Infections

Infection: Modes of Transmission

Infection involves several modes of transmission, which include penetration, direct contact, ingestion, and inhalation. Common sources of infectious agents are eggs, poultry, contaminated water or soil, animal bites, and sexual intercourse, as well as oral or nasal secretions and blood contact. Infectious diseases originate from a source, such as infected hosts or contaminated objects, and require a specific portal of entry and vector. The host is the organism that supports the growth of pathogens, and its susceptibility varies according to resistance levels.

Types of Infections

There are two primary types of infections: nosocomial infections, which are acquired in hospital settings, and community-acquired infections, which occur outside of healthcare facilities.

Chain of Infection

The chain of infection comprises various factors affecting resistance, including general health, pre-existing conditions, age, and the virulence of the infectious agent. Mechanisms of disease production are attributed to virulence factors such as toxins, which can be categorized as endotoxins, found in gram-negative bacteria that affect the immune response, and exotoxins, which are protein toxins leading to cell death, for instance, those found in botulism and cholera. Pathogens utilize adhesion factors to attach to hosts, evasive factors to prevent destruction by the host, and invasive factors in the form of enzymes that aid in tissue invasion.

Disease Course

The disease course can be classified into acute, marked by sudden onset and severe symptoms, and chronic, which persist over time with milder symptoms. Local infections are limited to one area, exhibiting signs such as swelling and warmth, while systemic infections affect the entire body, presenting symptoms like fever and malaise.

Clinical Manifestations

Specific symptoms can include respiratory distress in children, while non-specific symptoms may range from fever to fatigue. The disease progresses through several stages: the incubation period, prodromal stage, acute stage, convalescent period, and resolution period.

Diagnostic Tests for Infections

Diagnostic tests serve the purpose of identifying infections and guiding treatment options, which may include a variety of test types such as culture, serology, DNA/RNA sequencing, blood panels, and diagnostic imaging.

Cellular Response to Infection

In response to infection, leukocytosis, or increased white blood cells, typically occurs in bacterial infections, while leukopenia, or decreased white blood cells, may suggest a severe infection.

Treatment Options

Treatment for infections may involve antimicrobial agents, including antibacterial, antiviral, and antifungal medications, each possessing various mechanisms of action such as the inhibition of cell wall synthesis and protein synthesis in bacteria, targeting viral replication, or inhibiting fungal cell wall synthesis.