9-year-old Female with Fever and Headache

Presented by:

Dr. D. Yamamura¹ and Mr. L. Wilcox²
¹MDS Laboratories and ²Hamilton Regional Laboratory Medicine Program

Clinical Case:

A previously healthy 9-year-old female was admitted to Children's Hospital with a 10 day history of fever up to 103ºF and headache. The patient developed a raised red rash with some pustules 7 days prior to admission beginning on her lower extremities and soles of her feet progressing to involve her upper extremities, palms, face and trunk. Multiple joints involving her right hand, left hand, right elbow, left wrist, left shoulder and bilateral knees and ankle joints were red and swollen. The polyarthritis was asymmetric and migratory. The patient denied any history of arthritis. There was no preceding dairrheal or respiratory illness. The patient was not sexually active and had not travelled. There was no significant past medical history. A maternal aunt had rheumatoid arthiritis. The patient was on Acetaminophen and Ibuprofen. All members of her family had a recent upper respiratory infection. The patient had a pet rat.

On physical examination, the patient appeared toxic and listless. She had temperature of 36.9ºC and had an elevated heart rate. The respiratory and cardiovascular examination was unremarkable. Swelling, erythema and decreased ROM were seen in multiple joints. Pustular lesions were seen on the soles of her feet. There was no enlargement of her lymph nodes, or lesions in the oral cavity.

Laboratory investigation revealed that the patient had a WBC 8.3, Platelets 328, ESR 85, CRP 168, and a negative ASOT. Rheumatoid factor was normal. Joint aspirate of her knee showed 45.5 x 10⁹ nucleated cells/L with 89% neutrophils. One of 2 sets of blood cultures using the BACTEC 9240 (Bectom Dickson Microbiology Systems) became positive after 28 hours of incubation. The gram stain revealed a moderate to large, pleomorphic gram negative bacilli (GNB) with long filaments and irregular swellings (Figure 1). Aspirate of the right knee did not reveal any organisms by gram stain and the culture was negative. A pleomorphic GNB was seen on the gram stain of a swab of a pustule on the right foot.

The patient was treated with intravenous penicillin and gentamicin and improved clinically. A transthoracic echocardiogram did not reveal endocarditis. The patient was discharged home on amoxicillin.

Results from further microbiology investigations are summarized. The blood culture was sub-cultured to sheep blood agar (SBA) incubated anaerobically, chocolate agar (CA) incubated in 5% CO2, and MacConkey agar (MAC) with crystal violet incubated aerobically. No growth was seen on MAC or CA. Pinpoint growth was seen at 48 hours on SBA. The colonies were round, smooth, and gray. Initial work-up revealed a catalase and oxidase-negative organism. No reaction was seen on standard biochemical tests. The organism was incubated in supplemented thioglycollate broth (Figure 2). Further biochemical tests were performed. A reference laboratory confirmed the identification.

Questions:

What are the possible infectious and non-infectious causes of rash, fever, and polyarthritis? After viewing the gram stain what are the most likely cause(s)?
What zoonotic (animal) sources have been linked to this syndrome?
In a routine microbiology laboratory, what further tests and supplementation would aid in the diagnosis of this organism? What reaction do you see with the thioglycollate broth and what organism is most likely given the reaction? What other diagnostic modalities are available to confirm the identification?
What are L-forms and what implication does this have for treatment?
What clinical complications have been reported with this syndrome?

Figures:


Figure 1: Gram stained smear of isolate on blood agar medium	Figure 2: Supplemented Thioglycollate Broth

Discussion:

This is a case of Rat-bite Fever caused by Streptobacillus moniliformis. Rat-bite Fever can also be caused by another gram-negative bacillus, Spirillum minus. Infection with S. monilformis is characterized by the sudden onset of fever, sweats, headache and muscle aches typically followed by polyarthritis and a rash. The rash can be raised and red, vesicular, or pustular. The distribution of the rash is an important clinical clue as the extremities, the soles of feet, and palms are frequently involved. Rarely, the rash and arthritis are absent. Endocarditis is a rare complication with increased mortality of up to 50%. Other unusual manifestions such as genital tract infection, meningitis, amnionitis, pericarditis have been reported.

Infection caused by S. moniliformis is rare. It is not a reportable disease so the incidence is unknown. It is a zoonosis with transmission either by direct contact with a rat (Rat-bite Fever), usually a bite or scratch, or by ingestion of water or milk contaminated by rat urine or feces (Haverhill fever). Rarely, other animals such as guinea pigs, mice, squirrels and gerbils have been implicated. Colonization of the nasopharynx in wild rats is reported to be higher than rates in laboratory rats and the majority of reported cases are due to exposure to wild rats. Colonization rates in pet rats are not known. This patient had a pet rat and had also been exposed to her friend’s two young rats. Although there was no bite the patient did sustain some scratches from the young rats.

The differential diagnosis of rash and polyarthritis includes infectious and non-infectious causes. Other important bacterial causes are N. gonorrhoeae (disseminated gonococcal disease), N. meningitides, and H. influenzae. Viral pathogens such as rubella and parvovirus B12 can also cause rash and polyarthritis. Reiter’s syndrome, which likely occurs due to an immune response to an infectious agent such as Chlamydia trachomatis or following bacterial infectious gastroenterititis, can cause a polyarthritis; however, it is unusual to have a raised red or pustular rash. Rheumatoid arthritis is the non-infectious syndrome most likely to be misdiagnosed.

S. moniliformis is a highly pleomorphic gram negative bacilli measuring 0.3-0.5 µm by 1-5 µm with long unbranching filaments up to 150 µm and unusual fusiform swellings described as monilaceous. It is oxidase-negative, catalase-negative, and did not grow on MacConkey. It is nutritionally fastidious and will look inert with standard biochemical tests. Enrichment with sterile horse serum to a final concentration of 10% was performed and the following biochemical reactions were seen after aerobic incubation at 35°C for up to 7 days:

Weak acid production on the slant and butt of TSI;
Moeller decarboxylases: arginine positive, lysine negative, ornithine negative;
Andrade’s peptone water based carbohydrates: fermentation of dextrose, maltose but no reaction with sucrose or lactose;
Esculin showed weak hydrolysis. Characteristic colonies of S. moniliformis resembling small puffballs were seen in supplemented thioglycollate broth.

Based on the CDC description, the organism was reported as presumptive S. moniliformis. The organism was sent to Toronto Public Health Laboratory and the cellular fatty acid (CFA) composition showed a very high match with a reference strain of S. moniliformis. Swabs of the nares of the rats were also taken. One rat grew an oxidase-negative and catalase-negative gram negative bacillus. Although the organism was not pleomorphic on gram stain, cellular fatty acid showed the isolate was similar to S. moniliformis.

Interestingly, this organism has the ability to revert to L-forms. L-forms are atypical morphotypes that have lost their cell wall. They are able to divide and have a fried-egg colony morphology on agar. S. moniliformis is known to revert to L-forms and this may explain why culture of the joint fluid is usually negative. L-forms were not isolated with this patient. L-forms are not susceptible to penicillin and other antibiotics with activity against the cell wall. Erythromycin or an aminoglycoside (in combination with penicillin) have been shown to have in-vitro activity against other organisms with L-forms. This patient was treated with penicillin and gentimicin followed by oral amoxicillin. She continues to do well 1 year after her hospitalization.

References:

CDC. Streptobacillus moniliformis. In: Clark WA, Hollis DG, Weaver RE, Riley P, eds. Identification of unusual pathogenic gram-negative aerobic and facultatively anaerobic bacteria. Atlanta, Georgia: US Department of Health and Human Services, CDC, 1984:288-9.
Feingold DS. Biology and pathogenicity of microbial spheroplasts and L-forms. N Engl J Med 1969;281:1159-70.
Holroyd KJ, Reiner AP, Dick JD. Streptobacillus moniliformis polyarthritis mimicking rheumatoid arthritis: An urban case of rat bite fever. Amer J Medicine 1988;85:711-14.
Rupp ME. Streptobacilus moniliformis endocarditis: case report and review. CID 1992;14:769-72.
Ryan WM, Nims L, Keller DW, et al. Rat-bite Fever – New Mexico, 1996. JAMA 1998;279:740-1.
Shanson DC, Gazzard BG, Midgley J, et al. Streptobacillus moniliformis isolated from blood in four cases of Haverhill Fever. Lancet 1983;92-4.
Smith JW and Hasan MS. Infectious arthritis. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Disease, 5th ed. Churchill Livingstone, 2000: 1175-82.