JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-P08 (NP)

 

Signalment (JPC #1669224): 5-year-old female poodle.

 

HISTORY: None

 

HISTOPATHOLOGIC DESCRIPTION: Lung: Diffusely, the lung is consolidated, characterized by alveolar lumina filled with an exudate composed of numerous viable and necrotic neutrophils, foamy macrophages, few eosinophils, lymphocytes, plasma cells, and moderate numbers of reactive fibroblasts admixed with hemorrhage, fibrin, edema, necrotic debris, and numerous cross and tangential sections of larval cestodes. Larvae are up to 150 µm in diameter with a thick outer tegument surrounding a loose parenchymatous matrix, an invaginated unarmed scolex with suckers, and numerous calcareous corpuscles. Alveolar septa are frequently fragmented and discontinuous, replaced by cellular debris (septal necrosis), or are variably expanded by fibrin and few lymphocytes and plasma cells, and there is occasional type II pneumocyte hyperplasia. Multifocally there is loss of differential staining with retention of pulmonary architecture (coagulative necrosis). Multifocally, bronchiolar lumina contain an exudate of hemorrhage, fibrin, neutrophils, and macrophages. The pleura is mildly expanded by edema and fibrin with few macrophages, neutrophils, lymphocytes, plasma cells, reactive fibroblasts, and hemorrhage.  

 

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, neutrophilic and histiocytic, multifocal to coalescing, severe, with hemorrhage, necrosis, pleuritis and numerous cestode larvae, poodle, canine.

 

ETIOLOGIC DIAGNOSIS: Pulmonary mesocestodiasis

 

ETIOLOGY: Mesocestoides spp.

 

GENERAL DISCUSSION:  

 

PATHOGENESIS & LIFE CYCLE:

• Cyclophyllidean tapeworm with a complex life cycle, including two intermediate hosts (an insect or mite and a vertebrate) and a definitive host

• Intermediate host (insect or mite) contains cysticercoid à ingested by second intermediate host (mammal, reptile and some birds) and develops infective stage (tetrathyridia) in body cavities, liver, and lung à definitive host ingests tetrathyridia > develop into adult tapeworms which develop and replicate asexually within the intestine AND/OR tetrathyridia may penetrate the gut wall and proliferate within the peritoneal cavity (peritoneal larval cestodosis), pleural cavity, lung or liver

• Tetrathyridia differ from taeniid larvae (i.e. cysticercus, strobilocercus, coenurus, hydatid cyst) by absence of a bladder

 

TYPICAL CLINICAL FINDINGS:

• Incidental (if mild)
• Diarrhea, anorexia, vomiting, weight loss, depression
• Peritoneal effusion and abdominal distension 

 

TYPICAL GROSS FINDINGS:  

• Pyogranulomatous peritonitis or pleuritis +/- adhesions and fibroplasia 
• Parasitic ascites: abundant exudate with free floating 1-2mm tetrathyridia (flat, extremely contractile larva) and small white cyst-like structures 

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Peritonitis/serositis/pleuritis with villous mesothelial proliferation, fibroplasia, and fibrous adhesions, with pyogranulomatous or mixed interstitial inflammatory infiltrate of macrophages, plasma cells and neutrophils 
• Cyst-like structures +/- larvae, inflammatory cells, and calcified granules
• Flat larval cestodes (tetrathyridia) free or encysted in various tissues with a knot-like anterior end with a characteristic invaginated protoscolex, four suckers and no rostellum

• General identifying characteristics of cestodes include:

• Thick, layered tegument with basement membrane
• Segmented body, proglottids, each with male and female reproductive organs
• Absence of digestive tract
• Presence of calcareous corpuscles
• Longitudinal muscles just below the tegument 

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Cytology: Peritoneal or pleural aspirates are within the exudative range; may see small opaque flecks grossly; cytologically, may see suppurative inflammation and remnants of or intact tetrathyridium with numerous round to angular, clear to pink refractile calcareous corpuscles
• Molecular testing is usually necessary to identify different cestode species 

 

DIFFERENTIAL DIAGNOSIS:

Parasitic peritonitis or pleuritis in a dog:

• Plerocercoid larvae (Spargana) of Spirometra: Lack suckers 

• vs. Mesocestoides larvae: Invaginated scolex, four suckers, no hooks

• Acephalic coenuri of Taenia multiceps: Bladder

• Cysticercoid larvae of Taenia crassiceps: Fully developed scolex with four muscular suckers and two rows of rostellar hooks, bladder

• Pentastome: Arthropods typically found as adults in lungs of reptiles

• Porocephalus crotali: Uncommonly found in nasal cavity, liver, mesenteric lymph nodes, subserosa, omentum, mesentery, and lungs; 

• Nymphs within a cyst surrounded by fibroblastic proliferation
• Pseudosegmented body, a chitinous cuticle with pit-like openings to skin glands, chitinous hooked mouth parts, prominent body cavity, numerous acidophilic glands, striated muscle, and digestive tract

 

COMPARATIVE PATHOLOGY:  

• Tetrathyridia frequently found in reptiles (snakes, lizards)
• Reports in skunk, bobcat, opossum, raccoon, coyote, fox, cat, and various old world monkeys and apes 

 

References:  

1. Boes KM. Body Cavity Fluids. In: Raskin RE, Meyer DJ, Boes KM, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 4^th ed. St. Louis, MO: Elsevier; 2023: 256. 
2. Gardiner CH, et al. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology; 1999:50-55.
3. Matz-Rensing K et al. New World and Old World Monkeys. Terio KA et al., eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 368.e11.
4. Origgi FC. Lacertilia. Terio KA et al., eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 889.e9.
5. Ossiboff RJ. Serpentes. Terio KA, et al., eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 914
6. Spagnoli ST, Gelberg HB. Alimentary system and the peritoneum, omentum, mesentery, and peritoneal cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7^th ed. St. Louis, MO: Elsevier; 2022: 410, 459.
7. Strait K, Else JG, Eberhard ML. Parasitic diseases of nonhuman primates. In: Abee CR, Mansfield K, Tardif S, eds. Nonhuman Primates in Biomedical Research. Vol 2. 2^nd Ed. San Diego, CA: Academic Press;2012:253, 257-258. 
8. Uzal FA, et al. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals, Vol 2, 6th ed. St. Louis, MO: Elsevier; 2016: 223.
9. Valenciano AC, Rizzi TE. Abdominal, thoracic, and pericardial effusions. In: Cowell and Tyler’s Diagnostic Cytology and Hematology of the Dog and Cat. 5^th Ed. St. Louis, MO: Elsevier;2020:245. 

 

 

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