JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-P04 (NP)

 

Signalment (JPC #1847808): Black-footed penguin (Spheniscus demerus)

 

HISTORY: Died suddenly

 

HISTOPATHOLOGIC DESCRIPTION: Lung: Diffusely, air capillary septa are moderately thickened by macrophages, fewer heterophils and lymphocytes, rare plasma cells, eosinophilic fibrillar material (fibrin), and small amounts of edema and cellular debris. Multifocally macrophages and erythrocytes contain intracytoplasmic parasitic schizonts measuring up to 10 µm in diameter; schizonts contain up to twenty 1-2 µm diameter, round, basophilic merozoites.  Occasional macrophages contain intracytoplasmic, granular to spicular, brown to black, variably birefringent pigment (hemozoin). Diffusely, the perivascular interstitium is mildly expanded by edema. 

 

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, interstitial, histiocytic, diffuse, moderate, with intrahistiocytic and intraerythrocytic schizonts and intrahistiocytic hemozoin, Black-footed penguin (Spheniscus demerus), avian.

 

ETIOLOGIC DIAGNOSIS: Plasmodial pneumonia

 

CAUSE: Plasmodium sp. (phylum Apicomplexa)

 

CONDITION: Avian malaria

 

GENERAL DISCUSSION:  

• Malaria is caused by parasites of the genus Plasmodium and is transmitted by mosquitoes
• Important disease of penguins (P. relictum, P. elongatum), raptors (P. relictum), and canaries
• Seasonal occurrence, dependent on mosquito vector

 

PATHOGENESIS:

• Culex, Anopholes are the most common mosquito vectors
• Sporogony occurs in insects; schizogony (merogony) and gametogony occur in vertebrate host
• Females mosquitos inject sporozoites into host à enter reticuloendothelial cells à develop into meronts à asexual multiplication (schizogony/merogony) and catabolize hemoglobin à merozoites à cells rupture à parasitemia à entry into erythrocytes (or other endothelial cells) à trophozoites à erythrocytic meronts or gametocytes (gametogony)à ingestion by insect host à sporogony à sporozoites
• Some passerines and other avian species may serve as asymptomatic carriers
• Plasmodial parasites feed on hemoglobin, resulting severe anemia and death

 

TYPICAL CLINICAL FINDINGS:

• Higher mortality in chicks, juveniles, naïve adults, stress
• Signs range from inapparent to severe anemia with hemolysis and death
• Anorexia, depression, vomiting, and dyspnea may occur hours or days before death
• Penguins may have seizures

 

TYPICAL GROSS FINDINGS:  

• Hepatomegaly and splenomegaly with brown to black discoloration 
• Pulmonary edema and hydropericardium
• +/- cerebellar patechiation

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Trophozoites, gametocytes, or schizonts (up to 25 µm in diameter) in peripheral blood, endothelial cells, or lung, liver, spleen, brain (may not be apparent in acute cases)
• Granulocytic interstitial pneumonia, hepatitis, splenitis, myocarditis
• Birefringent malarial pigment (hemozoin) in the erythrocyte and spleen and liver (hemoglobin digestion product)

 

ADDITIONAL DIAGNOSTIC TESTS: 

• Impression smears of liver, spleen, and lung are screening methods for hemoparasites in birds 
• Giemsa-stained smears
• PCR or serology 

 

DIFFERENTIAL DIAGNOSIS: 

Avian Plasmodium spp. may be speciated by the number of merozoites formed in the exoerythrocytic and erythrocytic stages, timing of the life cycle, and morphology of the gametocytes

 

Other intracellular parasites in avian blood smears:

• Leukocytozoon spp: Intracellular round-to-elongate gametocyte that causes the host cell (usually immature erythrocytes) to enlarge and appear to have two nuclei (marginalized host nucleus and parasite nucleus)
• Haemoproteus spp: Within erythrocytes, the gametocyte contains yellow to brown refractile spicules; the gametocyte occupies over 50% of the of the red cell cytoplasm that partially encircles the nucleus
• Atoxoplasma spp: Characteristic sporozoite in the mononuclear leukocyte cytoplasm; it is a pale-staining, round-to-oval intracytoplasmic inclusion that compresses the host cell nucleus into a crescent shape

 

COMPARATIVE PATHOLOGY:

• Plasmodia infect a variety of avian, reptilian, and mammalian species
• Rodents and non-human primates (H-P03) are often used as experimental models
• Often reported in penguins & flamingos from Chile 
• Raptors: Snowy owls and gyrfalcons are most susceptible
• Reported in free ranging bats and ratites, but does not cause clinical disease 
• P. elongatum reported in captive kiwi and rowi; associated with low parasitemia; most severe lesion was interstitial pneumonia, thrombposis, and hypertrophied endothelial cells, pulmonary macrophages, Kupffer cells; hemozoin in the spleen 
• Recent report of four cases of Plasmodium infection in captive tegus; presented with anorexia, lethargy, dehydration, stomatitis; leukopenia, thrombocytosis on labwork; responded to supportive care and sulphamethoxazole-trimethoprim (Pereira, JCP 2021)

 

References:

1. Buckles EL.  Phoenicopteriformes. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:691.
2. Crespo R, Franca MS, Fenton H, Shivaprasad HL. Galliformes and Columbiformes. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:741, 768.
3. Farina LL, Lankton JS. Sirenia. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:626.
4. Gardiner CH, Fayer R, Dubey JP.  An Atlas of Protozoan Parasites in Animal Tissues. 2nd ed. Washington, DC: Armed Forces Institute of Pathology; 1998:65-66. 
5. Pereira FMAM, de Oliveira AR, Mattioli MP, Carneiro FT. Diagnosis and Treatment of Plasmodium Infection in Captive Black and White Tegus. J Comp Pathol. 2021; 183: 9-12.
6. Schmidt RE, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2^nd ed. Ames, IO: John Wiley and Sons, Inc; 2015: 109, 188.
7. Smith DA. Palaeognathae: Apterygiformes, Casuariiformes, Rheiformes, Struthioniformes; Tinamiformes. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:647.
8. Stacy NI, Hollinger C. Introduction to Comparative Clinical Pathology. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:109.
9. Stidworthy MF, Denk D. Sphenisciformes, Gaviiformes, Podicipediformes, Procellariiformes, and Pelecaniformes. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:670.

 

 

 

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