What parasitic infections are prominently found in the United States?

Parasitic Infections Prominently Found in the United States

The most prominent parasitic infections found in the United States include babesiosis, tickborne rickettsial diseases, coccidioidomycosis, and strongyloidiasis. These infections represent significant public health concerns with varying geographic distributions across the country.

Babesiosis

• Babesiosis is primarily caused by Babesia microti in the United States, with cases concentrated in the Northeast and upper Midwest 1
• More recently, infections caused by Babesia duncani have been reported in California and Washington, while B. divergens-like organisms (including the MO-1 strain) have been detected in patients from Missouri, Kentucky, Washington, and Arkansas 1
• Diagnosis relies on microscopic examination of Giemsa-stained thick and thin blood films, which is considered the gold standard method 1
• This infection can progress to fatal outcomes if not diagnosed and treated accurately, making rapid and accurate laboratory testing essential 1

Tickborne Rickettsial Diseases

• Rocky Mountain Spotted Fever (RMSF), ehrlichioses, and anaplasmosis are significant tickborne rickettsial diseases in the United States 1
• These infections can occur in clusters among family members, coworkers, or persons frequenting particular common areas, especially those exposed to tick-infested habitats 1
• Diagnosis typically involves serologic testing, with the immunofluorescence assay (IFA) considered the gold standard 1
• PCR testing of whole blood specimens is particularly useful for confirming Human Monocytic Ehrlichiosis (HME), Human Granulocytic Anaplasmosis (HGA), and E. ewingii infection due to the tropism of these pathogens for circulating white blood cells 1

Coccidioidomycosis

• Coccidioidomycosis (Valley Fever) is caused by Coccidioides immitis or Coccidioides posadasii, which reside in soil in parts of central and southern California, Arizona's low deserts, southeastern New Mexico, western Texas, and several other areas of the southwestern United States 1
• Recently, unexpected endemic pockets have been found in southeastern Washington State, indicating that exposure may occasionally occur elsewhere in the Western United States 1
• Of the estimated 150,000 infections that occur annually in the US, approximately 50,000 produce illness warranting medical attention 1
• From 1998 to 2011, reported cases from endemic states rose 10-fold due to various factors, with considerable year-to-year variation related to climatic conditions 1

Strongyloidiasis

• Strongyloidiasis, caused by Strongyloides stercoralis, has a reported seroprevalence of approximately 4% in the United States, with most cases occurring in immigrants 2
• The parasite has been modeled to have suitable habitat in ten states beyond the southeastern United States where it has been recorded, including states on the south, east, northeast, and west coasts 3
• Strongyloidiasis is particularly concerning because of its ability to cause autoinfection and potentially fatal hyperinfection syndrome in immunocompromised individuals 2, 4
• Ivermectin is the drug of choice for treatment, with significantly greater efficacy than alternative agents such as albendazole 5

Filariasis

• While not endemic to the United States, filariasis cases are occasionally diagnosed in immigrants and travelers 6
• Diagnostic challenges include significant cross-reactivity among helminths in serological testing, which can decrease specificity of antibody tests 6
• Nucleic acid amplification tests (NAATs) may offer higher specificity for differentiating between filarial species when cross-reactivity is a concern 6

Risk Factors and Prevention

• For coccidioidomycosis, residence or travel to endemic regions is the primary risk factor, with yearly serologic screening and chest radiography recommended for patients within endemic regions 1
• For strongyloidiasis, risk factors include HTLV-1 infections, hypogammaglobulinemia, immunosuppressant use (particularly steroids), alcoholism, and malnutrition 2
• For tickborne diseases, exposure to tick-infested habitats through recreational or occupational activities is the main risk factor 1
• For babesiosis, exposure to ticks in endemic regions, particularly in the Northeast and upper Midwest, represents the primary risk 1

Diagnostic Considerations

• For parasitic infections, a combination of microscopic examination, serological testing, and molecular methods is often necessary for accurate diagnosis 1, 6
• Serological tests may show cross-reactivity between related organisms, potentially impeding epidemiologic distinction between infections 1
• PCR and other molecular methods can provide rapid diagnosis but may have variable sensitivity depending on the timing of sample collection and prior antibiotic treatment 1

By understanding the geographic distribution and clinical characteristics of these parasitic infections, healthcare providers can better recognize, diagnose, and treat these conditions in affected patients across the United States.