JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2017

P-P08 (NP)

 

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

HISTORY:  None

HISTOPATHOLOGIC DESCRIPTION:  Lung:  The is diffuse consolidation of the section.  Areas of consolidation are characterized by filling of alveoli with numerous viable and degenerate neutrophils, foamy macrophages, few lymphocytes, plasma cells, and moderate numbers of reactive fibroblasts admixed with hemorrhage, fibrin, necrotic debris, and numerous cross and tangential sections of cestode larvae.  Larvae are up to 150 um 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, few lymphocytes and plasma cells with occasional type II pneumocyte hyperplasia.  Multifocally there is loss of differential staining with retention of pulmonary architecture (coagulative necrosis).  Multifocally, bronchiolar lumina contain and 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:

• Cestode found in the small intestine, liver, and pancreas of carnivorous animals (dogs, cats, and wild carnivores), amphibians and reptiles

• Larvae penetrate intestinal wall > peritoneal cavity or lungs
• Tissue damage from the scolices, which are embedded deep into the mucosa

PATHOGENESIS & LIFE CYCLE:

• Complete life cycle is not known
• Adult cestodes are found in small intestine of carnivores and birds > first stage
• Intermediate stage is a cysticercoid in an anthropod > second intermediate stage is a solid form larva (referred to as tetrathyridia) in a vertebrate

• Tetrithyridia differ from taeniid larvae (i.e. cysticercus, strobilocercus, coenurus, hydatid cyst) by absence of a bladder
• Larva are capable of asexual multiplication which may lead to massive infections of intermediate hosts; adults are also capable of asexual replication
• Dogs and cats infected through predation and can be definitive host
• Transformation from larva into the adult tapeworm occurs in the intestinal tract of the definitive host, 16 to 21 days after ingestion of the second intermediate host

TYPICAL CLINICAL FINDINGS:

• Peritoneal infection
• Non-specific clinical signs including anorexia, depression, fever, vomiting, weight loss, diarrhea, hematochezia, abdominal distention; enteritis, and malabsorption

TYPICAL GROSS FINDINGS:

• Pyogranulomatous peritonitis or pleuritis
• “Parasitic ascites”: effusion with larva free in the abdomen or adhered to serosal surfaces; “tapioca‑like" fluid with 1‑3 mm diameter, slowly moving granules (larva)
• Larva: flat, non-segmented, contractile; resemble fine fibrin or connective tissue
• Adhesions and fibroplasia may occur with formation of a fibrous cyst
• May extend into vaginal tunics resulting in saccular dilatations, thickening of the spermatic cord, and pyogranulomatous inflammation

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
• Cystic structures in omentum; +/- larvae, inflammatory cells, and calcified granules
• Adult worms measure up to 40 cm in length
• 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
  • Adult and larval cestodes often have suckers on the anterior end
  • Some proglottids have a “skirt” of parenchyma (velum)
• Tetrathyridia of Mesocestoides organism differ from taeniid larvae by absence of a bladder, four suckers with no hooks (unarmed), large but less dense calcareous corpuscles, and absence of a rostellum
• Definitive diagnosis requires identification of suckers
• Ova are oval and measure 35 X 40 um

ADDITIONAL DIAGNOSTIC TESTS:

• Cytology: Tetrathyridium in the peritoneum or pleural aspirates
• Typical gravid proglottides in the feces
• PCR

DIFFERENTIAL DIAGNOSIS:

Parasitic peritonitis or pleuritis in a dog:

• Cestode
  • Plerocercoid larvae (Spargana) of Spirometra: Lack suckers
    • Mesocestoides larvae: invaginated scolex, four suckers, no hooks
  • Acephalic coenuri of Taenia multiceps
  • Cysticercoid larvae of Taenia crassiceps: Fully developed scolex with four muscular suckers and two rows of rostellar hooks
• 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 skunks, bobcats, opossum, racoons, coyotes, foxes, cats, and baboons

References:

1. Caruso KJ, et al. Cytologic diagnosis of peritoneal cestodiasis in dogs caused by Mesocestoides sp. Vet Clin Pathol. 2003;32(2):50-60.
2. Eberhard ML. Histopathological diagnosis. In: Bowman DD, ed. Georgis’ Parasitology for Veterinarians. 10th ed. Philadelphia, PA: WB Saunders; 2014: 416
3. Gardiner CH, et al. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology; 1999:50-55.
4. Gelberg HB. Alimentary system and the peritoneum, omentum, mesentery, and peritoneal cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6^th ed. St. Louis, MO: Mosby Elsevier; 2016: 339
5. Jacobson ER, et al. Infectious Diseases and Pathology of Reptiles: Color Atlas and Text. Boca Raton, FL: CRC Press; 2007: 634
6. Patten PK, et al. Cestode infection in 2 dogs: cytologic findings in liver and a mesenteric lymph node. Vet Clin Pathol. 2013;42(1):103-108.
7. 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

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