ID Flashcards
General features of E.Coli
A Gram-negative bacterium from the family
Enterobacteriaceae
• Most strains are motile via peritrichous
flagella
• Rod shaped (c. 2 µm long & 0.5 µm in
diameter)
• Facultative anaerobe
• Obtains energy by oxidation & reduction of
organic sources and ferments sugars
• Common inhabitant of the intestines of
warm-blooded animals and humans – almost
every sample grows it!
• Frequently a commensal but some variants
are adapted to cause disease
What is commensals, pathogens and opportunistic and which one is E.Coli
Commensals are microorganisms that coexist with their hosts -’true’
commensals have a mutually beneficial symbiotic relationship.
• Pathogens are equipped with genes and gene products they use to cause disease
• Opportunists are commensals enabled
to cause disease given an opportunity (ex. immune suppression, disruption of microbiome, previous antibiotics)
E.Coli can be all three
What does ubiquitous mean
Found everywhere
E.Coli is ubiquitous in microbiomes of mammals and birds
Role of E.Coli
Biosynthesis of Vitamin K and colonization resistance
Bioindicator of faecal contamination
How is E.Coli versatile?
-commensale and carried by most vertebrate
-infections can be opportunistic or caused by specific phatotypes
Infections can be: intestinal or extra-intestinal
Three types of E.Coli enteric diseases
EPEC Enteropathogenic E. coli
STEP Shiga-toxin producing E. coli
EHEC Enterohaemorrhagic E. coli
Serotyping of
pathogenic
E. coli
> 170 O antigens (LPS)
50 H antigens (Flagella)
100 K antigens (Capsule)
Some well-known E. coli serotypes associated with human foodborne illnesses:
• E. coli O157:H7
• The “big six”: E. coli O26, O45, O103, O111, O121, and O145
E.Coli virulence factors
Adherence factors: enable bacteria to attach to host cells and colonize specific
niches.
• Motility factors: Such as flagella, which enable bacterial movement and can
contribute to adhesion.
• Toxins: divided in endotoxins (e.g. lipopolysaccharide or LPS) and exotoxins (e.g.
STEC/ETEC)
• Secretion systems: used by bacteria to deliver virulence factors into host cells
E.Coli Flagella, Pili and Fimbriae
All may act as adhesins -factors
that allow adhesion to host cells
& tissues in infection
• Flagella are also important for
motility
• Some fimbrial types are strongly
associated with increased
virulence e.g. F4 (K88) and F5
(K99) and F41 in neonatal
diarrhoea and F18 in oedema
disease.
Evolution of virulence &
the role of horizontal
gene transfer
Horizontal gene transfer is a major driver of
pathogenic diversity in E. coli
• Pathogenicity Islands (or smaller Islets)
are regions of DNA acquired into the
genome encoding for virulence factors
such as T3SS
• Bacteriophage transfer of toxin genes- Stx
or Shiga-like toxins
Other mechanism allowing bacteria to
exchange their genetic material:
transposition (integration of Mobile
Genetic Elements [MGE] into different parts
of the chromosome and plasmids).
ETEC
Neonatal diarrhoea in
many animal species,
post-weaning
diarrhoea in pigs,
septicaemia etc.
Enterotoxins important in ETEC: Secretory
diarrhoea e.g traveller’s diarrhoea in
humans or post weaning diarrhoea in pigs
• Important also the Shiga-like toxins (or
verotoxins, STEC/VTEC) Stx1 and Stx2 act on
blood vessels and endothelial cells
(encoded by bacteriophage) in oedema
disease of pigs
STEC/VTEC:
Stx-toxins in pigs -
oedema disease
Pigs are affected by O138, O139 & O141
serotypes- distinct from human/cattle STEC/
EHEC
• Usually hemolytic strains, producing Stx2e and
expressing F18 adhesins.
• Toxin targets endothelial cells and inhibits protein
synthesis > cell apoptosis & vascular damage.
• Clinical signs from oedema of face and eyelids
(sleepy appearance) to severe neurological
problems (usually no diarrhea)
• Fluid accumulation or lesions in a range of tissues
including intestinal, cardio-pulmonary system &
brain (angiopathy with vessels fibrinoid necrosis).
E. coli that carry Stx are referred to as
STEC
• EHEC are a class of STEC
• EHEC (e.g. O157:H7) are carried
asymptomatically in the intestine of
healthy ruminants
• Main source from undercooked beef or
faecal contamination of veg/fruit
• Toxin during human infection may cause
haemorrhagic diarrheoa and hemolytic
uremic syndrome (HUS).
E.Coli Secretion systems
Bacteria evolved to develop various protein
nanomachines, which allow bacterial effector
proteins to be exported through the Gram-
negative membranes.
What is the LEE
The LEE T3SS is a key virulence factor in EPEC and EHEC: Attaching and effacing E.Coli
LEE=Locus of enterocyte effacement is a pathogenicity island
Characteristics attaching and effacing lesions in which the bacteria are intimately adherent to the host enterocytes with marked rearrangement of the cytoskeleton
Pedestal formation, effacement of brush border microvilli, premature enterocyte exfoliation and villous distortion
LEE encodes for T3SS, intimin, translocated intimin receptor and effector proteins mediating actin rearrangement to form the pedestal
• Unlike Salmonella SPI1 T3SS which mediates cell invasion, E. coli LEE translocate its own receptor to enterocytes
• This allows tight adherence to intestinal surface (bacteria sitting on the pedestals)
• Significant enterocyte rearrangement with brush border destruction leading to reduction of intestinal absorption surface and malabsorptive diarrhea
• Typical histopathologic findings
Disease is usually the result of what
Disease is usually the result of
virulence factors working in
concert
• Most disease is a consequence of several
factors
Host and environmental risk
factors are crucial to disease
establishment
• Insufficient passive immunity in neonates
• Husbandry practices (diet, overcrowding etc)
• Transportation
• Concurrent disease, immunosuppression,
previous antimicrobial treatments
What is the 2011 German Beansprout E Coli outbreak
O104 is an EAEC that usually causes
persistent diarrhoea
• The ‘German’ isolate acquired Stx
toxin genes-so became
persistent and ‘nasty’
• As the infection was common in
women 15-50 -unusual as EHEC
(which is what it was initially
considered to be) is usually an
infection of children & elderly
• Cucumbers were wrongly identified as
the source-though did have EHEC
contamination
Extra-intestinal pathogenic E.
coli (ExPEC) –
intestinal escape artists
• ExPEC include neonatal meningitis (NMEC), sepsis
(SepEC), urinary tract (UPEC) and avian pathogenic
(APEC) pathotypes
• Have distinct but variable virulence factors involved
in invasion and systemic survival
• No distinct genotype or virulence factor associated
with pathotypes
• Genomic plasticity, global emergence of hyper-
virulent and antibiotic-resistant strains
• Pathogenic and opportunistic infections
APEC
• Important endemic disease associated with significant
economic losses (reduced meat and egg production,
with mortality up to 20% in young broiler outbreaks).
• Disease (‘avian colibacillosis’) by APEC pathotypes and
opportunistic commensals from microbiota
• APEC can affect all species of poultry in all types of
production systems
Most common infections:
o Broiler chickens: septicaemia, perihepatitis,
airsacculitis, pericarditis, coligranuloma, swollen head
syndrome
o Laying hens: egg peritonitis and salpingitis (salpingo-
peritonitis syndrome, SPS)
o Chicks: omphalitis, septicaemia, high mortality
o Turkeys: respiratory disease and osteomyelitis/arthritis
• Can act either as a primary
pathogen or secondary to viral (ex.
infectious bronchitis and avian
influenza) and Mycoplasma spp.
infections, immunosuppressive
disease (infectious bursal disease),
or environmental stresses
(overcrowding, poor hygiene etc)
• APEC utilizes different virulence
factors to cause disease in chickens,
primarily adhesins, invasins, iron
acquisition systems, and toxins.
• Recent studies suggest APEC as
potential foodborne disease in
humans with extra-intestinal
disease.
E.Coli in small animals
infections in dogs.
• UPEC (uropathogenic): most common cause of
urinary tract infection (35-69% of canine UTIs
caused by UPEC).
o Virulence factors include specialised fimbriae to
colonise and persist on urothelial cells, iron uptake systems, cytotoxins, uropathogenic-
specific proteins and others
o Global emergence of successful clones carrying high virulence and antimicrobial resistance (ex.
ST131)
o Identical genotypes identified in people and their pets (mutually transmitted)
• UPEC but also other strains also associated with:
o Pyometra – common uterine disease in bitches
o Prostatitis in male dogs
o Other opportunistic infections
E Coli and cattle mastitis
E. coli mastitis a particular problem in housed dairy cattle over winter
• Primary agents of environmental clinical
mastitis (‘coliform mastitis’)
• E. coli colonise the udder during calving and early lactation and during the dry period
• Intramammary infection elicits a strong inflammatory response (swelling of the udder, pain, pyrexia)
• Excessive response to LPS can lead to systemic
effects and endotoxic shock (toxic mastitis
General features of Salmonella
Another Gram negative rod from the
family Enterobacteriaceae
• Facultative anaerobe, most serovars are motile,
do not ferment lactose and produce H2S
• Discovered in 1885 in pigs - wrongly described
as the cause of “Hog Cholera”
• Complex taxonomy, based on the Kaufmann &
White scheme (somatic ‘O’, flagellar ‘H’ &
capsular ‘Vi’ antigens)
• Reservoir for salmonellae is the intestinal tract
of warm & cold-blooded animals (transient,
persistent or latent carriage in mammals, birds
and reptiles)
• Broad range of serovars, host and tissue
tropism and clinical manifestations
• Facultative intracellular pathogen
Salmonella Phage Typing
for example. S. typhimurium DT104, multidrug-resistant food-
borne infection or acquired through animal and environmental
direct/indirect contact.
Genus: Salmonella
Species: S.enterica or S.bongori
Subspecies: S.enterica-> enterica I, salamaeII, arizonaIIIa diarizona IIIb houtneae IV indica Vi
S.bongori-> subsp V
Why is Salmonella important
01
02
Major foodborne
zoonoses (covered
in Veterinary Public
Health in 2nd and
3rd year)
Major cause of
enteritis in humans
and animals
03
Major cause of
systemic disease in
humans (Typhoid
fever) and animals
Veterinary significance of Salmonella
Subclinical carriage
and shedding in the
environment by many
domestic and wild
host species
In food-producing
animals, crucial
hazard of meat
contamination - pork,
poultry, beef
Vertical transmission
to eggs, foetus and
milk
Disease in food producing
animals (esp. cattle, pigs
and poultry) includes
enteritis and enterocolitis,
septicaemia, abortion and
other systemic disease
Enteric disease in
companion animals (horses
and dogs)
Salmonella (enteric) diseas
Broad host range Salmonella serovars can colonise the distal small intestine and colon and cause
enteritis/enterocolitis.
Pathogenesis involves the close interaction between salmonellae and the host innate immune system
Clinical infection, subclinical and latent carriage are possible (ex. S. Dublin)
Salmonella penetrate the intestinal epithelium and lymphoid follicles of the Peyer’s patches, inducing an acute localised inflammatory response
Invasive strains producing systemic disease can escape beyond the intestinal barrier
Salmonella enteric
disease -
Pathogenesis
Salmonellae can respond to the gastric
acidic environment through a complex
adaptive system
• Organisms that survive the low-pH
environment proceed to the lumen
(ileum, cecum & colon)
• It competes with the gut microflora to
make initial contact with enterocytes
and M cells of the Peyer’s patches
• Adhesion to the intestinal epithelium is
facilitated by flagella and fimbriae
present on the bacterial cell surface
• After adhesion, bacteria are internalised either
through the uptake via phagocytosis or by active
invasion of enterocytes and phagocytic cell
• Subsequent events include an inflammatory
response with neutrophil recruitment and
cytokine release leading to mucosal damage
with ulceration
Salmonella enteric
disease –
virulence factors
Salmonella Pathogenicity Islands (SPI)
encode specific virulence factors mediating
cell invasion
• 18 SPIs are found (not all in one strain)
• SPI1 located on the chromosome is found in
all serotypes and controls infection of the
intestinal epithelium
• SPI1 encodes for a type 3 secretion system
(T3SS)
The translocation of effectors via the SPI1 T3SS
allows Salmonella to enter nonphagocytic cells,
such as M cells, and the intestinal epithelium
• The invasive process of enterocytes involves
massive ruffling of the host cell membrane
(rearrangements of the host cell actin
cytoskeleton) and bacterial uptake into large
vescicles
• Once internalised, it can replicate inside the
vescicle resisting cell-mediated degradation
(superoxide dismutase).
• Infected cells release pro-inflammatory cytokines playing an important role in Salmonella-induced diarrhoea
Salmonella –
Innate immunity
• The phagocytosis process of Salmonella
involves intricate mechanisms relying on
the engagement of multiple molecules
found on microbes and cells of the innate
immune system;
• The innate immune system is 1st line of
defence and quickly recognises pathogens
as a danger to the host
• Adaptive immunity (antibody & cellular
responses) are more effective; however,
they are slower more to develop
Host cells have Pattern Recognition
Receptors (PRRs) which sense specific
microbial structures of bacteria, viruses
etc. collectively named pathogen-
associated molecular patterns (PAMPs).
This recognition influences the maturation of
phagosomes, triggers signalling pathways
modulating the inflammatory cascade
(production of cytokines and chemokines), and modulates gene expression all of which further activate the immune response
The PRRs include Toll-Like Receptors (TLRs), which recognise pathogen-associated molecular patterns (PAMPs) like lipopolysaccharides (LPS, TLR4) and flagellin
(TLR5) located on the cell surface or within phagosomes.
Salmonella systemic
disease -
Pathogenesis
Salmonellae within M cells are carried to
the regional mesenteric lymph node for
presentation to the macrophages
• At this point infection is usually cleared
• Invasive salmonellae producing septicaemia
and systemic disease can however resist
clearance, survive and replicate within
macrophages
The T3SS SPI2 has a key role
in systemic infection and
intracellular pathogenesis as
it allows survival, replication
and spread of the bacteria
within macrophages and
other APCs
Invasive salmonellae ‘hide’ within macrophages to
evade the immune system and are disseminated
from the mesenteric lymph node via the lympho-
reticular and vascular systems to the liver and
spleen and to other organs
Intracellular replication within cells
trafficking salmonellae throughout the body
leads to severe endotoxaemia
If uncontrolled by the immune system, septicaemia leads to
death
Immune clearance may occur, and animals recover
Low level persistent infection-carrier state may develop
Salmonella systemic
disease - Stealth and
typhoidal infection
Unlike most salmonellae, S. typhi and typhoidal
(i.e. systemic) infections can have limited
intestinal inflammation
➢ Typhoidal serovars evade recognition by
TLR4, thus preventing the recruitment of
neutrophils and the expression of pro-
inflammatory molecules
This is achieved by:
i. The Vi capsule of S. typhi prevents LPS or
flagella being recognised
ii. ‘Switching on/off’ the expression of
flagellar genes (S. typhi) to avoid TLR5
recognition and/or switch between types of
flagella expressed.
iii. Not having flagella (S. gallinarum & S.
pullorum are non-motile)
• S. typhi in humans
• S. gallinarum and S. pullorum in poultry
• S. choleraesuis in pigs
• S. Dublin in cattle
What is a vaccine
-any preparation intended to produce immunity to a disease by
stimulating the production of antibodies.
• Include suspensions of killed or attenuated microorganisms, or products or derivatives of microorganisms.
• Most common method of application = injection, but some are
given by mouth or nasal spray
Examples of vaccines and how they worked
-Eradication of smallpox
• Eradication of Rinderpest
• Reduction of Salmonella-positive chicken flocks 250 to 7 within four years of vaccinating laying hens in UK (1998)
• Lack of effective control for many non-vaccine preventable diseases
• Increase in mumps and measles following drop in MMR usage.
The first vaccines
Edward Jenner-1st description of ‘modern’ Western vaccination in
1796 -> Cowpox-infected pustules to vaccinate against smallpox
• ‘Vaccine‘ coined by Pasteur to honour Jenner
from Latin for cow: vacca
• 1872Pasteur developed, the first
laboratory-produced vaccine:
against fowl cholera in chickens
• A range of vaccines developed from 1900s on.
What can the vaccine do
Protect individual against disease
Good for individual but does not always stop
infection spread in population
• Prevent transmission of infection
Good for population-no help to individual
• Prevent or reduce infection
Good for individual, Good for population
Features of effective vaccines.
Safe- must not cause illness or death
Protective-must protect against illness resulting from exposure to live pathogen
Gives sustained protection-protection against illness must last for several years
Induces neutralizing antibody- some pathogens infection cells that cannot be replaced. Neutralizing antibody is essential to prevent infection of such cells
Induces protective T cells- some pathogens, particularly intracellular, are more effectively dealt with by cell-mediated responses
Practical considerations-low cost per dose, biological stability,ease of administration, few side-effects
The cost of vaccines
Equine & small companion animal cost is less important
Farm animal for food production-very low costs
Administration of vaccines
Easy administration to production animals
e.g. Spraying, drinking water etc.
Single dose for livestock but annual booster for pets ensures
animals are seen by a vet regularly
Vaccine types
• Killed/inactivated
• Live attenuated
• Live recombinant/vector
• Sub-unit
• DNA/RNA
Killed or inactivated vaccines
• Simplest vaccine form
• Produced from heat or chemically killed
pathogen
• Widespread use in human & veterinary
medicine
Live attenuated vaccines
Viruses, bacteria or protozoa that typically
have been passaged away from host repeatedly until they have reduced virulence
Eg Mycobacterium bovis
Live and killed vaccination response
Live: IgG, IgA, T cells
Killed:IgG, little T cells
Rational vs Empirical design
Traditional vaccines designed empirically-
attenuation through random mutation e.g. BCG
• Most live vaccines are empirical in design
• Rational design uses targeted mutations in
specific genes
• As GM there are greater regulatory issues for
veterinary or human use though there is an
increasing use of such vaccines
Attenuation and drift mutation
• Viruses
Usually by passage through cells
• Bacteria
Chemical mutagenesis frequently used
Drift mutation-culture to produce changes in
metabolism
Rational vaccine design
Rational vaccine design uses viral
or bacterial genomes to identify
‘virulence factors’
• Insertional or deletion mutations
targeted to genes required for
virulence
• Mutation will be avirulent or highly
reduced in virulence
• Will be highly immunogenic-and
show similar biology to wild type-
therefore should stimulate a
response similar to wild type
Reverse vaccionology-exploiting the pathogen genome
Start with the pathogen genome to
predict antigenic targets
• Rapid production and testing of
candidates in animal models
• Development of potential
candidates towards commercial
vaccines
• Can produce novel vaccines in
months rather than years
What are recombinant/vector vaccines
Live attenuated viruses (e.g. Vaccinia,
Canarypox, adenovirus) or bacteria(eg
Salmonella) acting as carriers of recombinant
antigens
• High level (over) expression of antigen may be
achieved through use of some promoters in
bacteria.
• Potential of several antigens, from same or
different pathogens, to be delivered together
• Immunity also produced to vector (advantages and disadvantages)
What are subunit vaccines
Subunit vaccines are constructed from
antigenic components of pathogens:
• Proteins/peptides
• Synthetic Peptides
• Recombinant proteins
• Carbohydrate antigens
Recombinant proteins
• Identify genes for target antigen/epitope (usually
surface expressed)
• Clone and express (ideally overexpress) in bacterial
or eukaryotic vector
• Purify protein and use as vaccine
• Cheap
• Successfully used for Hepatitis B in man (HBsAg),
Men B in humans and Lyme disease in dogs
• Problems associated with protein/peptides remain for
synthetic and recombinant proteins
DNA and RNA Vaccines
DNA vaccines incorporate into
host nucleus & are transcribed
and translated into antigen
• Can be delivered into muscle
• Can be delivered into muscle
on particles and used in
poultry in ovo vaccines in US
• mRNA vaccines are delivered
in lipid-based carriers
• The synthetic RNA is
translated into the antigen by
host
Carbohydrates and conjugate polysaccharides vaccines
Good candidates as often surface
expressed
• Possibility of innate activation in some
cases
• Often poorly immunogenic-especially in
young
● Bacterial polysaccharide capsules are a good target for
vaccination-easily produced
● T-cell independent antigens-induce good antibody
responses in older subjects (humans 2 years+)
● Conjugation with a protein (often Tetanus toxoid
Fragment C) converts to a T-cell dependent antigen
● This allows successful induction of antibody responses
in young
● Highly successful conjugate vaccines against human
meningitis- Haemophilus influenzae B (Hib) and
Group C Neisseria meningitidis
Anti-toxin vaccines
● Do not protect against infection but against toxin produced by
pathogen
● Important in veterinary and medical field
● Most common are to toxins produced by Clostridium species
e.g. tetanus
● Diptheria toxin vaccine
● Usually produced from inactivated toxins
What to consider
AGE
Neonates are poorly responsive versus need for protection at
young age
Maternal antibody may affect success of some vaccines
• NEED for BOOSTERS
Length of immunity
• VACCINE TYPE
Safety of live vaccines in especially in food chain
Does vaccine affect disease surveillance etc.
• COST
• HERD IMMUNITY
• SINGLE v MULTIPLE VACCINES
convenience and cost v safety
?Enhancement/adjuvant effect e.g. DPT in humans
Adjuvants and vaccine additives
Comes from the Latin adjuvare- ‘to help’
• Compounds delivered with antigen in vaccine
that help develop the immune response
• Most killed and many live vaccines have an
adjuvant component
• Other additives such as stabilizers and
preservatives may be included
How can vaccines be given
Needle
-needle free systems
• Orally or nasally
• Eye drops
• Drinking water
• Spray/inhalation
• Gel drop
• In ovo (birds)
Phenotypic traits of Spirochete
• Unique - Helically shaped
• Free living/host associated
• Gram-negative
• Motile
• Outer sheaf surrounds protoplasmic
cylinder
• Periplasmic flagella at interface
Borrelia
microaerophilic, host associated, pathogen,
transmitted to man and animals by arachnid vector.
Brachyspira
anaerobic, consume O2 using NADH oxidase,
some species are pathogenic to man and animals.
Leptospira
obligately aerobic spirochetes and include free
living saprophytes and host associated pathogens. Infect man
and animals.
Treponema
anaerobic, host associated spirochetes, some of
which are pathogenic to man and animal.
Koch’s Postulates and difference with Stanley Falkow
Reviens quand tu tombes dessus
Tick transmition stages
Tick transmission to mammals involves both larval and
nymph stages.
Ixodes ticks can also carry and transmit other parasites BORRELIA_LYME DISEASE
Lyme disease symptoms
Stage I: Erythema migrans (early localized). Spirochete
localisation at bite site causing a rash. Not seen in
domestic species.
Stage 2: Early disseminated disease. Move to joints heart,
nervous system: causes arthritis, carditis and neuropathies.
Includes early & late infection on last slide
Stage 3: Persistent/Chronic disease including
recurring/relapses of arthritis, neuroborreliosis and skin
diseases.
Virulence factors identified with Lyme disease
• Decorin-binding proteins A and B. Identified in mice using mutants. Decorin is abundant in the ECM.
• Major outer surface protein C (OspC). Function not identified.
Knock out mutants prevent infection of host.
There is interchange between OspC and OspA depending on host (e.g. Mammal or tick).
Lyme disease and treatment
Is present in dogs and horses in UK and worldwide.
• Probably the most relevant spirochete to you.
• Diagnosis is based on symptoms (neurological signs, shifting arthritis), a history of tick exposure/tick attached as well as
positive serology.
• Detection is typically serology (detecting host antibodies to Borrelia spp). PCR methods have been developed but are not widely used.
• Treatment is with doxycycline (tetracycline) or amoxicillin (penicillin derivative). Longer treatment for late stages.
• However, infection in dogs, cats and horses normally does NOT cause clinical disease.
Prévention of Lyme Borreliosis
OspA vaccine available for use in canines
-withdrawn from use in humans (side effects)
Brachyspira swine dysentery
Swine dysentery (SD) is worldwide spread.
• A clinically important enteric disease in pigs.
• Characterised by a mucohemmorrhagic colitis and
rapid loss of weight.
• Affected herds often suffer devastating production
losses.
• Swine dysentery is caused by proliferation of
Brachyspira hyodysenteriae.
_mucohemmorrhagic colitis and rapid loss of weight
BRACHYSPIRA: PORCINE INTESTINAL
SPIROCHAETOSIS
Porcine Intestinal Spirochaetosis (PIS) is a non-fatal, wasting
diarrheal disease caused by Brachyspira pilosicoli,
• Different from swine dysentery, as its aetiology and the clinical
appearance are different.
• It has been shown that the aetiological agent has a worldwide
spread, with high prevalence.
• The disease is also known as intestinal spirochetosis or
spirochaetal diarrhoea.
BRACHYSPIRA: SWINE DYSENTERY
• Virulence factors:
Flg - flagellar protein – required for motility and therefore tissue
invasive capability. Inactivation led to virulence being severely
attenuated in a murine model.
Nox (NADH oxidase) responsible for limited oxygen utilisation.
Inactivation led to reduced virulence in swine.
Brachyspira transmission
Transmitted by faecal-oral route.
• Spreads from pig to pig and may be spread by flies, mice, birds and dogs.
• Some pigs may become carriers.
Leptospirosis transmission
Leptospirosis is transmitted in the urine of an infected animal.
• Leptospirosis is transmitted in the urine of an infected animal.
• Rodents are important primary hosts. Dogs, deer and ruminants
are able to carry and transmit disease as secondary hosts.
Common sufferers are humans, dogs and cattle
Leptospirosis symptoms
The liver and kidney are most commonly damaged by
leptospirosis. Eye jaundice, vomiting, fever, failure to eat,
reduced urine, lethargy are indications of the disease.
• Serology and PCR used for detection.
• Treatment is penicillin.
• Loa22 is the first virulence factor identified in 2007. Identified
using a guinea pig model of infection. Function unknown.
Prevention of leptospirosis
Vaccines
Dogs-bivalent/ new quadrivalent vaccine as studies suggest different serovars have emerged
cattle-vaccine against a single serovar
HUMAN AND CANINE ORAL INFECTIONS
Periodontal disease:
• Various treponemes implicated including Treponema
denticola and Treponema medium.
• Polymicrobial with other microorganisms also implicated e.g. Porphyromonas gingivalis.
• Treatment: penicillin derivatives such as amoxicillin
Bovine digital dermatitis and CODD
Bovine Digital Dermatitis (BDD) is an infectious
lameness in cattle, first identified in 1974.
• Now endemic in many countries across the world.
• The disease is responsible for considerable economic
loss.
• Very painful for the animals concerned. Causes
reduction in milk yields and reproduction.
• A recent report calculated the cost of BDD to be as
high as $190 million per year in the USA alone.
Bovine digital dermatitis
Diagnosis is normally visual.
• Treatment. Chemical footbaths and topical antibiotics
(oxytetracycline) but penicillin (systemic) or
macrolides (systemic/oral) likely better: BUT milk
withhold issues
• Ruminant GI tract, slurry, direct contact and foot
trimming equipment all identified as infection
reservoirs/transmission routes.
• No virulence factors identified as yet. Only vaccine
withdrawn from market (lacked efficacy).
• These microorganisms are now causing contagious ovine digital dermatitis
SPIROCHAETES & POLYMICROBIAL
DISEASES
Polymicrobial diseases may occur between organisms in
different kingdoms, genera, species or strains.
Common Polymicrobial Disease virulence
determinants/mechanisms:
• Biofilm formation
• Formation of a (red) complex
• Synergistic triggering of proinflammatory molecules
• Immune suppression by one microorganism allowing colonisation of others
Spirochaetes commonly play a part in polymicrobial
infections:
• Treponemes implicated with a variety of other bacteria in
human and canine periodontal infections.
• Digital dermatitis identified as polytreponemal.
• Coinfection with several Brachyspira species in chicken
Two groups of clinically relevant mycobacteria
Bovine and human TB is caused by members of a group of phylogenetically closely related bacteria collectively known as the Mycobacterium tuberculosis complex
(MTBC).
• Avian tuberculosis and Johne’s disease are caused by members of the Mycobacterium avium complex (MAC)
which are also phylogenetically closely related .
Examples of phenotypic
-Cell Morphology: cocci, bacilli etc..
• Stains: Gram positive, negative and acid
fast.
• Oxygen requirements:
– aerobic
– anaerobic
– microaerophillic
• Culture properties: conditions required for growth
• colonial morphology
• Biochemical reactions
Myctobacteria phenotypic characteristics
Phenotypic characteristics:
• Aerobic
• Non-spore forming & non-motile,
• Rod shaped/bacilli,
• Acid-Fast
• Require complex egg-enriched media for growth of
pathogenic species
• Pathogenic species grow slowly, colonies only
visible after several weeks.
• Major diseases include tuberculosis and Johne’s disease.
Despite cell wall structure historically reported as as
that of Gram-positive bacteria, they stain poorly
(ghost bacilli!) -> and are not
• Thick cell wall contains peptidoglycan,
considerable lipids and mycolic acid within
peptidoglycan layer + weak outer membrane
• The high lipid and mycolic acid content protects
from acids, alkalis and digestion in macrophages.
• Impedes entry of molecules
• Slow growing
• Responsible for inflammatory response
Myctobacteria typical habitats
Despite cell wall structure historically reported as as
that of Gram-positive bacteria, they stain poorly
(ghost bacilli!) -> and are not
• Thick cell wall contains peptidoglycan,
considerable lipids and mycolic acid within
peptidoglycan layer + weak outer membrane
• The high lipid and mycolic acid content protects
from acids, alkalis and digestion in macrophages.
• Impedes entry of molecules
• Slow growing
• Responsible for inflammatory response
Mycobacteria typing
Ziehl-Neelsen (ZN) method used to stain and stain
red
Differentiation of pathogenic mycobacteria uses:
• Cultural characteristics
• Biochemical tests
• Animal inoculation
• Molecular techniques.
Mycobacteria host adaptation example
M. bovis used to be a significant cause of human TB,
primarily in children who consumed raw milk.
• M. bovis infections in humans decreased markedly
following the introduction of pasteurization and meat-
control practices.
• M. bovis does not easily transmit between humans
• Similarly, while M. tuberculosis has been isolated from
various animal species, including cattle, there is currently
no evidence of animal-to-animal transmission of M.
tuberculosis or M. africanum.
• Hence, different members of MTBC appear to be best
adapted to their particular host species.
What is mycobacterium bovis
Bovine tuberculosis
• Extremely important worldwide disease
• Zoonotic implications
• Eradication programs worldwide
• Eradication has been successful in some countries
• Has severe economic costs associated.
Transmission mycobacterium bovis
Transmission through aerosols created from cattle
• Risk factors for transmission include housing and
wildlife reservoirs (possums/badgers)
• Calves infected by ingesting contaminated milk
• Pasteurisation of milk greatly reduced human
exposure
Mycobacterium bovis pathogenesis
• Relates to the ability to survive and multiply in host
macrophages
• Macrophages accumulate at infection site is
response to presence of cell wall waxes and lipids
• Granuloma formation = inflammatory response in
lungs
• Recognizable tubercle formed
Clinical signs mycobacterium bovis
Only present in advanced disease.
• Cattle with extensive lesions may still appear in
good health.
• In advanced plumonary TB animals develop cough
/intermittent pyrexia.
• Infection of mammary tissue causes lymph node
enlargement & mastitis increases spread.
How to diagnose mycobacterium bovis
Diagnosis - Tuberculin test
• Standard ante-mortem test
• Usually reactive 30-50 days after infection
• Delayed type hyper-sensitivity to M. bovis
tuberculoprotein (‘tuberculin’)
• Purified protein derivative (PPD) is injected
intradermally
• PPD injected and site checked a few days later
• Some other tests used in conjunction e.g. ELISA
• If animal dies pathology and staining (ZN) of tissue
section thought to be tubercle locations
• Isolation of bacteria to characterise ->Commercial kits
Treatment mycobacterium bovis
Treatment/Vaccination inappropriate
• Most countries worldwide = tuberculin testing of
cattle followed by isolation and slaughter of
reactors (typical eradication scheme)
• Routine meat inspection part of surveillance
• Culling of wildlife reservoirs (badgers/possums)
Control in UK considerations:
• One of larger studies into badger culling showed that:
– Badgers are involved in transmission
– Middle of cull = reduction in bovine TB
– Edge of cull = increase in TB. Uncertain why.
Considerations:
- animal conservation
- financial: farmer and national
• Recent additional badger cull trial
• Cattle and badger vaccination as the way forward?
Why does the vaccine against MB doesn’t work
Vaccination shows efficacy, but does not remove already infected,
and until recently no way of differentiating infected from
vaccinated.
Mycobacterium bovis Bacille Calmette-Guérin (BCG) currently
most suitable cattle TB vaccine. Reduces the progression,
severity and excretion of bacteria -> show can reduce
transmission
Development of alternative vaccines is a longer-term research
goal.
Vaccination of cattle with BCG results in some animals becoming
positive to standard TB diagnostic tests (both tuberculin skin
test and conventional interferon-gamma blood test) = false
positives for BCG-vaccinated, TB-uninfected cattle.
BADGER_ need to be trapped and injected but culling cheaper
Human tuberculosis symptoms
Disease similar to cattle pathology
• Easily transmitted by respiratory route-
– Coughing
– Speaking –highly contagious!
Tuberculin test used
• Antibiotic ‘Isoniazid’ (INH) very effective –
interacts with synthesis of mycolic acid.
• Not used in animals due to fears of resistance and the long
treatments needed.
• Vaccination :
with M. bovis strain: bacillus Calmette- Guerin
(BCG) strain .
M lepraemurium
Feline (and rodent) leprosy
• Cutaneous disease of worldwide distribution
• Endemic in wild rodents in some parts of the world
• Relatively low prevalence in cats. Rare in UK/USA.
• Transmission occurs through bites from infected
rodents.
NOT considered zoonotic, cause nodular lesions in subcutaneous tissues, tend to be in head region or limbs
Nodules are fleshy, moveable and tend to ulcerate
Typically aggressive and locally recurrent
Mycobacterium avium
Avian tuberculosis = important (although rare in the
UK) disease which affects companion, captive exotic,
wild & domestic birds.
Typically characterised by chronic and progressive
wasting and weakness. Diarrhoea common.
Principal lesions of tuberculosis in birds are seen in
intestine, where presents with nodules which
frequently ulcerate
Intracellular pathogen – macrophages again!
Once established, TB induces decreased egg
production, and increased mortality, which culminates
into severe economical losses.
Mycobacterium avium control
-no vaccine available, purified protein derivative is the standard preparation
-control entire flock depopulated and repopulated on non infected soil, removal of faecal material is single most important factor in preventing transmission
Johne’s disease
Chronic contagious enteritis = fatal
Young animals (first few months) are more susceptible
to infection and generally become infected through
the ingestion of contaminated milk.
Transmission can be through faecal shedding and
contaminated milk
Not all animals suffer (& intermittent faecal shedding)
Persists in environment (1 year)
After ingestion the bacilli cross the intestinal epithelial
layer where subepithelial macrophages phagocytose
the bacilli
Intracellular pathogen – macrophages again!
Immune mediated granulamatous reaction
Thickening of intestinal mucosa
Enteropathy causes loss of plasma proteins and
malabsorption of nutrients/water
Johne’s disease difficulties
> 2 when first symptoms (incubation period of 2-4
years)
Diarrhoea, intermittent, then persistent and profuse
Weight loss, reduction in appetite
Death 1 year after detection
Worldwide distribution
Endemic in Europe & U.S.A
Responsible for significant economic losses
Costs include premature culling, lost productivity,
infertility, diagnosis and control.
How to detect Johne’s disease
Detection through pathology and ZN technique
Isolation from tissue/faeces is sensitive and diagnostic
but time consuming
ELISA or Johnin test (c.f. Tuberculin) possible
Control: isolation and slaughter
Vaccine available but not widely used
