Ollulanus Infection

Ollulanus infection is a parasitic disease caused by nematodes of the genus Ollulanus, primarily Ollulanus tricuspis, which reside in the stomach of domestic and wild felids, and occasionally in other carnivores. The infection is often subclinical but can lead to chronic gastritis, vomiting, and weight loss in heavy infestations. The parasite is unique among nematodes due to its direct life cycle, with autoinfection and transmission via vomitus, making it a challenging pathogen to diagnose and control.

The causative agent is Ollulanus tricuspis, a small (0.7–1.0 mm) trichostrongyloid nematode. It is characterized by a trilobed caudal bursa in males and a vulvar flap in females. The parasite is transmitted through ingestion of infective third-stage larvae (L3) present in vomitus of infected animals. The life cycle is direct: adult females in the stomach produce L1 larvae, which develop to L3 within the stomach and are passed in vomit. No intermediate host is required. Other species, such as Ollulanus skrjabini, have been reported but are less common.

Ollulanus infection is reported worldwide, with higher prevalence in free-roaming and feral cat populations. Domestic cats, especially those with outdoor access, are at increased risk. The infection is more common in multi-cat households and shelters where vomiting and coprophagia facilitate transmission. Dogs, foxes, and other carnivores can also be infected, but cats are the primary definitive host. There is no breed or sex predilection, but young animals may be more susceptible due to immature immune systems. The prevalence varies geographically, with studies showing infection rates of up to 30% in some feral cat populations.

The adult nematodes reside in the gastric mucosa, causing mechanical irritation and inflammation. The host immune response leads to lymphoplasmacytic and eosinophilic infiltration of the gastric mucosa, resulting in chronic gastritis. The inflammatory response can disrupt gastric glandular architecture, leading to reduced acid secretion and altered gastric motility. In heavy infections, the parasite burden can cause mucosal erosion, ulceration, and hemorrhage. The chronic inflammation may progress to gastric fibrosis and atrophy, contributing to chronic vomiting and maldigestion. The exact mechanisms of immune modulation by the parasite are not fully understood, but it is thought to involve Th2-type immune responses.

Predisposing factors include outdoor access, hunting behavior, and living in crowded environments such as shelters or catteries. Immunosuppression, whether due to concurrent viral infections (e.g., feline immunodeficiency virus, feline leukemia virus) or corticosteroid therapy, may increase susceptibility and parasite burden. Poor sanitation and lack of regular deworming programs also contribute to the maintenance of infection within populations. Age is a factor, with kittens and young adults being more commonly affected.

Most infections are subclinical. When clinical signs occur, they are primarily gastrointestinal and include chronic intermittent vomiting, often postprandial, weight loss, and poor body condition. Vomitus may contain mucus or bile. In severe cases, hematemesis may occur due to gastric ulceration. Physical examination may reveal dehydration, poor coat condition, and mild cranial abdominal discomfort. Systemic signs such as fever are rare. Chronic cases may present with signs of protein-losing enteropathy, though this is uncommon.

Differential diagnoses for chronic vomiting in cats include: 1) Inflammatory bowel disease (IBD) – characterized by lymphoplasmacytic or eosinophilic infiltration of the intestines, diagnosed via intestinal biopsy; 2) Gastric lymphoma – often shows weight loss and vomiting, diagnosed via gastric biopsy; 3) Chronic renal disease – associated with azotemia and isosthenuria; 4) Hyperthyroidism – typically in older cats with elevated T4; 5) Pancreatitis – elevated fPLI and abdominal pain; 6) Gastrointestinal foreign body – may be intermittent, diagnosed via imaging; 7) Dietary intolerance or allergy – responds to dietary trial; 8) Other parasitic infections (e.g., Physaloptera) – diagnosed via fecal examination or endoscopy.

The diagnostic approach begins with a thorough history and physical examination. Fecal flotation is often unrevealing because larvae are not passed in feces. The gold standard for diagnosis is gastroscopy with direct visualization of the worms and collection of gastric fluid or biopsy samples. During endoscopy, the stomach may appear hyperemic, with excess mucus and visible small worms. Gastric lavage and cytological examination of the fluid can reveal larvae. Histopathology of gastric biopsies may show adult worms within the lumen or embedded in the mucosa. PCR-based assays have been developed for research purposes but are not widely available. In cases where endoscopy is not feasible, a therapeutic trial with anthelmintics may be considered, but response is not specific.

Routine laboratory tests are often unremarkable. Complete blood count may show mild eosinophilia in some cases. Serum biochemistry may reveal mild hypoalbuminemia in chronic cases due to gastric protein loss. No specific biochemical markers are available. Fecal examination is typically negative for parasite eggs because the parasite does not shed eggs in feces. Gastric fluid analysis may show increased numbers of eosinophils and neutrophils. PCR on gastric fluid or tissue can confirm the presence of Ollulanus DNA.

Radiography and ultrasonography are generally not diagnostic for Ollulanus infection. Abdominal radiographs may show a thickened gastric wall in chronic cases. Ultrasonography may reveal gastric wall thickening and loss of normal layering, but these findings are nonspecific. Endoscopy is the primary imaging modality for diagnosis, allowing direct visualization of the parasites and assessment of mucosal changes.

Cytological examination of gastric lavage fluid may reveal larvae and inflammatory cells. Histopathology of gastric biopsies typically shows chronic lymphoplasmacytic and eosinophilic gastritis, with adult worms or larvae present in the gastric pits or lumen. The mucosa may be hyperplastic or atrophic, with fibrosis in chronic cases. Special stains such as Giemsa or hematoxylin-eosin are sufficient for visualization.

Treatment of Ollulanus infection involves anthelmintic therapy. Fenbendazole is the drug of choice, administered at a dosage of 50 mg/kg orally once daily for 3 consecutive days. Alternatively, ivermectin at 0.2 mg/kg subcutaneously or orally, repeated after 2 weeks, has been used. Supportive care includes antiemetics (e.g., maropitant at 1 mg/kg SC or 2 mg/kg PO q24h) and gastroprotectants (e.g., omeprazole at 0.7–1.0 mg/kg PO q24h) if gastritis is severe. In cases of dehydration, fluid therapy with balanced electrolyte solutions is indicated. Environmental decontamination is important to prevent reinfection, as larvae can survive in vomitus. Strict hygiene and isolation of infected animals are recommended.

The prognosis is generally good with appropriate anthelmintic treatment. Clinical signs typically resolve within a few days to weeks. However, reinfection is possible if environmental contamination persists. In immunocompromised animals or those with severe chronic gastritis, the prognosis may be guarded, and long-term management may be required.

Follow-up should include monitoring for resolution of clinical signs. Repeat endoscopy may be performed 2–4 weeks after treatment to confirm clearance of the parasite. Fecal examinations are not useful for monitoring. In multi-animal environments, all in-contact animals should be treated and preventive measures implemented. Annual fecal examinations are not recommended for this parasite, but routine deworming protocols for outdoor cats may help reduce prevalence.

Pearls: 1) Ollulanus should be considered in cats with chronic vomiting and negative fecal examinations. 2) Endoscopy is the most reliable diagnostic method; gastric lavage during endoscopy increases diagnostic yield. 3) Fenbendazole is effective and safe. Pitfalls: 1) Relying solely on fecal flotation can lead to misdiagnosis. 2) Overlooking the possibility of reinfection from the environment. 3) Using anthelmintics without addressing environmental contamination may result in treatment failure.

Based on Plumb's Veterinary Drug Handbook: Fenbendazole (Panacur) – 50 mg/kg PO q24h for 3 days. Ivermectin – 0.2 mg/kg SC or PO, repeated in 14 days. For supportive care: Maropitant (Cerenia) – 1 mg/kg SC q24h or 2 mg/kg PO q24h for up to 5 days. Omeprazole – 0.7–1.0 mg/kg PO q24h. Fluid therapy: Lactated Ringer's solution at maintenance rates (60–80 ml/kg/day) adjusted for dehydration. All dosages should be adjusted for hepatic or renal impairment if present.

There is limited published literature on Ollulanus infection. A study by Bowman et al. (2002) reported the efficacy of fenbendazole in eliminating infection in experimentally infected cats. Another study by Elsheikha et al. (2008) described the pathology and diagnosis in a feral cat population. Consensus guidelines from the Companion Animal Parasite Council (CAPC) recommend considering Ollulanus in cats with chronic vomiting and include fenbendazole as a treatment option. More research is needed to establish optimal treatment protocols and prevalence data.