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Jodie Green, Internal Medicine Resident

Millie, a six-month female neutered domestic short hair, was presented to RVC Small Animal Referrals due to poor weight gain and a one-week history of progressive lethargy and hyporexia.

On presentation to our Emergency Service, Millie was found to be icteric and pyrexic. She was severely hypoglycaemic and suffered a hypoglycaemic seizure, requiring aggressive glucose supplementation. Millie was also severely anaemic, with a PCV of 12%, and required a feline packed red blood cell transfusion.

Biochemistry identified hyperbilirubinaemia, hyperglobulinaemia and hypoalbuminaemia, with an albumin/globulin ratio of 0.36. Millie was found to have a protein-rich abdominal effusion, with pyogranulomatous inflammation. Haematologic examination also identified a severe non-regenerative anaemia with evidence of erythrophages and microscopic agglutination suggestive of immune-mediated destruction.

Millie’s clinical picture and investigations were most suspicious for a diagnosis of effusive feline infectious peritonitis (FIP). However, Millie’s picture was complicated by her severe hypoglycaemia and anaemia. Many factors were likely contributing to Millie’s anaemia, including consumption and immune-mediated destruction as a result of her FIP.

Millie required an extensive stay in our ICU for supportive care, intravenous glucose and potassium supplementation, and Millie was started on intravenous remdesivir (20m/kg) for treatment of her FIP.

Due to her severe anaemia, Millie’s condition initially deteriorated, and she required a xenotransfusion and a further feline packed red blood cell transfusion in order to stabilise her. Millie continued to show clinical improvements following treatment for her FIP and, after six days, her anaemia had become regenerative and her red blood cell concentration was able to recover.

Millie was discharged after 10 days in hospital to complete her 12-week course of GS-441524 (a nucleoside analogue antiviral drug) at home. Millie was the 63rd cat with FIP to be treated at the RVC with a combination of remdesivir and GS-441524. Over 80% of cats undergoing treatment for FIP at the RVC have survived to make a full recovery but Millie is the first cat with both hypoglycaemia and anaemia severe enough to require a blood transfusion to survive.

Millie was discharged from the Queen Mother Hospital for Animals (QMHA) in early December last year and remains in clinical remission from FIP.

Millie’s successful outcome would not have been possible without the collaboration of specialists, residents and nurses from our Emergency and Critical Care team, Internal Medicine team and Transfusion Medicine teams.

Evolving FIP treatment at the RVC

Feline infectious peritonitis is a rare disease caused by a mutated enteric coronavirus. Historically the disease was considered almost always fatal, due to a lack of efficacious treatment.

However over the past few years, a small number of studies showed that the antiviral drug remdesivir and its parent nucleoside GS-441524 could be the key to successfully treating FIP in cats. Remdesivir became licensed to treat COVID-19 infections in human patients early in the pandemic and the drug then became widely accessible in the UK to treat FIP.