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Lymphatic filariasis

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VOL: 97, ISSUE: 38, PAGE NO: 59

BARRY THOMPSON, RGN, is a nurse practitioner, Cabinda Gulf Oil Company, Cabinda, Angola

John Wilson, a 55-year-old man, has spent the vast majority of his working life in various parts of sub-Saharan Africa as a field engineer for an oil company.

John Wilson, a 55-year-old man, has spent the vast majority of his working life in various parts of sub-Saharan Africa as a field engineer for an oil company.

His working schedule was composed of 28 days on location somewhere in Africa, followed by 28 days at home. He had worked in numerous countries, including Nigeria, Cameroon, Sudan, Gabon, Ivory Coast and the Congo. At the time of presentation he was based in Angola.

He had always been diligent regarding the maintenance of his immunisations. In addition, he was among a relatively small number of expatriate employees who continued taking malaria prophylaxis for the duration of his working life abroad.

His medical history was largely unremarkable. He was a non-smoker and consumed alcohol only socially. Apart from antimalarial tablets (mefloquine), his only other regular medication was a daily diuretic, prescribed for mild and asymptomatic hypertension.

He experienced one severe episode of viral illness in 1986 while working in the Cameroon. It was never positively identified but, based on his symptoms at the time, he was treated for plasmodium falciparum malaria and responded well to therapy. Otherwise, he had enjoyed a healthy working life on the African continent.

In September 1999, during a leave period in England, Mr Wilson visited his GP, complaining of oedema in his lower legs. In particular, the swelling in his left leg appeared to be more pronounced. Due to his past medical history, and after a brief examination, the GP concluded that an increase in his diuretic prescription was indicated.

Mr Wilson returned to his post in Africa, but found it necessary to visit the oil company clinic because the swelling in his legs was worsening. In addition, he reported a gradual swelling of his scrotum.

On questioning, Mr Wilson stated that he had experienced two episodes of fever in the past two months, each lasting around five days. He had dismissed these as being related to colds and minor chest infections. He had also been treated for a minor skin rash which responded well to topical hydrocortisone cream.

However, the clinic doctor suspected that the symptoms might be related to a tropical infection and, more specifically, to filariasis infestation. Physical examination revealed enlargement of the inguinal and axillary lymph nodes, marked bilateral ankle oedema and a minor hydrocele.

Blood tests were ordered, which included a full blood count, serology investigations and blood films for microscopy. The blood film slides provided a definitive diagnosis: Mr Wilson was acutely infected with a species of roundworm - the nematode Wuchereria bancrofti - the organism responsible for lymphatic filariasis.

He was started on diethylcarbamazine (DEC) at a dose of 1mg per kilogram per day, in three daily divided doses after meals. As he showed no adverse reactions to therapy, the dose was increased to 6mg per kilogram per day, in three divided doses. Again, he experienced no adverse effects. This regime was continued for three weeks. However, due to the resistant nature of the mature nematode, it was explained to Mr Wilson that he would probably need repeated courses of DEC to destroy the adult worm.

Added to this, a single dose of another filaricide, ivermectin (400 micrograms per kg) was given, as recent research has proven that combination therapy is far more effective in eliminating the infestation (Ottesen et al, 1999). For additional peace of mind, the ivermectin dose would also be repeated once, after six months.

Mr Wilson responded rapidly and favourably to the drug therapy. Serial blood films were free of microfilariae, and there was no repeat of his systemic manifestations. In addition, his ankle swelling spontaneously resolved. A small residual hydrocele remained but caused no problems. He continued to have follow-up appointments and repeat blood tests, but all evidence suggested that the organism had been permanently eliminated.

The disease
Lymphatic filariasis is a common condition throughout the tropics and sub-tropics. It is estimated that 80 million people are infected worldwide; the World Health Organization estimates the total at closer to 120 million in 73 countries (Goldsmith, 1999). The most common causative organism is Wuchereria bancrofti (90% of cases), but two other nematodes - Brugia malayi and Brugia timori - are also responsible for the disease, mainly in parts of south east Asia and south America.

Transmission is by mosquito vector. Culex, Aedes and Anopheles species are all potential carriers of the worm, but in rural west Africa it is most commonly Anopheles, also responsible for the spread of malaria in the same regions. The mosquito ingests a blood meal containing the parasite; it matures to the larva stage, then migrates to the biting mouthpieces of the mosquito, to be inoculated into another host at the next feeding time.

The incubation period is generally between 8-16 months in expatriate patients, but may be longer in indigenous people. It can take from 6-12 months for the immature organisms, called microfilariae, to appear in the blood. These can number in the millions in heavy infestations and are up to a third of a millimetre in length.

The mature adult worms can reach eight to nine centimetres in length. They are particularly partial to establishing a permanent home in the lymphatic vessels and structures of the inguinal, femoral and scrotal regions. This, of course, causes the most common presenting features of the disease - hydrocele and lower limb swelling - which, if untreated, may progress to elephantiasis.

The adult worm has a somewhat curious habit of wriggling vigorously and almost continuously, once it has embedded in a fixed anatomical location. This movement can be clearly seen with ultrasound studies of the affected region. It is the same motion, combined with growth of the creature, that causes massive dilatation and eventual obstruction of surrounding lymph vessels.

Diagnosis
Diagnosis was traditionally by history combined with physical examination or by visualisation of the microfilariae in blood smears. The preferred time for obtaining the sample is between 10pm and 2am, as the organisms appear to be most active and migratory during these hours. Ideally, a thick film is taken for sensitivity assessment, while the thin film enables morphology studies.

The patient may complain of a variety of symptoms and presentations. In addition to lymphangitis and lymphoedema resulting in swollen limbs or appendages, the patient may disclose a history of periodic fevers, each one lasting several days. These correspond to surges in the numbers of circulating parasites.

Intermittent skin rashes and hives are another common occurrence, which may be pruritic. These may be scattered and generalised or more localised to the regions of greatest infestation. Changes in skin pigmentation are also frequent.

Chronic obstruction of the lymphatic flow in the limbs often results in repeated bacterial and fungal skin infections. This, in turn, leads to scarring, pigment changes and hypertrophy; when imposed on a grossly lymphoedematous extremity, this combination of factors is known as elephantiasis.

Scrotal oedema and hydrocele are extremely common in communities where the infestation is endemic. Indeed, in some areas, between 40% and 60% of males (excluding young children) live with this condition.

Blood serology testing may be positive for the organism and when the parasite count is high a marked eosinophilia may be present. Recent advances in laboratory diagnosis have included the estimation of IgG and IgE levels.

A specific test for circulating filarial antigen (CFA) has also been released, for detecting Wuchereria bancrofti infections. This rapid immunodiagnostic aid was the subject of research conducted by Nguyen et al (1999), and they concluded that the test was both accurate and reliable.

Treatment
Fortunately the infestation is easily controlled, providing it is diagnosed early and treated promptly. Drug therapy has two central purposes - to kill the circulating microfilariae in the blood and to kill the adult worms (macrofilariae).

Traditionally the drug of choice was diethylcarbamazine (DEC). This remains highly effective against the blood-borne microfilariae, but its effects on the adult worms are slow and unpredictable. There is also some debate regarding an effective regime; some doctors prescribe 6mg per kg per day in divided doses, continued for 12 days; others insist on multiple three-week courses at the same dosage.

Recent research conducted by Ottesen et al (1999) has suggested that a combination of DEC, with either ivermectin or albendazole, is far more effective in procuring a longer-term solution. The microfilariae are killed quickly and simply by all three drugs; unfortunately the adult nematode is much more resilient, and it is advisable to repeat the therapy annually for at least four to six years to eliminate the chance of recurrence.

Ivermectin is widely viewed as the ideal drug, because it kills the microfilariae and also, in research performed by Plaisier et al (1999), appears to partially incapacitate the adult worm, leading to a permanent reduction in microfilaria production of at least 65%.

Whatever therapy is selected, reactions to the treatment are not uncommon. Fever, headaches, dizziness, myalgia and malaise have all been reported. In addition, localised acute lymphadenitis, abscess formation and ulceration can occur following the death of an embedded adult worm.

Nursing care
Nursing care is primarily aimed at preventing the potential complications that may develop. If possible, elastic stockings or bandages are applied to the affected limbs, to assist venous return and prevent excessive oedema. Bedrest may be required in more severe cases, with elevation of the involved extremities. Suspensory bandages (scrotal supports) may provide comfort in the event of hydrocele.

Clinical observation must include monitoring for any alteration in respiratory function. Tropical pulmonary eosinophilia is a rare but potentially serious complication of lymphatic filariasis. Often, the condition may resemble an acute asthmatic episode. If allowed to progress unchecked, it can result in chronic pulmonary fibrosis.

Careful assessment for reactions to the drug therapy is mandatory. The patient must also be regularly screened for the appearance of secondary skin infections. If allowed to develop and extend, these may lead to the chronic hypertrophic changes seen in elephantiasis. Meticulous personal hygiene is actively promoted for the same reason. All topical infections, however minor, must be treated promptly.

There is no reliable diagnostic test to positively establish that the adult worm has been killed. Therefore, the emphasis is on regular periodic follow-up screening, with repeated treatment as and when indicated.

The global picture
The World Health Organization has recently embarked on a programme aimed at global eradication of lymphatic filariasis; the aim is to eliminate the disease in all countries by the year 2020. To this end the WHO has enjoyed benevolent support from a number of major pharmaceutical companies who have agreed to donate the required medications to affected countries free of charge (Yamey, 2000).

Worldwide, around 25 million people are affected by genital filariasis, and 15 million have progressed to lymphoedema and elephantiasis (Behbehani, 1999). It is hoped that, with the combined efforts of these organisations, this disfiguring and distressing condition will no longer be a burden to the populations of those nations where it is endemic.

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