NP4B

Question 1

Bacterial infection through the blood supply

Answer 1

hematogenous infection

Question 2

bacteria in the circulation

Answer 2

bacteremia

Question 3

Hematogenous Infections:

Answer 3

• Immune compromised animal – suppurative meningitis
• Immune competent older animal – meningoencephalitis or abscess

Question 4

• May be due to a severe combined immunodeficiency syndrome or failure of passive transfer of antibodies from the dam to the neonate via colostrum.
• Bacteria may enter the vasculature from the respiratory and/or gastrointestinal tracts without any grossly apparent point of entry.
• Bacteria are not recognized by antibody and so they circulate as individual infectious particles, falling out of solution when they hit extensive capillary beds. As such, they will elicit inflammatory responses in capillary rich locations:
  
  • Synovial lining of joints (polyarthritis)
  • Uvea of the eye (uveitis)
  • Alveolar capillaries of the lung (interstitial pneumonia)
  • Meninges and choroid plexus of the brain (meningitis and choroiditis)

Answer 4

Immune compromised animal – suppurative meningitis in neonates

Question 5

Immune compromised animal – suppurative meningitis:
The most common gross change are…

Answer 5

petechial hemorrhages and cloudiness of the meninges

Question 6

pinpoint foci of hemorrhage

Answer 6

petechial hemorrhages

Question 7

Immune compromised animal – suppurative meningitis:
in severe cases, you may see….

Answer 7

pus (i.e., the vast accumulation of neutrophils)

Question 8

Immune compromised animal – suppurative meningitis:
The bacteria involved are “common household varieties”

Answer 8

E. coli and Streptococcus species that are part of the normal flora

Question 9

Immune compromised animal – suppurative meningitis:
Attempts at culture may fail. The cultural result was a __________

Answer 9

false negative

Question 10

Immune compromised animal – suppurative meningitis:
Cause of death?

Answer 10

Increased intracranial pressure due to initiation of the edema cycle and plugging of the arachnoid granulations with exudate

Question 11

are tufts of arachnoid membrane invaginated into the dural sinuses through which cerebrospinal fluid (CSF) enters the venous system

Answer 11

arachnoid granulations

Question 12

Immune competent older animal – meningoencephalitis or abscess:
The animal is mounting an immune response, but that response becomes overwhelmed, resulting in…

Answer 12

bacteremia

Question 13

In these animals, there is a localized infection in another organ such as the lung (bronchopneumonia) or in the case of a neonate, the umbilical vein (omphalophlebitis)

Answer 13

Meningoencephalitis

Question 14

Bacteria can readily invade the necrotic tissue, and so we have inflammation of both meninges and the underlying tissue – meningoencephalitis. We see this with bacterial pathogens such as Pasteurella species in:

Answer 14

sheep

Question 15

Bacteria can readily invade the necrotic tissue, and so we have inflammation of both meninges and the underlying tissue – meningoencephalitis. We see this with bacterial pathogens such as Actinobacillus species in:

Answer 15

horses

Question 16

Bacteria can readily invade the necrotic tissue, and so we have inflammation of both meninges and the underlying tissue – meningoencephalitis. We see this with bacterial pathogens such as Choliform bacteria in:

Answer 16

cattle

Question 17

Sometimes the showering of the meninges and brain is survivable. Maybe it is only a couple of emboli arising from endocarditis. The infection may not be cleared, but it may be contained. In the meninges, containment draws upon fibroblasts to form a “classical” abscess with its sturdy connective tissue container. This may present as no more than a very slowly growing space-occupying mass.

Answer 17

Meningeal abscess

Question 18

Abscesses can form deeper in the nervous tissue, but the wall will be formed by reactive astrocytes. This wall is relatively weak compared to meningeal abscesses. Mild degrees of head trauma can cause the infection (pus and bacteria) to leak, initiating the edema cycle and resulting in death.

Answer 18

Brain abscess

Question 19

Bacterial infection by direct extension:
Examples of extension of chronic inflammation in a cavity close to the brain…

Answer 19

This scenario can be encountered with chronic bacterial infection of the guttural pouch in horses (guttural pouch empyema), or in chronic bacterial otitis media, which can extend to become an otitis interna.

Question 20

Bacterial infection by direct extension:
Trauma with penetration of the dura invites bacterial invasion, and here again, the results can be a rapid progression to death.

Answer 20

Loss of the dura mater barrier

Question 21

Neural invasion of brain:
We have one example in which a bacterium can actually enter an axon in the periphery, and then use axoplasmic transporters (the ones we discussed with neuroaxonal dystrophy) and be transported into the central nervous system.

The bacterium is _______________

Answer 21

Listeria monocytogenes

Question 22

Is source of food borne illness in people, but that is a different problem. Causes different types of infection based upon different routes of entry or host immune status.

Answer 22

Listeria monocytogenes

Question 23

Neural invasion of brain
L. monocytogenes causes:

Answer 23

• Abortion in pregnant individuals
• Septicemia – usually in neonates
• Brainstem infection – our focus

Question 24

The bacterium Listeria monocytogenes is associated with feeding of _______ or _______

Answer 24

silage or haylage

Question 25

These are collectively known as ensiled forages

Answer 25

silage or haylage

Question 26

corn in the instance of ________ and various types of grasses

Answer 26

silage

Question 27

legumes in the case of _________

Answer 27

haylage

Question 28

L. monocytogenes may enter the endings of the _______________.

Answer 28

Fifth cranial nerve

Question 29

_________ transport delivers the bacterium into the brainstem where infection spreads

Answer 29

Axoplasmic

Question 30

Animals present with neurological signs that are generally localized to one side of the brainstem. There may be no evidence of meningitis, and cross sections of the brainstem may appear grossly normal. But histologically this is a hot mess, with pockets of neutrophils in the parenchyma associated with bacteria, and large perivascular cuffs of lymphocytes and monocytes reflecting chronicity of the process.

Answer 30

Neural invasion of brain – Listeria monocytogenes

Question 31

What is the cause of death in an animal with suppurative meningitis?

Answer 31

initiation of the edema cycle in the brain

Question 32

You consider the culture to be a false negative and you can diagnose this as a bacterial infection typical of what is seen in an immune _____________ animal

Answer 32

compromised