Man’s Best Friend?

Abstract & Commentary

Synopsis: A 7-week-old infant developed purulent Pasteurella multocida meningitis that was originally thought to be caused by Haemophilus influenzae type b. The infection was believed to be transmitted by the fingers of a sibling that had been licked by a pet dog in the home.

Source: Wade T, et al. Pasteurella multocida meningitis in infancy—(a lick may be as bad as a bite). Eur J Pediatr 1999; 158:875-878.

Pasteurella multocida, a gram-negative coccobacillus, is the most common agent cause of local infections after a dog or cat bite. Approximately 70-90% of cats and 55% of dogs have this organism in their mouths. Meningitis caused by this organism is unusual, particularly in infants younger than 12 months of age, and a total of only 23 cases were reported in the literature between 1963 and 1996. Wade and associates from St. Mary’s College in London describe a seven-week-old infant who presented with fever, irritability, and a bulging fontanelle. Lumbar puncture revealed purulent cerebrospinal fluid (CSF) that contained gram-negative rods. CSF rapid antigen screen was positive for Haemophilus influenzae type b. Blood culture was also reported to be positive for H. influenzae type b. The child was treated with cefotaxime and, after a stormy course, recovered but was left with neurological sequelae.

Since 1995 any H. influenzae organism that is recovered from the blood or CSF in the United Kingdom is sent to a reference lab in Oxford for validation. Extensive testing showed that the organism was P. multocida, not H. influenzae.

The family of this child owned two dogs and one cat but there was no direct contact between the infant and a pet (no history of licking or of a bite or scratch). Later questioning revealed that a 2-year-old brother whose hands were often licked by the dogs had been seen trying to comfort the infant by letting the baby suck on his fingers.

Comment by Robert Baltimore, MD, FAAP

Wade et al note that of the 23 cases of P. multocida meningitis in infants that have been reported, 12 of the infants had exposure to dogs, eight cases had exposure to cats (3 were exposed to both), three cases had no animal contact information, and in only two cases did the parents specifically deny the possibility of any animal contact. In only two cases was there a history of a bite or scratch; in the other 15 there was only possible salivary contact. The probable mechanism for these infections in the absence of a bite or scratch may be that the pet licks the hands of a family member who then transmits the organism to the baby’s mouth, who, in turn, may develop pharyngeal colonization followed by invasion and hematogenous spread to the meninges.

P. multocida meningitis or sepsis is frequently misdiagnosed as H. influenzae or Neisseria meningitidis by microscopy or culture, but definitive identification can be made on the basis of characteristic fermentation patterns. The reason for the false-positive rapid antigen screen test in this case is not clear.

The widespread use of HiB vaccine has virtually eliminated infections with H. influenzae type b in the United States and the United Kingdom, and the occurrence of a case of invasive infection apparently caused by this organism should raise suspicion that something else may be going on.

This case and the others reported in the literature emphasize that there is a risk of having pets in households where there are infants. Nearly all of these cases are preventable by reminding parents in these homes that young infants should not come in close contact with the saliva of dogs and cats, and the rest of the family should be assiduous about hand washing, especially if they might put their fingers in the baby’s mouth.

A final point concerning P. multocida in older people. The organism can be responsible for severe and even fatal invasive infections in immunocompromised and asplenic individuals.1 (Dr. Baltimore is Professor of Pediatrics, Epidemiology, and Public Health, Yale University School of Medicine.)

Reference

1. Mellor DJ, et al. Man’s best friend: Life threatening sepsis after minor dog bite. BMJ 1997;314:129-130.

Pasteurella multocida:

a. is more commonly found in the mouths of pet dogs than pet cats.

b. may be mistaken for Haemophilus influenzae by microscopy or culture.

c. infections in infants are usually associated with a dog or cat bite.

d. is a common cause of meningitis in infants.