Eosinophilia occurs in a variety of haematological, allergic and inflammatory conditions.
It may also arise in HIV-1 and human T-cell lymphotropic virus (HTLV)-1 infection. However, eosinophils are important in the immune response to parasitic infections, in particular those involving parasites with a tissue migration phase. In the context of travel to or residence in the tropics, a patient with an eosinophil count of more than 0.4 × 109/L should be investigated for both non-parasitic and parasitic causes.
The response to parasite infections is often different when travellers to and residents of endemic areas are compared. Travellers often have recent and light infections associated with eosinophilia. Residents have often been infected for a long time, have evidence of chronic pathology and no longer have eosinophilia.
A history of travel to known endemic areas for schistosomiasis, onchocerciasis and the filariases will indicate possible causes. Assessment should establish how long patients have spent in endemic areas and the history should address all the elements.
Physical signs or symptoms that suggest a parasitic cause for eosinophilia include transient rashes (schistosomiasis or strongyloidiasis), fever (Katayama syndrome – pruritus (onchocerciasis) or migratingsubcutaneous swellings (loiasis, gnathostomiasis). Paragonimiasis can give rise to haemoptysis and the migratory phase of intestinal nematodes or lymphatic filariasis may cause cough, wheezing and transient pulmonary infiltrates. Schistosomiasis induces transient respiratory symptoms with infiltrates in the acute stages and, when eggs reach the pulmonary vasculature in chronic infection, can result in shortness of breath with features of right heart failure due to pulmonary hypertension. Fever and hepatosplenomegaly are seen in schistosomiasis, Fasciola hepatica infection.
The medicines that can be thought of use are:-