Infectious disease main page

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mahshid Mir, M.D. [2]

Overview

Among the almost infinite varieties of microorganisms, relatively few cause disease in otherwise healthy individuals. Infectious disease results from the interplay between those few pathogens and the defenses of the hosts they infect. The appearance and severity of disease resulting from any pathogen depends upon the ability of that pathogen to damage the host as well as the ability of the host to resist the pathogen. Infectious microorganisms, or microbes, are therefore classified as either primary pathogens or as opportunistic pathogens according to the status of host defenses.

Classification

Infectious disease are caused by pathogenic microorganisms. These disease can be categorized into 4 main categories:

• Bacterial infections
• Viral infecions
• Fungal infections
• Parasitic infections

Bacterial classification

Bacterial infections can be classified based on their cellular features and specificities including:

• Cellular wall thickness: Gram staining mathod
  • Gram positive bacteria
  • Gram negative bacteria
• Microscopic shape
  • Bacillus shaped bacteria
  • Branchig shaped bacteria
  • Coccus shaped bacteria
  • Coma shaped bacteria
• Use an O2-dependent system to generate ATP
  • Aerobics
  • Anaerobics
• Oxidative damage susceptibility=Catalase enzyme
  • Catalase positive bacteria
  • Catalase negative bacteria
• Oxidase containing method
  • Oxidase positive bacteria
  • Oxidase negative bacteria
• Lactose fermenting method
  • Lactose fermenting bacteria
  • Non-lactose fermenting bacteria
• Coagulase containing method
  • Coagulase positive bacteria
  • Coagulase negative bacteria

Bacteria

Gram staining

Gram positive

Aerobic

Anerobic

Bacillus shaped bacteria

Branching shaped bacteria

Bacillus shaped bacteria

Coccus shaped bacteria

Branching shaped bacteria

Listeria Bacillus Corynebacterium

Nocardia

Clostridium Propionibacterium

Staphylococcus Streptococcus

Actinomyces

Gram negative

Coccus shaped bacteria

Bacillus shaped bacteria

Comma shaped bacteria

Campylobacter jejuni Vibrio cholerae Helicobacter pylori

Diplococcus shaped gram negative bacteria

Coccobacillus shaped gram negative bacteria

Neisseria gonorrhoaea Neisseia meningtidis Moraxella

Haemophilus influenzae Pasteurella Brucella Bordetella pertussis Francisella tularensis

Lactose fermentation

Positive

Negative

Klebsiella Escherichia coli Enterobacter Citrobacter Serratia

Pseudomonas Shigella Salmonella Yersinia Proteus

Viral classification

Viruses can be classified based on different characteristics. The most important ways to categorize viruses are based on:

• Genetic material of virus
  • DNA virus
  • RNA virus
• Number of genetic copies in the virus
  • Single stranded genome
  • Double stranded genome

RNA viruses themselves can be categorized based on their ability to use host cell polymerizes or need to bring their own polymerizes with themselves into 2 categories:

• Positive stranded viruses
• Negative stranded viruses

Virus classification

Viral genome type

DNA viruses

RNA viruses

ssDNA

dsDNA

ssRNA

dsRNA

Parvovirus

Reoviridae

Linear genome

Circular genome

Positive strand

Negative strand

Herpes virus Adenovirus Poxvirus Parvovirus

Papillomavirus Polyomavirus Hepadnavirus

Picornaviruses Hepevirus Caliciviruses Flaviviruses Togaviruses Retroviruses Coronaviruses Arenaviruses

Arenavirus Bunyavirus Paramyxovirus Orthomyxoviruses Filoviruses Rhabdoviruses

Fungal classification

Fungal infections can be classified based on their infectious sites:

• Systemic mycoses
• Cutaneous mycoses
• Opportunistic fungal infections

Mycology classification

Main infectious sites and methods

Systemic mycoses

Cutaneous mycoses

Histoplasma Blastomyces Coccidioidomyces Paracoccidioidomyces

Opportunistic fungal infections

Candida albicans Aspergillus fumigatus Cryptococcus neoformans Mucor spp. Rhizopus spp. Pneumocystis jirovecii Sporothrix schenckii

Tinea dermatophytes

Tinea pityriasis versicolor

Tinea capitis Tinea corporis Tinea cruris Tinea pedis Tinea unguium

Malassezia spp. (a Pityrosporum spp.)

Parasitic classification

Parasites mainly can be classified into 3 categories:

• Ectoparasites
• Protozoas
• Worms

Protozoas may involve different body organs, but they can be classified based on the most prominent symptoms and their main organ involvement. Worm parasites are categorized based on their shapes. They include:

• Nematodes (roundworms)
• Cestodes (tapeworms)
• Trematodes (flukes)

Parasites classification

Main categories

Ectoparasites

Protozoas

Worms

Sarcoptes scabiei Pediculus humanus Phthirus pubis

gastrointestinal infections

CNS infections

hematologic infections

Visceral infections and Sexual transmitted diseases

Nematodes (roundworms)

Cestodes (tapeworms)

Trematodes (flukes)

Giardia lamblia Entamoeba histolytica Cryptosporidium

Toxoplasma gondii Naegleria fowleri Trypanosoma brucei

Plasmodium vivax Plasmodium ovale Plasmodium falciparum Plasmodium malariae Babesia

Trypanosoma cruzi Leishmania donovani Trichomonas vaginalis

Enterobius vermicularis (pinworm) Ascaris lumbricoides (giant roundworm) Strongyloides stercoralis (threadworm) Ancylostoma duodenale Necator americanus (hookworms) Trichinella spiralis Trichuris trichiura (whipworm) Toxocara canis Onchocerca volvulus Loa loa Wuchereria bancrofti

Taenia solium Diphyllobothrium latum Echinococcus granulosus

Schistosoma Clonorchis sinensis