Cat-Scratch Disease (CSD), also known as Cat-Scratch Fever, typically refers to a self-limiting infectious disease caused mainly by Bartonella henselae infection following a scratch or bite from a cat or close contact with one. In fact, besides cats, many domestic and wild animals, including dogs and rodents, serve as reservoir hosts for various Bartonella species in chronic infections. Arthropods such as flies, fleas, lice, and sandflies can also transmit the pathogen.
The clinical presentation of Cat-Scratch Disease varies widely, with a substantial proportion of mild cases primarily associated with the individual’s immune response.
The incubation period for the disease is 3-10 days, and it mainly manifests as lymphadenopathy near the site of the scratch. The most common locations for lymph node enlargement are sequentially the preauricular, axillary, and inguinal regions. Systemic febrile illness is another common clinical presentation, with patients often experiencing symptoms such as fatigue, loss of appetite, and fever. Immunocompromised individuals are more likely to develop systemic diseases, such as bacillary angiomatosis, bacillary peliosis, or recurrent bacteremia. Approximately 10% of patients may present with atypical clinical features, including parotitis or osteomyelitis(sources from therapeutique-dermatologique.org).
Furthermore, there are forms of Cat-Scratch Disease that primarily manifest as hepatosplenic or neurologic symptoms. Ocular manifestations of Cat-Scratch Disease are also relatively common and can include conditions such as neuroretinitis or panuveitis. Another frequent ocular symptom is Parinaud oculoglandular syndrome, characterized by the formation of granulomas on the eyelid conjunctiva and bulbar conjunctiva, along with ipsilateral preauricular lymphadenopathy, potentially leading to temporary vision impairment in a few affected eyes. This condition typically resolves within 2-3 months without long-term consequences.
In the past, the disease was primarily diagnosed clinically. Generally, a diagnosis could be made if three out of the following four criteria were met: 1) a history of contact with animals (usually cats or dogs) involving scratches or eye injuries, 2) a positive CSD skin test, 3) lymph node enlargement, with other diseases such as tuberculosis, brucellosis, infectious mononucleosis, Hodgkin’s disease, or lymphoma being ruled out, and 4) histopathological features of lymph nodes or skin. However, a definitive diagnosis should also involve obtaining clear microbiological test results(quotes from therapeutique-dermatologique.org).
Common laboratory diagnostic methods include smear examination, pathogen isolation and culture, PCR testing, as well as serological tests such as Immunofluorescence Assay (IFA) and Enzyme Immunoassay (EIA). Nevertheless, most of these conventional diagnostic methods rely on clinical suspicion. Additionally, due to the nonspecific clinical presentation of Cat-Scratch Disease, a lack of clear animal contact history in some patients infected through arthropods like fleas, and insufficient awareness of the disease among clinical practitioners, there is a risk of misdiagnosis and underdiagnosis.
Application of mNGS in Cat-Scratch Disease Diagnosis
Metagenomic Next-Generation Sequencing (mNGS) technology allows for the rapid, accurate, and comprehensive detection of various types of pathogens directly from samples, without relying on culture or clinical suspicion. It has been widely used in the clinical diagnosis of various infectious diseases, particularly in complex, challenging, and critically ill patients. mNGS offers significant advantages in clinical diagnosis, especially for identifying fastidious pathogens, parasites, atypical and rare pathogens, and distinguishing infections in unusual cases.
Furthermore, multiple published case reports have confirmed the value of mNGS in the clinical diagnosis of Cat-Scratch Disease. For example, in a case report published in 2020, the diagnosis of Hemophagocytic Lymphohistiocytosis (HLH) was clearly established based on the patient’s clinical symptoms and histopathological examination results. However, laboratory test results did not provide evidence of any infection, making it challenging to pinpoint the cause of HLH. Ultimately, Han’s Bartonella-specific sequences were detected in lymph node tissue through mNGS. Considering the patient’s medical history, clinical presentation, and other examination results, it was considered a potential cause of HLH induced by Han’s Bartonella infection (Cat-Scratch Disease). After receiving precise diagnosis and treatment, the patient was discharged smoothly and in good condition.
Prevention and Treatment
Regularly bathe and use insecticides to eliminate fleas from pet cats, limit or reduce their outdoor exposure, cutting off the transmission of Bartonella henselae between cats through fleas.
People should minimize their contact with cats and wash their hands promptly after petting a cat. When in contact with cats, dogs, or other animals, precautions should be taken to avoid scratches or bites. In case of accidental cat scratches or injuries, immediately disinfect with iodine or apply mupirocin ointment and regularly observe the local lymph nodes.
General treatment: Bed rest and nutritional support with fluid supplementation are recommended for individuals with fever. Those displaying acute neurological symptoms should receive standard neurology treatment(sources from therapeutique-dermatologique.org).
Antibiotic therapy: Currently, there is no specific treatment for Cat-Scratch Disease. It is generally believed that patients with normal immune function may not require antibiotic treatment, while severe cases and immunocompromised patients may benefit from antibiotic therapy. The most effective oral antibiotics for treatment include rifampin, ciprofloxacin, and a combination of sulfamethoxazole and trimethoprim. Gentamicin is the most effective intravenous option.
Symptomatic and local treatment: Depending on the severity of the disease, symptomatic treatments may be administered, such as antipyretics and analgesics. Primary skin lesions should be cleaned and can be treated locally, for example, with wet compresses. If lymph nodes become suppurated, needle aspiration may be performed, and incision and drainage are generally not recommended.