Epidemiological Investigation on Subcutaneous Nodule Containing a Live Worm Suspected to be Dirofilaria Repens Infection in a Woman from Rural Kerala, India.

Sir,

Infection due to Dirofilaria is very common among the dogs of tropical countries and the number of locations reported the human infections also increased in recent years. A 19-year-old girl, resident of a coastal area in Thiruvananthapuram district of Kerala, had presented to the nearest primary health center with an ocular nodule. The swelling was located on the medial canthus of her right eye. The exploration of the swelling revealed a pearly white, thin live worm of around 20 cm length ]Figure 1]. The worm was morphologically similar to dog filarial worm, Dirofilaria repens.

Figure 1

The adult worm, D. repens, found in the subcutaneous nodule. (The photograph taken by the ENT surgeon using her mobile phone)

We initiated an epidemiological investigation and followed up the girl to her area of residence. Microscopical examination of wet blood film and blood smear of the dog in the patient's household was performed. Smears were fixed in methanol and stained with Giemsa stain. Infection due to D. repens was confirmed in the domestic animal in the household [Figure 2]. A vector survey conducted around the area unmasked heavy breeding of Aedes albopictus, which is a known vector for the parasite Dirofilaria.[1]

Figure 2

Dirofialrai repens microfilaria found in the peripheral blood of the dog (Giemsa stained)

We separated the DNA of the worm isolated from the ocular nodule using phenol–chloroform isoamyl alcohol method.[2] Further PCR assay was conducted using specific primers to amplify the 246 bp repetitive sequence, which is specific for D. repens.[3] (Accession number: JQ706073). The search for regions of local similarity between sequences using BLAST (NCBI) showed identity of D. repens by 97% (Accession number: L15323).

Kerala, the southern state of India is endemic for both canine and human dirofilariasis.[4] Previous diagnosis of reported D. repens infection in humans were just based on morphological features of the worm.[45] However, the investigators of this case has gone one step ahead with the molecular conformation of D. repens by identifying and amplifying its specific gene product. Application of PCR technique to confirm the diagnosis of a parasitic infection in a patient from a rural area has never been attempted before. This highlights the novelty of this correspondence. Further, the field investigation also yielded strong supporting evidence to establish the diagnosis. All the domestic dogs of the study area were administered Ivermectin of 0.2 mg/kg body weight and mosquito control measures were also initiated.