CAR week 8: BBB, circulation, infection and septic foal

What are 3 ways microbial pathogens can damage the nervous system?

1. Invasion and replication in the tissues

2. inducing an immune response

3. releasing toxins

How can microbial pathogens damage the nervous system by invasion and replication in the tissues?

• direct invasion of peripheral tissues

• from adjacent structures such as the meninges

• from blood Haematogenous

How can microbial pathogens damage the nervous system by inducing an immune response

• inflammation of CNS

• damage cause by local inflammation to the CNS

• auto-immune response.

How can microbial pathogens damage the nervous system by releasing toxins?

• blocking signals

• damaging specific cells

What are the 3 ways microbes can spread and access the CNS?

• neurotropic

• neural abscess

• haematogenous

What do these mean:

1. neurotropic

2. neural abscess

3. haematogenous

1. from peripheral nerves: nerve to nerve

2. neural abscess

3. via blood

What words can be used to describe viruses and bacteria that spread via blood?

• bacteraemia

• viraemia

Why is the CNS at such high risk of haematogenous spread?

• for every neurone there’s a blood vessel

Outline 4 essential features of the BBB

1. endothelial cells (BMECs) form a tight barrier b/w blood and CNS-tissue

2. tight junctions stop paracellular flux

3. pinocytosis allows transfer of material from blood to brain

4. P-glycoprotein pumps and actively ejects undesired substances

What are 3 methods of breaching the BBB>

1. transcellular

2. paracellular

3. intracellular within leucocytes

Outline transcellular invasion:

1. what does it mean

2. active or passive?

3. examples

1. pathogens bind host cells and invade through the cell

2. passive or active

3. bacterial: Streptococci, Listeria sp.

• fungal: Candida (yeast), Cryptococcus (dia-morphic fungus)

Outline paracellular invasion:

1. what must happen

2. what can make it easier?

3. examples

1. tight junctions must be dramatically changed/new routes open

2. increased pinocytic activity → trans-endothelial channel formation/tight junction can be broken

3. viral: Nipah virus

• Bacterial: Borrelia burgodorferi

Outline intracellular infection from within leucocytes:

1. what does it require

2. how does it spread

3. examples

1. primary infection

2. where the virus migrates to - may be ‘hidden’ to antibodies once established

3. viral: SIV/HIV, canine distemper

What is central to infection of microbes crossing the BBB?

• expression of virulence factors

How can viruses cross the BBB?

• they have host cell binding proteins that bind receptors on endothelial cells, essential for infection to progress

How can bacteria cross the BBB?

• adhesion molecules

• common surface proteins/outer membrane proteins (OMPs) that increase adhesion of bacteria to the cell

• binding may trigger specific invasion mechanisms

• once inside the cell, bacteria require virulence factors to survive and acquire nutrients in intracellular environment

how can inflammation damage the CNS?

• accumulation of leucocytes → causing pressure to increase in cell numbers

• clinical signs reflect the damage caused by specific areas of the CNS

• pathogens ‘may’ cause cellular pathology

what may clinical signs of CNS damage include?

• depression

• pyrexia

• cervical pain

• hyperaesthesia

• photophobia

• generalised rigidity

• seizures

• paralysis local and general

• ataxia

• papilloedema

• possible ophthalmic inflammation

• systemic signs: septic shock and brachycardia

Outline normal CSF:

• colour

• total white cell count

• total red blood cell count

• cytology

• total proteins

• specific gravity

1. colourless

2. <6 cells per ul

3. 0

4. few monocytes, lymphocytes and rarely neutrophils

5. cisternal <0.3g/l, lumbar: <0.45g/l

6. 1.007

With CNS infection what variables can we test in the CSF

• glucose

• specific gravity

• immunology

• microbiology

• enzyme analysis for cell breakdown

How will glucose and specific gravity change with infection on assessing CSF?

• glucose decreases

• specific gravity increases

what 2 things do we test in immunology when testing CSF fluid for infection?

• serology

• cytology

how is the CSF maintained?

• it’s maintained as sterile

Name 3 diseases and the 3 different infection routes they take

1. canine distemper - viraemia (haematogenous/broad infection)

2. listeriosis - neurotropic spread-bacterial

3. rabies - neurotropic spread-viral

Outline CDV:

1. what is it

2. how does it develop

3. what kind of microorganism?

4. who does it infect

5. infectious?

6. how does it spread

7. how does the infection spread within the animal

8. what organs does it affect

9. what do we see in the acute phase

10. what do we see in the post-acute phase?

1. canine distemper virus

2. paramyxoviridae → morbillivirus → canine distemper virus

3. large RNA virus, single stranded. Enveloped - inactivated by most detergents and soap. narrow host range

4. infects mainly mammals and birds

5. highly infectious of dogs and other carnivores

6. urine, close contact or aerosols

7. URT → bronchial LN and tonsils → blood stream → various tissue organ systems → meningeal macrophages → neurones

8. CDV is pantropic - infection in many organ systems as receptors are common on many cells

9. encephalitis due to virus infection of neurones

10. encephalitis due to inflammatory response incited by virus

Outline CDV microbe:

1. what kind of virus

2. how does it attach to cells

3. how does it replicate

1. pleomorphic enveloped virus, negative sense single stranded RNA

2. F-protein

3. in cytoplasm buds as it’s enveloped

What is the relevance of CDV being an enveloped virus?

• relatively labile

  • sensitive to heat, desiccation, lipid solvents, non-ionic detergents and disinfectants

  • isolation of affected animals and disinfection can control outbreaks

• vaccines: H-protein can be used to induce neutralising antibodies

Outline CDV spread of infection:

1. where does it replicate

2. where does it spread to

3. what does replication lead to

4. what other sites does it affect

5. what neuronal tissue does it affect

6. how can it spread neurone to neurone

1. URT

2. tonsils and bronchial lymph nodes

3. lymphocytolysis/leukopenia → viraemia

4. GIT, urinary, CNS tissue

5. meningeal macrophages, astrocytes and neurones

6. without cytolysis

How do we diagnose CDV?

1. lateral flow test detecting CDV antigen

2. PCR

Outline use of lateral flow tests for detecting CDV antigen:

1. what do we need to use for it

2. what is recommended

3. what kind of test is it?

1. ocular and nasal secretioins

2. confirmation by PCR

3. pen site test

Outline PCR for CDV diagnosis:

1. how long does it take

2. what is it a measure of

3. what does it enable the test to do

4. when will we detect more?

1. 1-3 working days

2. quantitative measure of viral load

3. discriminate vaccine interference from infection with a wild-type of strain

4. during infection rather than because of recent - enabling us to determine whether the animal is actively infected

Outline listeriosis:

1. general features of the bacterium

2. is it zoonotic?

3. source?

4. main clinical manifestation?

1. gram +ve, rod, facultative anaerobe, small haemolytic colonies

2. yes

3. in cattle - poor silage, generally, source eating contaminated food

4. sepsis and meningitis

How is meningitis often complicated with listeriosis?

• it’s often complicated by encephalitis - an unusual pathology for bacterial infections

Outline Listeria monocytogenes:

1. how do they affect cells

2. how do they move?

3. what kind of infection method to the CNS

1. attach to and enter cells

2. move wtihin and b/w by nucleating actin

3. neurotropic: nerve cell to nerve cell

Outline listeriosis in ruminants:

1. where is it found

2. where can they replicate

3. when do we see outbreaks

4. how may it present

5. what’s a source of susceptibility

1. environment

2. poor quality silage, pH above 5.5

3. seasonally

4. encephalitis, abortion, septicaemia or endophthalmitis

5. decreased cell-mediated immunity associated with advanced pregnancy

Outline listeriosis in ruminants:

1. clinical signs

2. treatment

3. prevention

1. 14-40day incubation period, dullness, circling, tilting of head facial paralysis, unilateral facial paralysis → drooling and dropping of eyelids and ears

2. in early stages with antibiotics

3. don’t feed poor silage, ensure feed method reduced ocular contact and vaccines don’t work

Outline rabies:

1. what causes rabies

2. what kind of virus

3. shape

4. where is it found

5. how is it transmitted

6. incubation period

7. prognosis

8. relevance globally?

9. what is indistinguishable from it?

1. Rhadoviridae → lyssavirus → rabies virus

2. enveloped RNA virus

3. rod shaped

4. saliva

5. biting carnivores

6. 14-90 days, b/w bite and development of signs of neurological involvement

7. fatal

8. notifiable disease

9. a number of neurotropic lyssaviruses that are closely related to rabies

Outline the stages of rabies spread to nervous tissue

1. bite

2. virus replicated in muscle

3. high titre → reach sensory/motor nerve ends

4. binds ACh receptor

5. virus enters into distal nerve and second stage of infection begins

6. neuronal infection with centripetal passive movement within axons

7. delivery of virus to CNS initially spinal cord

8. reaches limbic system in the brain, replicates extensively → swelling → pain and behavioural changes

9. spread continues clinical replication in cortex, pathology low 

10. centrifugal spread to periphery 0> organs → salivary glands

what is meant by ‘furious rabies’

• when the virus reaches the limbic system of the brain and replicates extensively

• this leads to swelling of brain tissue

• pain and behavioural changes

What is meant by ‘dumb’ rabies

• when the spread of the virus continues clinical replication in the cortex

• cell pathology is low but cells all contain the virus

How do we diagnose rabies?

• post mortem brain material:

  • fluorescent antibody test (FAT) for viral antigen

How do we treat rabies:

1. confirmed cases

2. suspect cases

1. mandatory euthanasia

2. isolation

what do we have to do for rabies cases where there’s a potential risk of a person being bitten/scratched by the infected animal/

• VI (veterinary inspector) requires destruction of the animal in order to confirm or rule out diagnosis of rabies by post mortem

What is the rabies vaccination?

• inactivated vaccine/recombinant vaccine

• not required in UK for domestic species - only if travelling abroad, to obtain Animal Health certificate

How does the vaccine for humans for rabies differ to the one for animals?

• active vaccination for humans - needs to be administered rapidly, inactive once neurological signs present

• inactivated vaccine/recombinant vaccine

What are the 2 ways toxins become present in the body?

• ingestion

• infection

How are toxins produced via ingestion?

• by fungi, plants, microorganisms and ingested via contaminated pasture and feed

How are toxins found in the CNS by infection?

• toxins are produced by colonisation of young animals by toxin producing bacteria normally excluded from the intestine

• can be produced during infections

what are 3 examples of toxin producing bacteria?

1. tetanus - Clostridium tetani

2. Botulism - Clostridium botulinum

3. oedema disease

What are examples of toxins produced by fungi, and where?

• rye grass staggers (new zealand) - sporadically in UK with imported rye grass

• on pasture

What plants produce toxins (relevant)

• algae

give 3 examples of non-microbial toxins

• lead

• arsenic

• organophosphates

Outline clostridia:

• describe the morphology

• type of respiration

• how can we kill the cells

• what about the spores?

• relatively large, gram +ve, rods, form endospores

• strict anaerobe

• vegetative cells are killed by O2 exposure

• spores can survive long periods of exposure to air

what are 4 kinds of toxins?

1. neurotoxic

2. histotoxic

3. enteropathogenic

4. A-typical

what species of bacteria produce neurotoxic toxins, what kind of toxins are they

1. C.tetani

2. C.botulinum (types A-G)

3. potent AB neurotoxins

what are toxins

• proteins that area activated by proteolytic cleavage

Outline the tetanus toxin:

• type

• what does it cause and how

1. 1 antigenic type

2. synaptic inhibition → muscular spasms

Outline botulinum toxin:

• types

• what does it lead to and how?

• 7 antigenic types

• inhibits neuromuscular transmission → flaccid paralysis

Outline tetanus:

• what does it cause and how

• how is it produced

• what is a clinical sign

• what 2 kinds are there?

• continuous stimulaiton by stopping inhibitory transmitter binding at synapse

• organisms replicating locally in tissues/wounds → toxicoinfectious

• spastic paralysis: muscular spasms

• descending and ascending

Outline ascending tetanus:

• what is the pathway of the toxin and what does it lead to?

• toxin disseminated in bloodstream

• remote areas

• enters CNS at many levels

• generalised tetanus, often beginning cranially (horses)

Outline ascending tetanus:

• where does the toxin go

• what does it bind to

• what does it prevent

• what does it lead to

• peripheral nerves

• specific gangliosides on motor nerve terminals

• suppresses release of afferent inhibitory neurotransmitters

• spastic paralysis and characteristic spasms → carnivores

How do we diagnose tetanus

• clinical evaluation

• toxin presence confirmed by PCR assay of bacterial DNA from wound tissue

How do we treat tetanus:

• what’s available for horses

• what should we do

• vaccine and cattle

• early intervention: wound cleaning, boosting immunity, parenteral antitoxin administration and muscle relaxants

  • not vaccinated animal → antitoxin prophylactically

  • supportive therapy: monitor for normal parameters to return

  • antitoxins neutralise circulating toxin are only effective before the toxin has entered the nerve terminals

  • recovery is by axonal sprouting and re-innervation (slow (up to 3 months))

Outline botulism:

• where does the toxin move to and what does it prevent

• where is it produced

• sources?

• where does it enter in the body

• what does it cause

• nerve terminal and inhibition of ACh release  

• decaying organic matter 

• carrion/colonised, feed rotting hay/silage → intoxication

• absorbed into the bloodstream and distributed around the body

• flaccid paralysis

How do we treat botulism?

• supportive therapy

• antibiotics aren’t activated as they have limited effect on bound toxins

• euthanasia

why are ruminants with botulism usually euthanised?

• clinical signs won’t resolve until neurotoxin has decayed

• this takes weeks/months

• impractical to attempt nursing for this period of time and consideration of animal welfare needs to be given

 55 hr-old Thoroughbred colt has been rushed into your hospital with weakness and sudden onset respiratory distress. The foal was born at 335 days gestation, and was the first foal from this dam. The foaling was attended and the delivery process seemed normal, including expulsion of foetal membranes. The foal stood and sucked within 2 hrs of birth, passing normal-looking meconium, and behaved normally during the first 48 hrs of life. 
This morning (the 3rd day post-partum) the foal was found recumbent, dehydrated and breathing rapidly. It was immediately transported to your hospital. 
 
Physical examination: 

• On arrival the foal was weak and unable to stand without assistance 

 
 

• Body weight: 54 kg 

 
 

• Dehydration was estimated at 5-7% of body weight 

 
 

• Mucous membranes: dark pink 

 
 

• Capillary refill time: 2s 

 
 

• Pulse: weak and regular 

 
 

• Blood pressure: systolic 75mm Hg, diastolic 45mm Hg, mean 55 mm Hg (normal: 100/60, mean 80) 

 
 

• Rectal temperature: 103ºF/39.3ºC (should be 37.5-38.6) 

 
 

• Heart rate: 70-80 bpm. 

 
 

• Resp rate: 60 breaths per minute, weak and shallow 

 
 

• Thoracic auscultation: bilateral wheezes and crackles, more pronounced over the ventral lung field 

 

For a septic foal what should our emergency treatment plan be?

1. oxygen (preferably humidified if dehydrated) - face mask/nasal insufflation (6-10l/min)

2. blankets and heat lamps to keep foal warm

3. IV fluid in septicaemic foal to combat cardiovascular collapse, avoid too vigorous IVFT (riskk of pulmonary oedema)

4. sternal recumbency

 55 hr-old Thoroughbred colt has been rushed into your hospital with weakness and sudden onset respiratory distress. The foal was born at 335 days gestation, and was the first foal from this dam. The foaling was attended and the delivery process seemed normal, including expulsion of foetal membranes. The foal stood and sucked within 2 hrs of birth, passing normal-looking meconium, and behaved normally during the first 48 hrs of life. 
This morning (the 3rd day post-partum) the foal was found recumbent, dehydrated and breathing rapidly. It was immediately transported to your hospital. 
 
Physical examination: 

• On arrival the foal was weak and unable to stand without assistance 

• Body weight: 54 kg 

• Dehydration was estimated at 5-7% of body weight 

• Mucous membranes: dark pink 

• Capillary refill time: 2s 

• Pulse: weak and regular 

• Blood pressure: systolic 75mm Hg, diastolic 45mm Hg, mean 55 mm Hg (normal: 100/60, mean 80) 

• Rectal temperature: 103ºF/39.3ºC (should be 37.5-38.6) 

• Heart rate: 70-80 bpm. 

• Resp rate: 60 breaths per minute, weak and shallow 

• Thoracic auscultation: bilateral wheezes and crackles, more pronounced over the ventral lung field 

What is abnormal?

• rectal temperature

• pulse

• heart rate

• dehydration

• resp rate

• thoacic auscultation

• blood pressure

• unable to stand without assistance

what diagnostic tests can we perform on a septic foal

1. biochemistry

2. abdominal ultrasound

3. blood culture for bacterial infection

4. BGA

5. haematology

6. maternal antibody transfer test

7. thoracic radiography

8. thoracic ultrasound

9. urine sample

why do we perform abdominal ultrasound for a septic foal?

• check for potential sources of bacteraemia

Why do we perform biochemistry in a septic foal

• serum/plasma protein level to assess hydration

• hypoglycaemia is common in septicaemia

• plasma levels elevate in septic shock

• creatinine and urea values are often raised

• foals with concurrent enteritis may develop severe electrolyte imbalances

why do we test for maternal antibody transfer in foals with suspected septic shock?

• failure of passive transfer is the most common predisposing factor to neonatal infection

why do we perform thoracic radiography on foals with suspected septic shock

• radiology appearance of pneumonia may indicate aetiology and pathogenesis of the condition

why do we perform:

• thoracic ultrasound

• urine sample

in a foal with suspectiv septic shock

• demonstration of pleural fluid or consolidation of peripheral lung tissue - greatest value in conjunction with thoracic radiography

• assess kidney function

What will the haematology of a foal with pneumonia show?

• leucocytosis/leucopenia

• neutrophilia

• increased no. band neutrophils and toxic changes

• hypoglycaemia

• plasma lactate levels elevate

• creatinine and urea raised

• lymphopenia can occur in overwhelming infections

• plasma fibrinogen levels are elevated

What do these findings show?

• severe respiratory acidosis

• mild metabolic acidosis

• poor O2 perfusion of tissues

What do these show?

IgG levels >800: successful passive transfer of maternal antibodies has occurred

severe neutropenia: severe infection (usually opposite with bacterial pneumonia unless severe) - poor prognosis

lymphopaenia: stress associated with overwhelming infection

degenerative left shift: confirm presence of neonatal infection

what are the mortality rates for foals developing severe sepsis and septic shock?

• severe sepsis: 52%

• septic shock: 67%

How do we treat sepsis and bacterial pneumonia

Management: mare stabled, supportive treatment and antibiotic therapy

What supportive treatment can we provide for a foal with sepsis and bacterial pneumonia?

• padding

• frequent turning of recumbent foal

• O2 administration

• intravenous fluids preventing cardiovascular collapse

• nutritional support through nasogastric tube

• mare’s milk/substitude and/or parenteral nutrition

What cells have:

1. TLR2

2. TLR4

3. TLR5

4. TLR9

1. cell wall components of gram +ve bacteria: can form heterodimers with TLR1 or TLR6

2. LPS of gram -ve bacteria

3. flagellum

4. bacterial DNA through CpG molecules

Outline the process of bacterial infection to MODS

1. PAMPs are recognised by host receptors especially TLRs

2. adapter molecules

3. signalling network

4. production of inflammatory mediators

5. local inflammatory infection

6. bacteraemia/bacterial products in blood stream

7. systemic inflammatory response

8. sepsis/SIRS

9. sever sepsis

10. MODS: multiorgan dysfunction syndrome