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🔍 Ultrasound — Abdomen

Ultrasound Evaluation of Infectious Disease in Dogs & Cats

Abdominal ultrasound reveals the GI, hepatic, splenic, and renal manifestations of infectious diseases that bloodwork and radiographs cannot fully characterize. It is critical for differentiating infectious GI masses from lymphoma, staging systemic fungal disease, and guiding FNA for same-day cytologic diagnosis.

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Ultrasound for Infectious Disease at a Glance

Primary Use
GI wall evaluation, organ architecture, lymph node assessment, and guided FNA for cytology
Key Advantage
Real-time, no sedation usually needed; can perform diagnostic FNA during the same appointment
Critical Differential
Many infections (pythiosis, histoplasmosis) mimic GI lymphoma or carcinoma on ultrasound — cytology is essential
Complementary Imaging
Thoracic radiographs and MRI (if CNS signs present) complete the staging workup
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Fungal & Fungal-Like Infections

Pythiosis

Pythium insidiosum (oomycete — fungal-like organism)

Pythiosis is caused by Pythium insidiosum, an oomycete found in warm, stagnant water environments (swamps, ponds, rice paddies) primarily in the Gulf Coast states. Dogs are infected through skin contact (cutaneous form) or ingestion of contaminated vegetation (GI form). The GI form is the most common presentation and produces severe focal or segmental bowel masses that are frequently mistaken for aggressive neoplasia. The pyloric-duodenal junction (PDJ) and ileocolic junction (ICJ) are the most common sites of involvement.

Clinical Signs

  • Severe weight loss (often dramatic)
  • Chronic vomiting and diarrhea
  • Anorexia and progressive debilitation
  • Palpable abdominal mass
  • Cutaneous draining tracts (skin form)
  • Young to middle-aged large breed dogs

Ultrasound Findings

  • Severe focal or coalescing GI masses
  • Segmental bowel wall thickening with loss of layering
  • Incorporation of adjacent lymph nodes into mass
  • Loss of normal tissue planes between bowel and nodes
  • Alternate presentation: diffuse colon or SI thickening

⚠ Pythiosis vs. GI Cancer

On ultrasound, pythiosis can be indistinguishable from aggressive GI lymphoma or carcinoma. The mass often looks like severe cancer but has a characteristic lack of definition between bowel and lymph nodes. Geographic history (Gulf Coast exposure to standing water) and patient signalment (young to middle-aged large breed dog) are critical context clues. Ultrasound-guided FNA and immunoassay testing (anti-Pythium antibody ELISA) are essential for differentiation.

Histoplasmosis (Abdominal Form)

Histoplasma capsulatum

The abdominal form of histoplasmosis produces a distinctive ultrasound pattern, particularly in cats. Systemic histoplasmosis causes diffuse small intestinal thickening affecting the muscularis layer, hepatosplenomegaly, and lymphadenopathy. These findings overlap significantly with GI lymphoma, making cytologic sampling critical for diagnosis. Cats with histoplasmosis may present with concurrent pulmonary, joint, and ocular disease.

Clinical Signs

  • Lethargy and progressive weight loss
  • Anorexia and fever
  • Diarrhea (large or small bowel)
  • Trouble breathing (concurrent pulmonary form)
  • Lameness and joint swelling (cats)
  • Uveitis (cats)

Ultrasound Findings

  • Diffuse small intestinal muscularis thickening
  • Hepatosplenomegaly
  • Mesenteric and hepatic lymphadenopathy
  • Loss of normal bowel wall layering
  • Segmental thickening pattern
Concurrent thoracic radiographs may show diffuse interstitial to nodular pulmonary disease. Histoplasma organisms can be identified on FNA cytology of affected lymph nodes, spleen, or liver. For the pulmonary radiographic presentation, see our Radiographic Evaluation guide.

Cryptococcosis (Systemic/Abdominal Form)

Cryptococcus neoformans / C. gattii species complex

While cryptococcosis most commonly presents as nasal or CNS disease, the systemic form can produce dramatic abdominal ultrasound findings. Hematogenous dissemination can involve the kidneys, GI tract, liver, spleen, and lymph nodes. Cats are more commonly affected than dogs. The renal form is particularly distinctive, with marked architectural distortion that can be detected on routine palpation.

Clinical Signs

  • CNS signs (concurrent nasal/brain form)
  • Irregular kidneys palpable on PE
  • Weight loss and anorexia
  • Fever
  • Nasal discharge and facial deformity
  • Uveitis and ocular disease

Ultrasound Findings

  • Renomegaly with nodular change
  • Markedly altered renal architecture
  • Diffuse SI muscularis thickening
  • ± Hepatosplenomegaly
  • Lymphadenopathy (mesenteric, hepatic)
Renal FNA can provide rapid cytologic confirmation of Cryptococcus organisms. Cryptococcal antigen testing (latex agglutination) on serum is highly sensitive. For CNS evaluation with MRI, see our MRI guide.

Mycobacteriosis

Mycobacterium bovis / M. microti / M. avium complex

Mycobacterial infections in cats can produce ultrasound findings nearly identical to histoplasmosis and cryptococcosis. M. bovis is transmitted through unpasteurized milk or contact with infected cattle, while M. microti is transmitted from infected rodents — making prior feral cats and outdoor hunters at risk. FIV-positive cats are particularly susceptible. The disease causes progressive granulomatous inflammation in multiple organs.

Clinical Signs

  • Weight loss and anorexia
  • Fever of unknown origin (FUO)
  • Progressive anemia
  • Prior feral or outdoor history
  • FIV-positive status (risk factor)
  • Poor response to standard empiric therapy

Ultrasound Findings

  • Renomegaly with nodular change and altered architecture
  • Diffuse SI muscularis thickening
  • ± Hepatosplenomegaly
  • Lymphadenopathy
  • Pattern indistinguishable from histoplasmosis or crypto
Mycobacteriosis should be considered in FIV-positive cats with FUO, progressive anemia, and abdominal ultrasound findings consistent with systemic granulomatous disease but negative fungal testing. Acid-fast staining on cytology or tissue biopsy confirms diagnosis. The disease carries a poor prognosis.
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Parasitic Infections

Canine Schistosomiasis

Heterobilharzia americana

Heterobilharzia americana is a trematode (flatworm) parasite found in the Gulf Coast and southeastern United States. Dogs and raccoons are definitive hosts; freshwater snails serve as the intermediate host. Infection occurs when the parasite penetrates the skin during swimming or wading, or through ingestion of infected snails. The adult worms migrate from the lungs to the portal vein and then to the mesenteric veins, where they mate and deposit eggs in the intestinal wall and liver. The resulting granulomatous response produces highly characteristic ultrasound findings.

Clinical Signs

  • Vomiting and severe diarrhea
  • Anorexia and weight loss
  • Drooling
  • Chronic waxing/waning GI signs
  • Some coughing or choking (pulmonary migration phase)

Ultrasound Findings

  • Submucosal hyperechoic thickening with pinpoint mineral foci (hallmark)
  • Mineral foci in liver parenchyma
  • Mesenteric lymphadenopathy ± mineral foci
  • Hepatic and splenic changes

Lab Findings

  • Decreased albumin and total protein
  • Anemia
  • Eosinophilia
  • Hypercalcemia (± increased PTHrP)

Diagnosis

  • Fecal PCR (submit to Texas A&M University)
  • Differentiates acute vs. prior infection
  • Standard fecal float does NOT detect eggs
The combination of submucosal mineralization with hepatic mineral foci on ultrasound is highly suggestive of Heterobilharzia in an endemic area. Some dogs recover fully with fenbendazole or praziquantel treatment; others have chronic residual changes. Hypercalcemia can be severe and may be the presenting complaint.

Heartworm Disease (Echocardiographic Evaluation)

Dirofilaria immitis

Echocardiography (cardiac ultrasound) plays a critical role in advanced heartworm disease. In Class 4 caval syndrome, adult worms can be directly visualized in the right atrium, right ventricle, and main pulmonary artery. Echo also evaluates right heart function, identifies pericardial effusion, and differentiates heartworm-related right heart failure from other causes such as Chagas disease.

Clinical Signs

  • Severe right heart failure
  • Ascites and hepatomegaly
  • Collapse and weakness
  • Dyspnea and exercise intolerance
  • High worm burden on antigen testing

Echo Findings

  • Adult worms visible as parallel linear echoes in right heart/MPA
  • Right ventricular dilation and dysfunction
  • Tricuspid regurgitation
  • Absence of pericardial effusion helps differentiate from other causes
When right heart failure is present without pericardial effusion, the primary differential is heartworm disease vs. Chagas disease. For radiographic heartworm staging (Classes 1–4), see our Radiographic Evaluation guide.
Clinical Decision-Making

When to Choose Ultrasound for Suspected Infection

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Chronic GI signs with weight loss — especially in young to middle-aged dogs with access to standing water (pythiosis risk) or in endemic fungal areas. Ultrasound differentiates diffuse vs. focal disease and identifies targets for FNA.
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Fever of unknown origin (FUO) — ultrasound can reveal hepatosplenomegaly, lymphadenopathy, or GI wall changes that point toward systemic infection before serology returns.
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Hypercalcemia with GI signs — the combination of hypercalcemia, hypoalbuminemia, and eosinophilia in a dog from the Gulf Coast should prompt ultrasound evaluation for Heterobilharzia mineralization patterns.
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Right heart failure without pericardial effusion — echocardiography can identify adult heartworms or evaluate for Chagas cardiomyopathy as the underlying cause.
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FIV+ cats with progressive anemia and FUO — ultrasound can identify the organ pattern (renal, hepatic, GI) consistent with mycobacteriosis, histoplasmosis, or cryptococcosis, and guide targeted sampling.

Need an Abdominal Ultrasound?

Our board-certified radiologists perform comprehensive abdominal ultrasound with same-appointment FNA capability for rapid infectious disease diagnosis.

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Round Rock, Texas
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Spring, Texas
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Sandy, Utah
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Frequently Asked Questions

Ultrasound & Infectious Disease FAQ

Not reliably on imaging alone. Both pythiosis and aggressive GI neoplasia (lymphoma, carcinoma) can produce severe focal bowel wall thickening with loss of layering and lymph node involvement. However, pythiosis tends to show a characteristic lack of tissue plane definition between bowel and nodes, and typically occurs in young to middle-aged large breed dogs with access to standing water in the Gulf Coast region. Ultrasound-guided FNA with cytology and Pythium-specific ELISA testing is essential for definitive differentiation.
Most patients do not require sedation for abdominal ultrasound. The procedure is non-invasive and well-tolerated. A small area of fur on the abdomen is clipped for optimal image quality. If ultrasound-guided FNA is performed during the same appointment, light sedation may be recommended depending on the sampling site and patient temperament. The entire examination typically takes 30–45 minutes.
Heterobilharzia americana (canine schistosomiasis) is a flatworm parasite found in the Gulf Coast and southeastern United States, including Texas. Dogs become infected by swimming or wading in freshwater where infected snails are present. The parasite causes granulomatous inflammation in the GI tract and liver, leading to chronic GI signs, weight loss, and sometimes severe hypercalcemia. If your dog swims in natural freshwater in endemic areas and develops chronic GI signs, ultrasound can identify the characteristic mineralization pattern. Fecal PCR testing through Texas A&M confirms the diagnosis — standard fecal float will not detect the eggs.
Yes, this is one of the most valuable aspects of diagnostic ultrasound at SVI. When our radiologists identify suspicious masses, enlarged lymph nodes, or altered organ architecture, they can perform ultrasound-guided fine needle aspiration (FNA) during the same appointment. Samples are submitted for cytologic evaluation and can often identify organisms like Histoplasma, Cryptococcus, or Blastomyces the same day. This avoids the delays and added cost of scheduling a separate procedure or surgical biopsy.