Download Introduction to Environmentally Transmitted Pathogens, Pathogens

Introduction to Environmentally
Transmitted Pathogens, Part 2
Envr 421
Mark D. Sobsey
Spring, 2008
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, especially the respiratory tract
IMPORTANT HUMAN ENTERIC VIRUSES
Viruses/Groups
Enteroviruses:
(polios, echos*, coxsackies*, etc.)
Hepatitis A virus
Hepatitis E virus
Reoviruses
Rotaviruses
Adenoviruses*
Noroviruses*:
Norwalk, Snow Mountain, etc.
Astroviruses
Zoonotic (Animal)?
no
no (primates)
pigs, rats, others
yes
yes, maybe**
unlikely**
maybe**
unknown
*On EPA’s candidate contaminants list (CCL)
**Usually different ones infect humans & animals; but maybe not always
IMPORTANT HUMAN ENTERIC BACTERIAL
PATHOGENS AND OTHER SOURCES OF THEM
Bacterium/Group
Zoonotic?
Other Sources?
Salmonella spp.
(except S. typhi)
Campylobacter spp.
Escherichia coli
Helicobacter pylori*
Aeromonas hydrophila*
Yersinia enterocolitica
Vibrio cholerae; other Vibrio spp.
Leptospira
Mycobacteria spp. (non-tubercular)
Shigella spp.
yes
no
yes
yes
unknown
yes
yes
yes
yes
very rare
no
no
no
yes
maybe
unknown
yes
yes
yes
no
yes
no
*On EPA’s candidate contaminants list (CCL).
Important Human Enteric Protozoan Pathogens
Protozoan
Cryptosporidium parvum
Cyclospora cayetanensis*
Giardia lamblia
Entamoeba histolytica
Balantidium coli
Microsporidia*
(Enterocytozoon and Septata)
Toxoplasma gondii*
*On EPA’s candidate contaminants list (CCL).
Zoonotic?
yes
unknown
yes
rare
yes (pigs)
yes
unknown
yes
Helminths (Worms): Some of the Important
Ones in Developed (Western) Countries
Most acquired from ingestion of or contact with fecescontaminated 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 stercoralis
1
chronic anemia
• Cestodes (tapeworms):
– Hymenolepis nana
1
GI illness
Some Non-fecal Bacterial Pathogens
Bacteria:
Legionella spp.
L. pneumophila, etc.
Mycobacterium spp.
M. tuberculosis
1
M. avium-intracellulare
Other bacteria
>20
Pneumonia; febrile illness
Legionnaires’ disease
many Upper respiratory illness
tuberculosis
several Upper respiratory illness
many Variable; "opportunistic"
or "conditional pathogens
Some Non-fecal Protozoan Pathogens
Free living amebas:
Naegleria fowleri
1
Acanthamoeba spp.
few
Primary amebic meninoencephalitis
eye infections; encephalitis
Some Non-fecal Helminths
Agent:
• Dracunculus medinensis (N)
No.
1
• Schistosoma (T; blood fluke)
S. haematobium, S. mansoni
and S. japonicum
3
• Schistosoma spp. (T).
birds and fish
few
N = Nematode; T = Trematode
Illness and Sites
Tissue infections
(subcutaneous & deep;
esp. foot and/or leg
Liver, intestine, colon
bladder & rectum from
colonization of venous
vessels.
swimmers itch: larvae
penetrate skin; not in
bloodstream; no
maturation in human
Occurrence of Microbial Pathogens in Humans
• Microbial pathogens usually are not “normal flora” of
humans;
– But, opportunities for pathogenicity are possible; e.g., trauma
– 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” visitor illness from local E. coli strains
– “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 & in developing countries
• Not all enteric infections produce illness (asymptomatic or sub-clinical
infections)
– 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
Response of Human Volunteers to Norwalk Virus Infection
via the Oral Route
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.
Life Cycle of Cryptosporidium parvum
• Oocysts ingestion from
water and food
• Reach target site of
infection in intestine
• Attach to and enter cell
(sub-membraneous
compartment)
• Complex asexual/sexual
multiplication sequence of
events, leading to oocysts
• Mature oocysts produced
• Oocysts shed in feces
Examples of Pathogen Encounters and Prevention
Considerations
Type of
contact
Example
Type of
Agent
Source
Strategy for Preventive Aim
Prevention
Inhalation
Common cold
Virus
None
Difficult to
avoid contact
Ingestion
Coccidiodomycosis
Typhoid fever
Salmonella
food
poisoning
Gonorrhea
Fungus
Aerosol from
infected
persons
Soil
None
Hard to avoid
contact
Lower infecting
dose
Surgical
infections
Bacterium Normal flora
Aseptic
Avoid contact
surroundings techniques
Sexual
contact
Wound
Insect Bite Malaria
Bacterium Water, food
Bacterium Food
Sanitation
Sanitation
Bacterium Person
Social
Behavior
Protozoan Mosquito
Insect
control
Avoid contact
Eliminate
vector
Constitutive Defenses: Physical Barriers to Infection
System or Organ
Skin
Mucous
membranes
Cell Type
Clearing Mechanism
Squamous
Columnar nonciliated
(e.g., gastrointestinal tract)
Desquamation
Perstalsis
Columnar ciliated
(e.g., trachea)
Mucociliary movement
Tears, saliva, mucus,
sweat
Cuboidal ciliated
(e.g., nasopharynx)
Secretory
Flow of liquids
Constitutive Defenses: Chemical Barriers to Infection
System or Organ
Source
Skin
Mucous membranes
Sweat, sebaceous glands
Parietal cells of stomach
Secretions
Neutrophils
Lung
A cells
Salivary glands
Neutrophils
Small bowel and below
Liver via biliary tree
Gut flora
Substances
Organic acids
Hydrochloric acid, Low pH
Antimicrobial compounds
Lysozyme, peroxidase,
lactoferrin
Pulmonary surfactant
Thiocyanate
Myeloperoxidase
Cationic proteins
Lactoferrin
Lysozyme
Bile acids
Low molecular weight fatty
acids