Infectious disease

Disease caused by an infectious agent. Infection, detectable exposure and clinically damaging disease are distinct outcomes.

Acquired immunodeficiency syndrome, commonly AIDS, is the most severe stage of infection with a human immunodeficiency virus. Damage to immune defenses allows serious opportunistic infections and other characteristic illnesses. HIV-1 is a virus; acquired immunodeficiency syndrome is a clinical syndrome associated with advanced disease, not another name for the viral particle or for every positive infection test. Effective antiretroviral treatment can prevent progression to this stage.^[ref]

An early observation was a cluster of unusual infections rather than a direct measurement of a newly identified virus. The CDC's5June1981 report described five young men treated at three Los Angeles hospitals for biopsy-confirmed Pneumocystis pneumonia. The report also described other infections and profoundly reduced in-vitro proliferative responses in the three patients whose lymphocyte function was tested.^[ref]

The denominator matters: three abnormal tests out of three tested patients is not evidence that all five were tested, nor does it estimate the frequency of immune dysfunction in a general population. The pattern motivated investigation of a shared immunodeficiency, while the case series alone did not establish its cause or route of transmission.

The scientific distinction remains useful. An organism that is usually controlled can become pathogenic when host defenses fail; investigating the infection and investigating the underlying immune defect answer different questions. Conversely, a single nonspecific symptom cannot establish acquired immunodeficiency syndrome, and a human immunodeficiency virus infection need not have progressed to that syndrome.

Virulence is the degree to which a pathogen causes damage or disease in a specified host and setting. It is a quantitative aspect of pathogenic behaviour, not simply a label meaning that an organism can cause an infection.^[ref]

A comparison needs an endpoint and controlled conditions. One experiment might compare tissue damage after equal exposure; another might compare survival across a range of doses. If two strains differ in the dose required to produce an outcome, that result concerns the tested host, route and conditions. It is not automatically a universal ordering for every species or exposure route.

This also separates damage from transmission. A pathogen can spread efficiently without causing the most severe disease, while a damaging infection need not transmit efficiently. Keeping the outcomes separate makes evolutionary and experimental claims about virulence testable.

A sexually transmitted infection caused by Neisseria gonorrhoeae. Different mucosal sites can be involved, and absence of symptoms does not establish absence of infection.^[ref]

Presence of bacteria in the blood; it is not synonymous with every systemic inflammatory illness or with all forms of sepsis.

Infection established at a site distant from its primary focus through spread of microorganisms, commonly through the blood.

A parasitic infection acquired through ingestion of infected meat containing Trichinella larvae.^[ref]

A historical and clinical term associated with systemic infection involving the bloodstream; its use should not be treated as identical to every modern definition of sepsis.

A historical clinical designation for disseminated suppurative infection with multiple secondary foci; distinguish the term from a modern universal definition of sepsis.

A disease caused by Bacillus anthracis, with manifestations depending on the route of exposure. Spore persistence connects the organism’s biology with environmental transmission.^[ref]

A genital-ulcer infection caused by Haemophilus ducreyi. It is distinct from syphilis; lesion appearance can overlap with other infections and does not alone establish the causative organism.^[ref]

The primary infection caused by varicella-zoster virus; distinct from smallpox.

The infection caused by variola virus. Varioloid describes modified disease, rather than a distinct infection.

Historical name for modified smallpox, especially following vaccination; distinct from chickenpox.

A parasitic disease caused by the guinea worm Dracunculus medinensis. Ingestion of infected aquatic intermediate hosts connects contaminated drinking water with later development of an emerging adult worm.^[ref]

A disease transmitted through water carrying an infectious agent or another harmful exposure. The category describes a route, not one pathogen; sanitation and drinking-water treatment interrupt different parts of that route.

Infection with larval stages of Echinococcus tapeworms. Tissue lesions can develop after ingestion of eggs, distinguishing the human intermediate-host infection from an adult intestinal tapeworm.^[ref]

An infectious disease caused by Treponema pallidum.

Involvement of the nervous system by syphilis; it is not confined to a single chronological stage.

A late neurological manifestation of syphilis involving posterior sensory pathways of the spinal cord. Loss of position sense can impair coordination despite preserved muscle strength, connecting the affected pathway with the clinical pattern.

A late manifestation of neurosyphilis involving progressive cognitive, behavioral and neurological disturbance. Its historical psychiatric description preceded a secure explanation of its infectious cause, connecting changes in disease classification with microbiological evidence.^[ref]

A late form of syphilis with destructive granulomatous lesions called gummas. Their tissue effects differ from the primary chancre, illustrating how one infection can produce distinct pathological stages.^[ref]

A gumma is a destructive granulomatous lesion characteristic of late syphilis. It can involve skin, bone or internal organs, producing local damage through a chronic inflammatory process. It belongs to gummatous syphilis, rather than being another name for the primary chancre. ^[ref]

The distinction illustrates how one infectious agent can produce different pathological patterns at different stages. A lesion's gross appearance, its microscopic inflammatory organization and evidence of the underlying infection are different observations. The category therefore describes a clinicopathological pattern, not a claim that every late syphilis presentation has the same anatomy or contains a readily visible organism.

Primary lesion classically associated with acquired syphilis; appearance alone does not establish the diagnosis.

Infection acquired before birth; an infant may initially lack visible signs. Historical “hereditary” terminology does not imply Mendelian inheritance.

Inflammation of brain tissue. Infection and immune-mediated processes are different causes, so the anatomical term does not establish one organism or mechanism.

Inflammation of the membranes surrounding the brain and spinal cord. Its location differs from encephalitis, though both can occur together.

A disease caused by poliovirus; paralytic disease is one possible consequence, not the result of every infection.

An inflammatory intestinal syndrome with bloody diarrhea, often with mucus and cramping. Different infectious agents can produce the pattern, making the syndrome distinct from a specific microbiological diagnosis.

Inflammation or infection of the middle-ear space. Fluid behind the eardrum can affect sound conduction, connecting a local inflammatory process with temporary hearing loss.

Inflammation of lymph nodes. Enlargement and tenderness can reflect a response to a nearby process, while the anatomical finding alone does not identify its infectious or noninfectious cause.

Microbial infection of an anatomical joint. Inflammation can damage articular structures, distinguishing it from noninfectious crystal-associated or autoimmune arthritis.

Transmission in which infectious material from excreta reaches another person's mouth through such routes as food, water or hands.

A parasitic disease caused by Plasmodium, usually transmitted by infected mosquitoes. Distinct stages in the vector, liver and blood connect the organism’s life cycle with transmission and clinical illness.^[ref]

An intestinal infection caused by toxigenic Vibrio cholerae. Toxin-induced fluid secretion can produce profound watery diarrhea, connecting a molecular effect on transport with whole-body fluid loss.^[ref]

A toxin-mediated disease caused by Clostridium tetani. Tetanospasmin disrupts inhibitory neural signaling, producing rigidity and spasms; the wound is the microbial source rather than the site of every symptom.^[ref]

An antibody preparation that can bind and neutralize unbound tetanospasmin. It supplies passive protection and differs from a vaccine, which induces the recipient’s own immune response.^[ref]

The neurotoxin associated with tetanus. Neutralizing unbound toxin differs from reversing toxin already acting at neural targets.

A parasitic organism living in or associated with the intestine. Different species occupy different niches and have different life cycles, so detecting a parasite does not imply one uniform route of transmission.

An infection caused by members of the Mycobacterium tuberculosis complex. Infection can remain clinically inactive or progress to disease; pulmonary involvement is common, but other organs can be affected.^[ref]

Tuberculosis involving the urinary system. Local tissue damage and scarring can affect renal function or urinary drainage, connecting infection with later structural complications.

A historical pathological name for a small nodular lesion. Chemical examination can characterize the material in a lesion without establishing its infectious cause. The word does not name one pure chemical compound.

Tuberculosis involving intestinal tissue. Inflammation, ulceration and scarring can alter bowel function, while the diagnosis requires evidence beyond a nonspecific abdominal symptom pattern.

A granuloma arising in tuberculosis, comprising organized immune-cell responses to infection. Tissue appearance supports a pathological interpretation but does not replace microbiological evidence of the organism.

A group of rickettsial infections, including epidemic typhus associated with body lice. The name is distinct from typhoid fever, which has a different organism and transmission route.^[ref]

An infection caused by a member of Streptococcus. Species and site matter: the genus includes organisms with different clinical behavior and ecological roles.

An infection caused by group A streptococci, usually Streptococcus pyogenes. Local infection, toxin effects and later immune-mediated complications are biologically distinct outcomes.

An infection caused by fungi. Superficial, mucosal and invasive forms involve different tissue relationships, and recovery of a fungus from a surface is not automatically invasive disease.

An infection caused by members of Candida.

An opportunistic fungal infection of the oral mucosa, historically called Muguet. White plaques are distinct from an aphthous ulcer.

A dermatophyte fungal infection affecting keratin-containing tissue; the name does not imply a worm.

A dermatophyte fungal infection involving beard-area hair and follicles. It differs from every other inflammatory beard eruption, making sampling and organism identification useful when appearance overlaps.^[ref]

Ringworm of the body skin.

Life-threatening organ dysfunction caused by a dysregulated response to infection. Infection, bloodstream organisms and sepsis are related but different findings; sepsis need not be defined by a positive blood culture.^[ref]

Inflammation of the stomach and intestines, commonly associated with diarrhea and vomiting. The syndrome can arise from different infectious and noninfectious causes, so its name does not identify one pathogen.

A syndrome associated with toxin-producing Group A streptococcal infection, classically combining pharyngitis with a characteristic rash. The rash reflects a toxin-associated response rather than fungal invasion of skin.^[ref]

A systemic infection caused by Salmonella Typhi, usually acquired through contaminated food or water. Intestinal entry can be followed by dissemination, connecting a fecal–oral route with illness beyond the bowel.^[ref]

Diarrhoea occurring during typhoid fever. The stool symptom does not measure the severity of systemic infection or exclude intestinal complications.

An ulcer arising with destruction of intestinal lymphoid tissue in typhoid fever. The classical larger lesion follows the longitudinal shape of a Peyer's patch.

Intestinal infection with an adult Taenia.

Infection by tissue cysticerci of Taenia solium, acquired by ingestion of eggs.

An inflammatory disease of lung tissue, commonly caused by an infection, that can fill air spaces with inflammatory material. The term identifies a clinical and pathological syndrome; the responsible organism and pattern of involvement require additional evidence.^[ref]

The liver-like firmness of consolidated lung in classical descriptions of pneumonia. It is an appearance, not conversion into liver tissue.^[ref]

A pattern of pneumonia involving confluent consolidation of a substantial part of a lung lobe. The distribution is a pathological description rather than a unique identification of the causative organism.

A patchy pattern of pneumonia centered on airways and adjacent lung tissue. Its distribution differs from confluent lobar consolidation without requiring one specific pathogen.