Pathomorphology and pathogenesis of bacterial meningoventriculitis of neonatal ungulates

Septicaemia and meningitis caused by infection of New Zealand sea lion pups with a hypermucoviscous strain of Klebsiella pneumoniae

This study describes a syndrome of neonatal septicemia and meningitis in New Zealand sea lions, caused by a strain of Klebsiella pneumoniae that is phenotypically similar to strains causing environmentally-acquired septicemia and neuro-invasive disease in humans. Between late 2006 and early 2010, 123 pups from the Enderby Island breeding colony died of K. pneumoniae infection, with lesions including fibrinous to fibrinosuppurative meningitis, subdural hemorrhage, septic arthritis, herniation and hemorrhage of the cerebellar vermis, lymphadenitis and cellulitis. This infection was responsible for 58% of observed pup mortality over this time period, with most deaths occurring in the latter part of the breeding season (mid February onwards). The results of this study suggest that the pattern of this disease has changed since it was first described in 2002, when most deaths occurred early in the season (early to mid-January), and that it is an important and consistent cause of pup mortality in this population. In addition, a similar disease syndrome and bacterial strain was diagnosed in a single pup in a fragile recolonizing New Zealand sea lion population on mainland New Zealand, and the potential effect on this population is unknown but could have a negative impact on recolonisation at this site.

Septicemia and meningitis in the newborn calf

Neonatal infections and sepsis occur most frequently in calves with failure of passive transfer. If the invading bacteria are not rapidly controlled, they can set up focal infections, such as in growth plates, joints, or meninges, or generalized sepsis may occur. If not successfully treated, sepsis can lead to a systemic inflammatory response, multiple organ dysfunction syndromes, septic shock, and death. Treatments are based on selecting an appropriate antimicrobial drug and dosage, supportive therapy, fluid therapy, nonsteroidal anti-inflammatory drugs, and plasma transfusion. Preventing the failure of passive transfer through good colostrum management is essential.

A Neonatal Calf with Concurrent Meningoencephalitis by Enterobacter cloacae and Enteritis by Attaching and Effacing Escherichia coli (O128)

A neonatal calf developed nervous symptoms followed by diarrhea. The principal pathological changes were fibrinopurulent meningitis with necrosis of the cerebral parenchyma, and attaching and effacing lesions in the intestine. Cerebral necrosis was frequently associated with vascular changes. Enterobacter cloacae was isolated from the brain and Escherichia coli (O128) from the intestinal content. These suggest that cerebral and intestinal lesions were caused by the isolated organisms, and that most necrosis of the cerebral parenchyma might be infarctive.

Meningoventriculitis Caused by Streptococcus pluranimalium in a Neonatal Calf of Premature Birth

Pathological and bacteriological examinations were carried out on a neonatal calf that had developed nervous symptoms such as opisthotonus and blindness since it was born one month prior to full term. The principal lesions were characterized by fibrinopurulent inflammation of the meninges, choroid plexuses, and ventricular walls with limited extension to the subependymal parenchyma in the spinal cord. Purulent inflammation was also found in several visceral organs and tissues. Streptococcus pluranimalium was isolated from the brain and cerebrospinal fluid. These results suggest that the animal suffered from meningoventriculitis with septicemic S. pluranimalium infection.

Bacterial meningitis and encephalitis in ruminants

The clinical aspects of bacterial meningitis in neonates are described in this article. Specific types of meningitis affecting adult cattle are also described. Other conditions occurring less frequently,such as frontal sinusitis and brain abscess, are discussed.

Differences in patterns of meningoencephalitis due to bacterial kidney disease in farmed Atlantic and chinook salmon

A range of neural pathology, in particular meningitis with sporadic encephalitic extension, can develop in salmonids infected with Renibacterium salmoninarum, the agent of bacterial kidney disease (BKD). Tissues from 134 Atlantic salmon and 164 chinook salmon were selected on the basis of their having a positive diagnosis of BKD, with evidence of multi-tissue infection including the brain (214 fish), or brain involvement in the absence of systemic lesions attributable to BKD (58 fish). Although meningitis was a feature of BKD in both species, encephalitis was more common in the Atlantic salmon. Specifically, a higher portion of the Atlantic salmon had encephalitis accompanying meningitis (P = 0.0159), encephalitis in the absence of meningitis (P = 0.0756), and brain lesions (meningitis or encephalitis) in the apparent absence of systemic lesions (P = 0.0067). These findings suggest either that some aspects of the pathobiology of R salmoninarum are dictated by the host species, or that the farm management methods used to deal with BKD are sufficiently different for the two species of salmon that they affect the pathology of the disease.

Pathology associated with meningoencephalitis during bacterial kidney disease of salmonids

The neural pathology associated with spontaneous cases of bacterial kidney disease (BKD), in five species of commercially reared salmonids, was investigated histopathologically and with immunofluorescence. Patterns of localisation of the causative organism of BKD within the central nervous system suggest that haematogenous spread to the meninges, particularly the tela choroidea posterior, the tela choroidea and vascularised capsule of the saccus dorsalis and epiphysis of the epithalamus, and the saccus vasculosus of the hypophysis, appears to be a frequent route by which the central nervous system becomes infected. Retrograde extension from the posterior uvea to the floor of the diencephalon along the epineurium and perineurium of the optic nerve also may be a mechanism of neural invasion. Extension appeared to occur from these sites into adjacent areas of the meninges, the neural parenchyma and ventricles. Demonstration of bacteria within salmonid ependymal cells, as well as the apparent ability of salmonid ependymal cells to respond metaplastically suggest a similarity to mammalian type III ependymal cells (tanycytes). Based on this study, it is apparent that teleosts can survive protracted severe brain damage. This, combined with the apparent similarities of neural response to infection between the salmonids used in this study and higher vertebrates, suggests that teleosts may be a useful lower vertebrate model for studying the pathogenesis and sequelae of bacterial meningitis.

Monocyte-mediated entry of pathogens into the central nervous system

The origin of the microglia has long been a subject of debate. However it is now clear that monocytes enter the normal central nervous system and follow a series of morphological transformations as they differentiate into microglia. Thus, microglia are of monocytic origin. Since monocytes migrate into the normal CNS, they represent potential vehicles for the entry of pathogens into the nervous system and indeed may carry particulate matter into the CNS. Both viruses and bacteria use this 'Trojan horse' mechanism of entry in the pathogenesis of CNS disease.