scientists who study occurrences of injuries and illness in extinct life forms. Signs of infection have been discovered in the bones of carnivorous dinosaurs. When present, however, these infections seem to tend to be confined to only small regions of the body. A skull attributed to the early carnivorous dinosaur Herrerasaurus ischigualastensis exhibits pit-like wounds surrounded by swollen and porous bone. The unusual texture of the bone around the wounds suggests they were affected by a short-lived, non-lethal infection. Scientists who studied the skull speculated that the bite marks were received in a fight with another Herrerasaurus. Other carnivorous dinosaurs with documented evidence of infection include Acrocanthosaurus, Allosaurus, Tyrannosaurus and a tyrannosaur from the Kirtland Formation. The infections from both tyrannosaurs were received by being bitten during a fight, like the Herrerasaurus specimen.[93]
প্রাথমিক বনাম সুবিধাবাদী
আরও দেখুন: Coinfection
অণুজীবের অনেক বৈচিত্রের মধ্যে, অপেক্ষাকৃত কম স্বাস্থ্যবান ব্যক্তিদের মধ্যে রোগ সৃষ্টি করে। সংক্রামক রোগ সেই কয়েকটি রোগজীবাণু এবং তাদের সংক্রামিত হোস্টের প্রতিরক্ষার মধ্যে পারস্পরিক ক্রিয়াকলাপের ফলে। যে কোনো রোগজীবাণু থেকে সৃষ্ট রোগের চেহারা এবং তীব্রতা নির্ভর করে সেই রোগজীবাণুটির হোস্টের ক্ষতি করার ক্ষমতা এবং সেইসাথে হোস্টের প্যাথোজেনকে প্রতিরোধ করার ক্ষমতার উপর। যাইহোক, একটি হোস্টের ইমিউন সিস্টেম সংক্রমণ নিয়ন্ত্রণ করার প্রয়াসে হোস্টের নিজেই ক্ষতির কারণ হতে পারে। ক্লিনিশিয়ানরা, তাই, হোস্ট প্রতিরক্ষার অবস্থা অনুসারে সংক্রামক অণুজীব বা জীবাণুকে শ্রেণীবদ্ধ করে - হয় প্রাথমিক প্যাথোজেন বা সুবিধাবাদী প্যাথোজেন হিসাবে।
প্রাথমিক প্যাথোজেন
প্রাথমিক প্যাথোজেনগুলি স্বাভাবিক, স্বাস্থ্যকর হোস্টের মধ্যে তাদের উপস্থিতি বা কার্যকলাপের ফলে রোগ সৃষ্টি করে এবং তাদের অন্তর্নিহিত ভাইরাস (তারা যে রোগটি ঘটায় তার তীব্রতা) আংশিকভাবে তাদের পুনরুৎপাদন এবং বিস্তারের প্রয়োজনীয়তার একটি প্রয়োজনীয় পরিণতি। মানুষের সবচেয়ে সাধারণ প্রাথমিক প্যাথোজেনগুলির মধ্যে অনেকগুলি শুধুমাত্র মানুষকে সংক্রামিত করে, তবে, অনেকগুলি গুরুতর রোগ পরিবেশ থেকে অর্জিত জীবের কারণে বা অ-মানব হোস্টকে সংক্রামিত করে।
সুবিধাবাদী প্যাথোজেন
মূল নিবন্ধ: সুবিধাবাদী সংক্রমণ
সুবিধাবাদী প্যাথোজেনগুলি হতাশাগ্রস্ত প্রতিরোধের (ইমিউনোডেফিসিয়েন্সি) সহ হোস্টে একটি সংক্রামক রোগের কারণ হতে পারে বা যদি তাদের শরীরের অভ্যন্তরে অস্বাভাবিক অ্যাক্সেস থাকে (উদাহরণস্বরূপ, আঘাতের মাধ্যমে)। সুবিধাবাদী সংক্রমণ সাধারণত হোস্টের সংস্পর্শে থাকা জীবাণুর কারণে হতে পারে, যেমন গ্যাস্ট্রোইনটেস্টাইনাল বা উপরের শ্বাস নালীর প্যাথোজেনিক ব্যাকটেরিয়া বা ছত্রাক, এবং সেগুলি অন্যান্য হোস্ট থেকে অর্জিত (অন্যথায় নিরীহ) জীবাণু থেকেও হতে পারে (যেমন ক্লোস্ট্রিডিয়াম ডিফিসিল কোলাইটিস। ) বা ট্রমাজনিত প্রবর্তনের ফলে পরিবেশ থেকে (যেমন অস্ত্রোপচারের ক্ষত সংক্রমণ বা যৌগিক ফ্র্যাকচারে)। একটি সুবিধাবাদী রোগের জন্য হোস্টের প্রতিরক্ষার দুর্বলতা প্রয়োজন, যা জিনগত ত্রুটির (যেমন ক্রনিক গ্রানুলোমাটাস ডিজিজ), অ্যান্টিমাইক্রোবিয়াল ওষুধ বা ইমিউনোসপ্রেসিভ রাসায়নিকের (যেমন বিষক্রিয়া বা ক্যান্সার কেমোথেরাপির পরে ঘটতে পারে), আয়নাইজিং বিকিরণের এক্সপোজারের ফলে ঘটতে পারে। ইমিউনোসপ্রেসিভ কার্যকলাপ সহ একটি সংক্রামক রোগের ফলস্বরূপ (যেমন হাম, ম্যালেরিয়া বা এইচআইভি রোগ)। প্রাথমিক রোগজীবাণুগুলি হতাশাগ্রস্ত প্রতিরোধের সাথে একটি হোস্টে আরও গুরুতর রোগের কারণ হতে পারে যা সাধারণত একটি অনাক্রম্য হোস্টে ঘটতে পারে।
সেকেন্ডারি ইনফেকশন
যদিও একটি প্রাথমিক সংক্রমণকে কার্যত একজন ব্যক্তির বর্তমান স্বাস্থ্য সমস্যার মূল কারণ হিসাবে দেখা যেতে পারে, একটি গৌণ সংক্রমণ হল সেই মূল কারণের একটি সিক্যুলা বা জটিলতা। উদাহরণস্বরূপ, পোড়া বা অনুপ্রবেশকারী ট্রমা (মূল কারণ) কারণে একটি সংক্রমণ একটি গৌণ সংক্রমণ। প্রাথমিক রোগজীবাণু প্রায়ই প্রাথমিক সংক্রমণ ঘটায় এবং প্রায়ই সেকেন্ডারি সংক্রমণ ঘটায়। সাধারণত, সুবিধাবাদী সংক্রমণকে সেকেন্ডারি ইনফেকশন হিসেবে দেখা হয় (কারণ ইমিউনোডেফিসিয়েন্সি বা আঘাত ছিল প্রিডিস্পোজিং ফ্যাক্টর)।
অন্যান্য ধরনের সংক্রমণ
অন্যান্য ধরণের সংক্রমণের মধ্যে রয়েছে মিশ্র, আইট্রোজেনিক, নোসোকোমিয়াল এবং সম্প্রদায়-অর্জিত সংক্রমণ। একটি মিশ্র সংক্রমণ হল একটি সংক্রমণ যা দুই বা ততোধিক প্যাথোজেন দ্বারা সৃষ্ট হয়। এর একটি উদাহরণ হল অ্যাপেনডিসাইটিস, যা ব্যাকটেরয়েডস ফ্রেজিলিস এবং এসচেরিচিয়া কোলাই দ্বারা সৃষ্ট। দ্বিতীয়টি একটি আইট্রোজেনিক সংক্রমণ। এই ধরনের সংক্রমণ এমন একটি যা স্বাস্থ্যসেবা কর্মী থেকে একজন রোগীর কাছে প্রেরণ করা হয়। একটি নসোকোমিয়াল সংক্রমণও এমন একটি যা স্বাস্থ্যসেবা সেটিংয়ে ঘটে। নোসোকোমিয়াল ইনফেকশন হল যেগুলি হাসপাতালে থাকার সময় অর্জিত হয়। সবশেষে, একটি সম্প্রদায়-অর্জিত সংক্রমণ হল একটি যেখানে সংক্রমণ একটি সমগ্র সম্প্রদায় থেকে অর্জিত হয়।
সংক্রামক বা না
প্রদত্ত রোগটি সংক্রামক তা প্রমাণ করার একটি উপায় হল কোচের অনুমান (প্রথম রবার্ট কচ দ্বারা প্রস্তাবিত) সন্তুষ্ট করা, যার জন্য প্রয়োজন যে প্রথমত, সংক্রামক এজেন্ট শুধুমাত্র সেই রোগীদের মধ্যে সনাক্ত করা যায় যাদের রোগ আছে, এবং সুস্থ নিয়ন্ত্রণে নয়, এবং দ্বিতীয় , যে রোগীরা সংক্রামক এজেন্ট সংক্রামিত হয় তাদেরও এই রোগ হয়। মাইকোব্যাকটেরিয়া প্রজাতি যক্ষ্মা রোগের কারণ আবিষ্কারে এই পোস্টুলেটগুলি প্রথম ব্যবহার করা হয়েছিল।
যাইহোক, নৈতিক কারণে আধুনিক অনুশীলনে কোচের পোস্টুলেটগুলি সাধারণত পরীক্ষা করা যায় না। তাদের প্রমাণ করার জন্য একটি বিশুদ্ধ সংস্কৃতি হিসাবে উত্পাদিত প্যাথোজেন সহ একজন সুস্থ ব্যক্তির পরীক্ষামূলক সংক্রমণের প্রয়োজন হবে। বিপরীতভাবে, এমনকি স্পষ্টভাবে সংক্রামক রোগ সবসময় সংক্রামক মানদণ্ড পূরণ করে না; উদাহরণস্বরূপ, ট্রেপোনেমা প্যালিডাম, সিফিলিসের কার্যকারক স্পিরোচেট, ভিট্রোতে সংষ্কৃত করা যায় না - তবে জীবকে খরগোশের অণ্ডকোষে সংষ্কৃত করা যেতে পারে। এটা কম স্পষ্ট যে একটি বিশুদ্ধ সংস্কৃতি প্লেট সংস্কৃতি থেকে প্রাপ্ত জীবাণু থেকে উদ্ভূত যখন এটি থেকে প্রাপ্ত হোস্ট হিসাবে পরিবেশন একটি প্রাণী উৎস থেকে আসে।
এপিডেমিওলজি, বা কে, কেন এবং কোথায় রোগ হয় তার অধ্যয়ন এবং বিশ্লেষণ এবং বিভিন্ন জনগোষ্ঠীর একটি রোগ আছে কিনা তা নির্ধারণ করে, সংক্রামক রোগ বোঝার জন্য ব্যবহৃত আরেকটি গুরুত্বপূর্ণ হাতিয়ার। এপিডেমিওলজিস্টরা নির্ধারণ করতে পারেন !
07/01/2024
01/10/2022