A Case of Loiasis in a Patient Returning to China Diagnosed by Nested PCR Using DNA Extracted From Tissue

Xiaohui Wang PhD, Xiaoke Zhang MD, Zhiyong Zong PhD
DOI: http://dx.doi.org/10.1111/j.1708-8305.2012.00635.x 314-316 First published online: 1 September 2012


Recognition and diagnosis of loiasis is problematic in areas where this infection is not endemic but may be imported. A previously healthy Chinese male returned from Equatorial Guinea presenting with migratory masses. He was diagnosed with loiasis following detection of Loa loa by nested polymerase chain reaction using DNA extracted from tissue.

Loiasis is an infection caused by the nematode Loa loa, which belongs to the Filariodea family. Because of global movement of travelers and workers, this disease may be occasionally encountered in regions where it is not endemic and may be misdiagnosed. Here, we report a case of loiasis in a Chinese patient that was diagnosed by a nested polymerase chain reaction (PCR) using DNA extracted from soft tissue biopsy as template.

Case Report

A 35‐year‐old male patient was admitted to West China hospital with migratory masses present near his wrists and ankles for more than 8 weeks and feeling movement of a worm in his right eye for 3 days. Physical examination on admission revealed only slight swelling of his right wrist although skin color was normal. In the following days, the swelling mass migrated to a location nearby. The “moving worm” in his right eye could not be observed by the naked eye, and ultrasonography was performed, revealing spots of low density in the vitreous body. Blood tests revealed anti‐hepatitis C virus antibodies, a slightly increased lactate dehydrogenase level (558, reference range 110–220 IU/L), and eosinophilia [white blood cell (WBC) count, 19.75 × 109 L−1; eosinophil cells, 70.0%; and lymphocytes, 12%]. Hepatitis C viral load was 1.0 × 103 copy/mL. Serological tests by ELISA were positive for IgG‐type antibodies for Echinococcus spp., Taenia solium, Angiostrongylus cantonensis, Trichinella spiralis, Clonorchis sinensis, and Schistosoma japonicum. Neither parasite ova nor larvae were visible on examination of stool. No microfilariae were detected in the peripheral blood by microscopic examination of thick blood films collected during the day or at midnight.

As these results were unable to provide a final diagnosis and the right calf became swollen 8 days after hospitalization, ultrasonography of the right calf was therefore conducted, which revealed a pipeline‐shaped lesion (Figure 1). No worms were found on surgical excision and examination of this mass. Histopathological examination of the calf biopsy specimen, the surrounding skin, and subcutaneous tissue revealed only chronic inflammatory cell infiltration, mainly consisting of eosinophils.

Figure 1

Ultrasonograph of the right calf. Three arrows point out a pipeline‐shape lesion without signals of blood flow, which appears to be a worm.

The patient had been working in Equatorial Guinea for 13 months before returning to China 4 months prior to this presentation. Onchocerca volvulus and L loa infections are known to be endemic in Equatorial Guinea and loiasis was therefore suspected. No microfilariae were detected, and treatment with diethylcarbamazine (DEC) was initiated with a dosage regime of 50 mg on the first day, 50 mg three times on the second day, 100 mg three times on the third day, and followed by 150 mg three times daily for 18 days. Total DNA was extracted from the calf biopsy specimen using a FFPE DNA extraction kit (Omega Bio‐Tek, Norcross, GA, USA) and used as template for PCR. Nested PCR to amplify a 366‐bp fragment of the repeat 3 region of a gene encoding a 15‐KDa protein specific for L loa was performed as described previously. 1 Sequencing of the PCR amplicon revealed that it was identical to that of the L loa worm LL20 (GenBank accession number XM_003143088) confirming the diagnosis of loiasis. To reduce potential severe adverse reactions to parasite antigens and avoid fatal meningoencephalitis, prednisone (20 mg three times daily) was administered for the initial 5 days of DEC treatment. After 5 days of treatment, the patient was asymptomatic and the WBC was 9.92 × 109 L−1 with a normal eosinophil count (0.37 × 109 L−1, 3.7%). The patient received 21 days treatment with DEC and remains well at 10‐month follow‐up.


Diagnosis of loiasis is challenging, especially when the pathognomonic indicators of adult worms in the eye or microfilariae in the blood are absent. Imported cases of loiasis could thus be misdiagnosed because of non‐endemic regions. Others 2 have found that a travel history was documented in only 19.7% of 132 patients presenting “unwell post‐travel” in the UK, suggesting that healthcare workers should be aware of travel‐related illness and obtain an adequate travel history. China is endemic for Wuchereria bancrofti and Brugia malayi, with B malayi being the main endemic type in Sichuan. As this patient grew up and lives in this area where schistosomes are endemic, travel history was initially neglected. Only one case of loiasis has been reported in the last 25 years in China, 3 in a worker who had returned from Gabon, Africa, and who was diagnosed by detection of microfilariae in blood on microscopy. However, traditional microscopic examination is not helpful in diagnosing occult loiasis. Here, we present a case of imported loiasis, which was diagnosed with the aid of nested PCR using tissue samples. As seen in this case, months to years of exposure are usually required for loiasis, although infection has been reported after as short as 3 days of exposure. 4 The worm typically migrates at the rate of 1 cm/min as it crosses the conjunctiva. 5 Nonetheless, in this case, eye symptoms resolved spontaneously, leaving no sequelae. Although the eye ultrasonography did not detect a worm in this patient, the spontaneous resolution of eye symptoms may suggest the presence of a moving worm under the conjunctiva or the lower eyelid. This patient also had a prominent clinical feature, ie, the Calabar swelling, an episodic, non‐erythematous swelling caused by transient angioedema because of hypersensitivity reactions to the adult parasite migrating through subcutaneous tissue and/or to released microfilariae. 6 This patient also had a predominant eosinophilia, the eosinophil count reaching as high as 70.0%, something which is uncommonly seen in parasitic diseases. Accordance with all of the above, careful review of the patient's travel history combined with the marked eosinophilia and the characteristic swellings in the extremities made loiasis a likely diagnosis in this case. The increasing number of Chinese citizens working in central Africa, especially in rural areas, means that presentations with loiasis can be expected to increase in China within the next few years.

In this instance, the diagnosis was made using a PCR technique applied on the extract from a biopsy of a Calabar swelling. Previous studies have shown that serological tests by ELISA are able to detect microfilaremia and filarial antigens or antifilarial antibodies. 1,7 However, in this case, the infecting filarial species could not be identified because of extensive antigenic cross‐reactivity. Nested PCR using DNA extracted from blood as a template has been reported as a specific method and also had a 95% sensitivity in detection of occult loiasis. 1 Although not widely used, nested PCR provides an alternative diagnostic measure for loiasis when clinical features are not typical and parasites cannot be removed directly from tissue or blood samples. This case also provides verification that Calabar swellings are manifestations of localized angioedema that are probably related to the subcutaneous migration of L loa.

Ivermectin is a safe and popular choice for treatment of filariasis, 8 partially because of its inability to penetrate the blood–brain barrier. However, ivermectin has a minor effect on adult parasites and patients need retreatment annually. Unfortunately, this drug is not available in China; therefore, DEC, a piperazine derivative with activity against both microfilariae and adult worms of L loa, was used. According to the proposed treatment strategy, DEC can only be administered after having checked the level of microfilaremia, and it is most suitable for patients where the microfilarial density is below 2,000 mf/mL. 9 Although microfilaremia was not detected in this patient, physicians and technicians in areas where L loa is not endemic may not be experienced in recognizing the microfilariae under the microscope and DEC was administered. Patients with high loads of L loa microfilariae may experience serious adverse events including shock, encephalitis, and hemorrhage following the use of DEC because of rapid killing of the microfilariae, 10 and severe encephalopathy was reported recently in a patient with low microfilaremia (0.7 μL−1). 11 Our patient received prednisone at the start of therapy and reported no drug‐related adverse reactions.

In summary, we report a case of loiasis in a male returning from working in Equatorial Guinea, which was diagnosed by nested PCR using DNA extracted from tissue.

Declaration of Interests

The authors state that they have no conflicts of interest to declare.


The authors are grateful to Professor J. Iredell and Dr S. Partridge, Center of Infectious Diseases and Microbiology, Westmead Hospital, The University of Sydney, Australia, for the critical reading of this article.


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