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Human spotted fever rickettsial infections

Emerging Infectious Diseases, April, 2005 by George B. Schoeler, Cecilia Moron, Allen Richards, Patrick J. Blair, James G. Olson

Serum specimens from patients at 4 sites in Peru were tested for evidence of spotted fever group rickettsial infection. Results showed that 30 (18%) of 170 patients had spotted fever group rickettsial infections, which likely caused their illnesses. These findings document laboratory-confirmed spotted fever from diverse areas of Peru.

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Rickettsial spotted fever was first described in South America in 1931 in Sao Paulo, Brazil (1). The etiologic agent, Rickettsia rickettsii, and the tick vector, Amblyomma cajenennse (the Cayenne tick), were subsequently identified. Serologic evidence of R. rickettsii infections has been documented in several countries in South and central America, including Argentina (2), Brazil and Uruguay (3), Colombia (4), Costa Rica (5), Panama (6), and Mexico (7). A recent study documented for the first time serologic evidence for spotted fever group (SFG) Rickettsia infections in 1 region of northern Peru (8). We describe serologic evidence of SFG rickettsial infections in diverse areas of Peru, including laboratory-confirmed infections among patients with clinical febrile disease.

The Study

Serum samples were obtained from 4 areas in Peru: Chiclayito and Salitral (Piura Department); La Merced (Junin Department); and Cusco (Cusco Department) (Figure). Chiclayito is a small village (population 6,133) [approximately equal to] 30 m above sea level on the outskirts of the city of Piura in the northern coastal desert. Salitral is a small rural village (population 1,503) [approximately equal to] 162 m above sea level in a more temperate region of the Salitral District (Morropon Province, Piura Department) [approximately equal to] 3 h by car from Chiclayito. La Merced is the capital of the Chanchamayo District (Chanchamayo Province, Junin Department) and located [approximately equal to] 751 m above sea level [approximately equal to] 350 km east of the Peruvian capital city of Lima, on the eastern side of the Andes. The district has a population of 31,000; approximately half live in La Merced. Cusco (population 260,000) is located [approximately equal to] 3,350 m above sea level in the southern Peruvian Andes 1,089 km southeast of Lima.

[FIGURE OMITTED]

Sera from patients representing the 4 surveillance sites were tested for antibodies against SFG rickettsiae after written informed consent was provided by each patient (Department of Defense Institutional Review Board No. 31535). Patients enrolled had a fever [greater than or equal to] 38[degrees]C and at least 2 other signs or symptoms including headache, myalgia, arthralgia, rash, and bleeding. Patients with a positive blood film for malarial parasites or obvious disease such as diarrhea or upper respiratory illness were excluded.

Paired (acute- and convalescent-phase) patient serum samples were evaluated for immunoglobulin (Ig) G antibodies reactive with R. rickettsii antigen by either an indirect immunofluorescence assay (IFA) or enzyme immunoassay (EIA). Serum specimens were also tested by IFA for typhus group rickettsial antibodies and were uniformly negative. IFA analysis was conducted according to directions provided by the manufacturer (PanBio, INDX, Inc., Baltimore, MD, USA). Endpoint titers were recorded as the reciprocal of the last dilution exhibiting specific fluorescence. Titers [greater than or equal to] 1:64 were considered positive. Patients with confirmed spotted fever were those who showed a [greater than or equal to] 4-fold increase in R. rickettsii IgG titer from acute phase to convalescent phase of illness.

The EIA was conducted by using a 4-step indirect immunoassay to detect R. rickettsii IgG, as described (8). A positive serum dilution exceeded the mean plus 3 standard deviations between the absorbance of R. rickettsii antigen and the negative control antigen of 5 control serum specimens. Serum samples were titrated to endpoint and the highest dilution found positive was recoded as the R. rickettsii IgG titer. Serum from a serologically confirmed case-patient showed a [greater than or equal to] 4-fold increase in antibody titer from the acute to the convalescent phase.

A total of 170 patients, 50 from Chiclayito and the Salitral Health Centers (Piura Department), 67 from Cusco Hospital (Cusco Department), and 53 from La Merced Hospital (Junin Department), were tested for antibodies to SFG rickettsiae. IFA testing was done at the Peruvian National Institute of Health, while EIAs were conducted at Naval Medical Research Center Detachment. Not all patients were tested by both assays (Table 1). Of the 170 patients tested, 30 (18%) yielded results that suggested that SFG rickettsial infections were the most likely cause of their illnesses (Table 1). Patients from all 4 study sites in 3 departments of Peru had evidence of SFG rickettsiae infections as the cause of illness. Frequencies of confirmed patients in the 3 departments did not differ significantly (p > 0.52). Table 2 shows the frequencies of spotted fever by age and sex for the 164 patients for whom data were recorded. Age groups did not differ significantly (p > 0.5). The frequency of spotted fever was 27% in female patients and 10% in male patients (p < 0.005).

Health Care Industry

Human spotted fever rickettsial infections

Emerging Infectious Diseases, April, 2005 by George B. Schoeler, Cecilia Moron, Allen Richards, Patrick J. Blair, James G. Olson

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