Human Subcutaneous Dirofilariasis, Russia

We report 14 cases of human subcutaneous dirofilariasis caused by Dirofilaria repens, diagnosed from February 2003 through July 2004, in patients from Rostov-on-Don, Russia. Serologic analysis showed evidence of high risk of exposure to D. repens. Surveillance studies on prevalence and prevention effectiveness of canine infection are needed to control this emerging zoonosis.

sections of filarial nematodes (Figure 1A).The average diameter of adult worms was ≈450 µm.These worms had 95 longitudinal ridges on the external cuticle, 2-5 chord nuclei per section, and robust muscle cells, all of which are characteristic features of D. repens (10).Results of PCR analysis of a worm excised from 1 of the nodules was specific for D. repens (Figure 1B).All 9 patients with HSD had significantly higher OD values for total serum immunoglobulin G against D. repens somatic antigen (p=0.001)than controls (Figure 2).Thirty-three (10.4%) serum samples from a random hospital population from the area had positive OD values for antibodies against D. repens somatic antigen.Prevalence of infection was higher in males (28/235, 12%) than in females (5/81, 6%) and in persons >60 years of age (25%) (data not shown).

Conclusions
The cases of HSD described were all diagnosed in patients who had never traveled outside the Rostov area.This is the highest number of cases of HSD worldwide in such a short period.Histologic analysis and PCR indicate that D. repens is the causative agent of HSD in this area, and serologic analysis suggests that the risk for exposure is high.
Domestic and wild canids are definitive hosts of D. repens; the dog is the principal reservoir.No epidemiologic data are available on infection prevalence in dogs in southern Russia.In Piedmont, Italy, a region with a high incidence of human dirofilariasis, a survey of dogs conducted in 1966-1967 and repeated in 1991-1992 (11) showed a marked increase in the number of infected animals and size of the endemic area.Any increase in the population of vectors and infection of the reservoir may likely be associated with an increase in human dirofilariasis.
Information is also lacking on which mosquito vectors are involved in transmission of D. repens in the study area.In other geographic areas where human dirofilariasis is endemic, changes in climatic conditions (temperature, relative humidity, rainfall, rate of evaporation) favor the  development of vector mosquitoes (12) and of the larval phase of the nematode in the vector.
Medical awareness of infection risk is essential for a correct diagnosis, and the use of serologic analysis for D. repens somatic antigen merits further study as a diagnostic aid.Further monitoring of the HSD situation in this area is needed to establish guidelines for preventive measures, including effective chemoprophylaxis in animals.
Dr Kramer is associate professor of veterinary parasitology at the University of Parma.Her research interests include filarial infections and bacterial endosymbionts.

Figure 1 .
Figure 1.A) Histologic analysis of skin nodules caused by human subcutaneous dirofilariasis.Cross-sections of Dirofilaria repens surrounded by an inflammatory granuloma.Note the uteri with developing embryos (hematoxylin and eosin stain, original magnification 10×).B) Analysis of patient samples by agarose gel electrophoresis.Lane 1, 100-bp DNA molecular mass weight marker; lane 2, negative control; lane 3, positive control; lane 4, patient sample showing banding pattern typical of the positive control and similar to the banding pattern described in the original protocol (7).

Figure 2 .
Figure 2. Serologic analysis (box and whisker plot) for antibodies to Dirofilaria repens somatic antigen from normal controls (NC) and patients with human subcutaneous dirofilariasis (HSD).The horizontal line shows the optical density (OD) values of 25%-75% of the examined sera.The large box shows OD values between the first and third quartiles, the small box shows the median, and error bars show maximum and minimum OD values.A positive antibody response was defined as an OD value greater than the mean value ±3 standard deviations from 14 normal controls.