Febrile Rocky Mountain Spotted Fever: Overview

In this section, Dr. Lilian, a pediatric infectious disease specialist from UFMG, discusses Rocky Mountain spotted fever (RMSF), caused by the gram-negative bacterium Rickettsia rickettsii. She highlights its prevalence in Brazil and its transmission through infected ticks.

Transmission and Diagnosis

• RMSF is an acute febrile disease caused by the gram-negative bacterium Rickettsia rickettsii. The challenge lies in diagnosing it promptly due to potential severity.

• The disease is transmitted through the bite of infected ticks, including those found on dogs, capybaras, and horses. Humans can also act as carriers of the disease.

Geographic Distribution and Risk Factors

• RMSF primarily occurs in the Americas, with Brazil's Southeast region being a hotspot. States like São Paulo, Rio de Janeiro, Espírito Santo, Bahia, and Santa Catarina are most affected.

• Children under 10 years old and adults aged 40-64 face higher risks of contracting RMSF. Mortality rates are elevated among children under 10 and individuals over 70 years old.

Seasonal Patterns and Prevention

• The disease peaks during colder months (June to October) when ticks proliferate in grassy areas near water sources. Rural residents with animal exposure are at higher risk.

• Early diagnosis and prompt treatment significantly impact mortality rates. Initiating therapy within three days of symptom onset reduces mortality risks.

Pathogenesis of Rocky Mountain Spotted Fever

Dr. Lilian delves into the pathophysiology of RMSF, emphasizing the importance of early treatment initiation to mitigate severe outcomes.

Vector-Borne Transmission

• Tick species like Amblyomma sculptum play a crucial role in transmitting Rickettsia rickettsii to mammals such as horses, capybaras, dogs, and humans.

• Untreated cases exhibit mortality rates ranging from 20% to 30%, underscoring the urgency of timely diagnosis and intervention to prevent fatal outcomes.

Human Infection Dynamics

• Ticks become infected with Rickettsia rickettsii through vertebrate hosts before transmitting it to humans via blood meals. Early attachment duration influences infection risk.

• Crushing an infected tick can also lead to transmission if residual body parts containing Rickettsia remain embedded in the skin post-crushing.

Disease Progression

• Following transmission via tick bites or crushed remnants, Rickettsia invades vascular endothelial cells leading to endothelial dysfunction across various organs.

• Lymphatic dissemination precedes systemic circulation of Rickettsia within host bloodstreams, culminating in multiorgan dysfunction characteristic of severe RMSF cases.

Symptoms and Pathophysiology of Rocky Mountain Spotted Fever

This section discusses the symptoms and pathophysiology of Rocky Mountain Spotted Fever, focusing on the inflammatory response, coagulation cascade, vascular alterations, and clinical manifestations.

Symptoms and Inflammatory Response

• The disease triggers an inflammatory response in the acute phase, leading to the release of inflammatory mediators and affecting vascular endothelial mobility and integrity.

Coagulation Cascade and Thrombosis

• The condition initiates a coagulation cascade resulting in thrombosis in some blood vessels, necrosis of tissues, and potential coagulation disorders.

Vascular Alterations and Fluid Leakage

• Vascular changes cause increased capillary permeability, leading to fluid leakage from vessels into interstitial spaces. This can result in hypovolemia, shock, hypoalbuminemia, and elevated antidiuretic hormone levels causing hyponatremia.

Clinical Manifestations and Diagnosis of Rocky Mountain Spotted Fever

This section delves into the clinical manifestations of Rocky Mountain Spotted Fever, emphasizing the importance of recognizing the incubation period variability, common symptoms like fever and headache, differential diagnosis challenges with viral infections like dengue fever.

Incubation Period and Symptom Onset

• The incubation period ranges from two to 14 days but typically manifests within four to six days post-exposure to ticks. Early symptoms include fever, headache, myalgia (muscle pain), malaise (discomfort), vomiting, anorexia (loss of appetite), photophobia (light sensitivity).

Differential Diagnosis Challenges with Dengue Fever

• Initial symptoms closely resemble those of dengue fever prevalent in Brazil during early months. Distinguishing between both diseases is crucial due to similar symptomatology; however, considering seasonal prevalence aids differentiation.

Diagnosis Considerations for Rocky Mountain Spotted Fever

This segment focuses on diagnostic considerations for Rocky Mountain Spotted Fever concerning patient history regarding tick bites or exposure as well as the significance of eschars in pediatric cases.

Importance of Patient History

• A history of tick bites within two to 14 days is pivotal for diagnosis. Approximately one-third may lack this history; hence other diagnostic clues are essential.

Eschar Presence in Pediatric Cases

• Eschars are prevalent among children under ten years old but absent in around 10-12% cases. Their appearance typically occurs two to five days after fever onset starting at ankles/wrists then spreading centrifugally towards limbs' extremities.

Neurological Symptoms and Laboratory Findings

This section discusses neurological symptoms associated with vascular compartment treatments, such as cerebral edema leading to confusion, delirium, seizures, and coma. It also touches upon meningeal signs and altered cerebrospinal fluid (CSF) composition.

Neurological Symptoms

• The increase in vascular permeability can lead to dehydration, hypoglycemia, pre-renal insufficiency, and renal failure. CSF analysis may show altered cell counts and protein levels.

Laboratory Findings

• Common laboratory findings include leukocytosis or leukopenia with left shift, thrombocytopenia, hyponatremia, elevated transaminases, and possibly elevated bilirubin.

Diagnostic Considerations and Epidemiological Data

This part emphasizes the importance of considering epidemiological data for diagnosis. It highlights the need for recognizing infection seasonality and understanding tick exposure history.

Diagnostic Insights

• Laboratory tests should be interpreted cautiously due to nonspecific findings early in the disease course. Fever may be present along with potential thrombocytopenia or leukocytosis.

Epidemiological Data

• Understanding tick exposure history within the last 14 days is crucial. Early diagnosis is challenging due to nonspecific symptoms; close monitoring is necessary before confirming a diagnosis.

Diagnosis Confirmation and Treatment Initiation

This segment focuses on confirming diagnoses through serological methods like indirect immunofluorescence assay after 7-10 days of illness onset. Early treatment initiation is vital for successful outcomes.

Diagnosis Confirmation

• Serology testing for antibodies becomes reliable after 7-10 days post-onset; initial tests may yield false negatives. Serial testing over weeks aids in accurate diagnosis confirmation.

Treatment Initiation

• Immediate treatment initiation upon suspicion is crucial for better outcomes. Tetracyclines are first-line choices; doxycycline orally or intravenously based on disease severity are common options.

Treatment Regimen and Dosage Guidelines

Details regarding tetracycline dosages for adults and children are discussed alongside treatment duration considerations post-fever resolution.

Treatment Regimen

• Doxycycline oral therapy typically lasts 5-7 days post-fever resolution; intravenous therapy might be necessary in severe cases without effective oral intake.

Dosage Guidelines

• Adult dosage: 100mg every 12 hours orally for 5-7 days; pediatric dosage: 2.2mg/kg every 12 hours orally until adult dose equivalence.

Dosage Recommendations for Children

In this section, the speaker discusses dosage recommendations for children when administering medication.

Dosage Recommendations

• For children, it is recommended to provide soluble tablets that can be diluted in water or saline solution, especially for those who have difficulty swallowing pills.

• Older children can take adult-sized tablets whole. When unavailable, Chloramphenicol is a common intravenous option due to its effectiveness in treating patients.

Treatment Considerations for Rocky Mountain Spotted Fever

The discussion focuses on treatment considerations specific to Rocky Mountain Spotted Fever (RMSF).

Treatment Insights

• Contrary to previous beliefs, Doxycycline can be safely used in children without causing dental enamel issues during a 5 to 7-day treatment period.

• Chloramphenicol is less favored due to lower efficacy and higher hematological toxicity compared to Doxycycline. It has been associated with increased mortality risk in some studies.

Prophylaxis and Management Strategies

This part covers prophylactic measures and management strategies for RMSF.

Prophylaxis Guidelines

• Antibiotic prophylaxis is not recommended except in cases of tick bites where patients are asymptomatic. Prophylaxis only delays symptom onset, complicating diagnosis.

• Individuals bitten by ticks should wait out the incubation period before assessing symptoms. Prevention involves avoiding tick exposure by staying away from endemic rural areas and wearing protective clothing like long sleeves and boots.

Preventive Measures and Body Examination

The focus here is on preventive actions against RMSF transmission and the importance of body examinations.

Preventive Actions

• Primary prevention involves minimizing contact with ticks through mechanical protection like appropriate clothing choices.

• Regularly inspecting the body every three hours to promptly remove any attached ticks reduces infection risks. Proper tick removal with tweezers minimizes infection chances.

Final Considerations on Diagnosis and Mortality Rates

Final thoughts encompass high mortality rates attributed to delayed diagnosis and treatment initiation in Brazil compared to the United States.

Key Takeaways

• High mortality rates in Brazil stem from delayed diagnosis and appropriate therapy initiation. Healthcare professionals must consider RMSF diagnosis, especially between June and October when tick proliferation peaks.