Severe combined immunodeficiency (terrier type) is an inherited disease affecting Jack Russell terriers. Affected dogs are unable to produce a protein important for proper immune function, predisposing them to severe recurrent or chronic bacterial, viral and fungal infections. Affected dogs often present with symptoms of disease around 12 to 14 weeks of age including failure to thrive, poor growth, weight loss, lethargy, diarrhea, vomiting and lack of palpable lymph nodes. Affected dogs may also present with active respiratory, skin, eye or ear infections. Puppies may die shortly after vaccination with modified live vaccines. Affected dogs die within 4 months of age.