JPC SYSTEMIC PATHOLOGY
Signalment (JPC# A75-40-2): Puppy
HISTORY: Incidental finding from a puppy killed by a car.
HISTOPATHOLOGIC DESCRIPTION: Kidney (2 sections): Multifocally, effacing less than 5% of renal cortex and compressing adjacent tubules, there are variably sized granulomas. The granulomas are up to 300um in diameter, have a central core of necrosis surrounded by epithelioid macrophages, which are further bounded by lymphocytes, plasma cells, occasional eosinophilis, fibroblasts, fibrous connective tissue, and occasional multinucleated giant cells (foreign body and Langhans type). Occasionally, the granulomas center on cross and tangential sections of an often poorly discernible nematode larva. Larval nematodes are 40 um in diameter with a 2 um eosinophilic cuticle, and large lateral cords that fill the pseudocoelom. Within the renal interstitium, there are multifocal aggregates of low numbers of lymphocytes and plasma cells. Multifocally, scattered tubules are ectatic and lined by attenuated epithelium. The subcapsular surface is mildly irregular and undulant.
MORPHOLOGIC DIAGNOSIS: Kidney: Granulomas, multiple with mild multifocal lymphoplasmacytic interstitial nephritis and nematode larva, breed unspecified, canine.
ETIOLOGIC DIAGNOSIS: Renal toxicariasis
CAUSE: Toxocara canis
- Toxocara sp. - phylum Nemathelminthes, order Ascarid, suborder Ascaridinia,
- Ascarids are one of the most common intestinal parasites in birds and
Mammals; most are host specific and rarely develop to maturity in species other than their true host; eggs remain infective in soil for years
Common parasitic lesion in the kidneys of dogs; second stage larvae localize in the kidneys and other viscera during somaticmigration; focal areas of inflammation and scarring are occasionally observed as incidental lesions; renal function is rarely affected, even when numerous larvae are present
- Four possible modes of infection: ingestion, in utero, transmammary infection, and ingestion of a paratenic host
- Toxacara can survive in host tissue by secreting canis excretory/secretory (TES) products, which downregulate or divert the immune response
- Ingestion of embryonated eggs from the environment or larva from paratenic hosts (rodents, rabbits)
- Puppies up to three months old may have hepatic-tracheal migration. Eggs with second stage larvae (L2) ingested >eggs hatch in stomach or small intestine > L2 invade wall of intestine > travel in bloodstream via liver to lungs > molt to L3 > return to intestine via trachea > final two molts occur
- Dogs over three months of age are less likely to have hepatic-tracheal migration, and this no longer occurs by six months of age; in the second pathway larvae penetrate alveoli > distributed by circulatory system throughout body > L2 encyst in various tissues (somatic migration / larval migrans) including kidneys, liver, lungs, brain, heart, eyes, skeletal muscle, lymph nodes, and wall of GI tract; this does not produce patent infections
- In utero transplacental infection - In pregnant bitch, three weeks before parturition, L2 are reactivated and migrate to placenta > to liver of fetus > to lungs just after birth > molt to L3 > intestine (via trachea) > final molts
- Transmammary infection - L3 ingested in milk during first three weeks of lactation; there is no further migration in puppies when infection is acquired by this route
- The most important route of infection in young dogs is transplacental transmission
- Ingestion of embryonated eggs from environment or infective larva can cause visceral larval migrans in a variety of tissues in aberrant or dead end hosts
TYPICAL CLINICAL FINDINGS:
- Young puppies
- Abdominal discomfort, pot-bellied appearance, unthriftiness, stunted growth, and diarrhea; adult worms in vomit and/or feces
- In heavy infections, larval migration may cause pulmonary damage leading to coughing, tachypnea, and frothy nasal discharge or blindness
- Mortality is low; however, large numbers of adult worms may cause intestinal obstruction, intussusception, or intestinal perforation and death
- Older dogs - often asymptomatic
- Often incidental necropsy finding in dogs over 6 months of age; disturbance of renal function is rarely if ever attributable to the larvae of canis, even when numerous parasitic lesions are present
TYPICAL GROSS FINDINGS:
- Granulomas randomly scattered throughout kidneys, but primarily in the cortex
- Lesions initially are small 2-3 mm gray-yellow foci with soft centers; later, these areas become firm and white with pitting of the cortical surface
- Other lesions caused by migrating larvae include focal hemorrhages in lungs and granulomas in various tissues; in the eyes, there may be retinitis or post-inflammatory retinopathy
- Large numbers of maturing worms in intestine
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Small granulomas (2-3 mm in diameter) surround entrapped larva (may be difficult to find in sections) and are composed of epithelioid macrophages and lymphocytes with occasional eosinophils, surrounded by fibroblasts within concentrically arranged fibrous connective tissue; randomly scattered throughout the subcapsular renal cortex
- As larvae die, the become fragmented, and the debris is either phagocytosed and eliminated or retained with a resultant granulomatous response and fibrosis
ADDITIONAL DIAGNOSTIC TESTS:
- Fecal floatation
- Enzyme-linked immunosorbent assays (ELISA) for coproantigen detection of Toxocara canis in dogs and Toxocara cati in cats.
- Encaphalitozoon cuniculi - lymphoplasmacytic to granulomatous nephritis in puppies with systemic infections
- Xanthogranulomas - dogs with hypothroidism and severe atherosclerosis;
Foamy, lipid-laden macrophages, lymphocytes, plasma cells, and fibrosis interspersed with cholesterol clefts
- Fungi - Aspergillus, Phycomycetes, Histoplasma capsulatum
- Algae - Prototheca
- Bacteria - Mycobacterium - granulomas up to 10 cm in diameter; central area of necrosis surrounded by epithelioid macrophages and giant cells that contain acid-fast bacteria
- Cat, lion, leopard - Toxocara cati
- Dog, cat, lion, tiger, fox - Toxascaris leonina
- Cattle and water buffalo - Toxocara vitulorum
- Horse - Parascaris equorum
- Chickens, turkeys - Ascaridia galli
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