Overview
Definition:
Zoonoses are infectious diseases that are transmitted from animals to humans
This section focuses on three common pediatric zoonotic infections: Cat Scratch Disease (CSD), Rat-Bite Fever (RBF), and Leptospirosis
CSD is caused by Bartonella henselae, typically transmitted via cat scratches or bites
RBF can be caused by Streptobacillus moniliformis or Spirillum minus, transmitted through rodent bites or scratches, or ingestion of contaminated food/water
Leptospirosis is caused by Leptospira species, transmitted via direct contact with infected animal urine or indirectly through contaminated soil or water.
Epidemiology:
CSD is the most common cause of chronic lymphadenopathy in children and adolescents, with an estimated incidence of 0.1-0.8 per 100,000 population in the US
Cats, particularly kittens, are the primary reservoir
RBF is less common but can be endemic in areas with high rodent populations
outbreaks can occur
Leptospirosis is a global zoonosis, particularly prevalent in tropical and subtropical regions, affecting farmers, veterinarians, and children with outdoor exposure
Worldwide, estimates suggest millions of human cases annually.
Clinical Significance:
Understanding pediatric zoonoses is crucial for accurate diagnosis and timely management
These infections can present with a wide spectrum of illness, from mild, self-limiting febrile illnesses to severe, life-threatening conditions affecting multiple organ systems
Delayed diagnosis can lead to significant morbidity, including neurological sequelae, hepatic and renal dysfunction, and prolonged hospitalization
Effective history taking, physical examination, and targeted investigations are paramount for distinguishing these from other common pediatric illnesses.
Cat Scratch Disease
Definition:
Cat Scratch Disease (CSD) is an infectious disease caused by the bacterium Bartonella henselae, transmitted primarily by cats, especially kittens, through scratches or bites.
Pathogen:
Bartonella henselae is a Gram-negative facultative intracellular bacterium.
Transmission:
Transmitted through cat scratches or bites
fleas are vectors
Inoculation occurs at the site of scratch/bite.
Incubation Period:
Typically 3-14 days for the primary lesion, and 2-6 weeks for lymphadenopathy.
Clinical Features:
Primary inoculation lesion (papule or pustule) at the scratch site
Regional lymphadenopathy, usually unilateral and tender, is the hallmark
Constitutional symptoms may include fever, malaise, headache, and anorexia
Ocular manifestations (Parinaud's oculoglandular syndrome) and systemic complications are less common but significant.
Rat Bite Fever
Definition:
Rat-Bite Fever (RBF) is an infection caused by bacteria commonly found in rodents, transmitted through bites or scratches, or by consuming contaminated food or water.
Pathogens:
Two main types: Streptobacillus moniliformis (SM-RBF) and Spirillum minus (S-RBF)
SM-RBF is more common in the US and Europe, S-RBF more common in Asia.
Transmission:
Bites or scratches from infected rodents (rats, mice, squirrels)
Contaminated food or water ingestion for SM-RBF.
Incubation Period:
SM-RBF: 3-10 days
S-RBF: 7-21 days.
Clinical Features:
Abrupt onset of fever, chills, headache, myalgias, and rash (maculopapular or petechial)
Polyarthralgias or arthritis are common
A specific lesion at the bite site may be absent in SM-RBF, while in S-RBF, a localized pustular or ulcerative lesion with regional lymphadenopathy is often present
Untreated RBF can lead to serious complications.
Leptospirosis
Definition:
Leptospirosis is a systemic infection caused by pathogenic spirochetes of the genus Leptospira, acquired through direct contact with the urine of infected animals or indirectly through contaminated water or soil.
Pathogen:
Leptospira species, particularly L
interrogans serovars.
Transmission:
Contact with urine from infected animals (rodents, dogs, cattle, wildlife) or contaminated environments (water, soil)
Enters through skin abrasions, mucous membranes, or ingestion.
Incubation Period:
Typically 2-30 days, with an average of 7-14 days.
Clinical Features:
Biphasic illness
Phase 1 (leptospiremic): sudden onset fever, chills, severe headache, myalgias (especially calf and lumbar pain), conjunctival suffusion, anorexia, nausea, vomiting
Phase 2 (immune): occurs after a brief remission, characterized by fever, organ involvement (meningitis, uveitis, rash, pulmonary hemorrhage, liver dysfunction - jaundice, renal failure - anuria/oliguria)
The severe form, Weil's disease, is characterized by jaundice, renal failure, and hemorrhage.
Diagnostic Approach
History Taking:
Detailed history of animal contact (pets, stray animals, rodents), outdoor activities (swimming in fresh water, gardening, farming), recent travel, occupation, and tick/flea exposure
For CSD, inquire about cat ownership and exposure to kittens
For RBF, ask about rodent encounters or bites
For Leptospirosis, focus on exposure to potentially contaminated water or soil, or animal urine
Assess timeline of symptom onset and progression.
Physical Examination:
Thorough examination focusing on skin lesions (papules, pustules, rashes at bite sites), lymphadenopathy (location, size, tenderness), fever, conjunctival injection, muscle tenderness, hepatosplenomegaly, and signs of organ system involvement (neurological deficits, jaundice, respiratory distress, oliguria/anuria).
Investigations:
CSD: Serological tests (IgM/IgG ELISA, indirect immunofluorescence assay - IFA) for B
henselae antibodies are gold standard
PCR on biopsy tissue can also be used
RBF: Blood cultures for S
moniliformis (difficult to grow)
Serology for both S
moniliformis and S
minus
PCR on blood or tissue
Leptospirosis: Serology (microscopic agglutination test - MAT is the gold standard, ELISA, IgM/IgG)
PCR on blood or urine during the first week of illness
Culture of blood, urine, or cerebrospinal fluid (CSF) is possible but slow.
Differential Diagnosis:
CSD: Other causes of lymphadenopathy (tuberculosis, viral infections, other bacterial infections, malignancy)
RBF: Other febrile illnesses with rash and joint pain (viral exanthems, meningococcemia, rheumatic fever, Lyme disease)
Leptospirosis: Dengue fever, malaria, viral hepatitis, typhoid fever, hantavirus pulmonary syndrome, other bacterial sepsis
The combination of fever, myalgias, and conjunctival suffusion is suggestive of leptospirosis.
Management
Initial Management:
Supportive care is the cornerstone
Hydration, antipyretics (paracetamol, ibuprofen) for fever and pain
Isolation is generally not required for CSD or RBF, but standard precautions for leptospirosis
Monitor vital signs and organ function closely.
Medical Management:
CSD: Antibiotics are not routinely indicated for uncomplicated CSD, as it is often self-limiting
However, for severe disease, prolonged lymphadenopathy, or systemic complications, azithromycin (10 mg/kg once daily for 5 days) is the preferred agent
Other options include doxycycline, rifampin, or trimethoprim-sulfamethoxazole
RBF: Antibiotic therapy is essential
SM-RBF: Penicillin G or ampicillin, or doxycycline, azithromycin, or fluoroquinolones
S-RBF: Penicillin G or ampicillin is typically effective
Doxycycline is an alternative
Leptospirosis: Mild cases can be managed with doxycycline (4-10 mg/kg/day divided q12h for 7-14 days
max 100 mg/dose) or amoxicillin
Severe cases require intravenous antibiotics, typically penicillin G (1.5 million U/kg/day divided q6h), ceftriaxone (100 mg/kg/day divided q12-24h), or doxycycline (5-10 mg/kg/day divided q12h).
Surgical Management:
Rarely indicated
Incision and drainage of abscesses that may form in severe CSD or RBF cases
For leptospirosis, supportive measures for organ failure are critical
dialysis may be required for renal failure.
Supportive Care:
Pain management with analgesics
Nutritional support
Adequate fluid intake
Monitoring for signs of organ compromise (neurological, renal, hepatic, pulmonary)
Management of complications such as encephalitis, endocarditis, or disseminated intravascular coagulation (DIC) requires intensive care.
Complications
Early Complications:
CSD: Parinaud's oculoglandular syndrome, encephalitis, osteomyelitis, hepatitis, splenomegaly, endocarditis
RBF: Endocarditis, glomerulonephritis, myocarditis, hepatitis, meningitis, sepsis
Leptospirosis: Renal failure, hepatic dysfunction (jaundice), pulmonary hemorrhage, ARDS, myocarditis, meningitis, rhabdomyolysis, DIC.
Late Complications:
CSD: Chronic lymphadenopathy, uveitis, arthralgia
RBF: Chronic joint pain
Leptospirosis: Post-leptospirosis arthritis, uveitis, chronic fatigue.
Prevention Strategies:
For CSD: Educate owners on proper cat handling, avoid rough play with kittens, prompt wound cleaning after scratches/bites
For RBF: Rodent control measures, avoiding contact with rodents, immediate wound care after bites/scratches
For Leptospirosis: Avoid contact with stagnant water and potential animal urine
wear protective footwear in endemic areas
proper sanitation and rodent control.
Prognosis
Factors Affecting Prognosis:
Prompt diagnosis and initiation of appropriate treatment significantly improve prognosis
Severity of initial illness, presence of comorbidities, and development of complications like organ failure are key determinants
Young children may be more vulnerable to severe manifestations.
Outcomes:
Most cases of CSD and mild RBF resolve with supportive care and/or antibiotics
Leptospirosis has a mortality rate of 5-15% in severe (Weil's disease) forms, but overall mortality is lower with timely treatment
Sequelae can occur if complications are severe.
Follow Up:
Follow-up is important to monitor for resolution of symptoms and to identify any late complications, especially for leptospirosis and severe CSD/RBF
Patients with renal or hepatic involvement require prolonged monitoring
Resolution of lymphadenopathy in CSD can take weeks to months.
Key Points
Exam Focus:
Remember the characteristic triad of CSD: inoculation lesion, regional lymphadenopathy, and fever
For RBF, think of fever, rash, and arthralgia/arthritis after rodent exposure
Leptospirosis presentation varies from mild flu-like illness to severe multiorgan failure
conjunctival suffusion, myalgias, and fever are key early signs.
Clinical Pearls:
Always inquire about animal contact in children with unexplained fever and lymphadenopathy or rash
A history of exposure to rodents or contaminated water/soil should prompt consideration of RBF and leptospirosis respectively
Early recognition of leptospirosis is vital due to its potential for rapid deterioration.
Common Mistakes:
Misdiagnosing zoonotic infections as more common pediatric illnesses (e.g., viral exanthems)
Delaying antibiotic treatment for RBF and leptospirosis, which can lead to severe complications
Underestimating the severity of leptospirosis and its potential for rapid progression to multiorgan failure.