LACK OF BASOPHILIA IN HUMAN PARASITIC INFECTIONS EDWARD MITRE AND THOMAS B. NUTMAN Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland Abstract. While basophilia is often found in animal models of parasitic infection, it has not yet been established whether it occurs in parasite-infected humans. We investigated the relationship between basophilia and parasitic infec- tions in humans by reviewing charts from 668 patients with confirmed parasitic infection (472 with only helminths, 146 with only protozoa, and 50 with both helminth and protozoan infections) and from 50 patients without parasitic infections. Basophilia (> 290 cells/mm3 ) occurred in only four of the 668 parasite-infected patients (0.6%), and there were no statistically significant differences in the percentages of patients with basophilia or in the absolute basophil counts among either the helminth-infected, protozoa-infected, or uninfected populations. Analysis with regard to rela- tive basophil levels revealed that basophils constituted more than 3% of the peripheral white blood cell population in only four patients. Thus, basophilia occurs only rarely in human parasitic infections and is consequently not a useful clinical marker in the evaluation of suspected parasitic disease. INTRODUCTION It has long been known that basophilia occurs in animal models of parasitic infection. Two of the earliest reports of this phenomenon showed that bone marrow and circulating basophil counts increase within 48 hours following subcuta- neous injection of ascaris body 1 and ova fluid 2 into guinea pigs. Since then, several other investigators have reported similar findings in several different animal models of parasitic infection. Trichostrongylus colubriformis infection has been shown to increase basophil numbers in the bone marrow, small intestine, and peripheral circulation of guinea pigs. 3 In- fection of rats 4–6 and gerbils 7 with Nippostrongylus brasilien- sis results in up to a 50-fold increase in peripheral basophil counts after two weeks. Trichinella spiralis infection in rats 8 and guinea pigs 9 also results in a marked basophilia that pre- cedes the onset of eosinophilia by approximately one week. Fasciola infection of guinea pigs is associated with a chronic peripheral basophilia that is detectable up to four months after infection, 10 and Strongyloides infection of Erythrocebus patas monkeys causes peripheral basophilia that is occasion- ally detectable for more than a month after infection. 11 The presence of peripheral basophilia in human parasitic infections has not been as clear. While basophilia is men- tioned as occurring in human parasitic infections in immunol- ogy and parasitology book chapters and review articles, the majority of investigators, with the exception of one reference to a doctoral thesis reporting peripheral basophilia in humans infected with Necator americanus, 12 refer to other review ar- ticles, 13 cite unpublished results, 14 or provide no references for this finding. 15–17 Because of the frequent finding of basophilia in parasitic infections of animals and the many allusions in the parasito- logic and immunologic literature to such a phenomenon in humans, this study was conducted to determine whether pe- ripheral basophilia is common in human parasitic infections. MATERIALS AND METHODS Chart review. All available records of patients referred to the Clinical Parasitology Unit, Laboratory of Parasitic Dis- eases, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH) (Bethesda, MD) from 1979 to 2002 were manually reviewed by one in- vestigator (E.M.). Almost all patients were referred from either a physician or a medical organization for evaluation of a possible parasitic infection or for entry into one of many ongoing NIAID clinical research protocols, each of which had been approved by the NIAID Institutional Review Board. The following information was collected on every patient that met entry criteria: age, sex, parasitic diagnoses, complete white blood cell count with a differential count, IgE level (when available), and probable region of acquisition. Patients were classified as having acquired their parasitic infection as a consequence of being an immigrant to the United States, having visited friends and family abroad (VFF), or having been a traveler or temporary resident of a foreign country (expatriate). American patients whose source of exposure was the United States were classified in the expatriate cat- egory. The presence of basophilia was then evaluated in the following groups: all patients with helminths (AH), patients with only helminths (OH), patients with both helminth and protozoan infections (HP), and patients with only protozoan infections (OP). Additionally, data were collected on 50 sub- jects who were referred for possible parasitic infection (often because of eosinophilia), but whose evaluations failed to document a parasitic infection for use as a comparison group (U). Inclusion/exclusion criteria. Criteria for inclusion included parasitic infection diagnosed at NIH and the existence of a complete blood count with a differential count done at NIH before antiparasitic treatment was initiated. Exclusion criteria included acquired immunodeficiency syndrome (AIDS), ma- lignancy, ongoing systemic immunosuppression, primary he- matologic disorder, or a history of antiparasitic (generally anthelmintic) therapy within two months prior to the first NIH visit. Definition of parasitic infection. Parasitic infection was de- fined as either 1) positive identification of appropriate para- site stages on a stool examination, blood filtration, blood smear, urine sample, skin snip, or tissue biopsy; 2) positive result on a stool antigen-capture enzyme-linked immunosor- bent assay for Giardia lamblia; 3) positive result in a poly- merase chain reaction (PCR) for Loa loa in blood; 4) positive PCR result for Onchocerca volvulus in the skin; 5) positive circulating Wuchereria bancrofti antigen test result; 6) patho- gnomic magnetic resonance imaging findings or positive se- Am. J. Trop. Med. Hyg., 69(1), 2003, pp. 87–91 Copyright © 2003 by The American Society of Tropical Medicine and Hygiene 87