Infectious retroviruses have been detected in 22 of 45 randomly selected patients with acquired immune deficiency syndrome (AIDS) and in other individuals from San Francisco. The AIDS-associated retroviruses (ARV) studied in detail had a type D morphology, Mg2+-dependent reverse transcriptase, and cytopathic effects on lymphocytes. The viruses can be propagated in an established adult human T cell line, HUT-78. They cross-react with antiserum to the lymphadenopathy-associated retrovirus isolated from AIDS patients in France. Antibodies to ARV were found in all 86 AIDS patients and in a high percentage of 88 other homosexual men in San Francisco. This observation indicates the widespread presence of these lymphocytopathic retroviruses and their close association with AIDS.

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A virus given the name ground squirrel hepatitis virus (or GSHV), with many of the unique characteristics of human hepatitis B virus (HBV), has been found in Beechey ground squirrels in northern California. (2), the viral DNA (3), a DNA polymerase activity (4, 5), and probably hepatitis B e antigen (HBeAg) in a cryptic form (6). No crossreaction has been found between HBsAg and a large number of antigens of other viruses that have been tested (7). HBcAg and HBeAg were also considered unique to HBV.The viral DNA is circular and has a contour length consistent with that of double-stranded DNA of approximately 3200 base pairs (bp) (3). However, as isolated from virions, the DNA was not completely double stranded. Between 15% and 50% of the length of different molecules was single stranded (8-10). A DNA polymerase activity in the viral core catalyzed a repair reaction that converted the DNA to fully double-stranded circular molecules of approximately 3200 bp (8-10).Persistent infection with HBV is common, continues for years (11), and is accompanied by continuous circulation in the blood of high concentrations of incomplete viral forms consisting of small spherical HBsAg particles 16-25 nm in diameter and long filamentous HBsAg containing structures approximately 22 nm in width and up to 500 nm in length (1, 2, 12) as well as complete virions usually in much lower concentrations. Persistent infection in humans is associated with chronic hepatitis (13) Gerin, personal communication).Here we describe a virus found in ground squirrels in one region of northern California that is similar to HBV and WHV and may represent a third member of this class of viruses.MATERIALS AND METHODS Sera. Sera were obtained from all animals by cardiac puncture. Apparently healthy Beechey ground squirrels (Spermophilus beecheyi) were obtained from Point Lobos, CA (location A), a region adjacent to the Stanford University campus (location B), and a region near Santa Barbara, CA (location C). Sera containing high concentrations of HBV were obtained by plasmapheresis of a persistently infected patient after informed consent was obtained.Assay for Virion DNA Polymerase Activity. Particle-associated DNA polymerase levels in sera were determined by a modification of the method previously described (19). Serum samples were centrifuged in an Eppendorf centrifuge at 10,000 rpm for 10 min to remove precipitated protein and other debris; 200 Ml of each supernatant was layered over 500 ,ul of 30% sucrose (wt/vol) containing 10 mM Tris-HCI, 0.1 M NaCI, 5 mM EDTA, 0.1% 2-mercaptoethanol, and 1 mg of centrifuged bovine serum albumin per ml in 1-ml polycarbonate tubes and particles were pelleted in a Spinco type 25 rotor for 16 hr at 25,000 rpm and 4°C. Supernatants were removed by suction and discarded, and inner walls of the tubes were wiped dry. The pellets were resuspended in 50 ,l of 1.5% Nonidet P-40/0.1% 2-mercaptoethanol/10 mM Tris-HCI, pH 7.5/0.1 M NaCl. Then 25 ,ul of 0.2 M Tris-HCl (pH 7.5), 80 The publication costs of this article...

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