Signalment:  

18-year-old female putty-nosed monkey, Cercopithecus nictitans.The monkey lived in a German zoo since 2007. After a fight among group members, the animal showed apathy, tachypnea and vomiting. Physical examination under general anesthesia revealed a perforating wound on the right lateral thorax, resulting in severe unilateral pyothorax, which was treated by drainage of the thoracic cavity and repeated wound cleaning, accompanied by administration of antibiotics and analgesics for a couple of days. The monkey showed good response to treatment and initially improved, before its clinical condition deteriorated after 10 days with additional development of neurological signs. Due to poor prognosis, the animal was euthanized and submitted for post mortem examination.

Gross Description:  

Focally extensive within the right ventrolateral chest wall, a chronic, well encapsulated, intramuscular to subpleural abscess was present, reaching from the sixth to ninth intercostal space into the mediastinum with adhesions to the caudal lung lobe and perforation of the costal pleura, accompanied by moderate unilateral fibrinous to hemorrhagic pleural effusion. The right lung showed diffuse necro-suppurative to fibrinous pleuropneumonia with marked compression atelectasis of mainly the caudal parts, whereas the left lung was poorly retracted, hyperemic, and edematous with multifocal miliary to mid-sized abscesses disseminated throughout all lobes. Cerebral as well as cerebellar grey and white matter revealed randomly distributed foci of acute hemorrhagic necrosis, accompanied by diffuse meningeal hyperemia and mild to moderate multifocal to coalescing suppurative meningitis. 

Histopathologic Description:

Throughout grey and white matter as well as within meninges, there are multiple randomly distributed necrotic foci, composed of central debris, sometimes associated with bright eosinophilic material (Splendore Hoeppli phenomenon), and surrounded by numerous degenerate neutrophils and macrophages besides fewer lymphocytes and plasma cells. Frequently within necrotic centers, few to large numbers of faintly stained fungal hyphae of approximately 3-6 μm width, characterized by regular septation, thin, parallel walls, and dichotomous, progressive acute angle branching are present. Several small to mid-sized arterial blood vessels within the neuropil contain fibrin thrombi that are often admixed with the fungal hyphae described above, accompanied by moderate to marked fibrinoid change and necrosis of vessel walls. The surrounding tissue shows varying degrees of hemorrhage and lytic necrosis in combination with degenerate neutrophils, foamy macrophages (gitter cells), fewer lymphocytes, and plasma cells as well as moderate adjacent gliosis. 

Morphologic Diagnosis:  

Cerebral cortex: Meningoencephalitis, necrotizing, suppurative, acute, multifocal, marked, with multifocal thrombosis, necrosuppurative vasculitis, and numerous intralesional fungal hyphae consistent with Aspergillus fumigatus, putty-nosed monkey (Cercopithecus nictitans), nonhuman primate.

Lab Results:  

Aspergillus fumigatus was isolated by fungal culture from the brain.

Condition:  

Aspergillus fumigatus

Contributor Comment:  

More than 180 Aspergillus (A.) spp. have been described but only four species (A. fumigatus, A. flavus, A. terreus, A. niger) are commonly associated with invasive infection in primates,(5) with Aspergillus fumigatus being the most common cause (> 90 %) of human pulmonary fungal infections.(5,7) The uninucleate conidia, or spores, of Aspergillus sp. occur in soil, air, water and greatest numbers are found in hay and straw enriched with leaf and grass compost. They are easily dispersed by the wind and have a diameter small enough (2.5 to 3.5 μm) to reach down to the deep airways. They are considered to be the main vehicle for infective transmission, and when they get the chance to germinate inside the body, producing branched septate hyphae that invade tissues, different forms of aspergillosis can develop.(1)

However, the exact portal of entry for the fungal infection could not clearly be identified in the present case. It is possible that Aspergillus conidia entered through the perforating wound and germinated within the thoracic cavity, and from there they invaded the blood stream and spread to the lung and central nervous system. But it is also possible the infection route was via inhalation of Apergillus spores, resulting in penetration of distal alveolar spaces. Here, there are optimal environmental conditions for germination into angioinvasive filamentous hyphae that can produce local tissue damage, hemorrhage, infarction, and necrosis.(7)

In healthy, immunocompetent individuals, various elements of the pulmonary innate immune system are involved in recognition and elimination of inhaled Aspergillus conidia, thereby preventing colonization of the respiratory system. Ciliated and mucus secreting epithelial cells perform effective mucociliary clearance that is important for entrapment and elimination of inhaled conidia. Surfactant, mainly produced by type II pneumocytes and Clara cells, has been implicated in antimicrobial activity with surfactant protein A and D serving as collectins. Alveolar macrophages represent first line phagocytic defense by intracellular killing of swollen spores and prevention of germination. Recruited neutrophils play an essential role by extracellular (degranulation) as well as intracellular (phagocytosis) elimination of aspergilli. Dectin-1, expressed by macrophages, neutrophils and dendritic cells, is an important receptor of innate antifungal defense being essential for spore recognition and phagocytosis, as well as production of oxygenated free radicals (fungicide al activity). Above that, certain Toll-like receptors (TLR) have been found to play a predominant role in the recognition of A. fumigatus (TLR2: recognition of spores, TLR4: recognition of spores and hyphae).(8)

On the other hand, several pathogenicity factors were found in different Aspergillus spp. to overcome certain host defense mechanisms such as endotoxins that inhibit epithelial ciliary activity, as well as a variety of proteases (including elastase, collagenase and trypsin) that damage epithelial cells and, thus, impair effective mucociliary clearance.(1,5) Furthermore, A. fumigatus produces a phospholipid capable of decreasing the binding of complement factor C3b to its surface, resulting in disturbed complement activation.(7) Also other fungal proteins of A. fumigatus are probably related to virulence by promoting mycelial growth in lung parenchyma or structural alterations of conidia that are resistant to host defense mechanisms.(1)

Moreover, it is likely that Aspergillus mycotoxins can work as virulence factors due to direct cytotoxic effects. In vitro studies revealed that aflatoxin (produced by A. fumigatus) suppresses the function of macrophages, and ochratoxin (produced by A. ochraceus) is cytotoxic to lymphocytes and suppresses lymphocytic, monocytic and granulocytic activity. As other possible immunosuppressive mycotoxins, gliotoxin, fumagillin, fumigacin, fumitremorgin A and Asp-hemolysin are discussed while different mycotoxins together may have synergistic effects. However, further in vivo studies are needed for confirmation of direct relation to Aspergillus pathogenesis.(6) Beyond that, melanin pigment, mannitol, catalases and superoxide dismutases are suggested as antioxidant defenses produced by Aspergillus.(4) Although it seems that certain antioxidant molecules produced by A. fumigatus do not directly inhibit the oxidizing activity of phagocytes, inhibition of reactive oxygen species production by macrophages (e.g. with high blood cortisol levels or corticosteroid treatment) abolishes their ability to kill the spores while phagocytosis continues so that conidia can germinate and proliferate intracellularly.(8)

However, since pulmonary macrophages and neutrophils constitute a crucial part of first line innate host defense, neutropenia and long-term corticosteroid treatment or hyperglucocorticoidism, as observed in the present case, are generally regarded as major risk factors for the pathogenesis of invasive aspergillosis.(1,4)

JPC Diagnosis:  

Brain, cerebrum: Meningoencephalitis, necrosuppurative, multifocal, severe, with vasculitis, hemorrhage and numerous fungal hyphae. 

Conference Comment:  

This is a great case exhibiting the vascular affinity of Aspergillus spp. within the brain of this monkey, with its severity alluding to suspicion of an underlying immune compromising condition such as chronic steroid administration. The contributor mentions this may have played a role, and describes the complex interactions of the fungis virulence factors with the hosts immune response; an interaction which often allows it to run amok in susceptible patients. 

Aspergillosis is perhaps more readily recognized as the cause of granulomatous pneumonia and air sacculitis in avian species, mycotic rhinitis in dogs, abortion in cattle, secondary abomasal ulcers in ruminants following grain overload or mastitis, and hepatocyte megalocytosis and necrosis in dogs.(2,3) The latter is associated with production of aflatoxin of which there are several produced by Aspergillus spp. with B1 being the most significant and best studied example.(10) Toxin production tends to be greatest in stored or unharvested mature grains. Among nonhuman primates, reports of infection are seemingly rare, limited to a single outbreak at the London Zoo in conjunction with tuberculosis. During this outbreak, Old World monkeys were affected by disseminated lesions in the lungs, liver, kidneys and spleen.(9)

References:

1. Al-Alawi A, Ryan CF, Flint JD, et al. Aspergillus-related lung disease. Can Respir J. 2005;12(7):377-387.

2. Brown CC, Baker DC, Barker IK. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. Vol. 2. Philadelphia, PA: Elsevier Saunders; 2007:229.

3. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. Vol. 2. Philadelphia, PA: Elsevier Saunders; 2007:640.

4. Dagenais TRT, Keller NP. Pathogenesis of Aspergillus fumigatus in invasive aspergillosis. Clin Microbiol Rev. 2009;22:447-465.

5. Denning DW. Invasive aspergillosis. Clin Infect Dis. 1998;26(4):781-803.

6. Kamei K, Watanabe A. Aspergillus mycotoxins and their effect on the host. Med Mycol. 2005;Suppl43:S95-S99.

7. Latg+�-� JP. Aspergillus fumigatus and aspergillosis. Clin Microbiol Rev.1999;12(2):310-350.

8. Mansour MK, Tam JM, Vyas JM. The cell biology of the innate immune response to Aspergillus fumigatus. Ann NY Acad Sci. 2012;DOI: 10.1111:78-84.

9. Simmons J, Gibson S. Bacterial and mycotic diseases of nonhuman primates. In: Abee CR, Mansfield K, Tardiff S, Morris, T, eds. Nonhuman Primates in Biomedical Research: Diseases. 2nd ed. Vol. 2. San Diego, CA: Elsevier Inc. 2012:156-157.

10. Stalker MJ, Hayes MA. Liver and biliary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. Vol. 2. Philadelphia, PA: Elsevier Saunders; 2007:370-371.

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4-1. Telencephalon

4-2. Telencephalon

4-3. Telencephalon

4-4. Telencephalon

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