A Kitten Scratch Was the Clue Behind a Transplant Patient’s Hidden Blood Infection and Rare Immune Storm

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RODRIGO ARANGUA | AFP via Getty Images Share on Twitter Share on Facebook Share on Pocket A small scratch from a kitten appears to have set off a dangerous chain of events for a young woman living with a transplanted kidney. Doctors in China reported that the 33-year-old developed hemophagocytic lymphohistiocytosis, a rare and potentially life-threatening immune overreaction, after the bacterium that causes cat scratch disease got into her bloodstream.

The newly published case report in BMC Infectious Diseases, from the Second Affiliated Hospital of Chongqing Medical University, describes how routine tests failed to find the culprit. Genetic sequencing of her blood finally pointed to Bartonella henselae, and the patient then recalled being scratched by a kitten about a month before she fell ill.

She recovered after treatment, and her transplanted kidney kept working.

The woman had received her kidney transplant about three years earlier and was taking oral drugs to keep her immune system from rejecting the organ. Those medications protect a transplant, but they also make it harder for the body to fight infections.

She came to the hospital with fever and headache. Doctors started her on carbapenems, a class of powerful broad-spectrum antibiotics often used for serious infections. Her fever did not break.

Tests then revealed a far more alarming picture. Her counts of red cells, white cells, and platelets had all dropped, a condition called pancytopenia. Her ferritin, an iron-storage protein that rises sharply during intense inflammation, was elevated, as was soluble interleukin-2 receptor, a marker of immune activation. A bone marrow sample showed hemophagocytosis, in which immune cells engulf other blood cells.

Together, those findings pointed to hemophagocytic lymphohistiocytosis, commonly called HLH.

HLH happens when the immune system becomes overactivated and floods the body with inflammatory signals. Some forms are inherited. In the familial form, according to the National Library of Medicine’s MedlinePlus, the excess immune activity damages the liver and spleen and destroys blood-producing cells in the bone marrow. In adults, HLH is more often secondary, meaning something else sets it off, such as an infection, cancer, or autoimmune disease.

Finding the trigger in this case proved difficult. Screening for common viruses, including Epstein-Barr virus and cytomegalovirus, came back negative, as did routine bacterial and fungal tests. Bartonella henselae grows slowly and is notoriously hard to catch with standard blood cultures.

The breakthrough came from metagenomic next-generation sequencing, a technique that reads all the genetic material in a blood sample and matches it against known microbes. The test identified B. henselae as the most likely cause. Only then did the kitten scratch, about a month before her symptoms began, come into focus.

The complication is very unusual, but it is not unheard of. A 2014 report in Pediatric Transplantation described an 11-year-old girl who developed HLH and multi-organ failure from a B. henselae infection 13 months after a kidney transplant. She also recovered.

Treating the case required a careful balancing act. Doctors stopped her immunosuppressive drugs for a time, a risky move in a transplant patient because it can raise the chance of organ rejection.

She received a short course of two antibiotics aimed at the bacterium, doxycycline and rifampin, and doctors used repeated sequencing of her blood to help decide how long to continue them. To calm the runaway immune response, she was given the steroid dexamethasone along with intravenous immunoglobulin, a treatment made from donated antibodies.

Her symptoms and blood counts improved. Six months later, the HLH had not returned, and her transplanted kidney was still functioning steadily.

The authors argue that B. henselae deserves a place on the list of possible infectious triggers when HLH appears after a kidney transplant. They also suggest that repeat sequencing may help doctors tailor how long antibiotics are needed.

As a single case report, it cannot show how often this happens or which treatment approach works best for other patients.

Cat scratch disease itself is far more common than its rare complications. A CDC analysis of insurance claims from 2005 to 2013 estimated that each year about 12,000 Americans under 65 receive an outpatient diagnosis and about 500 are hospitalized for it. Rates were highest in children ages 5 to 9.

According to the CDC, people usually become infected when scratched by a cat, especially a kitten, and the scratch is contaminated with flea droppings. Cats most often pick up the bacteria through flea bites. Bites or licks on an open wound can also spread the infection. Swollen lymph nodes typically appear one to three weeks after exposure.

People with weakened immune systems are at higher risk of severe disease. The CDC says they can still own cats but should avoid owning cats younger than 1 year. It also advises avoiding scratches, bites, and licks, especially from kittens and stray cats; keeping cats indoors; using flea prevention; and cleaning any scratch with soap and water.

The case offers a practical lesson for clinicians, too: asking about pets can supply a vital clue when an infection will not reveal itself. Transplant recipients who develop a fever after a cat scratch should contact their transplant team promptly.

A 33-year-old kidney transplant recipient developed HLH, a severe immune overreaction, after Bartonella henselae entered her bloodstream. She later recalled a kitten scratch about a month before her symptoms began.

Hemophagocytic lymphohistiocytosis is a rare condition in which the immune system becomes overactivated, causing fevers, falling blood counts, and possible organ damage.

Routine tests came up empty. Metagenomic sequencing of her blood identified the bacterium’s genetic material.

Is this complication common after a cat scratch?

No. Cat scratch disease is usually mild, and HLH triggered by it in transplant patients is very rare.

The CDC says people with weakened immune systems can own cats but should avoid cats under 1 year old, keep cats indoors, control fleas, and clean scratches right away.