Common Human Infections and Causative Agents

The health disorder caused by a successful invasion, multiplication, and establishment of pathogenic microorganisms and/or harmful microbial products on or within the host’s body cells or system is called infection. Simply, it can be defined as a disease caused by microorganisms. Infection is also called an infectious disease or communicable disease or transmissible disease

Infections account for more than 13 million deaths each year; 13.7 million death in 2019 (G. Authia, S. Fablina, 2022). Among these 13.7 million deaths, 7.7 million are associated with bacterial infections. Due to the rapid emergence and spread of antimicrobial resistance, the case severity and mortality associated with infectious diseases are also increasing.

Common Human Infections and Causative Agents
Common Human Infections and Causative Agents

Infections can be classified on several bases; like microorganisms involved, presence of symptoms, anatomic location, etc. In this article, we will look over some common infections based on anatomic location i.e. organ/system involved along with their causative agents.

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Infections of the Blood Circulatory System

Myocardial Infarction (Heart Attack)
Myocardial Infarction (Heart Attack)

These are the infections associated with the cardiovascular system including blood i.e. infection of the heart, blood vessels, and blood. It is also called bloodstream infections or infections of the blood circulatory system. Some of the common infections associated with cardiovascular systems are:

Name of DiseaseMicroorganisms InvolvedDescription
Infective Endocarditis/Bacterial EndocarditisStaphylococcus aureus
Viridans Streptococci
Enterococcus faecalis 
Enterococcus faecium 
Streptococcus bovis
Staphylococcus epidermidis 
HACEK group (Haemophilus spp., Aggregatibacter spp., Cardiobacterium hominis, Eikenella corrodens, and Kingella spp.)

Some minor bacterial pathogens involved are: Pseudomonas spp.Clostridium septicumBartonella spp., Chlamydia psittaci, Coxiella spp., Cutibacterium spp., Citrobacter koseri, Tropheryma whippei, etc.  
Infection of endothelium i.e. inner lining of heart chambers and valves. It most commonly includes infection in the lining of heart valves. 
Fungal Endocarditis Candida albicans 
Histoplasma capsulatum
Aspergillus spp
Fungal infection of endothelium; most commonly heart valves  
Rheumatic Heart Disease Streptococcus spp. mainly Group A Streptococcus sppInfection of heart valves associated with rheumatic fever 
Bacteremia and Septicemia
Primary bacteremia
Secondary bacteremia
Staphylococcus spp. (mainly S. aureus),Streptococcus spp. (S. pneumoniae, Viridans Streptococci,),Enterococcus spp. (mainly E. faecalis),E. coli, Pseudomonas spp., Haemophilus spp., Neisseria spp., Klebsiella pneumoniae, Salmonella spp., Enterobacter spp., Proteus mirabilis, Listeria monocytogenes, etc. Bacteremia simply means the presence of viable bacteria in the bloodstream Septicemia means the entering of viable bacteria into the blood and establishing infection i.e. bacteremia leading to sepsis 
ViremiaHepadnaviruses, flaviviruses, enteroviruses, and togaviruses are commonly found circulating in the human bloodstream.

Common viruses include: HIV, Influenza viruses, Dengue virus (DENV), Zika virus, Japanese encephalitis virus (JEV), Cytomegalovirus (CMV), Hepatitis B and C viruses, Ebola virus, West Nile Virus, Varicella-Zoster virus (VZV)
Presence of viruses in the bloodstream. Most viruses are introduced in the bloodstream from other localized viral infection sites or infected organs. Viremia leads to the dissemination of viruses in the body resulting in a systemic viral infection. 
FungemiaCandida spp. (mainly C. albicans)
Saccharomyces spp. (mainly S. boulardii),
Cryptococcus spp.,
Aspergillus spp.,
Rhodotorula spp.
Presence of viable fungi (yeasts and molds) in the bloodstream. Candidemia is the most common type of Fungemia. Candidemia is the presence of Candida spp. in the bloodstream  
Parasitic Infections of BloodStream 
(Some common infections associated with parasites infecting blood cells are:
Babesiosis, Malaria, Leishmaniasis, Toxoplasmosis, Trypanosomiasis, Schistosomiasis) 

In infections like Filariasis, Onchocercasiasis, etc. parasites are present in the bloodstream) 
Babesia microti
Plasmodium spp. 
Leishmania spp. (mainly L. donovaniToxoplasma spp. (mainly T. gondii)
Trypanosoma spp. (mainly T. brucei, T. cruzi)
Brugia malayi,
B. timori 
Onchocerca volvulus 
Schistosoma haematobium
Wuchereria bancrofti 
It is the infection of blood cells by parasites like protozoans (hemoprotozoans), nematodes, Platyhelminthes, etc.). The infections may be limited to blood cells or may infect other organs along with blood cells.    

Infection of the Digestive System

The digestive system is the body system involved in food digestion. It includes the gastrointestinal tract (GI tract) and associated digestive organs. The GI tract is open at both ends and is the docking place for foreign, possibly contaminated materials including foods and drinks. This makes the digestive system highly vulnerable to infection.

Helicobacter pylori Infection
Helicobacter pylori Infection

Infection of the digestive system includes infection in any section of the GI tract (from mouth to anal opening) and any digestive organs like the liver, pancreas, and gall bladder. The digestive system is infected by bacteria, viruses, protozoans, and parasites, and less frequently by fungal pathogens.

Name of DiseaseMicroorganisms InvolvedDescription
Bacterial gastroenteritis
(Salmonellosis, Shigellosis, Yersinia enteritis, Campylobacteriosis, etc.) 
Viral gastroenteritis
Parasitic gastroenteritis
Fungal gastroenteritis 
BacteriaE. coli, Campylobacter spp., Salmonella spp., Shigella spp., Clostridium difficile, Yersinia enterocolitica, Vibrio parahaemolyticus, Aeromonas spp., etc. 

Viruses: Rotaviruses, Noroviruses, Adenoviruses, and Astroviruses

Parasites: Giardia lamblia, Entamoeba histolytica, Cryptosporidium spp., etc. 

Fungi: Candida spp
Gastroenteritis is an infection of the intestine and stomach.  It is commonly called the “stomach flu”. Viral gastroenteritis is the most common form of gastroenteritis. 
Bacterial Diarrhea
Viral Diarrhea 
Bacteria: E. coli, Salmonella spp., Shigella flexneri, Campylobacter spp., etc.

Virus: Rotaviruses, Noroviruses, Adenoviruses 
It is the condition of passing loose, watery stool frequently (often more than 3 times a day).

It is the most common manifestation of gastrointestinal infection. 
Amoebic dysentery
Bacillary dysentery 
Shigella spp. (S. dysenteriae)
Entamoeba histolytica
E. coli O157:H7 (EHEC) 
It is the condition of severe diarrhea along with blood sometimes along with the mucus. 

Dysentery associated with Entamoeba is called amoebic dysentery, while dysentery caused by Shigella is termed bacillary dysentery. 
CholeraVibrio cholerae Cholera is the acute infection of the small intestine by strains of Vibrio cholerae resulting in severe acute diarrhea. 
Typhoid and ParatyphoidSalmonella enterica subspp. enterica serovar Typhi
Salmonella enterica subspp. enterica serovar Paratyphi 
It is the infection of the small intestine, liver, spleen, and gall bladder by Salmonella Typhi and Salmonella Paratyphi strains.  
Food Poisoning
Clostridial Food Poisoning
Staphylococcal Food Poisoning
Bacillus Food Poisoning
Campylobacter Food Poisoning
Fungal Food Poisoning (Aflatoxicosis) 
Bacteria: Campylobacter jejuni, Clostridium perfringens, Clostridium botulinum, Bacillus cereus, Salmonella enteritis, Staphylococcus aureus, Listeria monocytogenes, Shigella flexneri, Brucella spp., etc.

Fungi: Aspergillus parasiticus, Aspergillus flavus, Alternaria spp., Fusarium spp., etc. 
It is a gastrointestinal disease caused by the ingestion of toxins produced by microorganisms or toxins synthesized by ingested microorganisms in the GI tract. It results in vomiting, diarrhea, dysentery, abdominal pain, fever, paralysis, and even death. 
Infectious Colitis Bacteria: Campylobacter spp., E. coli, Clostridium difficile, Yersinia spp., Non-typhoidal Salmonella spp., etc. 

Viruses: Rotaviruses, Noroviruses, Adenoviruses
It is the inflammation of the large intestine (colon) due to infection at its inner lining. 
Helicobacter pylori infection
(H. pylori Peptic Ulcer)
Helicobacter pyloriIt is the formation of open sores (damage in the outer lining) in the lining of the stomach and upper part of the small intestine. 
Infectious Hepatitis 
Viral Hepatitis
Bacterial Hepatitis
Parasitic Hepatitis
Viruses: Hepatovirus (Hepatitis virus) A, B, C, D, and E
Epstein-Barr virus

Bacteria: Neisseria spp., Bartonella spp., Borellia spp., E.coli, Brucella spp., Campylobacter spp., Rickettsia spp., etc.

Parasites: Plasmodium spp., Leishmania spp., Trypanosoma cruzi, E. histolytica, Fasciola hepatica, etc.  
Hepatitis is the inflammation of the liver. Hepatitis due to any infectious agent is termed infectious hepatitis. Viral hepatitis is the most common form of infectious hepatitis. 
(Infectious Pancreatitis)
Viruses: Cytomegalovirus, Hepatitis B virus, Coxsackie virus, Varicella-zoster virus, etc.

Bacteria: Salmonella spp., Legionella spp., Mycoplasma spp., etc.

Parasites: Toxoplasma spp., Cryptosporidium spp., etc. 
Pancreatitis is the inflammation of the liver. Pancreatitis due to any infectious agent is termed infectious hepatitis.
Infectious Proctitis Viruses: Herpes Simplex virus 1 and 2, 

Bacteria: Treponema pallidum, Neisseria gonorrhoeae, Chlamydia spp.,
It is the infection of the lining of the rectum and the anus leading to inflammation. 
Small Intestinal Bacterial Overgrowth
Enteric bacteria SIBO means the excessive growth of bacteria in the small intestine disturbing digestion or even causing conditions like diarrhea, abdominal pain, bloating, constipation, indigestion, etc. 
Protozoan Infection of the Digestive System
– Amoebiasis
– Cryptosporidiosis
– Cyclosporiasis 
Giardia spp. (mainly G. lamblia)
Entamoeba histolytica,
Cryptosporidium parvum,
C. hominis,
Cyclospora cayetanensis 
It includes infection of the digestive system by protozoa. 
Helminthic Infection of the Digestive System (Helminthiasis/Worm infection)
Nematodes (Roundworms): Ascaris lumbricoides, Trichuris spp., Ancylostoma duodenale, Necator americanus, Trichostrongylus spp

Cestodes (Tapeworms): Taenia spp., Echinococcus spp., Hymenolepis spp.

Trematodes (Flatworms): Fasciola hepatica, Clonorchis sinensis
It includes infection of the digestive system by worms (helminths). Nematodiasis is an infection by roundworms. Similarly, infections by tapeworms and flatworms are called cestodiasis and trematodiasis respectively. 

Infection of the Respiratory System

Person Infected with Mycobacterium Tuberculosis (TB)
Person Infected with Mycobacterium Tuberculosis (TB)

Respiratory tract infections (RTIs) are infections of any organs of the respiratory system. It is the most common type of infection in humans. Based on the parts of the respiratory tract infected, RTIs are classified as either upper RTIs (URTIs)( i.e. infection of nose, sinus, pharynx, and larynx) and lower RTIs (LRTIs) (i.e. infection of the trachea, bronchi, bronchioles, and lungs).

Name of DiseaseMicroorganisms InvolvedDescription
Common coldViruses are responsible for the common cold. The most common virus involved (up to about 80% cases) is strains of Rhinovirus. Others include; coronaviruses, adenoviruses, influenza viruses, and enteroviruses. The most common but trivial infection of the mucosal membrane of the upper respiratory tract. 
PneumoniaBacteria: Streptococcus pneumoniae, Klebsiella pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila, Moraxella catarrhalis, S. aureus, Pseudomonas aeruginosa

Virus: Coronaviruses, Respiratory syncytial virus (RSV), influenza virus, parainfluenza virus, adenovirus

Fungi: Histoplasma capsulatum, Blastomyces spp., Pneumocystis jiroveci, Coccidioides immitis, Cryptococcus neoformans  
It is the acute respiratory infection of the lungs leading to the inflammation of the lungs and filling of alveoli with pus, mucus, or any fluid.  
Pulmonary Tuberculosis Mycobacterium tuberculosis complex Infection of lung tissues by Mycobacterium spp
Flu (Influenza)Influenza viruses Infection of respiratory systems by the influenza virus. 
DiphtheriaCorynebacterium diphtheriae Infection of nose and throat region by Corynebacterium diphtheriae 
Infective Sinusitis Viruses: Rhinoviruses, Coronavirus, Influenza virus, RSV, Parainfluenza virus

BacteriaStreptococcus pneumoniae, H. influenzae, Moraxella catarrhalis, S. aureus 
Inflammation of mucous membrane lining the sinuses (air-filled chamber of nasal cavity) 
Infective Tonsillitis, Pharyngitis, Laryngitis Bacteria: Group A Streptococci, Neisseria spp., Corynebacterium diphtheriae, H. influenzae, Mycoplasma spp., Fusobacetrium spp., Bacillus spp., Bordetella spp.

Viruses: Rhinoviruses, Adenoviruses, Measles virus, Influenza virus, Parainfluenza virus, Epstein-Barr virus, RSV, HSV, Coxsackievirus, Coronaviruses 
Tonsillitis – Inflammation of tonsils. Pharyngitis – Inflammation of the pharynx.Laryngitis – Inflammation of the larynx. 
Bronchitis Viruses: RSV, Rhinoviruses, Adenoviruses, Influenza viruses, Coronaviruses, Metapneumoviruses, Parainfluenza viruses

Bacteria: Moraxella catarrhalis, Bordetella pertussis, Mycoplasma pneumoniae, Chlamydia pneumoniae, Streptococcus pneumoniae, Viridans Streptococci, etc. 
Inflammation of bronchi and bronchioles 
Pulmonary Cryptococcosis Cryptococcus neoformans, Cryptococcus gattii  Infection of the lungs by the fungi Cryptococcus leads to severe pneumonia. 
Histoplasmosis Histoplasma capsulatum
Histoplasma duboisii 
Infection of the lungs by the fungi Histoplasma
Pulmonary Coccidioidomycosis Coccidioides immitis,
Coccidioides posadasii
Infection of the lungs by the fungi Coccidioides leads to pneumonia.
Pulmonary Candidiasis Candida spp.
(mainly Candida albicans
Formation of invasive lesions and foci in lungs and respiratory tract by Candida spp. 
Severe Acute Respiratory Syndrome (SARS)

Middle East Respiratory Syndrome (MERS)

COVID- 19 
Coronaviruses (SARS-coronaviruses, MERS-coronaviruses, SARS-CoV2) Infection of lungs and respiratory tract by coronaviruses 

Infection of the Nervous System

Nervous system infection is any form of infection in the brain, spinal cord, and/or nerves of our body. Such neurological infections are potentially life-threatening. They are caused by different microorganisms, mostly viruses, and bacteria.

Name of DiseaseMicroorganisms InvolvedDescription
Bacterial encephalitis
Viral encephalitis
Parasitic encephalitis 
Bacteria: Neisseria meningitidis, Haemophilus influenzae, Streptococcus spp., Bartonella henselae, Mycoplasma spp., Rickettsia, etc.

Viruses: Japanese encephalitis (JE) virus, Dengue viruses, Chikungunya virus, Enteroviruses, HSV, Tick-borne encephalitis virus, West Nile virus, Zika virus, Murray valley encephalitis virus, Epstein-Barr virus, Cytomegaloviruses, VZV, East equine encephalitis virus, HIV, etc.

Parasites: Plasmodium spp., Toxoplasma spp., etc. 
Inflammation of encephalon (brain) i.e. part of CNS inside the cranium.  
Bacterial meningitis
Viral meningitis
Bacteria: Group B Streptococci (Streptococcus agalactiae), E. coli, Listeria monocytogenes, Neisseria meningitidis, Haemophilus influenzae, Streptococcus pneumoniae, etc. 

Viruses: Enteroviruses, West Nile virus, HSV I and II, VZV, Mumps virus, Measles virus, Lymphocytic choriomeningitis (LCM) virus, HIV, etc.  
Inflammation of meninges (the protective covering of brain and spinal cord). 
CNS Toxoplasmosis/Cerebral Toxoplasmosis Toxoplasma gondii
Toxoplasma encephalitis 
Inflammation of the brain and spinal cord by Toxoplasma.  
Central nervous system (CNS) tuberculosis (Tuberculous meningitis) Mycobacterium tuberculosis Infection of CNS by Mycobacterium spp. It demonstrates meningitis, tuberculoma, and spinal arachnoiditis. 
Naegleriasis (Amoebic meningoencephalitis) Naegleria fowleri Inflammation of meninges and encephalon by Naegleria fowleri. 
Cryptococcal meningitis Cryptococcus neoformans 
Cryptococcus gattii 
Meningitis due to the fungi Cryptococcus spp
Neuroborreliosis Borrelia sppNeurological manifestation of Lyme disease.  
RabiesRabies lyssavirus Infection of meninges, brain, spinal cord, and nerves by the rabies virus. 
Poliomyelitis  Poliovirus (Enterovirus C) Infection of nerves by Poliovirus 
Brain abscessBacteria: Staphylococcus aureus, Streptococcus spp., Pseudomonas spp., Bacteroides spp., Fusobacterium spp., Nocardia spp., Mycobacterium spp.

Fungi: Cryptococcus spp., Candida spp., Blastomyces spp., Aspergillus spp., Mucorales spp., etc.

Parasites:Toxoplasma spp., Trypanosoma spp.
It is the collection of pus within brain tissues. They are commonly caused by bacteria. 

Infection of the Urinary System

The urinary system includes the urethra, urinary bladder, ureters, and kidneys. Infection of any of these organs is called urinary tract infection (UTI). UTIs are mainly caused by bacteria, but rarely fungal and viral UTIs are also reported. UTIs are more provident in females than in males due to their shorter urethra.

Name of DiseaseMicroorganisms InvolvedDescription
CystitisUropathogenic E. coli (UPEC), S. aureus, Klebsiella spp., Proteus spp., Salmonella spp., Ureaplasma spp., Mycoplasma spp.,  Streptococcus spp., Serratia spp., Citrobacter spp., Candida spp., etc. It is the infection and inflammation of the urinary bladder. 
Pyelonephritis UPEC, S. aureus, Neisseria spp., Streptococcus spp., Enterococcus spp., Streptococcus spp., Providencia spp., Bacteroides spp., etc.  It is the infection and inflammation of the kidneys and ureters.
UrethritisUPEC, S. aureus, Klebsiella spp., Proteus spp., Chlamydia trachomatis, Mycoplasma genitalium, Neisseria spp., Serratia spp., Candida spp., Lactococcus spp., etc. It is the infection and inflammation of the urethra. 
Systemic Bacterial Infection
Systemic Bacterial Infection

Infection of the Reproductive System

The reproductive system includes all the organs involved in the reproduction process. It is in close proximity to the urinary system in humans. Many microorganisms causing UTIs are responsible for the infection of the reproductive system. The infection of the reproductive system is classified into three types: sexually transmitted diseases (STDs), endogenous infection (infection by overgrowth of microbes in the urogenital tract), and iatrogenic infections (infections by improper medical care and invasion of foreign microorganisms).

Name of DiseaseMicroorganisms InvolvedDescription
GonorrheaNeisseria gonorrhoeae Sexually transmitted disease (STD) caused by Neisseria gonorrhoeae
SyphilisTreponema pallidum subspecies pallidum STD caused by Treponema pallidum marked by the development of painless sores in genitals and/or mouth.  
Chlamydia (Chlamydia infection)Chlamydia trachomatis  STD caused by Chlamydia trachomatis  
ChancroidHaemophilus ducreyi STD is marked by the development of painful sores in the genitals. 
Genital ulcerHaemophilus ducreyi,
Herpes simplex virus
Formation of open sores/ulcers in genitals. 
TrichomoniasisTrichomonas vaginalis An STD parasitic infection caused by Trichomonas vaginalis characterized by foul vaginal discharge in women and mostly asymptomatic cases in males. 
Vaginosis and vaginitis
Vaginal Candidiasis
Bacterial Vaginosis/Vaginitis
Fungi: Candida albicans, C. krusei, C. tropicalis

Bacteria: Gardnerella spp., Neisseria spp., Chlamydia spp., Campylobacter spp., Mycoplasma spp.

Viruses: Herpes simplex virus
Vaginosis is the excessive growth of bacteria in the vagina. Vaginitis is the infection of the vagina and vulva leading to inflammation and irritation in those areas. 
Pelvic Inflammatory Disease (PID)Neisseria gonorrhoeae, Chlamydia trachomatis, Bacteroides spp., Streptococcus spp., Prevotella spp., Gardnerella vaginalis, Acinetobacter sppIt is the infection of the upper reproductive organs of the female reproductive system. The organs infected are the uterus, fallopian tubes, and ovaries. 
Genital HerpesHerpes simplex virus 2 (HSV 2) Formation of blisters progressing into ulcers around genitalia by HSV. 
Genital Warts Human papillomavirus (HPV)Development of warts (keratinized or soft warts) around genitals and anal regions. 

Infection of the Lymphatic System

The lymphatic system is a network of lymphatic vessels, lymph nodes, and lymph organs inside which lymph flows. It is a part of the immune system as well as part of the circulatory system. Lymphatic infections are not common, but several bacterial and parasitic infections are reported.

Name of DiseaseMicroorganisms InvolvedDescription
Infective Lymphangitis
Infective Lymphadenopathy
Infective Lymphadenitis 
Bacteria: Group A Streptococci (Streptococcus pyogenes) and other Streptococci, Mycobacterium tuberculosis, Treponema pallidum, Staphylococcus spp., Rickettsia spp., Nocardia spp., etc.

Fungi: Sporothrix schenckii, Scedosporium spp., etc. 
Infective lymphangitis is the infection of lymphatic vessels. Inflammation of lymph nodes is called lymphadenopathy. Infection on multiple lymph nodes is called lymphadenitis. 
Lymphatic filariasis (Elephantiasis) Wuchereria bancrofti, Brugia malayi, Brugia timoriInfestation of filarial worms in lymphatic vessels obstructing the normal lymph flow.

Infection of Integumentary System

The integumentary system includes all the external covering of a body. It includes skin, hair, and nails. The integumentary system is the first layer of defense for our body. It is the house of millions of microorganisms as normal flora. Pathogens first come in contact with integuments before invading the body. Hence, the integumentary system gets infected time and again.

Name of DiseaseMicroorganisms InvolvedDescription
Herpes Infection
Herpes labialis (Cold sores)
Herpes simplex virus Development of fluid-filled blisters around the mouth or in lips. 
Acne (Infectious acne)
Bacterial acne
Fungal acne
Bacteria: Cutibacterium acnes, Staphylococcus spp.

Fungi: Malassezia spp.  
Formation of nodules, pustules, or papules due to clogging of hair follicles.
ImpetigoStaphylococcus aureus, Streptococcus pyogenesBacterial infection of the epidermis forms pyogenic sores or crusts in the skin. 
Cellulitis and Folliculitis Bacteria: Staphylococcus spp., Streptococcus spp., Bacteroides spp., Haemophilus spp., Aeromonas spp., Pseudomonas aeruginosa, Pasteurella spp., Eikenella spp., etc.

Fungi: Malassezia spp., Trichophyton rubrum, Candida spp., etc. 
Cellulitis is the bacterial infection of dermal and/or subcutaneous layers of skin. 

Folliculitis is the infection of hair follicles. It is mostly by bacteria but fungi are also involved.  
Erysipelas Streptococcus pyogenes, Streptococcus agalactiae, Staphylococcus aureusInfection of the upper layer of the dermis and lymphatic vessels forming a raised red rash. 
Necrotizing fasciitis  Staphylococcus aureus, Streptococcus pyogenes, Haemophilus spp., Bacteroides fragilis, anaerobic E. coli, Clostridium spp., Aeromonas hydrophila, etc. Destruction of soft tissues. 
RubellaRubella virusSkin infection by the Rubella virus leads to the formation of red rashes. 
Skin ulcers and wounds Staphylococcus spp., Streptococcus spp., Actinomyces spp., Pseudomonas spp., Haemophilus spp., etc. Formation of sores in the skin and destruction of the skin of that area. 
Tinea versicolor Malassezia furfur, Malassezia globosa Formation of white colored patches on skin by fungi Malassezia
Dandruff Malassezia furfurFlaking of skin; mostly of the scalp. 
Tinea (Ringworm infection) Trichophyton spp., Microsporum spp., Epidermophyton spp. Formation of red, itchy, and mostly circular rash.  
Cutaneous candidiasisCandida albicans, C. glabrata, C. rugose, C. auris, C. tropicalis, etc. Skin infection caused by Candida spp
Warts Human papilloma virus (HPV)Skin bumps or lesions caused by Human papillomavirus (HPV)
ChickenpoxVaricella zoster virus (VZV)Itchy red rashes by VZV. 
Hand, foot, and mouth (HFM) disease Enteroviruses, CoxsackievirusesFormation of flat, discolored rashes or spots on the skin of hands, feet, and mouth area. 

Infection of the Muscular System

The muscular system includes all the muscles of our body. Infections of muscles are generally hematogenous or contagious spread, but they are usually serious and need immediate treatment.

Name of DiseaseMicroorganisms InvolvedDescription
Myonecrosis (Gas gangrene)Clostridium spp., Streptococcus spp., Bacteroides spp., Klebsiella pneumoniae, Aeromonas hydrophila, etc. Necrotic damage of muscle tissues with the formation of tissue gas. 
Infectious myositis and pyomyositisStaphylococcus aureus, Streptococcus pyogenes, Neisseria spp.Myositis is the inflammation of muscles.
Pyomyositis is the inflammation of muscle along with the production of pus. 

Infection of the Skeletal System

Infection of the skeletal system includes bone infection. Bone infection is not common, but it is very serious, even fatal if left untreated.

Name of DiseaseMicroorganisms InvolvedDescription
Infectious osteomyelitis Staphylococcus spp. (mainly Staphylococcus intermedius), Bacteroides spp., Actinomyces spp., Clostridium spp., Fusobacterium spp., Peptococcus spp., Peptostreptococcus spp. Infection of bone leads to its swelling. 
Septic arthritis Staphylococcus spp., Streptococcus spp., Pasteurella spp., Mycoplasma spumans, Borrelia spp., Mycobacterium tuberculosis, etc.Infection of bones in joints. 
Skeletal Tuberculosis (Bone Tuberculosis) Mycobacterium tuberculosis complex Extrapulmonary tuberculosis of bones. 
Mycotic bone infections (Mycotic osteomyelitis and Mycotic arthritis) Cryptococcus neoformans, Aspergillus spp., Fusobacterium spp., Histoplasma capsulatum, Coccidioides immitis, etc. Infection of bones and joints by fungal pathogens. 

Infection of the Endocrine System

The endocrine system is composed of endocrine glands. Infections of endocrine glands are mainly due to the hematogenous spreading of infection or progressive systemic infection.

Name of DiseaseMicroorganisms InvolvedDescription
Pituitary abscessStaphylococcus spp., Streptococcus spp.,
E. coli, Neisseria spp.
It is a rare infection of the pituitary gland leading to its swelling and pus formation. 
Acute suppurative thyroiditis
Subacute thyroiditis
Staphylococcus aureus, Streptococcus spp., Haemophilus spp., Moraxella spp., Nocardia spp., Klebsiella spp.It is the inflammation of thyroid glands due to infection.
Infectious epididymitis N. gonorrhoeae, C. trachomatisInflammation of epididymis 
Tubo-ovarian abscessNeisseria gonorrhoeae, Chlamydia trachomatis, Bacteroides spp., Streptococcus spp., Prevotella spp., Gardnerella vaginalis, Acinetobacter spp.Infection of fallopian tubes and ovaries leads to inflammation and pus formation. 
Tuberculosis of the adrenalMycobacterium tuberculosis
Mycobacterium avium intracellular
Tuberculosis of the adrenal gland.


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About Author

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Prashant Dahal

Prashant Dahal completed his bachelor’s degree (B.Sc.) Microbiology from Sunsari Technical College, affiliated with Tribhuvan University. He is interested in topics related to Antimicrobial resistance, the mechanism of resistance development, Infectious diseases (Pneumonia, tuberculosis, HIV, malaria, dengue), Host-pathogen interaction, Actinomycetes, fungal metabolites, and phytochemicals as novel sources of antimicrobials and Vaccines.

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