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Indian Journal of Medical Microbiology, Vol. 28, No. 4, October-December, 2010, pp. 394-396 Case Report Human subcutaneous dirofilariasis in India: A report of three cases with brief review of literature S Khurana, G Singh, HS Bhatti, N Malla Department of Parasitology, P.G.I.M.E.R., Chandigarh-160 012, India Date of Submission: 10-Nov-2009 Code Number: mb10116 PMID: 20966580 Abstract Human subcutaneous dirofilariasis is a rare infection caused by filarial worms of the genus Dirofilaria. The parasites are transmitted to man by mosquitoes and the infection is manifested as subcutaneous nodules. Excision of the lesion is both diagnostic and therapeutic. Hereby we report three cases of human subcutaneous dirofilariasis. The worms were sent to our department for identification over a period of four years (2006-2009). Of these three patients, two men and one woman were between 15 and 45 years of age. In two cases, the infection manifested as a nodule on face, in one case near lower eyelid and in the other on the cheek, while in the third case as an itchy nodule on the abdomen. It is emphasized that both clinicians and microbiologists should have an increased awareness of this entity and include dirofilariasis in the differential diagnosis of patients presenting with subcutaneous nodules.Keywords: Dirofilariasis, human, subcutaneous Introduction The genus Dirofilaria includes various species that are natural parasites of dogs, cats, and wild mammals. The naturally occurring species commonly encountered in the subcutaneous tissues of dogs is Dirofilaria repens which has also been reported from different parts of the world.[1] Mosquitoes belonging to the genera Culex, Aedes, and Anopheles have been recognized as suitable vectors for this parasite. The life cycle of this parasite is the same as that of other filariae; microfilariae are in the blood of wild and domestic animals such as the dog, cat, and raccoon, and transmission occurs to humans by infected mosquito bites. Humans are a dead-end host and the parasite will not produce any microfilariae. [1] Human infection with Dirofilaria repens is not widely recognized in India, however, several cases are reported in last few years.[2],[3] Dirofilaria repens is a common zoonotic infection in neighbouring countries like Sri Lanka as well. [4] Increasing number of infection in India as well as throughout the world suggest the need for the diagnosis and reporting of this infection. Case Reports Case 1 A 16-year-old male from Karnataka presented with an itchy subcutaneous nodule on the upper right side of his abdominal wall. It was not associated with any pain or tenderness. The exploration of the lesion revealed a long whitish thread-like worm measuring 9 cm by 0.5 mm. The worm was mechanically extracted and recovered intact. It was presumptively identified as immature female worm of D. repens. Case 2 A 45-year-male patient from Maharashtra had a tense swelling in the right cheek since one month, which had gradually increased within the past 15 days. It was not associated with any pain or tenderness. On surgical excision, an 8 cm long by 0.5 mm thick whitish worm was recovered and was removed completely. It was presumptively identified as immature female worm of D. repens. Case 3 This case was of a 15-year-old female from Maharashtra, who had a cystic swelling near the lower eyelid. On exploring, a long white thin worm measuring 11.5 cm by 0.5 mm was recovered, which could be completely extracted. It was not associated with any pain or tenderness. It was presumptively identified as immature female worm of D. repens. As all the three cases were from rural areas in their respective states they could not be followed-up for any progression or recurrence of the disease. Each worm was received intact in 10% formaldehyde. The specimens were measured and later cleared in increasing concentrations of alcohol. The worms were presumptively identified as female D. repens based on morphology, geographical location from where they were recovered, and clinical presentation. Under the microscope, the outer surface of the nematode's cuticle was found to have fine transverse striations and prominent longitudinal ridges [Figure - 1]. The body cavity contained a female reproductive system, with the vulva about 1 mm from the anterior end. The proximal portion of the vagina was bulbous [Figure - 2]. The vagina looped and ended in a uterine bifurcation. The uteri almost filled the body cavity. The ovaries and oviducts were highly coiled. [5] Discussion Human dirofilariasis is a rare helminthic infection. This may be due to the fact that the diagnosis of Dirofilaria infection in human beings remains difficult as symptoms exhibited by the patient are diverse. The symptoms, which signal their presence in human beings, include transitory inflammatory swellings or nodules that may or may not be painful. When living worms enter the conjunctiva, they may cause acute symptoms like redness of conjunctiva, foreign body sensation, excessive lacrimation and the affected individual then seeks medical attention. Similarly, gradual development of the worm to a nodule or formation of abscess in the subcutaneous tissue has also been reported to be painful. The most important risk factors regarding human infections are mosquito density, warm climate with extended mosquito breeding season, outdoors human activities and the abundance of microfilaraemic dogs. [6] Blood eosinophilia or elevated serum IgE levels are rarely observed. The diagnosis of human subcutaneous dirofilariasis can be made with certainty only after biopsy on fresh specimens. The external longitudinal ridges are characteristic of species, which live in the subcutaneous tissues of their natural hosts. The number of reproductive tubes and their contents (eggs, microfilariae or sperm) help to determine the sex of the parasite and the reproductive state of female worm. [7] Precise identification of Dirofilaria species may be achieved with DNA analysis, based on polymerase chain reaction but the large number of specific probes required limits, the usefulness of this method. [8] The initial cases of human ocular Dirofilaria infection in India were reported from South India (Kerala) in 1976 and 1978, respectively. [9],[10] In 1989, the first case of subcutaneous infection with Dirofilaria showed a child manifesting portal cavernoma with pulmonary dirofilariasis from India. [11] Sabu et al. identified 12 worms from different human patients as D. repens based on morphology from southern part of India. [12] Dirofilaria repens and D. tenuis cause subconjunctival dirofilariasis. Subconjunctival dirofilariasis due to D. repens has been rarely reported from North India. [13] In order to predict the natural history of dirofilarial infection in this region, 160 blood smears of dogs were also examined from this region. Microfilariae (D. repens) were detected in 11 samples (7%). This suggests that humans are at an enhanced risk of acquiring Dirofilaria infection from dogs. Simple extraction of the worm or complete surgical excision of the dirofilarial lesion is the treatment of choice for human dirofilariasis. If difficulty is encountered in surgical removal of the worm because of excessive movement, a cryoprobe can be used for immobilizing it as described by Gendelman et al.[14] There is no need for chemotherapy as microfilaraemia is extremely rare.[12],[15] In a small number of cases, ivermectin and/or diethylcarbamazine has been tried with good results.[16] The symbiosis of filarial nematodes and intracellular Wolbachia bacteria has recently been exploited as a target for antibiotic therapy of filariasis. Antibiotic treatment of filarial nematodes results in sterility and inhibits larval development and adult worm viability. In the first trial on human onchocerciasis, depletion of bacteria following treatment with doxycycline resulted in a complete and long-term block of embryogenesis. [17] Based on the present observations, it may be concluded that dirofilariasis in humans due to D. repens infection is a fast emerging zoonosis in India. Acknowledgement Authors are thankful to Dr. M.N. Dravid, former Professor & Head and Dr. M.N. Prasad, Professor & Head, Dept. of Microbiology, S.B.H. Govt. Medical College (Dhule) and Dr. R. D. Kulkarni, Professor & Head, Dept. of Microbiology, S.D.M College of Medical Sciences (Dharwad) for sending us the worms for identification. References
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