Almeida [née Hart], June Dalziel (1930–2007), virologist, was born on 5 October 1930 at 10 Duntroon Street, Glasgow, the daughter of Harry Leonard Hart, bus driver, and his wife, Jane Dalziel, née Steven. On leaving school in 1947 she became a laboratory technician in histopathology at Glasgow Royal Infirmary on a salary of 25s. per week. She then moved to St Bartholomew's Hospital, London, working in the same discipline. On 11 December 1954, at Hampstead register office, she married Enriques Rosalio (Henry) Almeida (1913–1993), a Venezuelan artist, and son of Cirilo Almeida Crespo, also an artist. They had one daughter, Joyce.

After their marriage June Almeida and her husband emigrated to Canada, where she was appointed an electronmicroscopy technician in the Ontario Cancer Institute in Toronto. On the other side of the Atlantic there was less emphasis on formal training requirements and the necessity of having to overcome academic hurdles. Within a short time her skills and enthusiasm became apparent, her name being included on numerous scientific publications, particularly relating to viral structure. Fortuitously, in 1964 A. P. Waterson, recently appointed to the chair of microbiology at St Thomas's Hospital medical school, visited Toronto, was impressed by her work, and persuaded her to join him at St Thomas's. She moved with him to the Postgraduate Medical School of London three years later. These years were the start of a particularly fruitful period in June Almeida's career; her numerous high-quality publications were rewarded with the degree of DSc, and by the time of her death most virology review articles and chapters in textbooks contained her photoelectronmicroscopy of viruses.

The technique employed and pioneered by June Almeida, immuno-electronmicroscopy employing negative contrast, had a simplicity and originality that characterized her work. Virus preparations were mixed with specific antibodies to the virus, which resulted in the clumping of virus particles that could be visualized by electronmicroscopy; the concentration of antibody could then be reduced to reveal details of the fine structure of the virus, sometimes with bridging of the virus particles by the specific antibody. This technique made it possible to visualize directly the fine structure of viruses that failed to grow to sufficiently high concentrations to display by negative staining. Notable among her achievements with this technique was the first visualization of the fine structure of the rubella virus. One of her most important discoveries, which provided a landmark for those investigating hepatitis B, again using the technique of immune electronmicroscopy on detergent-treated virus particles, revealed a new antigen-antibody system. There were two immunologically distinct components to the virus, an outer coat and a small inner component. She also collaborated with David Tyrrell, director of the Common Cold Research Unit in Salisbury, who had developed a new technique employing organ cultures from respiratory material. They jointly characterized new viruses—the coronaviruses—which caused acute respiratory infections; SARS is now recognized as belonging to this group of viruses.

It was particularly fortunate that in 1970 Albert Z. Kapikian, from the National Institutes of Health in the USA, spent six months' sabbatical in Waterson's department, at the suggestion of his laboratory chief, R. M. Chanock, and while there attained first-hand experience of immuno-electronmicroscopy from June Almeida. He took the technique with him on returning to the USA and exploited it at the National Institutes of Health with his colleagues, leading to the discovery of viruses hitherto unseen. These included the virus responsible for an outbreak of non-bacterial gastroenteritis in a school in Norwalk, Ohio. By immuno-electronmicroscopy of clinical samples from this outbreak fed to volunteers, aggregates of small-structured round virus particles were visualized and antibody responses could be assessed, employing acute and convalescent phase serum samples. These viruses, considered to be the first viruses identified in the etiology of infectious gastroenteritis, were originally named Norwalk viruses (now noroviruses, a term June Almeida vehemently disliked) and similar viruses are now known to be the commonest cause of non-bacterial gastroenteritis among adults. A further notable achievement deriving from Almeida's technique was the visualization for the first time of the elusive hepatitis A virus, using similar immuno-electronmicroscopy methods to those of the Norwalk virus discovery, by Stephen M. Feinstone, Kapikian, and Robert H. Purcell, at the National Institutes of Health. Although the epidemiology and clinical features of hepatitis A had long been established, not least because of epidemics of infection in wartime and in institutionalized populations, the virus had not itself been seen until Almeida's techniques were used.

Almeida had a remarkable enthusiasm and the ability to interact equally well with her technical, scientific, and medical colleagues, regardless of their seniority. Meetings with her were full of fun. She taught many virologists, whether working on the more fundamental or the clinical aspects of virology. She enabled laboratory workers to identify viruses within a few minutes of clinical specimens arriving in the laboratory, which contrasted with the hitherto more laborious and time-consuming techniques then available. Almeida had the capacity to put over her methods and ideas in a delightfully direct and simple way, whether this was to one or two sitting beside her in the electronmicroscope suite, or to an audience of several hundred in a lecture theatre.

Almeida finished her career at the Wellcome Research Laboratory, where she worked on developing diagnostic assays and vaccine development. Her first marriage having ended in divorce, on 1 December 1982 at Greenwich register office she married a fellow virologist, Phillip Samuel Gardner, formerly Weidengarten (1925–1994), son of Arnold Weidengarten, diamond merchant. In 1985 they retired to Bexhill. In the late 1980s she returned to St Thomas's in an advisory role, publishing with colleagues in virology some of the first high-quality negative staining electronmicrographs of human immunodeficiency virus. Nevertheless her career took different directions. She trained and qualified as a yoga teacher, running several successful classes in the town, and (having developed an interest in collecting antiques through regular visits to East Street bric-a-brac market in Walworth) also trained in china restoration and achieved considerable expertise, which led to a productive and enjoyable career trading in antiques with her husband, Phillip. In later life she enjoyed being a grandmother, providing daycare for her two granddaughters during holidays and taking great pleasure in learning the computer skills beloved of their generation.

The career of June Almeida demonstrated how an academically able Scottish schoolgirl, despite leaving school aged sixteen, became an internationally renowned clinical scientist whose skills in electronmicroscopy enabled her not only to identify viruses the structure of which had hitherto been unknown, but also to shed light on the pathogenesis of virus infections and to pioneer and improve techniques for the diagnosis of virus infections. She died on 1 December 2007 at her home, 56 Sea Road, Bexhill, after a heart attack, and was survived by her daughter, Joyce, a consultant psychiatrist, and her granddaughters.