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A 30 year old black African Christian missionary lady presented to our accident and emergency department with a mildly swollen left arm. She had left Liberia 11 months before coming to the UK and had been in this country for two months. Her first attendance was a GP referral to the medical on call team. Complaints were an itchy left arm, which had become red over a month. Her symptoms had not resolved with antihistamines or other medication for allergy. There were no other symptoms at this time and she appeared well with no lymphadenopathy or neurovascular deficit in the affected arm. Her breast and chest examination were normal as was her chest radiograph and on investigation there was a mild eosinophilia. All other blood tests were normal including a malaria and sickle cell screen. A working diagnosis of an axillary vein thrombosis was made. She was given low molecular weight heparin while an ultrasound scan was arranged. She was well and the physicians discharged her with outpatient follow up. The next day she attended casualty with pain at rest in the same arm, which was gradually getting worse. The arm was hot, tender and swollen, but there was no pitting oedema or neurovascular changes. She still had full function of the arm. An emergency ultrasound scan did not confirm the presence of an axillary vein thrombosis. However, a serum sample was taken for possible parasitic infection. There were no new findings on examination. Two weeks later, her left arm had become grossly swollen from the fingertips to the shoulder, with loss of function from the elbow downwards. She was now unable to raise her arm against gravity and felt systemically unwell, with a mild dry cough, a low grade fever, lethargy and malaise. Further investigation showed her eosinophilia had increased. The diagnosis was confirmed by a serum sample sent to the School of Hygiene and Tropical Medicine in London. A working diagnosis of filariasis was made. Filarial worms were present in the serum.
Filarial infections are common in Africa, Latin America, the Mediterranean and Asia. They are caused by parasitic filarial worms, which dwell in the tissue and are transmitted by mosquitoes and other biting insects. There are two main groups of filarial infections; lymphatic and subcutaneous types.1 The filarial worm genus Wuchereia has only one species, Bancrofti. The life cycle was first worked out by Sir Patrick Manson in 1878.2 Microfilariae enter the mosquito's stomach and collect in the gut. At the end of 16 hours, a writhing mass is formed in the gut. The mosquito's proboscis then sucks up these microfilariae by positive chemotaxis and the proboscis is populated by a large concentration of microfilariae. The mosquito on landing on human skin bites in to the flesh and abstracts a cubic millimetre of blood at each feed and in doing this concentrates the embryos in the blood meal. They then enter the mosquito's thorax where they lie between the muscular fibres. Within two days the girth of the microfilariae increases and they assume a squat sausage shape form. Three papillae develop on the larvae that help ease the penetration through human skin. On the 10th day, the larval filarial, travels forward to the mosquito's head. At high temperatures and in a humid environment the complete cycle takes 10 to 14 days but can be retarded to six weeks in the cold. When an infected mosquito bites humans the larvae (attracted to the warmth) puncture the mosquito's proboscis and wriggle out onto the skin, which they penetrate near puncture sites caused by the stylets of the mosquito. In the human host the infective larvae pass through peripheral blood vessels to the lymphatics maturing in approximately three months to one year. Humans are the only known definitive host. Once in the serum, a lymphatic filariasis may occur with varying clinical features (fig 1).
In this case, it is most likely that our patient was exposed to infection in her later adult life and reacted more severely once she had come to live in a temperate climate found in the UK. Regarding lymphatic filariasis some patients only have microfilaraemia and others show an immunological response with positive filarial antigens.3 There may be a filarial fever with recurrent episodes lasting three to seven days and be accompanied by a headache, malaise and adenolymphangitis. Repeated adenolymphangitis causes lymphoedema. If not treated severe elephantiasis will result. It is common in the lower limbs but can occur in the upper limbs as in this patient. The eosinophilia presents as a persistant, paroxysmal night-time cough and signs similar to bronchial asthma. This would explain the progression of the symptoms found in this case. This patient was treated with a course of diethylcarbamazine citrate, which kills the microfilariae and a proportion of the adult worms. This teatment proved very successful, and on follow up, she made an excellent recovery with no residual loss of function in her arm.
In conclusion, the duty doctor should have a high index of suspicion for a filarial worm infestation in patients presenting with swollen limbs with a history of travel in Africa, Asia, Latin America and the Mediterranean within the last year. The importance of a careful travel history cannot be overly emphasised.
Conflicts of interest: none.
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