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Infectious Diseases

Biology of Infectious Disease
Laboratory Diagnosis of Infectious Disease
Immunization
Anaerobic Bacteria
Approach to Parasitic Infections
- Approach to Parasitic Infections
Arboviruses, Arenaviridae, and Filoviridae
Bacteria and Antibacterial Drugs
Cestodes (Tapeworms)
Chlamydia and Mycoplasmas
- Chlamydia
- Mycoplasmas
Enteroviruses
Extraintestinal Protozoa
Fungi
Gram-Negative Bacilli
Gram-Positive Cocci

Gram-Positive Bacilli
Herpesviruses
Human Immunodeficiency Virus (HIV)
- Human Immunodeficiency Virus (HIV) Infection
- Cancers Common in HIV-Infected Patients
Intestinal Protozoa and Microsporidia
Mycobacteria
Neisseriaceae
Nematodes (Roundworms)
Pox Viruses
- Monkeypox
- Smallpox
Respiratory Viruses
Rickettsiae and Related Organisms
Sexually Transmitted Diseases (STDs)
Spirochetes
Trematodes (Flukes)
Viruses
- Overview of Viruses
- Types of Viral Disorders

The human body is constantly vulnerable to infection or invasion by harmful organisms such as viruses, bacteria, fungi, and parasites. Infectious disease is a subspecialty of internal medicine that focuses on the diagnosis, prevention, and treatment of communicable diseases, including the use of public health measures and vaccines.

Infectious DiseasesSections (A-Z)

Anaerobic Bacteria

Bacteria can be classified by their need and tolerance for O 2 :

Overview of Anaerobic Bacteria
Actinomycosis
Overview of Clostridial Infections
Botulism
Infant Botulism
Clostridium difficile –Induced Diarrhea
Clostridial Intra-abdominal and Pelvic Infections
Clostridial Necrotizing Enteritis
Clostridium perfringens Food Poisoning
Clostridial Soft-Tissue Infections
Tetanus
Mixed Anaerobic Infections

Approach to Parasitic Infections

(See also Cestodes , Extraintestinal Protozoa , Intestinal Protozoa , Nematodes , and Trematodes .)

Approach to Parasitic Infections

Arboviruses, Arenaviridae, and Filoviridae

Arbovirus (arthropod-borne virus) applies to any virus that is transmitted to humans and/or other vertebrates by certain species of blood-feeding arthropods, chiefly insects (flies and mosquitoes) and arachnids (ticks). Arbovirus is not part of the current viral classification system, which is based on the nature and structure of the viral genome. Families in the current classification system that have some arbovirus members include

Overview of Arbovirus, Arenavirus, and Filovirus Infections
Dengue
Hantavirus Infection
Lassa Fever
Lymphocytic Choriomeningitis
Marburg and Ebola Virus Infections
Yellow Fever
Zika Virus (ZV) Infections
Other Arbovirus Infections

Bacteria and Antibacterial Drugs

Bacteria are microorganisms that have circular double-stranded DNA and (except for mycoplasmas) cell walls. Most bacteria live extracellularly. Some bacteria (eg, Salmonella typhi ; Neisseria gonorrhoeae ; Legionella , Mycobacterium , Rickettsia , Chlamydia , and Chlamydophila spp) preferentially reside and replicate intracellularly. Some bacteria such as chlamydiae, Chlamydophila sp, and rickettsiae are obligate intracellular pathogens (ie, able to grow, reproduce, and cause disease only within the cells of the host). Others (eg, Salmonella typhi , Brucella sp, Francisella tularensis , N. gonorrhoeae , N. meningitidis , Legionella and Listeria spp, Mycobacterium tuberculosis ) are facultative intracellular pathogens.

Overview of Bacteria
Overview of Antibacterial Drugs
Aminoglycosides
Spectinomycin
β -Lactams
Carbapenems
Cephalosporins
Monobactams
Penicillins
Chloramphenicol
Daptomycin
Fluoroquinolones
Fosfomycin
Lincosamides, Oxazolidinones, and Streptogramins
Clindamycin
Linezolid and Tedizolid
Quinupristin and Dalfopristin
Macrolides
Telithromycin
Metronidazole
Mupirocin
Nitrofurantoin
Polypeptide Antibiotics: Bacitracin, Colistin, Polymyxin B
Rifamycins
Sulfonamides
Trimethoprim and Sulfamethoxazole
Telavancin
Tetracyclines
Tigecycline
Vancomycin

Biology of Infectious Disease

A healthy person lives in harmony with the microbial flora that helps protect its host from invasion by pathogens, usually defined as microorganisms that have the capacity to cause disease. The microbial flora is mostly bacteria and fungi and includes normal resident flora, which is present consistently and which promptly reestablishes itself if disturbed, and transient flora, which may colonize the host for hours to weeks but does not permanently establish itself. Organisms that are normal flora can occasionally cause disease, especially when defenses are disrupted.

Introduction to the Biology of Infectious Diseases
Host Defense Mechanisms Against Infection
Factors Facilitating Microbial Invasion
Manifestations of Infection
Fever
Fever of Unknown Origin (FUO)
Abscesses
Bacteremia

Cestodes (Tapeworms)

All tapeworms (cestodes) cycle through 3 stages—eggs, larvae, and adults. Adults inhabit the intestines of definitive hosts, mammalian carnivores. Several of the adult tapeworms that infect humans are named after their intermediate host:

Overview of Tapeworm Infections
Diphyllobothriasis (Fish Tapeworm Infection)
Dipylidium caninum Infection
Echinococcosis
Hymenolepis diminuta Infection
Hymenolepis nana (Dwarf Tapeworm) Infection
Sparganosis
Coenurosis ( Taenia multiceps, T. serialis , or T. brauni Infection)
Taenia asiatica (Asian Tapeworm) Infection
Taenia Saginata (Beef Tapeworm) Infection
Taenia Solium (Pork Tapeworm) Infection and Cysticercosis

Chlamydia and Mycoplasmas

Three species of Chlamydia cause human disease, including sexually transmitted diseases and respiratory infections. Most are susceptible to macrolides (eg, azithromycin), tetracyclines (eg, doxycycline), and fluoroquinolones.

Chlamydia
Mycoplasmas

Enteroviruses

Enteroviruses include

Overview of Enterovirus Infections
Epidemic Pleurodynia
Hand-Foot-and-Mouth Disease (HFMD)
Herpangina
Poliomyelitis
Postpoliomyelitis Syndrome

Extraintestinal Protozoa

African trypanosomiasis is infection with protozoa of the genus Trypanosoma , transmitted by the bite of a tsetse fly. Symptoms include characteristic skin lesions, intermittent fever, headache, rigors, transient edema, generalized lymphadenopathy, and often fatal meningoencephalitis. Diagnosis is by identification of the organism in blood, lymph node aspirate, or CSF or sometimes by serologic tests. Treatment is with suramin, pentamidine, melarsoprol, or eflornithine, depending on the infecting subspecies, clinical stage, and drug availability.

African Trypanosomiasis
Babesiosis
Chagas Disease
Free-Living Amebas
Leishmaniasis
Malaria
Toxoplasmosis

Fungi

(See also Fungal Skin Infections .)

Overview of Fungal Infections
Antifungal Drugs
Aspergillosis
Blastomycosis
Candidiasis (Invasive)
Chromoblastomycosis
Coccidioidomycosis
Cryptococcosis
Histoplasmosis
Mucormycosis
Mycetoma
Paracoccidioidomycosis
Phaeohyphomycosis
Sporotrichosis
Miscellaneous Opportunistic Fungi

Gram-Negative Bacilli

Gram-negative bacilli are responsible for numerous diseases. Some are commensal organisms present among normal intestinal flora. These commensal organisms plus others from animal or environmental reservoirs may cause disease.

Introduction to Gram-Negative Bacilli
Overview of Bartonella Infections
Cat-Scratch Disease
Oroya Fever and Verruga Peruana
Bacillary Angiomatosis
Trench Fever
Brucellosis
Campylobacter and Related Infections
Cholera
Noncholera Vibrio Infections
Escherichia coli Infections
Infection by Escherichia coli O157:H7 and Other Enterohemorrhagic E. coli (EHEC)
Haemophilus Infections
HACEK Infections
Klebsiella , Enterobacter , and Serratia Infections
Legionella Infections
Melioidosis
Pertussis
Plague and Other Yersinia Infections
Proteeae Infections
Pseudomonas and Related Infections
Overview of Salmonella Infections
Typhoid Fever
Nontyphoidal Salmonella Infections
Shigellosis
Tularemia

Gram-Positive Bacilli

Anthrax is caused by Bacillus anthracis , toxin-producing, encapsulated, facultative anaerobic organisms. Anthrax, an often fatal disease of animals, is transmitted to humans by contact with infected animals or their products. In humans, infection is typically acquired through the skin. Inhalation infection is less common; oropharyngeal, meningeal, and GI infections are rare. For inhalation and GI infections, nonspecific local symptoms are typically followed in several days by severe systemic illness, shock, and often death. Empiric treatment is with ciprofloxacin or doxycycline. A vaccine is available.

Anthrax
Diphtheria
Erysipelothricosis
Listeriosis
Nocardiosis

Gram-Positive Cocci

Enterococci are gram-positive aerobic organisms. Enterococcus faecalis and E. faecium cause a variety of infections, including endocarditis, UTI, prostatitis, intra-abdominal infection, cellulitis, and wound infection as well as concurrent bacteremia.

Enterococcal Infections
Pneumococcal Infections
Staphylococcal Infections
Streptococcal Infections
Toxic Shock Syndrome (TSS)

Herpesviruses

Eight types of herpesviruses infect humans (see Table: Herpesviruses That Infect Humans ). After initial infection, all herpesviruses remain latent within specific host cells and may subsequently reactivate. Herpesviruses do not survive long outside a host; thus, transmission usually requires intimate contact. In people with latent infection, the virus can reactivate without causing symptoms; in such cases, asymptomatic shedding occurs and people can transmit infection.

Overview of Herpesvirus Infections
Chickenpox
Cytomegalovirus (CMV) Infection
Herpes Simplex Virus (HSV) Infections
Genital Herpes
Herpes Zoster
Infectious Mononucleosis

Human Immunodeficiency Virus (HIV)

Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain infections and cancers. Initial infection may cause nonspecific febrile illness. Risk of subsequent manifestations—related to immunodeficiency—is proportional to the level of CD4+ lymphocytes. HIV can directly damage the brain, gonads, kidneys, and heart, causing cognitive impairment, hypogonadism, renal insufficiency, and cardiomyopathy. Manifestations range from asymptomatic carriage to AIDS, which is defined by serious opportunistic infections or cancers or a CD4 count of 200/ μ L. HIV infection can be diagnosed by antibody, nucleic acid (HIV RNA), or antigen (p24) testing. Screening should be routinely offered to all adults and adolescents. Treatment aims to suppress HIV replication by using combinations of ≥ 3 drugs that inhibit HIV enzymes; treatment can restore immune function in most patients if suppression of replication is sustained.

Human Immunodeficiency Virus (HIV) Infection
Cancers Common in HIV-Infected Patients

Immunization

Immunity can be achieved

Overview of Immunization
What's New in Immunization
Diphtheria-Tetanus-Pertussis Vaccine
Tetanus-Diphtheria Vaccine
Meningococcal Vaccine
Haemophilus influenzae Type b Vaccine
Hepatitis A Vaccine
Hepatitis B Vaccine
Human Papillomavirus Vaccine
Influenza Vaccine
Measles, Mumps, and Rubella Vaccine
Pneumococcal Vaccine
Poliomyelitis Vaccine
Varicella Vaccine
Herpes Zoster Vaccine
Passive Immunization

Intestinal Protozoa and Microsporidia

The most important intestinal protozoan pathogens are

Overview of Intestinal Protozoan and Microsporidia Infections
Amebiasis
Cryptosporidiosis
Cyclosporiasis and Cystoisosporiasis
Giardiasis
Microsporidiosis

Laboratory Diagnosis of Infectious Disease

Laboratory tests may identify organisms directly (eg, visually, using a microscope, growing the organism in culture) or indirectly (eg, identifying antibodies to the organism). General types of tests include

Introduction to Laboratory Diagnosis of Infectious Disease
Microscopy
Culture
Susceptibility Testing
Immunologic Tests for Infectious Disease
Non-Nucleic Acid–Based Identification Methods for Infectious Disease
Nucleic Acid–Based Identification Methods for Infectious Disease

Mycobacteria

Mycobacteria are small, slow-growing, aerobic bacilli. They are distinguished by a complex, lipid-rich cell envelope responsible for their characterization as acid-fast (ie, resistant to decolorization by acid after staining with carbolfuchsin) and their relative resistance to Gram stain. The most common mycobacterial infection is tuberculosis; others include leprosy and various diseases caused by Mycobacterium avium complex.

Introduction to Mycobacteria
Tuberculosis (TB)
Extrapulmonary Tuberculosis
Other Mycobacterial Infections Resembling Tuberculosis
Leprosy

Neisseriaceae

All pathogenic aerobic gram-negative cocci belong to the Neisseriaceae family, which is composed of 5 genera:

Introduction to Neisseriaceae
Acinetobacter Infections
Kingella Infections
Meningococcal Diseases
Moraxella catarrhalis Infection
Oligella Infections

Nematodes (Roundworms)

Angiostrongyliasis is infection with larvae of worms of the genus Angiostrongylus ; intestinal symptoms or eosinophilic meningitis occurs depending on the infecting species.

Angiostrongyliasis
Anisakiasis
Ascariasis
Baylisascariasis
Dracunculiasis
Overview of Filarial Nematode Infections
Dirofilariasis
Loiasis
Bancroftian and Brugian Lymphatic Filariasis
Onchocerciasis (River Blindness)
Hookworm Infection
Pinworm Infestation
Strongyloidiasis
Toxocariasis
Trichinosis
Trichuriasis

Pox Viruses

Monkeypox virus is structurally related to the smallpox virus and causes similar, but usually milder illness.

Monkeypox
Smallpox

Respiratory Viruses

Overview of Viral Respiratory Infections
Adenovirus Infections
Common Cold
Influenza
Avian Influenza
Pandemic 2009 H1N1 Influenza
Parainfluenza Virus Infections
Coronaviruses and Acute Respiratory Syndromes (MERS and SARS)

Rickettsiae and Related Organisms

Rickettsial diseases (rickettsioses) and related diseases (anaplasmosis, ehrlichiosis, Q fever, scrub typhus) are caused by a group of gram-negative, obligately intracellular coccobacilli. All, except for Coxiella burnetii , have an arthropod vector. Symptoms usually include sudden-onset fever with severe headache, malaise, prostration, and, in most cases, a characteristic rash. Diagnosis is clinical, confirmed by immunofluorescence assay or PCR. Treatment is with tetracyclines or, except for anaplasmosis and ehrlichiosis, chloramphenicol.

Overview of Rickettsial and Related Infections
Ehrlichiosis and Anaplasmosis
Epidemic Typhus
Murine (Endemic) Typhus
Other Spotted Fever Rickettsioses
Q Fever
Rickettsialpox
Rocky Mountain Spotted Fever (RMSF)
Scrub Typhus

Sexually Transmitted Diseases (STDs)

Sexually transmitted diseases (STDs), also termed sexually transmitted infections (STIs), can be caused by a number of microorganisms that vary widely in size, life cycle, symptoms, and susceptibility to available treatments.

Overview of Sexually Transmitted Diseases
Chancroid
Chlamydial, Mycoplasmal, and Ureaplasmal Mucosal Infections
Genital Warts
Gonorrhea
Granuloma Inguinale
Lymphogranuloma Venereum (LGV)
Sexually Transmitted Enteric Infections
Syphilis
Trichomoniasis

Spirochetes

Bejel, pinta, and yaws (endemic treponematoses) are chronic, tropical, nonvenereal spirochetal infections spread by body contact. Symptoms of bejel are mucous membrane and cutaneous lesions, followed by bone and skin gummas. Yaws causes periostitis and dermal lesions. Pinta lesions are confined to the dermis. Diagnosis is clinical and epidemiologic. Treatment is with penicillin.

Bejel, Pinta, and Yaws
Leptospirosis
Lyme Disease
Rat-Bite Fever
Relapsing Fever

Trematodes (Flukes)

Flukes are parasitic flatworms that infect the blood vessels, GI tract, lungs, or liver. They are often categorized according to the organ system they invade:

Introduction to Trematodes (Flukes)
Clonorchiasis
Fascioliasis
Fasciolopsiasis
Heterophyiasis and Related Trematode Infections
Opisthorchiasis
Paragonimiasis
Schistosomiasis

Viruses

Viruses are the smallest parasites, typically ranging from 0.02 to 0.3 μ m, although several very large viruses up to 1 μ m long (megavirus, pandoravirus) have recently been discovered. Viruses depend completely on cells (bacterial, plant, or animal) to reproduce. Viruses have an outer cover of protein and sometimes lipid, an RNA or DNA core, and sometimes enzymes needed for the first steps of viral replication.

Overview of Viruses
Types of Viral Disorders

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Test your knowledge

Extensive vaccination has almost eliminated poliomyelitis worldwide. However, cases still occur in regions with incomplete immunization, such as sub-Saharan Africa and southern Asia. Which of the following types of poliomyelitis is the most common?

Asymptomatic poliomyelitis Paralytic poliomyelitis Nonparalytic poliomyelitis Abortive poliomyelitis

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PROCEDURES & EXAMS

Quizzes

Cases

Infectious Diseases

Infectious DiseasesSections (A-Z)

Anaerobic Bacteria

Approach to Parasitic Infections

Arboviruses, Arenaviridae, and Filoviridae

Bacteria and Antibacterial Drugs

Biology of Infectious Disease

Cestodes (Tapeworms)

Chlamydia and Mycoplasmas

Enteroviruses

Extraintestinal Protozoa

Fungi

Gram-Negative Bacilli

Gram-Positive Bacilli

Gram-Positive Cocci

Herpesviruses

Human Immunodeficiency Virus (HIV)

Immunization

Intestinal Protozoa and Microsporidia

Laboratory Diagnosis of Infectious Disease

Mycobacteria

Neisseriaceae

Nematodes (Roundworms)

Pox Viruses

Respiratory Viruses

Rickettsiae and Related Organisms

Sexually Transmitted Diseases (STDs)

Spirochetes

Trematodes (Flukes)

Viruses

Also of Interest

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A MEDICAL EDUCATION BLOG