Tropical Eosinophilia

Tropical eosinophilia (TE) occurs in patients who have filariasis, which is an infection caused by certain types of roundworm, exemplified by Wuchereria bancrofti and Brugia malayi [1]. The presence of these parasites in the body leads to an exaggerated immune response in some individuals characterized by markedly high levels of eosinophils in the blood and even higher concentrations in the lungs [2]. This immune response, in turn, provokes transient episodes of acute respiratory symptoms such as wheezing, coughing, shortness of breath and chest pain, often worse at night [3]. Systemic symptoms such as fever, loss of weight and appetite, lymphadenopathy, hepatomegaly, and splenomegaly may also occur, although, in a small percentage of patients, no pulmonary symptoms are present.

TE is most frequently seen in areas where filarial infections are endemic, however, cases in non-endemic areas have been reported, aided by travel and immigration, albeit some cases are misdiagnosed due to failure to recognize the syndrome [4] [5]. Males are four times more affected by the illness than females. More serious clinical manifestations include permanent widening of the airways, pneumothorax, consolidation of the lungs and granulomas. Cardiac activity can also be affected, and this is demonstrated by electrocardiogram (ECG) abnormalities [6]. Changes in the lung tissue that result in chronic disease have also been reported in a minority of cases, where symptoms do not resolve despite adequate treatment with diethylcarbamazine (DEC) [7].

Patient history is important, especially in non-endemic areas, as a recent travel history to tropical regions may give diagnostic clues. Laboratory investigations such as white cell count as well as measurement of antibody titers are performed. In individuals with TE, leukocytes are increased, with a predominance of eosinophils. Furthermore, there are high titers of specific as well as non-specific immunoglobulins (Ig), namely IgE, IgG, and IgM, in response to filarial antigens [8].

Pulmonary function tests are necessary, and reveal a mixed picture of obstructive and restrictive lung disease, with a decrease in parameters such as the forced expiratory volume (FEV) and the diffusing capacity for carbon monoxide (DLCO) [7] [9]. In some cases, a purely restrictive picture is seen.

In addition, the following studies are also done:

• Arterial blood gas analysis: May reveal lower than normal concentrations of oxygen due to a ventilation-perfusion mismatch [3].
• Chest X-ray: This may be normal in up to one fifth of patients. Usually, widespread nodular opacities are visible, similar to those seen in miliary tuberculosis.
• Computerized tomography scan: Useful in showing structural lung damage such as bronchiectasis [10].
• Bronchoscopy and bronchoalveolar lavage: This allows the visualization of inflammation of the parenchyma as a direct consequence of the presence of a large number of eosinophils in the lungs [2]. Furthermore, anti-filarial antibodies, as well as, nonspecific antibodies can also be seen.
• Lung biopsy: Biopsy is usually done in the context of chronic disease which is first confirmed via spirometry, in the years following treatment.

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