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Copyright 2004 Tara K. Harper.  All rights reserved.

TKH Bacteriology Notes:
Cat Scratch Fever (CSD)  -- updated!

•  Description      •  Mechanism      •  Vaccine
•  Vector      •  Symptoms      •  Odds 'n' Ends
     •  Diagnosis      •  Author's Note
     •  Treatment      •  Links

Science and Literary  Links for Writers
Science and Technical  References for Writers

NOTE:  This file is for information only.  It is not intended for diagnosis.

Cat Scratch Fever (Cat Scratch Disease)

Description.  Cat-scratch fever, or cat scratch disease (CSD) is a controversial disease whose vector is not yet positively known.  The disease is usually contracted through the bite or scratch of a cat or kitten that carries the bacteria.  It's characterized by a brownish pustule or pimple at the bite/scratch site, and by swollen, tender lymph nodes.  Most patients (80% to 90%) are under the age of 17, and less than 50% of patients show mild fever or malaise.  It is a self-limiting disease, and most patients recover fully on their own.

The exact vector for the disease is not known.  Currently, the disease is thought to be caused by Bartonella henselae (possibly by Rochalimaea henselae).  Previously, in the 1980s, CSD was thought to be caused by the pleomorphic, gram-negative bacilli Afipia Felis, but this microorganism has been discredited.

Also, doctors do not yet know whether the complications associated with CSD are a result of infection with different strains of the same bacterial species, or a result of the function of the dose of bacteria you become infected with, or determined by the route by which you are infected, etc.

CSD is not a disease caused solely by cats, as was originally thought.  The disease has been confirmed in patients who have no history with cats, and/or who have been scratched by dogs, crab claws, barbed wire, cactus spines, etc.

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Vector.   The vector for CSD has not yet been positively and definitively identified.  However, several studies of small numbers of pet cats (numbers of cats in the studies ranged from 13-61 cats) have shown that 41-81% of cats living in households show evidence of being microbial reservoirs of B. henselae.  CSD was cultured directly from the cats and also cultured from cat fleas combed from cats which tested positive for the bacteria.

There is no experimental data to demonstrate that fleas (or ticks or other arthropods) act as vectors to humans for the disease.  However, researchers at the Texas Department of Health, Austin, (Jared M. Frandson, et al) have found that fleas, which carry the bacteria in their gut and excrete it in their feces, can transmit the bacteria between cats.

Part of the reason the exact vector isn't known is that researchers have not been able to culture the bacteria from scrapings from under the claws of infected cats.

Also, some patients with confirmed cases of cat scratch disease have had no contact with cats.  Cases of CSD have been confirmed in patients who have been scratched by dogs, crab claws, goats, squirrels, porcupine quills, cactus spines, and barbed wire.

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Mechanism.  -- not yet available.

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Symptoms.  Cat scratch disease is characterized by a subacute illness following the bite or scratch of a cat, usually that of a young kitten.  Symptoms of CSD are fairly consistent from case to case. About 10-15% of patients present with more systemic symptoms.  However, the latter cases may be presenting with symptoms of secondary, opportunistic infections, rather than CSD itself.

Symptoms of cat scratch disease include:   

1) A primary lesion which develops usually within 3-10 days of the bite or scratch, but which can take up to 30 days to develop.  The lesion is usually a single papule or pustule, about 2-5 mm in diameter.  In some cases, there are several lesions that look like pimples.  These usually last 1 to 4 weeks.

2) Infection of the lymph nodes (lymphadenopathy) in most patients, with swelling and tenderness of the nodes, which usually lasts 4 to 6 weeks.  The skin over the nodes may become red, tough, and warm.  Infection is commonly seen in the following lymph nodes:  axillary, inguinal, epitrochlear, cervical, and submandibular nodes.  Regional lymphadenopathy presents usually within 1-2 weeks of injury.

Other associated symptoms include (but are not limited to):
     •  low-grade fever - 50% of patients
     •  anorexia and/or weight loss
     •  nausea and vomiting
     •  sore throat
     •  splenomegaly (possibly)
     •  malaise and/or fatigue
     •  headache

The previous symptoms may be indicative of mild leukocytosis, eosinophilia, tuberculosis, brucellosis, and other conditions.  Leukocytosis is an abnormally large number of leukocytes--white blood cell count of 10,000 or more per cubic mm.  Eosinophilia means that there are organisms in the pulmonary system; these organisms can usually be seen on a chest x-ray.

Recently, doctors are beginning to recognize an increasing number of atypical manifestations of cat scratch disease.  About 5-10% of patients present with more systemic symptoms and atypical manifestations.  These include tonsillitis, encephalitis, myelitis, osteolytic lesions, arthritis, synovitis, pneumonia, etc.  Also, some patients present with short-lived, nonspecific maculopapular eruptions, erythema nodosum, figurate erythemas, and thrombocytopenic pupura.

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Diagnosis.   Diagnosis of cat scratch disease is usually made by three criteria:
  1. A typical histological appearance including lymphoid hyperplasia and granuloma formation with central areas of necrosis containing neutrophils.    
2. Positive cat-scratch blood test or biopsy of the infected lymph node.  The traditional skin test is no longer considered accurate.
3. Negative laboratory evaluation for other causes of adenopathy

Because CSD has been confirmed in patients who have had no contact with cats, a history of contact with a cat, and an associated scratch or eye lesion (caused by a cat) is no longer required for diagnosis of CSD.

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Treatment.  Most patients recover on their own and do not require treatment.  Recently, some antibiotics have been shown to shorten the course of the illness.  However, since most patients do recover well on their own, treatment is usually not administered except for immunosuppressed patients, such as cancer or AIDS patients.

Most patients fully recover in 2 to 5 months.  Occasionally, it can take up to a year for swollen lymph nodes to return to normal.

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Vaccine.  No vaccine has yet been developed.

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Odds 'n' Ends.
  The first description of cat scratch fever was published by a French doctor in 1889, Henri Parinaud.  The cat vector wasn't identified until 1931, by Dr. Robert Debre.  Debre is also the physician who coined the phrase "cat-scratch disease."    
Researchers have found that, depending on the region of the US they look into, an average of 25% to 41% of clinically healthy adult cats carry the bacteria that cause CSD.  For example, researchers have found that 40% of the cats in California are carriers of B. henselae, while 60% of cats in the southeast US carry the bacteria.  The lowest rates of cats with the bacteria (4% to 7%) have been found in colder regions of the US, in the midwest and great plains.  The speculation is that , in colder regions, there are fewer fleas to transmit the bacteria from cat to cat; however, this has not been confirmed
About 3/4 of all cases of cat scratch disease occur in fall or winter.  It is likely that, because cats are indoors more in foul and cold weather, the closer proximity to humans means more chances for humans to get scratched.

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Author's Note.  Cat scratch fever (cat scratch disease) is a bacterial, not a viral disease.  The title of my critically acclaimed science-fiction novel, Cat Scratch Fever, comes from the word-play.  In the novel, the main character's fever is caused by an engineered virus carried by cats.

In the novel, animals are used as hosts for a variety of engineered viruses which are used to slowly adjust human physiology to better survive alien environments.  Over the course of years of infections, a human becomes sensitized to and reacts best to the infections caused by viruses and bacteria carried by a specific animal host.  In the case of the main character, this is the felines.  The final set of human "mutations" are halted when the final virus is killed via infection with another engineered virus carried by the host animal (in this case, the cats).  If the final set of mutations are not halted, the prior infection continues to progress, symptoms become more extreme, and the patient usually dies.

The actual disease, cat-scratch disease (CSD), is currently thought to be caused by bacteria, and which can be complicated by secondary infections.

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Links.  Some sites with general information on CSD:
  Dr. Neal Chamberlain's Infections Diseases Lectures - Medically oriented cat scratch disease lecture notes on lymphoreticular and hematopoetic infections.    
Dr. Joseph R. Lex, Jr. MD - general, but technically oriented article on the disease, hosted by - clearly written description of the history and current knowlege of the disease.
Susan Little, DVM - another clearly written article on the disease, hosted by the Winn Feline Foundation.
Vetrinary Health Network - another source for general information about CSD.

Copyright 2004 Tara K. Harper

All rights reserved.  It is illegal to reproduce or transmit in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, any part of this copyrighted file without permission in writing from Tara K. Harper.  Permission to download this file for personal use only is hereby granted by Tara K. Harper.

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