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Zoonotic infections (bacterial)
• Definition: Infectious diseases of animals that are transmitted to humans
either by contact, food sources or by a vector (insects)
• Many bacterial pathogens are zoonotic pathogens because they display host
ranges involving multiple mammalian species and are to humans and vice
versa; examples are, Lyme disease, Rocky Mountain Spotted Fever, S. aureus,
Salmonella gastroenteritis, EPEC, EHEC.
• Other bacterial pathogens cause disease only in humans; animals, wild or
domesticated, play no role in ecology and disease establishment: Neisseria
gonorrhoea, Neisseria meningitidis, Streptococcus pyogenes, Streptococcus
pneumoniae, Haemophilus infleunzae, Mycobacterium tuberculosis,
Corynebacterium diphtheriae.
• This lecture will discuss bacterial zoonotic pathogens causing severe and
frequently lethal infectious diseases in humans: anthrax, plague, tularemia
and brucellosis.
• The pathogens Bacillus anthracis, Yersinia pestis and Francisella tularensis
are considered biological weapons of mass destruction and their possession,
storage and proliferation is regulated by the US Patriot Act.
Biological warfare agents (CDC)
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Select Agents, Category A
Plague (Yersinia pestis)
Anthrax (B. anthracis)
Tularemia (F. tularensis)
Botulism (BoNTs)
Smallpox
Viral Hemorrhagic Fevers
(Ebola, Marburg etc.)
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Category B (partial)
Brucellosis
Typhus (R. prowazekii)
Q Fever (C. burnetii)
Plague, a recently evolved disease impacts
humanity
Mass graves of plague victims
Lazzaretto Vecchio Island, Venice
Xenopsylla cheopsis
Black rat
(oriental rat flea)
Three plague pandemics decimate the human
population (50-60%)
Justinian (541-740), Black Death (1346-1731), Asian (18551935)
Wagner et al. (2014) Lancet Infect. Dis. 14:319
Ancient Y. pestis genomes – SNPs, deletions
and mobile elements
Wagner et al. (2014) Lancet Infect. Dis. 14:319
Current plague epidemiology
Global distribution of Y. pestis, low incidence of human disease
Stenseth et al. (2008) PLoS Med.5:e3
Natural cycles of plague in the United States
Yersinia pestis
• Enterobacteriaceae, evolved from Y.
pseudotuberculosis (1,500-20,000 years
ago)
• Y. pestis shares 70 kb pCD1 plasmid &
type III secretion pathway (LcrV needle
cap protein) with Y. pseudotuberculosis
and Y. enterocolitica
• Acquired two unique plasmids pFra (F1
capsule/pilus production) and pPCP
(Pla, plasminogen activator) for
virulence and plague pathogenesis
• Acquired factors for flea-borne
transmission to mammals
• Infects most vertebrate animal species
to cause lethal plague disease
Bubonic plague
• Transmission: Y. pestis inoculated via flea bite from
insects that fed on infected human or rodent
• Incubation: 2-6 days
• Clinical: Fever, chills, headache, myalgias,
prostration, occasionally nausea and diarrhaea,
swollen lymph node or bubo
• Diagnosis: Lymph node aspirate, Wayson staining,
culture; serological test (F1 specific antibody
positive after 8-14 days) used for retrospective
diagnosis
• Treatment: streptomycin or gentamycin,
(ciprofloxacin, levofloxacin as alternatives)
• Prognosis: 40-60% fatal without treatment (14% of
U.S. cases fatal, 1970-present) because Y. pestis
disseminates to cause septicemic plague; bubonic
plague survivors are immune to Y. pestis infection
(F1-specific antibodies).
• Epidemiology: 4-40 cases in the US rural West
Pneumonic & septicemic plague
• Transmission: Pneumonic plague -Y. pestis inhaled via
aerosol droplets typically from plague infected humans
(~5-10% develop secondary pneumonia) under
crowded conditions; septecimic – flea inoculation into
the bloodstream, animal bite/scratch, direct inoculation
• Incubation: 1-3 days
• Clinical: acute, fulminating disease with sepsis, shock
and lethal outcome within 1-3 days
• Diagnosis: Blood cultures (Wayson stain), NAAT (PCR);
serological test (F1 specific antibody positive after 8-14
days) used for retrospective diagnosis
• Treatment: ICU, symptomatic, streptomycin or
gentamycin, (ciprofloxacin, levofloxacin as alternatives)
• Prognosis: 100% fatal without treatment
• Epidemilogy: 1-10 cases in the US rural West
Pneumonic plague
Septicemic plague
Septicemic plague
Plague pathogenesis
Marketon et al. (2005) Science 309:1739
Yop effectors subvert innate defenses of
immune cells
Y. pestis establishes a biofilm and blocks the
flea proventriculus
blood meal
midgut
esophagus
proventriculus
uninfected flea
blocked flea
Y. pestis biofilm
Y. pestis infected flea
Asian plague pandemic ends in 1935
Girard and Robic (Institut Pasteur) inoculatd 500,000
Malagasies with Y. pestis EV76 (pgm-iron defective) and
achieve plague protection
Girard & Robic (1942)
Bull. Soc. Pathol. Exotique 35:42
Yersiniabactin, a siderophore for iron scavenging
from transferrin, is absent from the EV76 vaccine
Crosa and Walsh (2002) MMBR 66:223
LcrV vaccine protects animals (mice, rats, guinea
pigs, non-human primates) against plague
currently no licensed vaccine in the US
Tularemia – Francisella tularensis
• Definition: infection with Francisella tularensis, Gram-negative facultative
intracellular pathogen, whose natural reservoirs are wild-animals, small
rodents, hares, rabbits; 100-200 cases/year in the US
• Transmission: ticks (other arthropods), deer flies , contact or aerosol; very
low infectious dose; 1-14 day incubation period; untreated 7% mortality for
all disease forms
• Clinical: six clinical entities depend on site and route of transmission:
ulceroglandular (75% of tularemia), glandular, oropharyngeal,
oculoglandular & pneumonic or typhoidal (highest mortality; fever, malaise,
shock and death; subacute disease occurs frequently; lymphadenopathy
with necrosis of immune cells.
• Diagnosis: lesion swab, LN biopsy, sputum, pharyngeal wash: growth on
buffered-charcoal and yeast extract (BCYE); 4x increase in F.t. serology also
diagnostic; NAATs (PCR), fluorescent antibody: presumptive diagnosis
• Treatment: 21 days streptomycin/gentamycin, doxycycline or ciprofloxacin
• Prevention: live-attenuated vaccine (LVS) is not licensed for general use;
protective equipment and precaution for hunters; avoiding ticks
Tularemia
disease states &
transmissiom
ticks
lawn mower
hare
deer fly
ulceroglandular: most common form, characterized by
ulcer at entry site and swelling of regional lymph nodes;
insect or contact transmission
glandular: similar to above, but without ulcer
oculoglandular: bacteria enter through the eye; contact
with infected animals
oropharyngeal: sore throat, mouth ulcers, tonsillitis,
glandular swelling in the neck; transmission by eating
infected animals
pneumonic: most serious form characterized by cough,
chest pain and respiratory distress; result from
inhalation of the pathogen (lawn mowers aerosolize F.t.
from dead animals)
typhoidal: systemic infection in the RES, high mortality
US tularemia cases, 2003-2013
Tularemia
ulceroglandular
ulceroglandular
ulceroglandular
pneumonic
Francisella pathogenesis
escape from the endosome and intracellular replication
Francisella survival inside macrophages requires
escape from the phagosome and specific genes
Brucellosis
• Definition: Gram-negative, facultative-intracellular coccobacillus
transmitted from animals; replicates in cells of the RES to cause
persistent infection with granuloma formation in liver/spleen,
undulating fever and secondary manifestations
• Epidemiology: 500,000 new cases/yr worldwide; 90-150 US cases
Sir David Bruce
• Transmission: inhalation (aborted animal fetus), consumption of
contaminated milk & milk products, or direct contact of bacteria with
skin lesions (animal workers)
• Initial symptoms: fever, malaise, anorexia, headache, muscle pain,
arthralgia, hepatomegaly, splenomegaly
• Recurrent symptoms: fever, arthritis, osteomyelitis,
meningoencephalitis and endocarditis (1-2%)
• Diagnosis: Blood culture (Castaneda bottle- 6 weeks); Brucella
microagglutination test (BMAT, to detect serum Abs against B.
abortus, B. melitensis & B. suis: 2x for increase in Ab titer)
• Treatment: 6-8 week course of rifampin and doxycycline
• Prevention: no vaccine available for humans; milk pasteurization;
protective equipment; vaccinate animals
• At risk: farmers, animal workers, veterinarians, laboratory scientists
Brucella species and their potential to cause
human disease
Species
Brucella melitensis
Brucella abortus
Brucella suis
Brucella canis
Brucella ceti
Brucella pinnipedialis
Brucella inopinata
Brucella ovis
Brucella neotomae
Brucella microti
Brucella sp. (baboon)
Host preference
Sheep, goat
Cattle
Pig
Dog
Dolphin, porpoise, whale
Seal
Unknown
Sheep
Desert woodrat
Common vole
Baboon
Zoonosisa
High
Moderate
Moderate
Mild
Mild
Mild
Mild
No
No
No
No
Ecology of zoonotic Brucella infections
Brucella replicate in ER vesicles within
macrophages
Subversion of innate immune responses by
Brucella melitensis Btp1/TcpB
Non-opsonic entry and subsequent trafficking
of Brucella spp. in macrophages
Microgranuloma formation by Brucella spp.
in the liver
Undulant fever during brucellosis
Blood
culture
Castaneda bottle
U.S. bovine brucellosis eradication program
RB51 vaccination and culling
Affected Herds
– in 1957 : 124,000
– in 2000 : 6
Financial impact
– in 1957 : > $400 million
– in 2000 : < $1 million
Feb, 1957 Brucellosis infected herds
Surveillance, vaccination, eradication
Anthrax
• Definition: Gram-positive spores of Bacillus anthracis transmitted from
animals or the environment germinate and replicate in host tissues and
cause fatal disseminated disease; not transmitted between humans
• Epidemiology: worldwide incidence unknown; 1-2 cases in the US/yr
• Transmission: contact with spores (cutaneous A.), ingestion (gastrointestinal A.), injection by IVDAs (i.A.), inhalation (respiratory A.; wool
sorter’s disease)
• Symptoms: eschar, lymphadenopathy (c.A.); fever, sore throat, nausea,
vomiting, diarrhea (g.-i.A.); fever, chest pain, cough, respiratory distress
(r.A.); eschar, local necrosis, meningitis (i.A.); anthrax is rapidly fatal
• Diagnosis: Culture B. anthracis from lesion (swab), blood, CSF, sputum;
retrospective diagnosis (8-14 days) anti-PA antibody titer
• Treatment: 8 week course of antibiotics (ciprofloxacin and others);
spores do not germinate in the presence of antibiotics; anti-toxin (PA)
• Prevention: AVA vaccine (FDA approved); anti-PA injection,
ciprofloxacin for 60 days.
• At risk: farmers, hunters, veterinarians, laboratory scientists
B. anthracis life cycle
Spore
vegetative
forms
B. anthracis spores contaminate soil, are taken up by herbivores and invade GI tract.
Animals develop gastrointestinal anthrax and die. Sores contaminate the environment
Clinical appearance of anthrax
cutaneous anthrax
respiratory anthrax
cutaneous anthrax
CDC
Anthrax in intravenous drug (heroin) users
B. anthracis virulence plasmids, pXO1 & pXO2
attenuated strains and whole cell live-attenuated vaccines
Max Sterne:
B. anthracis
pXO1+, pXO2-
Louis Pasteur:
B. anthracis
pXO1-, pXO2+
The Sterne vaccine strain 4F32 is used world-wide to prevent anthrax in
domesticated farm animals; the Soviet Union and other countries used a Sterne
type strain to prevent cutaneous anthrax in humans, vaccinating 30 million people
pXO1-encoded protective antigen (PA), lethal
factor (LF) and edema factor (EF) are secreted
to form the lethal (PA+LF) and edema (PA+EF) toxins
pXO2-encoded genes synthesize the poly-D-γglutamic acid capsule of B. anthracis
Sverdlovsk (Ukraine), 1979 anthrax outbreak
and anthrax weapon facility
B. anthracis as a weapon for biological warfare
• Definition: Preparation and dissemination of
infectious spores, e.g. with explosives, to harm
large segments of the population
• Target: inhalational anthrax causes lethal
infections within 24-48 hours
• Generation of Bacillus anthracis strains resistant
to antibiotics
• Generation of recombinant Bacillus strains
evading the protective immunity of vaccinated
individuals
• Prevention: AVA vaccination
• Treatment: Monoclonal antibody against PA