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Case Report and Brief Commentary |
Address correspondence to Jaber Aslanzadeh, Ph.D., Department of Pathology, Hartford Hospital, 80 Seymour Street, Hartford, CT 06102-5037, USA; tel 860 545 4128; fax 860 545 2726; e-mail jaslanz{at}harthosp.org.
Abstract
Filarial infection is endemic in the tropics and is a public health problem in Africa, Asia, South and Central America, and the Pacific Islands. Co-infection with filarial nematodes, if unrecognized, can result in untoward therapeutic consequences. We report a case of co-infection of Wuchereria bancrofti and Onchocerca volvulus that was diagnosed by direct blood smear (W. bancrofti ) and serology (O. volvulus) in a native of Sierra Leone. We comment briefly on the therapeutic implications of the co-infection.
(received 24 September 2004; accepted 18 March 2005)
Keywords: filariasis, wuchereriasis, onchocerciasis, co-infection, Mazzotti’s reaction
Case Report
A 21-yr-old male refugee from Sierra Leone, who had been living in the USA for 4 mo, received a provisional diagnosis of malaria at a health clinic and was referred to Hartford Hospital. His main complaint was chronic intermittent chills and hot/cold sensations in his arms, associated with pain and heaviness in the left axillary region. He denied other symptoms including fever, rigors, sweating, visual disturbances, scrotal swelling, or nodules in any part of the body. Physical examination was unremarkable except for a grade 2 (of 6) systolic murmur.
Laboratory test results included blood hemoglobin, 12.1 g/dl; mean corpuscular volume, 75.7 fl; and leukocyte count, 7600 cells/mm3, with 29% eosinophils. The absolute eosinophil count was 2020 cells/mm3. A blood smear that was stained for malaria revealed sheathed micofilaria consistent with Wuchereria bancrofti (Fig. 1
), which was confirmed by examinations at the Parasitology Laboratory of the Connecticut State Health Department. The patient’s serum was sent to the Laboratory of Parasitic Diseases, National Institutes of Health, Bethesda, MD, for antifilarial antibody test, which was positive at 80.9 µg/ml (normal <14 µg/ml). A test for antibody to onchocercal recombinant antigen ov-16 was also positive, indicating that the patient was co-infected with Wuchereria and Onchocerca.
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Commentary
Filariasis is caused by vector-borne tissue dwelling nematodes called filariae. Transmission of human filariae is confined to the tropics, since high ambient temperature is requisite for the parasites to develop in their vectors [1]. Filariasis is endemic in Africa, Asia, South and Central America, and the Pacific islands [2]. The major disease forms caused by human filariae include lymphatic filariasis (W. bancrofti, Brugia malayi, Brugia timori), onchocerciasis (O. volvulus), and loiasis (Loa loa); their respective vectors are Mosquito sp, Similium sp (black fly), and Chrysops sp. The WHO estimates that 150 million persons are infected with microfilaria worldwide, including lymphatic filariasis (120 million), loasis (25 million), and onchocerciasis (17 million) [2,3].
Given the current global nature of travel and trade, physicians can encounter cases of filariasis outside the tropics. In our particular case, filariasis was not considered initially, but when a blood smear was examined under low power magnification, the presence of sheathed microfilaria was apparent.
Humans acquire W. bancrofti when the infective larvae gain entry into the skin by mosquito bite. They migrate to lymphatics and develop into adult worms. The female measures 80–100 x 0.25 mm and the male 40 x 0.1 mm. The life span of the adult female is about 20 yr [1]. Microfilariae are produced from ova in the uterus of the adult female and enter the circulating blood. They are sheathed, measuring 260 x 8 µm, and their life span is about 1 yr [1]. The female mosquito ingests microfilariae during a blood meal. They ex-sheath in the mosquito’s stomach and become first-stage larvae, which migrate to the insect’s thoracic muscles after penetrating the stomach wall. After moulting twice, the infective third-stage larvae migrate to the mouthparts of the mosquito from whence they enter the skin of the human host during a blood meal.
Microfilariae are mostly nocturnal, but their presence in peripheral blood has diurnal or nocturnal periodicity, depending on the feeding pattern of the vector, the biologic rhythm of the microfilariae, and the circadian rhythm of the host [1]. The life cycle of O. volvulus is similar to W. bancrofti except that the vector is Similium sp and adult worm live in the skin and subcutaneous region instead of the lymphatics.
Acute manifestations of filariasis include repeated episodes of lympadenitis and lymphangitis associated with fever and malaise. Chronic manifestations include hydrocele and chronic lymphoedema, which can lead to elephantiasis of the legs. Rare manifestations are chyluria and tropical pulmonary eosinophilia. Among persons exposed to W. bancrofti there are individuals who have neither microfilaremia nor obvious clinical manifestations, but most have subclinical lymphatic abnormalities. Clinical features of onchocerciasis range from papules to extensive pigmentary and atrophic skin changes, and include the formation of subcutaneous granulomas. If untreated, the disease may involve the eyes, causing sclerosing keratitis, optic nerve atrophy, and choroidoretinitis, leading to blindness.
Presence of fever, groin pain, swollen lymph nodes, and edematous legs in a patient who has recently lived in or traveled to a tropical country should suggest possible filarial infection [1,4]. In addition to routine examination of a blood smear, diagnostic tests include detection of circulating filarial antigens using monoclonal antibodies. Use of the ICT filarial card test has facilitated the laboratory diagnosis of these infections [4,5]. Diagnosis of onchocerciasis is based on the clinical features, plus a slit lamp examination of the eye, which may reveal live microfilariae or characteristic punctate keratitis [1]. Confirmatory tests include demonstrating microfilariae in bloodless skin snips. Sensitive, specific serologic tests based on ELISA and immunochromatography using specific recombinant antigen are available to detect antibodies to O. volvulus [5–7]. There are PCR-based tests for most filarial nematodes, but they have limited clinical use, owing to their high cost and the limitations of laboratory facilities in endemic areas [8].
Lymphatic filariasis was formerly treated with diethylcarbamazapine (DEC) in 3 doses/day for 12 days, but recent data suggest that a single dose of DEC may be equally effective. Other drugs used to treat microfilarial infection are ivermectin and albendazole [1–3]. Current strategies are to administer single doses of a 2-drug combination of albendazole with ivermectin or diethylcarbamazapine [9,10].
Search for co-infection is advisable when one form of microfilariasis is diagnosed. This is important especially if DEC is considered as a treatment option because of the severe reactions that may occur when DEC is administered to patients co-infected with O volvulus. The so-called "Mazzotti reaction" may be local (pruritis, skin rash, visual disturbances) or systemic (fever, headache, joint pains, postural hypotension, collapse, and respiratory distress)[1]. DEC can aggravate existing eye lesions and precipitate new ones. For these reasons, DEC is either avoided or used after steroid adminisration to blunt inflammatory reactions. Often the treatment of choice is the combination of ivermectin and albendazole [9].
The Wolbachia sp of bacteria may co-exist symbiotically in all filarial adult worms except L. loa [11]. Wolbachia evidently plays a significant role in the embryogenesis of filaria. Targeting of Wolbachia using doxycycline has been reported to sterilize the adult worm, leading to the elimination of microfilariae from the blood [12]. A 6-wk course of doxycycline (100 mg/day for O. volvulus; 200 mg/day for W. bancrofti) may deplete the bacteria and lead to long-term filarial sterility [13].
References
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