NP4B Flashcards
Bacterial infection through the blood supply
hematogenous infection
bacteria in the circulation
bacteremia
Hematogenous Infections:
- Immune compromised animal – suppurative meningitis
- Immune competent older animal – meningoencephalitis or abscess
- 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)
Immune compromised animal – suppurative meningitis in neonates
Immune compromised animal – suppurative meningitis:
The most common gross change are…
petechial hemorrhages and cloudiness of the meninges
pinpoint foci of hemorrhage
petechial hemorrhages
Immune compromised animal – suppurative meningitis:
in severe cases, you may see….
pus (i.e., the vast accumulation of neutrophils)
Immune compromised animal – suppurative meningitis:
The bacteria involved are “common household varieties”
E. coli and Streptococcus species that are part of the normal flora
Immune compromised animal – suppurative meningitis:
Attempts at culture may fail. The cultural result was a __________
false negative
Immune compromised animal – suppurative meningitis:
Cause of death?
Increased intracranial pressure due to initiation of the edema cycle and plugging of the arachnoid granulations with exudate
are tufts of arachnoid membrane invaginated into the dural sinuses through which cerebrospinal fluid (CSF) enters the venous system
arachnoid granulations
Immune competent older animal – meningoencephalitis or abscess:
The animal is mounting an immune response, but that response becomes overwhelmed, resulting in…
bacteremia
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)
Meningoencephalitis
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:
sheep
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:
horses
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:
cattle
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.
Meningeal abscess
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.
Brain abscess
Bacterial infection by direct extension:
Examples of extension of chronic inflammation in a cavity close to the brain…
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.
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.
Loss of the dura mater barrier
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 _______________
Listeria monocytogenes
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.
Listeria monocytogenes
Neural invasion of brain
L. monocytogenes causes:
- Abortion in pregnant individuals
- Septicemia – usually in neonates
- Brainstem infection – our focus
The bacterium Listeria monocytogenes is associated with feeding of _______ or _______
silage or haylage
These are collectively known as ensiled forages
silage or haylage
corn in the instance of ________ and various types of grasses
silage
legumes in the case of _________
haylage
L. monocytogenes may enter the endings of the _______________.
Fifth cranial nerve
_________ transport delivers the bacterium into the brainstem where infection spreads
Axoplasmic
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.
Neural invasion of brain – Listeria monocytogenes
What is the cause of death in an animal with suppurative meningitis?
initiation of the edema cycle in the brain
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
compromised
