6.4 Infectious diseases and the human immune system
4 min read•august 16, 2024
Infectious diseases have shaped human evolution, driving genetic adaptations and immune system development. Our shift to agriculture and increased global connectivity accelerated disease spread, while pathogens evolved to evade our defenses. This ongoing battle highlights the dynamic relationship between humans and microbes.
The human immune system is a complex defense network, combining innate and adaptive responses. provides rapid, non-specific protection, while develops targeted defenses. Understanding these mechanisms is crucial for comprehending how humans adapt to disease challenges.
Coevolution of Humans and Diseases
Reciprocal Evolutionary Changes
Top images from around the web for Reciprocal Evolutionary Changes
Discovering the deadly diversity of malaria | Pursuit by The University of Melbourne View original
Is this image relevant?
Trapping malaria in a gene net | Pursuit by The University of Melbourne View original
Is this image relevant?
Preventing the spread of malaria | Pursuit by The University of Melbourne View original
Is this image relevant?
Discovering the deadly diversity of malaria | Pursuit by The University of Melbourne View original
Is this image relevant?
Trapping malaria in a gene net | Pursuit by The University of Melbourne View original
Is this image relevant?
1 of 3
Top images from around the web for Reciprocal Evolutionary Changes
Discovering the deadly diversity of malaria | Pursuit by The University of Melbourne View original
Is this image relevant?
Trapping malaria in a gene net | Pursuit by The University of Melbourne View original
Is this image relevant?
Preventing the spread of malaria | Pursuit by The University of Melbourne View original
Is this image relevant?
Discovering the deadly diversity of malaria | Pursuit by The University of Melbourne View original
Is this image relevant?
Trapping malaria in a gene net | Pursuit by The University of Melbourne View original
Is this image relevant?
1 of 3
- Coevolution drives reciprocal evolutionary changes between humans and pathogens
- Human populations developed genetic adaptations to infectious diseases
- confers resistance to
- Glucose-6-phosphate dehydrogenase (G6PD) deficiency protects against malaria
- Pathogens evolved strategies to evade human immune responses
- in influenza viruses alters surface proteins
- in influenza viruses leads to major changes through genetic reassortment
Societal Changes and Disease Emergence
- Shift from hunter-gatherer to agricultural societies increased disease emergence
- Higher population density facilitated pathogen transmission
- Proximity to domesticated animals led to zoonotic diseases (, influenza)
- Global trade and travel accelerated infectious disease spread
- Silk Road facilitated the spread of bubonic plague
- Air travel contributed to rapid global spread of
- Medical interventions influenced pathogen evolution
- Antibiotic use led to the emergence of antibiotic-resistant bacteria ()
- Vaccination programs eradicated but led to strains
Immune System Function
Innate Immunity
- Innate immunity provides rapid, non-specific responses to pathogens
- Physical barriers form the first line of defense
- Skin acts as a mechanical barrier
- Mucous membranes trap pathogens and contain antimicrobial compounds
- Inflammatory responses recruit immune cells and promote healing
- Cytokines trigger inflammation and fever
- Histamines increase blood flow and vascular permeability
- eliminates pathogens through cellular ingestion
- and engulf and destroy microorganisms
- process antigens for presentation to adaptive immune cells
Adaptive Immunity
- Adaptive immunity develops highly specific responses to pathogens
- produce for humoral immunity
- Antibodies neutralize pathogens and mark them for destruction
- provide long-term protection against specific antigens
- T lymphocytes mediate cellular immunity
- activate other immune cells and coordinate responses
- directly kill infected or abnormal cells
- (MHC) facilitates antigen presentation
- MHC class I presents intracellular antigens to CD8+
- MHC class II presents extracellular antigens to CD4+ T cells
- enhances antibody and phagocytic cell function
- Complement proteins form membrane attack complexes to lyse pathogens
- Complement fragments opsonize pathogens for easier phagocytosis
Cultural and Ecological Impacts of Disease
Cultural Practices and Disease Transmission
- Food preparation methods influence pathogen exposure
- Raw or undercooked meat consumption increases risk of foodborne illnesses ()
- Traditional fermentation practices can reduce pathogen load in foods
- Burial rituals affect disease spread in some cultures
- Touching or washing deceased bodies can transmit infections ()
- Cremation practices can reduce transmission of certain pathogens
- Sexual behaviors impact sexually transmitted infection rates
- Cultural attitudes towards contraception affect STI prevention
- Polygamous practices can increase the spread of STIs in some communities
Socioeconomic and Environmental Factors
- Access to healthcare affects disease prevention and control
- Limited healthcare access in rural areas can delay treatment and increase transmission
- Socioeconomic disparities lead to unequal health outcomes across populations
- Environmental conditions influence vector populations and pathogen survival
- Climate change expands the range of mosquito-borne diseases (malaria, )
- Deforestation increases human-wildlife contact, promoting zoonotic disease emergence
- Urbanization creates conditions conducive to disease transmission
- High population densities in cities facilitate rapid spread of respiratory infections
- Inadequate sanitation in urban slums increases risk of waterborne diseases ()
- Agricultural practices contribute to zoonotic disease development
- Intensive livestock farming can lead to antibiotic resistance in bacteria
- Wet markets with live animals increase risk of zoonotic spillover events ()
Immune System vs Pathogens
Evolutionary Arms Race
- describes ongoing evolutionary struggle between hosts and pathogens
- Continuous adaptation required to maintain fitness in both populations
- Explains the maintenance of sexual reproduction in many species
- Pathogens evolve mechanisms to evade or suppress host immune responses
- in trypanosomes allows evasion of antibody recognition
- Molecular mimicry in Streptococcus pyogenes mimics host proteins to avoid detection
- Human immune systems developed diverse recognition and response mechanisms
- detect conserved pathogen-associated molecular patterns
- Diversity in MHC genes allows recognition of a wide range of antigens
Rapid Adaptation and Genetic Diversity
- High mutation rates in pathogens enable rapid adaptation
- RNA viruses (influenza, ) have particularly high mutation rates
- formation in viral populations increases adaptability
- Balancing selection maintains genetic diversity in human populations
- preserves sickle cell allele in malaria-endemic regions
- Frequency-dependent selection maintains
- Antibiotic resistance exemplifies rapid pathogen adaptation
- (MRSA) evolved through horizontal gene transfer
- Multidrug-resistant emerged due to incomplete treatment regimens
- Host-pathogen coevolution led to development of tolerance mechanisms
- African buffalo tolerate foot-and-mouth disease virus without severe symptoms
- Human populations in malaria-endemic regions evolved to minimize disease severity
Key Terms to Review (50)
Abo blood type diversity: Abo blood type diversity refers to the variation in blood group types within the ABO blood group system, which includes A, B, AB, and O blood types. This diversity is significant in understanding human genetics, population biology, and how different blood types can influence susceptibility to certain infectious diseases and immune responses. These variations also have implications for blood transfusions, organ transplants, and evolutionary studies related to human adaptation and health.
Adaptive immunity: Adaptive immunity is a specialized immune response that develops over time and provides long-lasting protection against specific pathogens through the recognition of unique antigens. This type of immunity involves the activation and proliferation of lymphocytes, particularly B cells and T cells, which create a memory of the encountered pathogens. Adaptive immunity is crucial in combating infectious diseases, as it tailors its response to effectively eliminate specific threats the body has previously encountered.
Antibodies: Antibodies are specialized proteins produced by the immune system in response to foreign substances known as antigens. These proteins play a crucial role in identifying and neutralizing pathogens such as bacteria and viruses, acting as a key component of the adaptive immune response. By binding to specific antigens, antibodies help mark them for destruction by other immune cells, highlighting their importance in the defense against infectious diseases.
Antigenic drift: Antigenic drift refers to the gradual and continuous process by which small mutations in the genes of viruses lead to changes in their surface proteins, specifically the antigens. This evolution allows the virus to evade the immune system, making it more difficult for previously developed antibodies to recognize and combat the virus. Antigenic drift is particularly important in the context of influenza viruses, as it contributes to seasonal outbreaks and complicates vaccine development.
Antigenic shift: Antigenic shift is a process in which significant changes occur in the antigens of a virus, particularly influenza, leading to the emergence of new viral strains. This occurs when two different strains of a virus infect the same cell and exchange genetic material, resulting in a novel antigenic profile that can evade the host's immune response. Such shifts can lead to pandemics as the human immune system may not recognize the new strain, highlighting the dynamic interaction between infectious diseases and the immune system.
Antigenic variation: Antigenic variation is a process by which pathogens, particularly viruses and some bacteria, alter their surface proteins or antigens to evade the host's immune response. This ability allows these organisms to persist in a host by constantly changing their identity, making it difficult for the immune system to recognize and effectively eliminate them. Antigenic variation plays a crucial role in the pathogenesis of infectious diseases, influencing how the immune system responds and the effectiveness of vaccines.
B cells: B cells, or B lymphocytes, are a type of white blood cell that plays a crucial role in the adaptive immune response by producing antibodies. These cells originate in the bone marrow and are vital for recognizing specific pathogens, such as bacteria and viruses, enabling the body to mount an effective immune defense against infectious diseases. Upon activation, B cells can differentiate into plasma cells, which secrete large amounts of antibodies into the bloodstream, helping to neutralize pathogens.
B lymphocytes: B lymphocytes, also known as B cells, are a type of white blood cell that plays a crucial role in the immune response by producing antibodies to neutralize pathogens. These cells are essential for humoral immunity, the part of the immune system that involves the production of antibodies that can recognize and bind to specific antigens on invading microbes. When activated, B cells can differentiate into plasma cells that produce large quantities of antibodies, providing long-term immunity.
Bubonic plague: The bubonic plague is an infectious disease caused by the bacterium Yersinia pestis, typically transmitted through the bite of infected fleas that live on rodents. It is characterized by swollen lymph nodes, fever, chills, and weakness, and has historically resulted in significant mortality during outbreaks, notably the Black Death in the 14th century. Understanding the bubonic plague is essential to exploring infectious diseases and the human immune response.
Cholera: Cholera is an acute diarrheal illness caused by the bacterium Vibrio cholerae, which is typically transmitted through contaminated water or food. This infectious disease can lead to severe dehydration and, if untreated, can be fatal within hours. Understanding cholera is essential in the context of infectious diseases and the human immune system, as it highlights how pathogens interact with the host and how the immune response can be mobilized to combat such infections.
Clinical Trials: Clinical trials are research studies conducted with human participants to evaluate the safety and effectiveness of new medical treatments, drugs, or interventions. These trials are essential in understanding how the human immune system responds to various infectious diseases and how new therapies can improve patient outcomes. They provide a systematic way to assess whether a treatment is safe and beneficial before it is approved for widespread use.
Complement System: The complement system is a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism. It consists of a series of proteins that work together to identify and eliminate foreign invaders, such as bacteria and viruses, and plays a crucial role in both innate and adaptive immunity.
Covid-19: COVID-19 is a contagious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first identified in Wuhan, China, in late 2019. The disease has significantly impacted global health, economies, and social systems, becoming a prime example of how infectious diseases can rapidly spread and challenge the human immune system's response.
Cytotoxic t cells: Cytotoxic T cells, also known as cytotoxic T lymphocytes (CTLs), are a type of immune cell that play a crucial role in the body's defense against infectious diseases and cancer. These cells are responsible for directly killing infected or cancerous cells, recognizing them through specific antigens presented on the surface of these cells. By identifying and destroying compromised cells, cytotoxic T cells help maintain the integrity of the immune system and prevent the spread of infections.
Dendritic Cells: Dendritic cells are specialized antigen-presenting cells that play a crucial role in the immune system by capturing, processing, and presenting antigens to T cells. They act as a bridge between the innate and adaptive immune responses, enabling the body to recognize and respond to pathogens effectively. Their ability to activate T cells is essential for developing an adaptive immune response against infectious diseases.
Dengue: Dengue is a viral infection transmitted by mosquitoes, primarily the Aedes aegypti species, and is characterized by high fever, severe headache, pain behind the eyes, joint and muscle pain, rash, and mild bleeding. The disease is significant because it poses a major public health challenge in tropical and subtropical regions worldwide, and understanding its interaction with the human immune system is crucial for prevention and treatment strategies.
Ebola: Ebola is a severe and often fatal viral hemorrhagic fever caused by the Ebola virus, primarily affecting humans and nonhuman primates. It is known for its rapid spread, high mortality rates, and significant impact on human health and healthcare systems, particularly in regions with limited resources.
Epidemiological studies: Epidemiological studies are research investigations that focus on the distribution and determinants of health-related states or events in specific populations. They play a crucial role in understanding how infectious diseases spread, their impact on communities, and the effectiveness of public health interventions. These studies can inform healthcare policies and strategies to prevent and control diseases, making them essential in studying infectious diseases and the human immune system.
Glucose-6-phosphate dehydrogenase deficiency: Glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency) is a genetic disorder that affects the body's ability to produce an important enzyme called glucose-6-phosphate dehydrogenase, which plays a crucial role in the pentose phosphate pathway. This deficiency can lead to hemolytic anemia, especially during oxidative stress, and has significant implications for an individual’s response to infections and their overall immune function.
Helper T cells: Helper T cells, also known as CD4+ T cells, are a type of white blood cell that plays a crucial role in the immune system by helping other immune cells respond to infections. These cells are essential for activating and regulating the immune response, as they assist in the activation of B cells and cytotoxic T cells, which are vital for combating infectious diseases. By releasing signaling molecules called cytokines, helper T cells orchestrate the immune response, ensuring that the body can effectively fight off pathogens.
Herd immunity: Herd immunity is a form of indirect protection from infectious diseases that occurs when a large percentage of a population becomes immune, either through vaccination or previous infections. This high level of immunity reduces the overall spread of the disease, protecting those who cannot be vaccinated, such as individuals with certain health conditions or allergies. When enough people are immune, the transmission of the disease is significantly decreased, leading to the potential eradication of the pathogen from the community.
Heterozygote advantage: Heterozygote advantage refers to the phenomenon where individuals with two different alleles at a gene locus (heterozygotes) have a greater fitness than individuals with two identical alleles (homozygotes). This concept is particularly relevant in the context of infectious diseases and the human immune system, as it can explain how genetic diversity contributes to improved resistance against certain pathogens, allowing populations to adapt and survive in changing environments.
HIV: HIV, or Human Immunodeficiency Virus, is a virus that attacks the body's immune system, specifically targeting CD4 cells, which are crucial for fighting off infections. If left untreated, HIV can lead to AIDS (Acquired Immunodeficiency Syndrome), a condition characterized by a severely weakened immune system. Understanding HIV is essential for grasping how infectious diseases can compromise human health and the body's natural defenses.
Hygiene Hypothesis: The hygiene hypothesis suggests that a lack of early childhood exposure to infectious agents, microorganisms, and parasites increases susceptibility to allergic diseases by suppressing the natural development of the immune system. This idea connects the role of cleanliness and reduced microbial exposure with the rise in autoimmune and allergic conditions in developed countries, highlighting the delicate balance the immune system must maintain in distinguishing between harmful pathogens and harmless substances.
Immune evasion strategies: Immune evasion strategies are mechanisms employed by pathogens to avoid detection and elimination by the host's immune system. These strategies enhance the survival of the pathogen within the host and contribute to the persistence of infectious diseases. Understanding these strategies is crucial for developing effective treatments and vaccines, as they reveal how pathogens exploit weaknesses in the immune response.
Innate immunity: Innate immunity is the body's first line of defense against pathogens, consisting of physical, chemical, and cellular barriers that respond immediately to infections. This type of immunity is non-specific, meaning it acts against a wide range of invaders without the need for prior exposure. Innate immunity includes various components such as skin, mucous membranes, and immune cells like macrophages and neutrophils, all working together to prevent the spread of infectious diseases.
Live attenuated vaccine: A live attenuated vaccine is a type of vaccine that contains a weakened form of the pathogen that causes a particular infectious disease. This weakened pathogen can still replicate in the host but does not cause disease, allowing the immune system to respond and build immunity without the risk of severe illness. These vaccines stimulate a strong immune response and provide long-lasting protection against specific diseases.
Macrophages: Macrophages are a type of white blood cell that play a crucial role in the immune system by identifying, engulfing, and destroying pathogens, dead cells, and debris. They are essential for both the innate and adaptive immune responses, acting as frontline defenders against infections while also helping to activate other immune cells.
Major Histocompatibility Complex: The major histocompatibility complex (MHC) is a set of cell surface proteins essential for the immune system to recognize foreign molecules. These proteins play a crucial role in the immune response, particularly in presenting peptide fragments from pathogens to T cells, which helps the body distinguish between self and non-self cells. MHC molecules also have implications in mating strategies, as individuals with diverse MHC alleles are often preferred as mates, potentially enhancing offspring's immune competence.
Malaria: Malaria is a life-threatening infectious disease caused by parasites transmitted to humans through the bite of infected female Anopheles mosquitoes. It leads to severe illness and can result in death if not treated promptly. The disease is characterized by symptoms such as fever, chills, and flu-like illness, and it has a complex relationship with the human immune system, often resulting in different immune responses that can affect disease severity. Understanding malaria also involves examining its historical context and the evolutionary adaptations that have arisen in both humans and the malaria parasite over time.
Memory B Cells: Memory B cells are a type of white blood cell that plays a critical role in the adaptive immune response by providing long-term immunity against previously encountered pathogens. After an initial infection, these cells remain in the body and can quickly recognize and respond to the same pathogen if it is encountered again, allowing for a faster and more effective immune response during subsequent infections.
Methicillin-resistant staphylococcus aureus: Methicillin-resistant Staphylococcus aureus (MRSA) is a type of bacteria that has developed resistance to methicillin and other common antibiotics. This resistance makes MRSA infections more difficult to treat, posing significant challenges in healthcare settings and the community. Understanding MRSA is crucial in the study of infectious diseases, as it highlights the evolving relationship between bacteria and the human immune system.
MRSA: MRSA, or Methicillin-Resistant Staphylococcus Aureus, is a type of bacteria that has become resistant to many antibiotics, including methicillin. This resistance makes MRSA a significant concern in healthcare settings, as it can lead to severe infections that are difficult to treat. Understanding MRSA is crucial in the context of infectious diseases and the human immune system, as it highlights how pathogens can evolve and pose challenges to effective treatment and prevention strategies.
Neutrophils: Neutrophils are a type of white blood cell that plays a crucial role in the body's immune response by acting as the first line of defense against infections. They are part of the innate immune system and are essential for fighting off pathogens, particularly bacteria and fungi, through processes such as phagocytosis and the release of antimicrobial substances. Their rapid response and ability to migrate to sites of infection make them vital in protecting the body from infectious diseases.
Pattern Recognition Receptors: Pattern recognition receptors (PRRs) are proteins expressed by immune cells that recognize specific patterns associated with pathogens or damage. These receptors play a crucial role in the innate immune response by detecting microbial components or danger signals, leading to the activation of immune responses to combat infectious diseases.
Phagocytosis: Phagocytosis is a cellular process in which certain cells, known as phagocytes, engulf and digest pathogens, debris, or other foreign particles. This mechanism plays a crucial role in the immune response, allowing the body to protect itself from infectious diseases by removing harmful invaders and promoting healing.
Quasispecies: Quasispecies refers to a group of related genetic variants of a virus that exist in a dynamic equilibrium within a host. This term highlights the concept that viruses, particularly RNA viruses, do not just exist as a single sequence but rather as a cloud of closely related sequences that can evolve rapidly. This genetic diversity is crucial for the virus's ability to adapt to immune responses and antiviral treatments, making it a key factor in understanding infectious diseases and how they interact with the human immune system.
Red Queen Hypothesis: The Red Queen Hypothesis is an evolutionary theory that suggests organisms must constantly adapt and evolve not just for reproductive advantage, but also to survive against ever-evolving opposing organisms, such as pathogens and parasites. This concept emphasizes that in a co-evolutionary environment, species are in a constant race to stay ahead of each other, leading to an ongoing cycle of adaptation and counter-adaptation.
Salmonella: Salmonella is a genus of bacteria that can cause foodborne illness in humans, commonly known as salmonellosis. This infection is primarily linked to the consumption of contaminated food, particularly undercooked poultry, eggs, and unpasteurized dairy products. Understanding salmonella is essential for grasping the broader implications of infectious diseases on public health and the immune system's response to such pathogens.
SARS-CoV: SARS-CoV, or Severe Acute Respiratory Syndrome Coronavirus, is a viral pathogen that emerged in the early 2000s and is responsible for the disease known as SARS. This virus belongs to the family Coronaviridae and is characterized by its ability to cause severe respiratory illness, leading to significant morbidity and mortality, highlighting its impact on the human immune system and infectious diseases.
Sickle cell trait: Sickle cell trait is a genetic condition where an individual inherits one normal hemoglobin gene and one sickle hemoglobin gene, leading to the presence of both normal and abnormal hemoglobin in their red blood cells. This trait provides some level of protection against malaria, making it more prevalent in certain regions where the disease is common, while also posing risks under specific conditions such as extreme physical exertion or low oxygen levels.
Smallpox: Smallpox is a highly contagious and deadly viral disease caused by the variola virus, characterized by fever and a distinctive skin rash that forms pus-filled blisters. Its historical significance lies in its devastating impact on human populations, leading to widespread outbreaks and mortality until its eradication in 1980 through a successful global vaccination campaign.
Spanish flu: The Spanish flu was an influenza pandemic that occurred in 1918-1919, caused by the H1N1 influenza A virus. This pandemic is significant due to its rapid global spread and high mortality rate, affecting approximately one-third of the world's population and leading to an estimated 50 million deaths worldwide. The Spanish flu highlighted the vulnerabilities of the human immune system in the face of novel pathogens and served as a critical learning point for public health responses to infectious diseases.
T cells: T cells are a type of white blood cell that play a crucial role in the immune response by recognizing and responding to pathogens, including viruses and bacteria. They originate from stem cells in the bone marrow but mature in the thymus, where they develop the ability to identify infected or abnormal cells. T cells are vital for adaptive immunity, helping the body remember past infections and mount stronger responses upon re-exposure.
The Black Death: The Black Death was a devastating global epidemic of bubonic plague that struck Europe and Asia in the mid-14th century, killing an estimated 25 million people. This catastrophic event not only drastically reduced the population but also had profound effects on the social, economic, and cultural landscape of the time, significantly influencing human immune responses to infectious diseases.
The germ theory of disease: The germ theory of disease posits that many diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. This theory revolutionized the understanding of how infections spread and significantly advanced medical practices, emphasizing the importance of hygiene and sanitation in controlling infectious diseases and protecting the human immune system.
Tuberculosis: Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis, primarily affecting the lungs but can also impact other parts of the body. The disease is transmitted through the air when an infected person coughs or sneezes, leading to significant public health challenges. Understanding TB is crucial for grasping how infectious diseases interact with the human immune system and for implementing effective disease prevention strategies.
Vaccine-derived poliovirus: Vaccine-derived poliovirus (VDPV) refers to a strain of the poliovirus that has mutated from the live attenuated virus used in the oral polio vaccine (OPV). While OPV is designed to provide immunity and prevent poliovirus transmission, in rare cases, the weakened virus can revert to a more virulent form, leading to outbreaks of poliomyelitis. This phenomenon connects to the broader understanding of infectious diseases and the human immune system, as it highlights the delicate balance between vaccination benefits and potential risks associated with live vaccines.
Vector-borne disease: A vector-borne disease is an illness caused by pathogens and parasites transmitted to humans through vectors, which are typically insects like mosquitoes, ticks, or fleas. These diseases are significant in public health due to their ability to spread rapidly and affect large populations, often resulting in outbreaks that require coordinated epidemiological responses. Understanding these diseases involves looking at how vectors facilitate transmission and the immune system's role in combating these infections.
Zoonosis: Zoonosis refers to diseases that can be transmitted from animals to humans. These diseases often have significant implications for public health, as they can lead to outbreaks and affect the spread of infectious diseases. Understanding zoonosis is crucial for controlling disease transmission, developing vaccines, and implementing effective public health strategies.