Cat scratch disease (CSD) is a common bacterial infection that is transmitted by infected cats. It is estimated that up to 50% of cats may be asymptomatic carriers and spread the bacteria to humans via bites and/or scratches. Occasionally, infected fleas and ticks may also transmit the disease to humans.
Bartonella henselae is the microorganism implicated in CSD and has a high prevalence in warm and humid regions. There is a slightly higher incidence in males according to some studies and children/adolescents seem more likely to be at risk of exposure. Within 1 – 2 weeks after exposure, the site of inoculation may become mildly infected with proximal lymphadenopathy and other systemic symptoms.
Approximately 9 out of 10 patients with CSD develop non-tender papules within 3 – 10 days at the site where the bacteria are introduced. As the primary lesions begin to recede, lymphadenopathy occurs at the node draining the site of inoculation. More than 50% of patients present with single node enlargement and the regions most frequently involved include the axillae or posterior or anterior neck nodes. Up to 1 in 5 patients may present with lymphadenopathy of the inguinal nodes.
Swollen lymph nodes are generally tender and the overlying skin is red and warm to touch. The nodes may become suppurative and require aspiration. This is seen in 10 to 30 percent of cases. Lymphadenopathy associated with CSD typically remains regional and resolves within 2 – 4 months. However, in some cases, it may become chronic for up to a year. It rarely lasts longer than 12 or more months.
Approximately half of all CSD patients experience systemic symptoms. These include fever, malaise/fatigue, headache, and anorexia. Other symptoms such as arthralgia and sore throat may also be seen. These are typically observed in immunocompromised patients (e.g., HIV/AIDS). In immunocompromised patients, a very severe form of CSD, bacillary angiomatosis, may occur. Any tissue may be affected, especially the skin, which presents with tumors, nodules, or papules.
Parinaud oculoglandular syndrome (POS) is an atypical manifestation of CSD. It occurs due to direct inoculation of the eye with B. henselae. POS is characterized by a granulomatous conjunctivitis, which is unilateral and suppurative pre-auricular lymphadenopathy on the same side. POS is seen in up to 20% of patients with CSD.
The most common neurological manifestation associated with CSD is encephalopathy. This clinical manifestation tends to have an abrupt onset and occurs in about 3% of patients up to 6 weeks after the onset of the lymphadenopathy. It is more frequent in adults than in children and patients may become disoriented, confused and fall into a coma. Hemiparesis, reflex abnormalities and seizures may also be seen in these patients.
Another atypical manifestation of CSD is neuroretinitis, which occurs in approximately 2% of affected patients. Patients typically present with acute visual loss. Signs include retinal lesions, swelling of the optic disc, and occlusion of the retinal vein. Other rare conditions associated with CSD include thrombocytopenic purpura, osteolytic lesions, and erythema nodosum.