A pathogen is an organism that bears ("gen") suffering ("pathos") upon another organism.
A vector, in pathology, is an organism that carries pathogens from one organism to another (examples: rats, mosquitoes, ticks).
The Case of Hepatitis C
Pathogens are disease causing microorganisms such as viruses, bacteria, parasites, and fungi. They can be transmitted through various routes, including direct contact, ingestion, airborne exposure, or via biological vectors. Vectorssuch as mosquitoes, ticks, and fleas are living organisms that transmit pathogens from one host to another, and are central to the spread of many infectious diseases like malaria or Lyme disease.
However, not all pathogens rely on vectors. For example, the Hepatitis C virus (HCV) is a bloodborne viral pathogen transmitted primarily through direct blood-to-blood contact, including contaminated needles or medical equipment. While HCV is not vector-borne, it remains a major global health concern due to its chronic impact on liver health, often leading to cirrhosis, liver failure, or hepatocellular carcinoma. Understanding the different modes of pathogen transmission vectorial or otherwise is crucial for effective public health strategies.
Lactobacillales: Medically Important Pathogens
Taxonomic Classification
Domain: Cellular organisms
Phylum: Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Read more
Streptococcaceae , Streptococcus , Streptococcus pneumoniae
Most common pathogen of community-acquired pneumonia. Read more
The nasopharynx of children is an important global ecological reservoir of drug-resistant pneumococcus (DRP) and may also play a critical role as the favoured anatomical site for the evolution of DRP.
CDC Notifiable Agent : This bacterium is officially recognized by the Centers for Disease Control and Prevention (CDC) as a notifiable pathogen, meaning cases must be reported to public health authorities due to its impact on human health.
Globally Important Human Pathogen : It is considered a major global health concern, responsible for widespread and potentially severe infections across populations worldwide.
Colonization and Disease Progression of Streptococcus pneumoniae
- Colonizes mucosal surfaces of the host nasopharynx and upper airway.
- Can spread from the upper respiratory tract to sterile regions of the lower respiratory tract, causing pneumonia.
- Can also cause: meningitis, otitis media, and sinusitis.
References:
- Kadioglu A et al. (Nat Rev Microbiol. 2008)
- Lynch JP 3rd et al. (Semin Respir Crit Care Med. 2009)
- De Lencastre H et al. (J Antimicrob Chemother. 2002)
Streptococcaceae , Streptococcus , Streptococcus pyogenes
Common pathogen of hospital- and community-acquired infections, transmitted through contact with symptomatic and asymptomatic carriers. Read more
- Medically important human pathogen
- CDC Notifiable Agent
Causes:
- Severe soft tissue infections
- Bacteremia
- Meningitis
- Toxic shock syndrome
Also known as: Group A Streptococcus
Scientific name: Streptococcus pyogenes
01 Plant Pathogens
Fungal species affecting important crops:
- Gibberella moniliformis (Fusarium) : causes fusarium-related diseases in plants.
- Magnaporthe grisea : responsible for rice blast, a major disease of rice crops.
- Phytophthora infestans : causes potato blight, the pathogen behind the historic Irish potato famine.
- Ustilago maydis : causes corn smut, a fungal disease affecting maize.
02 Dog Pathogens
Worms (helminths):
- Ancylostoma caninum : a hookworm that infects the intestines of dogs.
- Dirofilaria immitis : known as heartworm; transmitted by mosquitoes and can cause fatal heart disease in dogs.
Viruses:
- Canine Distemper Virus (CDV) : a highly contagious viral disease affecting a dog’s respiratory, gastrointestinal, and nervous systems. Read more
03 Fish Pathogens
Microorganisms:
- Ichthyophthirius multifiliis : known as “ich” or “white spot disease,” a common protozoan infection in freshwater fish.
- Pfiesteria piscicida : a toxic dinoflagellate sometimes referred to as the “cell from hell,” associated with fish kills.
Crustacean parasites:
- Argulus sp. : also known as the fish louse; ectoparasites that attach to the skin of fish and feed on blood and mucus.
04 Bee Pathogens
Mites:
- Varroa destructor : the mite responsible for varroosis, a major parasitic threat to honeybee colonies worldwide.
Taxonomic Classification:
Cellular organisms → Bacteria → Firmicutes → Clostridia → Clostridiales
Transmission:
Associated with food, historically, with sausages (Latin word for sausage = "botulus") , can temporarily colonize the intestinal tract of infants who ingested bacteria. Toxin can enter the body via inhalation, ingestion or injection.
Importance:
Medically important human pathogen
- CDC Notifiable Agent
- Validated Biocrime Agent
- NIAID Category A Priority Pathogen
- USDA High Consequences Animal Pathogen
- HHS Select Pathogen
Disease Description:
Has 4 naturally occurring syndromes:
All of these produce symmetrical cranial nerve palsies followed by descending, symmetric flaccid paralysis of voluntary muscles, which may progress to respiratory compromise and death.
Selected Literature:
- Fenicia L et al. (Ann Ist Super Sanita. 2009)
- Brook I. (Rev Neurol Dis. 2006)
“clostridium botulinum”, “botulism”
Transmission:
A major cause of antibiotic-associated diarrhea within the hospital setting; risk factors include fluoroquinolone exposure and gastric acid suppression.
Can be commonly found in food animals and food, but whether ingestion of contaminated food can result in colonization or infection remains unclear.
Importance:
- Emergent Infectious Agent
- Medically Important Human Pathogen
Disease Description:
Violent infectious diarrhea and fulminant colitis , may cause death.
Selected Literature:
- Hookman P et al. (World J Gastroenterol. 2009)
- Weese JS. (Clin Microbiol Infect. 2010)
“clostridium difficile”
Clostridiaceae , Clostridium , Clostridium perfringens
Transmission:
A common cause of food-borne illness due to:
- Ability to form heat-resistant spores that survive cooking
- Rapid growth rate in warm food
- Production of enterotoxin (CPE) in the human gut
Importance:
- Emergent Infectious Agent
- Principal Foodborne Pathogen
- Medically Important Human Pathogen
- Validated Biological Weapon
- USDA High Consequences Animal Pathogen
Disease Description:
Causes food poisoning accompanied by acute gastroenteritis, and has been reported in association with necrotizing enteritis.
Selected Literature:
- Brynestad S et al. (Int J Food Microbiol. 2002)
- Meer RR et al. (Rev Environ Contam Toxicol. 1997)
“Clostridium perfringens”
Clostridiaceae , Clostridium , Clostridium tetani
Transmission:
Natural habitat is soil, dust, and intestinal tracts of various animals.
Infection occurs via bacterial contamination of lacerations or skin wounds.
Can also result from burns, umbilical stump infections (tetanus neonatorum), and surgical-site infections.
Importance:
- CDC Notifiable Agent
- Globally Important Human Pathogen
- Validated Biocrime Agent
Disease Description:
Causes neuromuscular dysfunction from tetanal exotoxin (tetanospasmin):
- Begins with tonic spasms of skeletal muscles
- Progresses to paroxysmal contractions
- Starts with jaw stiffness (lockjaw) and neck rigidity, followed by generalized muscle stiffness
Selected Literature:
- Brook I. (Expert Rev Anti Infect Ther. 2008)
“Clostridium tetani”
Arthropod Vectors
Acyrthosiphon pisum (pea aphid)
Ctenocephalides felis (cat flea)
Ixodes scapularis (tick)
Mosquitoes
Triatominae (kissing bugs)
Human Pathogens
- Ascaris lumbricoides (roundworm)
- Ancylostoma duodenale, Necator americanus (hookworms)
- Enterobius vermicularis (pinworm)
- Schistosoma spp.
- Taenia spp. (human and zoonotic tapeworms)
- Wuchereria bancrofti, Brugia malayi (lymphatic filariasis)
- Toxoplasma gondii (toxoplasmosis)
- Trypanosoma cruzi (Chagas disease)
- Borrelia burgdorferi (Lyme disease)
- Legionella pneumophila (Legionnaires disease)
- Methicillin-resistant Staphylococcus aureus (MRSA) Read more
- Treponema pallidum (syphilis) Read more
- Cimex lectularius (bedbug) Red more
- Pediculus humanus (louse) Read more
- Sarcoptes scabiei (scabies mite)
- Epstein-Barr virus (EBV)
- Hantavirus
- Human papillomavirus (HPV)
- Influenza viruses A, B, C (flu)
- Hepatitis C Virus (HCV)
- Human Immunodeficiency Virus 1 (HIV)
- West Nile virus (WNV) Read more
Bacterial Pathogens by Order
(Based on Ecker DJ et al., BMC Microbiol. 2005; 5:19)
Bacillales
|
Bacillus anthracis |
Bacillus cereus |
Staphylococcus aureus |
Listeria monocytogenes |
Lactobacillales |
Streptococcus pneumoniae |
Streptococcus pyogenes |
Clostridiales
|
Clostridium botulinum |
Clostridium difficile |
Clostridium perfringens |
Clostridium tetani |
Spirochaetales
|
Borrelia burgdorferi |
Treponema pallidum |
Chlamydiales
|
Chlamydia trachomatis |
Chlamydophila psittaci |
Actinomycetales
|
Corynebacterium diphtheriae |
Mycobacterium tuberculosis |
Mycobacterium avium |
Rickettsiales
|
Rickettsia prowazekii |
Rickettsia rickettsii |
Rickettsia typhi |
Anaplasma phagocytophilum |
Ehrlichia chaffeensis |
Rhizobiales
|
Brucella melitensis |
Burkholderiales
|
Bordetella pertussis |
Burkholderia mallei |
Burkholderia pseudomallei |
Neisseriales
|
Neisseria gonorrhoeae |
Neisseria meningitidis |
Campylobacterales
|
Campylobacter jejuni |
Helicobacter pylori |
Legionellales
|
Legionella pneumophila |
Pseudomonadales
|
Acinetobacter baumannii |
Moraxella catarrhalis |
Pseudomonas aeruginosa |
Aeromonadales
|
Aeromonas sp. |
Vibrionales
|
Vibrio cholerae |
Vibrio parahaemolyticus |
Thiotrichales
|
(Note: No specific pathogens listed in your input) |
Pasteurellales
|
Haemophilus influenzae |
Enterobacteriales
|
Klebsiella pneumoniae |
Proteus mirabilis |
Yersinia pestis |
Yersinia enterocolitica |
Shigella flexneri |
Salmonella enterica |
Escherichia coli |
Spirochaetales, Chlamydiales and Actinomycetales
Key Pathogens
Spirochaetales
Taxonomy:
Cellular organisms → Bacteria → Spirochaetes → Spirochaetes (class) → Spirochaetales
Spirochaetaceae , Borrelia , Borrelia burgdorferi
Transmission:
Tick-borne; circulates in endemic areas between Ixodes sp. ticks and a large number of vertebrate hosts upon which ticks feed.
(Ixodes scapularis, black-legged tick, deer tick , vector of Lyme disease , facts and life cycle at MetaPathogen)
Importance:
- High Potential For Bioengineering
- Emergent Infectious Agent
- CDC Notifiable Agent
- Medically Important Human Pathogen
Disease Description:
Lyme disease usually starts with erythema migrans; later infection becomes systemic.
- ~5% of patients: cardiac involvement
- 10–15%: neurological symptoms
Notes:
Borrelia burgdorferi, Lyme disease spirochete taxonomy, facts, pathogenicity, bibliography at MetaPathogen
Transmission:
Transmitted through sexual intercourse or skin-to-skin contact; epidemiology highly depends on subspecies.
Importance:
- CDC Notifiable Agent
- Globally Important Human Pathogen
Disease Description:
Subspecies cause:
- Syphilis
- Yaws
- Bejel
- Pinta
Notes:
Treponema pallidum, spirochete causative agent of syphilis: taxonomy, history, biology at MetaPathogen
Chlamydiales
Taxonomy:
Cellular organisms → Bacteria → Chlamydiae → Chlamydiae/Verrucomicrobia group → Chlamydiae (class) → Chlamydiales
Transmission:
The most common sexually transmitted infection; also transmitted from mother to child.
Importance:
- Emergent Infectious Agent
- CDC Notifiable Agent
- Globally Important Human Pathogen
Disease Description:
- Causes genital tract infections in men, women, and children
-
Even asymptomatic infections may lead to:
- Infertility
- Tubal pregnancy
- Cervical cancer
- Exposed infants often develop conjunctivitis or pneumonia
Selected Literature:
- Lyons JM et al. (Drugs Today (Barc). 2009)
- Steben M. (J Obstet Gynaecol Can. 2004)
"Chlamydia trachomatis"
Transmission:
- From infected birds, especially in the poultry industry
- From Psittaciformes: cockatoos, parrots, parakeets, and lories
Importance:
- Zoonotic Agent
- Emergent Infectious Agent
- CDC Notifiable Agent
- Important Animal Pathogen
- Medically Important Human Pathogen
- Potential Biological Weapon
Disease Description:
Causes pneumonia; may progress to respiratory failure and death
Selected Literature:
- Beeckman DS et al. (Clin Microbiol Infect. 2009)
"Chlamydophila psittaci"
Actinomycetales
Taxonomy:
Cellular organisms → Bacteria → Actinobacteria → Actinobacteria (class) → Actinobacteridae → Actinomycetales
Transmission:
Transmitted by droplets or nasopharyngeal secretions through close contact
Importance:
- Emergent Infectious Agent
- CDC Notifiable Agent
- Validated Biocrime Agent
Disease Description:
- Causes nasopharyngitis, tonsillitis, or laryngitis plus a pseudomembrane
-
Severe complications:
- Endocarditis
- Airway obstruction
- Neck swelling
- Petechial hemorrhages
- Renal failure
- Myocarditis
- Motor paralysis
- Death
Selected Literature:
- Mokrousov I.
- Wilson AP. (J Antimicrob Chemother. 1995)
"Corynebacterium diphtheriae"
Transmission:
Airborne, via droplets or nasopharyngeal secretions from patients with smear-positive pulmonary TB
Importance:
- Emergent Infectious Agent
- CDC Notifiable Agent
- Validated Biocrime Agent
- Globally Important Human Pathogen
- NIAID Category C Priority Pathogen
Disease Description:
- ~20% of infected individuals develop tuberculosis (TB)
-
Histological signs include:
- Exudative inflammation in lungs
- Granulomatous lesions with necrotic centers
Selected Literature:
- Comas I, Gagneux S. (PLoS Pathog. 2009)
- API Consensus Expert Committee. (J Assoc Physicians India. 2006)
"Mycobacterium tuberculosis"
Transmission:
Possibly through contaminated milk
Importance:
- Zoonotic Agent
- Emergent Infectious Agent
- Important Animal Pathogen
- Medically Important Human Pathogen
Disease Description:
- Causes Johne’s disease, a chronic enteritis in ruminants
- Emerging evidence suggests possible link to Crohn’s disease in humans
Selected Literature:
- Pierce ES. (PLoS Pathog. 2009)
- Biet F. (Vet Res. 2005)
"Mycobacterium avium"