Outcomes of infection
The termination of an infectious disease can follow several scenarios. It is important to distinguish between clinical recovery (when symptoms disappear and the pathogen is eliminated) and complete morphological tissue repair, which takes longer.
Main outcome options:
- Complete recovery.
- Transition to a chronic form.
- Development of microbial carriage.
- Fatal outcome.
Additionally, immunological consequences are distinguished. Post-infection immunity may develop after the disease. For some infections, it is persistent and lifelong (measles, plague), while for others, it is weak and short-lived, allowing reinfection (shigellosis). The infectious process also frequently leads to the development of secondary immunodeficiency.
Classification by symptom severity
Depending on the presence and intensity of signs characteristic of a specific disease, infections are divided into the following forms:
- Typical — all leading symptoms are present.
- Atypical — deviate from the classic picture. They include:
- Mild (abortive/muffled) — some symptoms are absent, while others are weakly expressed.
- Inapparent (subclinical) — no symptoms at all, diagnosis is established solely by laboratory testing.
- Abortive — begin typically, but symptoms quickly and abruptly disappear (often in vaccinated individuals).
- Fulminant — extremely severe, rapid course with a high probability of a fatal outcome.
Based on the presence of symptoms, manifest infection (with overt clinical signs) and inapparent infection (without manifestations) are also distinguished.
Localization and forms of presence in the blood
According to the pathogen's ability to spread beyond the portal of entry, the following are distinguished:
- Focal infection — the pathogen remains solely at the site of entry.
- Generalized infection — the microbe spreads via lymph, blood, nerves, or respiratory tracts. A focal form can progress to a generalized form when immunity is compromised.
Presence in the blood (lymph):
- Transient (bacteremia, viremia) — the microbe is present in the blood briefly and does not multiply there. This is a transport stage.
- Antigenemia — microbial antigens circulate in the blood even if the pathogen itself is absent.
- Toxemia — toxins circulate in the blood, while the pathogen remains at the entry site (diphtheria, tetanus).
- Sepsis — the blood becomes a permanent habitat and site of reproduction for microbes. Septicemia (portal of entry unknown) and septicopyemia (secondary purulent metastases form) are distinguished.
Features of the course and reinfections
The infection may proceed smoothly or unsmoothly (with complications).
According to the timing of secondary infection occurrence, the following are distinguished:
- Secondary infection — the addition of another species of microbe to an ongoing disease against the background of a weakened body.
- Superinfection — reinfection with the same pathogen before complete recovery, which aggravates the condition.
- Reinfection — reinfection with the same pathogen, but after complete recovery.
During the course of the disease, symptom returns may occur: an exacerbation occurs during the recovery stage, whereas a relapse occurs after the disappearance of symptoms (clinical recovery).
Persistence: microbial carriage and latency
Prolonged presence of the microbe in the body without acute clinical signs takes several forms:
- Microbial carriage — a subclinical process with the shedding of the pathogen into the environment. Accompanied by immune shifts, but without pronounced tissue changes (except for "healthy carrier state"). It may be the result of a previous illness or an incubation stage.
- Latent infection — the microbe is present for a long time ("dormant"), but is not shed into the environment (syphilis, herpes).
- Chronic infection — lasts longer than 6 months (continuously or with relapses). Microbes are shed for months and years (tuberculosis, brucellosis).
Briefly: answers to topical questions
What types of infection are distinguished by their duration?
Based on the duration of the infectious process, acute, subacute, and chronic infections are distinguished.
- Acute course — the disease resolves within 1–3 months (in acute intestinal infections — up to 13 days).
- Subacute course (protracted) — lasts up to 4–6 months (in intestinal infections — 14–29 days).
- Chronic course — lasts over 6 months (in intestinal infections — 30 days or more).
What developmental periods are distinguished in the cyclic course of an infectious disease?
In the cyclic course of an infectious disease, five consecutive periods determined by pathogenesis are distinguished.
- Incubation period (latent) — the time from the entry of the infectious agent to the completion of its replication cycle.
- Prodromal period (initial) — the appearance of the first non-specific symptoms.
- Period of height (acme) — the stage of main or maximally expressed clinical manifestations.
- Period of symptom decline — early convalescence with the gradual disappearance of clinical signs.
- Period of recovery — complete convalescence.
What types of infection are distinguished by the number of pathogen species?
Based on the number of pathogen species, the infectious process is subdivided into monoinfections and mixed infections.
- Monoinfection — caused by a single microbial species.
- Mixed infection (coinfection) — caused simultaneously by several microbial species.
Infections frequently present as mixed infections (polymicrobial associations).
What types of pathogen carriage are distinguished by the duration of pathogen shedding?
Based on the duration of pathogen shedding, pathogen carriage is classified into transient, acute, and chronic.
- Transient carriage is the single-time shedding of the causative agent with a complete absence of clinical manifestations.
- Acute carriage is when the shedding of the microorganism continues for a short period of time (up to 3 months after recovering from the disease).
- Chronic carriage is the prolonged shedding of the causative agent lasting more than 3 months, which may become lifelong.
Differences in repeated infections: SUPERinfection — the microbe layers "super" fast (before recovery), REinfection — you get infected "regularly" (after recovery), SECONDARY — a "second" (different) microbe arrives.
Class and exam questions
How does a relapse differ from an exacerbation?
Exacerbation occurs when symptoms were already subsiding, but complete clinical recovery has not yet occurred. A relapse is the return of symptoms after they have completely disappeared.
What is an abortive form of infection?
This is a form that begins with typical symptoms, but they suddenly and rapidly disappear. It is often encountered in individuals vaccinated against this disease.
What is the difference between a latent infection and pathogen carriage?
In pathogen carriage, the causative agent is actively shed into the environment, presenting an epidemiological hazard. In a latent infection, the microbe "slumbers" in the body and is not shed into the environment.
What else to study on this topic
- Complications of the infectious process: specific and non-specific
- Methods of laboratory diagnostics for infectious diseases
- Principles of etiotropic and specific therapy
- Exogenous and endogenous (autoinfections) infections by origin
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