A 36-year-old male patient presented with complaints of dry cough and shortness of breath on exertion for two months. His cough was worse at night. He also complained of low-grade intermittent fever for two months. His appetite was normal and he denied any history of weight loss, joint pain, night sweats, chills, rash, rhinorrhea, epistaxis, hemoptysis, hematuria or burning sensation in hands and feet. There was no history of smoking or any kind of drug intake. His past medical history was unremarkable. He was a resident of a village in the eastern part of India and worked as a manager on a poultry farm.
Two weeks before presenting to our medical care facility, he was diagnosed with a lower respiratory tract infection by a private practitioner and was prescribed a short course of oral antibiotics. But he continued to have fever, cough, and breathlessness. On presentation to our facility, his physical examination was notable for rhonchi throughout both lung fields. His vital signs were normal. The results of initial laboratory investigations were as follows: hemoglobin 12.8 gm/dL (reference range: 13-17 gm/dL), total leukocyte count 50,230/microL (reference range: 4,000-11,000/microL), absolute eosinophil count 37,510/microL (reference range: 40-440/microL), platelet count 151,000/microL (reference range: 150,000-400,000/microL), and random blood sugar 93 mg/dL (reference range: 70-100 mg/dL). Peripheral blood smear showed leukocytosis with marked eosinophilia without any left shift. Liver function tests and kidney function tests were within normal range. The chest radiograph showed the presence of reticulonodular opacities involving all zones of both lung fields (Figure 1).
High-resolution computed tomography (HRCT) scan of the thorax revealed the presence of mosaic attenuation in the bilateral lung parenchyma. There were multiple centrilobular nodules along with smooth interlobular septal thickening involving all the lobes bilaterally (Figure 2).
Cytological analysis of bronchoalveolar lavage fluid (BAL) showed marked eosinophilia. Smear examination and cultures of BAL fluid revealed no pathogenic microorganism and GeneXpert MTB/RIF did not detect Mycobacterium tuberculosis. Spirometry was suggestive of combined obstructive and restrictive changes.
The Mantoux test was negative. The stool examination did not show any parasites. Urine examination did not reveal any protein, red blood cells, or sediment. Serum immunoglobulin (Ig) E level was 9915 U/L (reference range: less than 150 U/L). Serum Aspergillus fumigatus-specific IgE level was 0.08 kU/L (reference range: less than 0.35 kU/L), while serum A. fumigatus-specific IgG level was 13 mg/L (reference range: less than 27 mg/L). Antineutrophil cytoplasmic antibodies were negative. Anti-filarial antibody was positive by the immunochromatographic method. 
The patient was started on DEC therapy at a dose of 100 mg thrice daily. Cough improved within three days of treatment initiation and the fever subsided after five days. Subsequent serial blood counts showed a decrease in eosinophil count (Table 1).
Diethylcarbamazine was administered for three weeks. The patient became completely asymptomatic. After four weeks of completion of the DEC course, the chest radiograph and spirometry were repeated. Chest X-ray showed the persistence of reticular opacities bilaterally (Figure 3).
Also, follow-up spirometry showed partial improvement in lung function with the persistence of restrictive abnormality (Table 2).