Some Important Pathogens of Aquatic and Terrestrial Environments
• Microbial Agents:
– Most are from feces or other excreta (urine, respiratory exudates, etc.) of humans and/or other animals
– Some are of natural origin
• either exclusively or in addition to fecal contamination
• Enteric Microbial Agents:– Infect the human and/or animal gastrointestinal (GI) tract
• Some enteric microbes also infect or invade other sites in the body
IMPORTANT HUMAN ENTERIC VIRUSES
Viruses/Groups Animal Feces
Enteroviruses: no
(polios, echos*, coxsackies*, etc.)
Hepatitis A virus no (primates)
Hepatitis E virus pigs, rats, others
Reoviruses yes
Rotaviruses yes**
Adenoviruses* yes**
Noroviruses*: maybe**
Norwalk, Snow Mountain, etc.
*On EPA’s candidate contaminants list (CCL).
**humans & animals usually infected by different ones; but perhaps not always.
IMPORTANT HUMAN ENTERIC BACTERIAL PATHOGENS AND OTHER SOURCES OF THEM
Bacterium/Group AnimalsOther SourcesSalmonella spp. yes no
(except S. typhi) no noCampylobacter spp. yes yesEscherichia coli yes noHelicobacter pylori* unknown unknownAeromonas hydrophila* yes yesYersinia enterocolitica yes yesVibrio cholerae; other Vibrio spp. yes yesLeptospira yes noMycobacteria spp. (non-tubercular) very rare yesShigella spp. no no
*On EPA’s candidate contaminants list (CCL).
IMPORTANT HUMAN ENTERIC PROTOZOAN PATHOGENS
Parasite Animal Feces
Cryptosporidium parvum yesCyclospora cayetanensis* unknownGiardia lamblia yesEntamoeba histolytica rareBalantidium coli yes (pigs)Microsporidia* yes
(Enterocytozoon and Septata) unknown
Toxoplasma gondii* yes
*On EPA’s candidate contaminants list (CCL).
Helminths (Worms): Some of the Important Ones
Most acquired from ingestion of or contact with feces-contaminated soil or food
• Nematodes (Roundworms):– Ascaris lumbricoides 1 GI illness; pneumonitis– Trichuris trichuria 1 chronic GI
• Hookworms:– Ancylostoma duodenale 1 chronic anemia– Necator americanus 1 chronic anemia– Strongyloides stercoralis1 chronic anemia
• Cestodes (tapeworms):– Hymenolepis nana 1 GI illness
Some Non‑fecal Bacterial PathogensBacteria:Legionella spp. >20 Pneumonia; febrile illness
L. pneumophila, etc. Legionnaires’ diseaseMycobacterium spp. many Upper respiratory illnessM. tuberculosis 1 tuberculosisM. avium-intracellulare several Upper respiratory illnessOther bacteria many Variable; "opportunistic"
or "conditional pathogens
Some Non‑fecal Protozoan Pathogens
Free living amebas:
Naegleria fowleri 1 Primary amebic menino-encephalitis
Acanthamoeba spp. few eye infections; encephalitis
Some Non-fecal HelminthsAgent: No. Illness and Sites• Dracunculus medenensis (N) 1 Tissue infections (subcutaneous & deep;
esp. foot and/or leg• Schistosoma (T; blood fluke) 3 Liver, intestine, colon
S. haematobium, S. mansoni bladder & rectum fromand S. japonicum colonization of venous
vessels.• Schistosoma spp. (T). few swimmers itch: larvae birds and
fish penetrate skin; not in bloodstream; no maturation in human
Occurrence of Microbial Pathogens in Humans
• Microbial pathogens usually are not “normal flora” of humans; opportunities for pathogenicity are possible– Some are “normal flora” of animals:
• Salmonella enteriditis and Campylobacter jejuni in poultry– “Normal flora” for local populations may be pathogenic
for visitors and transient populations:
• “Traveller’s diarrhea” due to local strains of E. coli– “Some “normal flora” are pathogenic for sensitive
populations, such as immunocompromised persons:• Example: Pneumocystis carinii (a protozoan or fungus)
– causes fatal pneumonia in AIDS patients– immunocompetent people get asymptomatic infections
Occurrence of Enteric Microbial Pathogens in Humans and Pathogen Shedding
• Enteric (gastrointestinal) illnesses are second only to respiratory illnesses in the population
• Most people get 1 enteric illness per year in the developed world:– Annual illness rates are higher in infants, children, the elderly,
child caregivers, health professionals, the poor, male homosexuals and other high risk groups & developing countries
• Not all enteric infections produce illness (asymptomatic or sub-clinical infections)– So, rates of infection are even higher (by perhaps 2 to 100 times)
• People (and animals) with enteric infections fecally excrete high concentrations of pathogens for days, weeks, months or longer.
• Pathogen concentrations can be >106 to >109 per gram of feces.• Community pathogen shedding is often 1-10% at any time.
Disease Due to Some Important Waterborne Enteric Virus Pathogens
Norwalk Virus Gastroenteritis: A Localized Infection• Fecal‑oral transmission• Localized infection of small intestine• Damage to microvilli of intestinal epithelium
– “blunting” of the microvilli• Incubation period 1‑3 days • Illness 1‑3 days • Major symptoms: diarrhea, vomiting, nausea, abdominal pain and low
grade fever • Fecal shedding from onset of illness for several days.
– Virus concentration in feces as high as 108/gram• Low infectious dose; perhaps as few as 10-100 virus particles
– Virus has not been cultured in laboratory animals or cell cultures
Disease Due to Some Important Waterborne Enteric Virus Pathogens
Hepatitis A Virus and Infectious Hepatitis: A Systemic Infection• Fecal‑oral transmission• Systemic (generalized; disseminated) infection• Liver as "target organ" • Incubation period 2‑6 weeks; average 4 weeks • Illness for several weeks or months• Destruction of liver hepatocytes• Jaundice (in some but not all cases) and severe "flu‑like"
symptoms, including gastrointestinal symptoms. • Virus shed fecally from 2 weeks before to a few weeks after onset
of symptoms.
Disease Due to Some Important Waterborne Enteric Bacterial Pathogens
Salmonella gastroenteritis: (S. enteriditis): localized infection• Fecal‑oral transmission• Localized infection of intestines• Damage and inflammation to lamina propria• 0.5‑2 day incubation period• Watery diarrhea, nausea, vomiting, abdominal cramps,
low grade fever, lasting several days• Bacteria shed fecally at billions per gram
• Infectious dose is relatively high: >103 ID50 for many strains
Disease Due to Some Important Waterborne Enteric Bacterial Pathogens
Typhoid fever: (S. typhi and S. paratyphi): Systemic Infection• Fecal-oral transmission• Systemic infection:
– Macrophages, reticuloendothelial system (esp. liver, spleen and bone marrow), gallbladder and intestines as major sites of damage
• 1.5‑2 week incubation period • Symptoms: fever, headache, malaise, anorexia, then bloody
diarrhea • Mortality rate 10%, if untreated• Carrier state possible
– "Typhoid Mary”: infamous food handler; infected hundreds• Fecally shed at billions/gram by ill persons and carriers
Disease Due to Some Important Waterborne Enteric Protozoan Pathogens
Giardiasis (Giardia lamblia): localized enteric infection• Fecal‑oral transmission; hardy cyst ~10 m diameter• Human and numerous non‑human animal reserviors• Infectious dose: low: ID50 ~10 cysts• Infection: cysts excyst in small intestine; trophozoites attach to microvilli
of intestinal epithelium, tissue damage and• Interference with transport processes • Profuse watery to semi‑solid, greasy, bulky, malodorous diarrhea;
abdominal cramps,nausea, vomiting, anorexia, low grade fever, headache
• 1‑1.5week incubation period• Duration of Illness: few days to months• Subchronic infection possible
Disease Due to Some Important Waterborne Enteric Protozoan Pathogens
Cryptosporidium and cryptosporidiosis• Cryptosporidium parvum: coccidian (sporozoan) parasite• Numerous animal reservoirs: feral, domestic and agricultural• Fecal-oral transmission of hardy oocyst, ~5 m diameter• Infectious at low dose: ID50 ~10 oocysts for some strains• Excysts in small intestine; trophozoites attach to epithelial cells• Complex life cycle; 6 major stages, some asexual, other sexual• Infection and illness in immunocompetent hosts: similar to giardiasis:
diarrhea, nausea, vomiting, anorexia, fever, malaise– Incubation period ~1 week; duration ~1.5 weeks, range 1-4 weeks
• Infection in immunocompromised hosts (ex, persons with AIDS):– Life threatening, excessive fluid loss, chronic, no drug therapy– ISpread to extra-intestinal sites: respiratory tract; pneumonia.
Constitutive Defenses: Physical Barriers to Infection
System or Organ Cell Type Clearing Mechanism
SkinMucousmembranes
SquamousColumnar nonciliated(e.g., gastrointestinal tract)Columnar ciliated(e.g., trachea)Cuboidal ciliated(e.g., nasopharynx)Secretory
DesquamationPerstalsis
Mucociliary movementTears, saliva, mucus,sweat
Flow of liquids
Examples of Encounters and Disease PreventionType ofcontact
Example Type ofAgent
Source Strategy forPrevention
Preventive Aim
Inhalation Common cold Virus Aerosol frominfectedpersons
None Difficult to avoidcontact
Ingestion Coccidiodo-mycosisTyphoid feverSalmonella foodpoisoning
Fungus
BacteriumBacterium
Soil
Water, foodFood
None
SanitationSanitation
Hard to avoidcontactLower infectingdose
Sexualcontact
Gonorrhea Bacterium Person SocialBehavior
Avoid contact
Wound Surgicalinfections
Bacterium Normal florasurroundings
Aseptictechniques
Avoid contact
Insect Bite Malaria Protozoan Mosquito Insectcontrol
Eliminate vector
Constitutive Defenses: Chemical Barriers to Infection
System or Organ Source Substances
SkinMucous membranes
Sweat, sebaceous glandsParietal cells of stomachSecretionsNeutrophils
Organic acidsHydrochloric acid, Low pHAntimicrobial compoundsLysozyme, peroxidase,lactoferrin
Lung A cellsSalivary glandsNeutrophils
Pulmonary surfactantThiocyanateMyeloperoxidaseCationic proteinsLactoferrinLysozyme
Small bowel and below Liver via biliary treeGut flora
Bile acidsLow molecular weight fattyacids