Immunity
These white blood cells are the most abundant WBCs in humans. They are phagocytes that respond quickly to bacterial infections.
Neutrophils
These Gram-negative bacilli cause dysentery through cytokine-mediated inflammation and colitis. Complications include toxic megacolon and hemolytic uremic syndrome.
Shigella
This double-stranded DNA virus causes oral or genital sores that can reactivate due to latency in sensory ganglia
Herpes simplex virus
This yeast is a normal part of the flora in the GI tract and skin, but can become an opportunistic infection in immunocompromised patients or while taking antibiotics
Candida albicans
This flagellated protozoan is found in contaminated water and commonly seen in campers and travelers. It disrupts epithelial function and causes malabsorption of fats and fat soluble vitamins.
Giardia
These white blood cells are involved in parasitic infections and allergic reactions
Eosinophils
These Gram-negative coccobacilli are spread to humans from fleas and rodents. Their type III secretion system and capsule inhibit phagocytosis, while plasminogen activator spreads the bacteria to lymph nodes where painful buboes form.
Yersinia pestis
This negative-sense single-stranded RNA virus can undergo antigenic drift mutations to cause seasonal epidemics or antigenic shift genome reassortments to cause pandemics
Influenza virus
This fungus causes a foamy proteinaceous exudate in the alveoli of patients with CD4+ T-cell deficiency. It is treated with trimethoprim-sulfamethoxazole rather than antifungals because its cell wall lacks ergosterol.
Pneumocystis jirovecii
This protozoan enters the bloodstream via mosquitoes, travels to the livers, and infects red blood cells. It causes cyclic red blood cell lysis, fevers, and rarely cerebral disease.
Plasmodium
This mediator released by mast cells leads to inflammation by causing vasodilation and increased vascular permeability
Histamine
These atypical, Gram-negative bacilli lack a peptidoglycan layer in their cell wall. Their elementary body form is infectious, while their reticulate body form causes inflammation that can lead to scarring in host tissues.
Chlamydia trachomatis
This negative-sense, single-stranded RNA paramyxovirus has an envelope that contains hemagglutinin and F protein. It causes a prodrome of flu-like symptoms and conjunctivitis, followed by a maculopapular rash and rare complications like encephalitis.
Measles (morbillivirus)
This encapsulated budding yeast is found in soil worldwide and transmitted by inhaled spores. It can cause lung infection in primary disease or chronic meningitis and CNS infection in disseminated disease.
Crytococcus neoformans
This intracellular protozoan is transmitted in the feces of domestic cats. It causes mild disease in immunocompetent patients, but can cause severe congenital abnormalities if contracted by pregnant women.
Toxoplasma gondii
This group of white blood cells includes helper cells that coordinate immune responses and cytotoxic cells that directly kill pathogens
T-lymphocytes
These Gram-negative bacilli are commonly found in man-made water systems. They replicate inside host cells, form intracellular vacuoles to hide from host immune defenses, and promote inflammation that leads to pneumonia with GI symptoms.
Legionella
This non-enveloped, single-stranded, positive-sense RNA virus survives well on surfaces and is the #1 cause of the common cold
Rhinovirus
This fungus is found mostly in the soil of the Ohio and Mississippi River Valleys. Infection may be mild or asymptomatic in immunocompetent patients, but it may cause severe lung disease and cavitary lesions similar to TB in immunocompromised patients.
Histoplasma
This tissue nematode is transmitted via ingestion of undercooked pork or wild game. It forms encysted larvae in human striated muscle.
Trichinella spiralis
Found on the surface of most human cells, this complex displays antigens that identify the cell as part of the host rather than a foreign invader
Major histocompatibility complex
These Gram-positive cocci have an antiphagocytic capsule, an M protein that causes autoimmune cross reactivity, and exotoxins that can cause necrotizing fasciitis or toxic shock syndrome.
Streptococcus pyogenes
These two viruses utilize reverse transcriptase to transcribe RNA into DNA
Hepatitis B and HIV
This mold with branching hyphae produces gliotoxin to impair phagocyte function. It can invade blood vessels, cause lung infection, and form fungus balls in pre-existing cavitary lesions.
Aspergillus
This nematode infects humans after larvae penetrate the skin, migrate to lungs, and are swallowed into the intestines. Autoinfection can continue for decades as larvae migrate between infective and noninfective forms.
Strongyloides stercoralis