To better understand what William S. Burroughs might have had in mind with the phrase 'language is a virus' let us begin with the well known passage from his novel The Ticket That Exploded (1962):
The 'Other Half' is the word. The 'Other Half' is an organism. Word is an organism. The presence of the 'Other Half' a separate organism attached to your nervous system on an air line of words can now be demonstrated experimentally. One of the most common 'hallucinations' of subjects during sense withdrawal is the feeling of another body sprawled through the subject's body at an angle ... yes quite an angle it is the 'Other Half' worked quite some years on a symbiotic basis. From symbiosis to parasitism is a short step. The word is now a virus. The flu virus may once have been a healthy lung cell. It is now a parasitic organism that invades and damages the lungs. The word may once have been a healthy neural cell. It is now a parasitic organism that invades and damages the central nervous system. Modern man has lost the option of silence. Try halting your sub-vocal speech. Try to achieve even ten seconds of inner silence. You will encounter a resisting organism that forces you to talk. That organism is the word. 
Secondly, here is a passage from Nova Express (1964), 'Technical Deposition of the Virus Power', written with the assistance of Ian Sommerville, describing a new technological habitat of the virus in which subatomic radiation of a cyclotron is focused upon a virus made of computer code 'developed by the information theorists' containing 'our own image':
It was found that the binary information could be written at the molecular level ... However, it was found that these information molecules were not dead matter but exhibited a capacity for life which is found elsewhere in the form of virus. 
Thus, over thirty years ago Burroughs had developed viral tropes of genetic mutation, genetic algorithms, binary code as genetic information of the human organism, computers and viruses, i.e., concerns of present-day artists, many of whom have Laurie Anderson's contagious ditty running through their heads: 'language is a virus, oooooo'. Although the old man of the Beats seems to grow younger against an increasingly pervasive backdrop of viral tropes and technological rhetoric, it is best to temper thoughts of prophecy when listening to Anderson's pop praise song because it just so happens to be a paean to L. Ron Hubbard, the founder of Dianetics and the Church of Scientology.
Burroughs' notion of the virus had developed through his engagement with a series of organismic theories, the first one being the General Semantics of Count Alfred Korzybski, the second the orgone theories of Wilhelm Reich, and the third the Dianetics of Hubbard. The first two theories were an important source for the uncanny bodies familiar to Burroughs' readers, bodies capable of amoeba-like osmotic ingestion of other bodies as though their entire surface had become orifice, bodies with the gelatinous consistency of protoplasm, entire bodies, in other words, that mimicked cells. Culminating with Naked Lunch, these goo bodies were the culture in which Burroughs' first variety of virus grew, what I call the usurper virus, one that overtakes completely through the pathologising of Burroughs' self-described gay erotics of becoming one and the same, through the monomaniacal drives of junk and sex, through an association with the global metaphors of cancer, or through incorporative operations of metaphoricity itself.  Dianetics, on the other hand, influenced the virus' first major mutation in his writings immediately following Naked Lunch, creating a new virus that shifted from its formerly crass amoeboid behaviour to a differentiated and technically sophisticated entity and, most importantly, to something that functioned so similarly to language that it became language.
This capacity for and of language was a product of the combined effect of Hubbard's engrams and the Dianetic demon, namely, of inscription and voice. Furthermore, it was fused at every point with communications technologies which recorded absolutely everything into the core of cells, took over the internal broadcasts prefiguring the voice, and rendered people inveterate senders or receivers. On an evolving historical backdrop of twentieth century psychotechnologies (in the non-Cartesian framework of organismic theories, psychophysiological), the movement from Burroughs' usurper virus to its mutation is repeated in the transformation of Korzybski's psychogalvanic tests, used to assert the existence of psychosomatic responses, to Scientology's E-meter, something akin to a lie detector used to 'clear' the 'aberee' of engrams. In the same manner Reich's atmospheric orgone energy became intermixed in the post-war period with both the mutative background radiation of above-ground atomic testing and the mind-control transmissions of telecommunications.
In addition, the functional inscriptive and transmissional attributes of actual viruses - their organic-inorganic threshold status mimicking the requirements of writing to find a living host in order to reproduce, the biolinguistic segmentations of genetic code with syntax and phonetics, and the sociality produced by their communicability - came to find their technologies within Burroughs' practices (with Brion Gysin) of literary cut-ups and tape recorder experiments, attempts at recording sub-vocal speech, and the tech specs in his writings afforded by wiz-kid lover Ian Sommerville.  Indeed, Burroughs occupies a place of historical importance with his insistence that the endophasic and mnemonic psychotechnologies of modernism be practically realised. That this occurred at the same time that other concurrences of language and technology lodged at the cellular level moved from being couched in organismic theories to those of genetics, also places Hubbard and Burroughs at the heart of the historical shift from mechanics, with its modernist surface-rendered cuts and wounds and sutures, to a mechanistic genetics and all it can grow, engineer, communicate or infect.
By the time Burroughs read L. Ron Hubbard's Dianetics , it must have seemed very familiar, for here was not only the third in a sequence of influential organismic theories, but one obviously influenced by his first love - Korzybski's General Semantics. It was also a theory whose pathological sphere was practically limitless, eagerly ascribing all those areas to which Korzybski granted a benign existence a veritable plague of evil agency: the 'engram', an entity highly conducive to the (fallen) personifications that constituted Burrough's character studies and equally susceptible to the heroics of a correspondingly expanded therapeutic that constituted the cornerstone of Hubbard's pretentiousness and popularity.
For Hubbard, the engram is, most simply, an injurious or otherwise painful moment literally recorded, not as memory, but into the cell as a 'definite and permanent trace left by a stimulus on the protoplasm of a tissue' (D, 87). The recording is done within the cells themselves and 'is not a memory; it is a cellular trace of recordings impinged deeply into the very structure of the body itself'. The recordings themselves contain absolutely everything and would be very much 'like phonograph records or motion pictures, if these contained all perceptions of sight, sound, smell, taste, organic sensation, etc.' (D, 87). If these engrams stay in place and are not 'discharged' through therapeutic means, they will predispose the individual to psychosomatic illnesses, mental disorders and always something less than complete psychophysiological sanity. The therapeutic process basically entails discovering these recordings and playing them back over and over again until these lose their power, become boring and are shifted out of the reactive mind into regular memory banks where they will do no harm. When Burroughs first read Dianetics he wrote to Ginsberg that therapy was a way to 'simply run the tape back and forth until the trauma is wiped off. It works'. 
Hubbard secured the term 'engram' from Richard Wolfgang Semon's idea of the mneme, developed early this century.  His mnemic principle is based upon how stimuli produce a 'permanent record ... written or engraved on the irritable substance', i.e., upon cellular material energistically predisposed to such inscription ... (M, 24). The resulting 'mnemic trace' (or 'engram') can be revivified when an element resembling a component of the original complex of stimuli is encountered. Thus, Semon recounts how the smell of Italian cooking oil invoked 'most vividly the optic engram of Capri' (M, 92) from a trip years before. It did not invoke 'the melody of the barrel-organ, the heat of the sun, the discomfort of the boots' which were equally part of the original engram complex, but this does not rule out that sometime in the future a pair of tight boots might revivify Capri. The complete engram complex of the entire organism is thereby effectively reproducible from small units anywhere throughout the organism. Cut-up planaria, hydra, stentors, and begonias provided ample evidence for mnemic dispersal and regeneration from pieces approaching the size of 'germ-cells'. But Semon ran into difficulty when confronted with the evidence for cortical localisation of memory in vertebrates, for how could it be reconciled with a capacity for cellular recording and reproduction of stimuli throughout the organism?
Semon found evidence in the way that different parts of the body relate to each other involuntarily, such as 'reflex spasms, co-movements, sensory radiations' to infer distribution of 'engraphic influence' (M, 123). He also took inventive recourse to phonography, the mneme machine, to explain the uneven distribution and revivification of engrams. Here, each phonograph represents a primary site of excitation that privileges its immediate vicinity yet nevertheless contains fainter impressions of the entire orchestra, the organism. Thus, 'tight shoes' might invoke walking to Capri but the smell of cooking would be weaker:
Let us imagine that in an opera house of the usual construction a great number of very similar phonographic recording machines are distributed in different parts of the building, among the boxes, the stalls, the dress and upper circles, on and behind the stage, and also in the orchestra between the seats of the players. In the separate reproductions of the various records made during the playing of the orchestra it will be found that no two of the records are alike, despite the similarities of the machines. According to the location of the machines, it will be possible to distinguish differences of clearness and power in the reproduction of the music. Among the instruments distributed in the orchestra itself, those in the vicinity of the basses will reproduce the renderings of the bass parts out of all proportion to the designed effect of the total production. The phonographs placed between the 'cellos will in their reproduction give us the impression that during the performance the 'cellos played the leading part, and that the rest of the instruments provided merely a pianissimo accompaniment. So, with the records made by the other machines, there would be differences of emphasis according to their position (M, 125).
Although Semon explicitly warned against following this model too closely because the relationship of an engram to a phonogram was the same as 'a horse pulling a carriage to a locomotive propelling one' (M, 124), his qualification was based upon the complete sensory register of the engram - 'photic, thermal, and electric influences, that is, with stimuli belonging to all possible kinds of energies' (M, 125) - versus the singular acoustics of the phonograph. In other words, he would have been perfectly happy to compare his engram with some more advanced, multisensory technology; it was not recording technology per se or its prosthetic applicability to the organism that bothered him. What at the time besides the phonograph, with its historic displacement of the voice, could disperse a sense of mind and memory throughout the entire organism to decentralise cortical localisation?
Similar to his disposition toward Korzybski, Hubbard transformed what Semon considered functionally neutral into something intrinsically pathogenic. Hubbard's engram was first and foremost inscribed as a record of trauma, the most unadulterated cases being those instances where the individual/organism is abused while in an unconscious state resulting from accident, anaesthesia or some other means. The cells are recording these physical and verbal abuses while the usual mechanism of the conscious self, the 'analytic mind' which would otherwise be recording absolutely everything, is completely shut down for pure survival reasons. However, if engrams were created only by the exceptional traumatic circumstances Hubbard initially describes, then few people would have need for therapy. Therefore, he retains the unconsciousness of severe trauma for its rhetorical clout while extending the capacity for engram formation to any degree of reduced consciousness. In other words, any shortfall of complete, lucid consciousness on the part of the analytic mind will be met with a proportionate degree of 'unconsciousness' and with it a recording of engrams. In fact, much of Hubbard's Dianetics is concerned with describing means by which engrams proliferate. For instance, we are alerted to the fact that foetuses are busy accumulating engrams not just by the underestimated frequency of attempted abortions but seemingly by any little bump or jostle. Furthermore, motherly love is a cruel hoax: the act of leaving that prenatal hell of a womb creates another slew of engrams in both baby and mother and continues to do so as the baby's voice invokes within the mother the trauma of childbirth and as the engramic production of this 'revivification' itself finds its way back to the baby, and so forth in a truly vicious cycle. Since 'zygote, embryo, foetus, infant, child, adult: these are all the same person' (D, 188) - there will never be any shortage of therapy required.
The accumulated bank of these recorded and stored engrams produce the 'combined cellular intelligence' constituting the 'reactive mind', the mind of a coalesced trauma body, an evil phantom double to the 'analytic mind', the intrinsically good and perfectly running calculating machine that is always recording everything as a matter of consciousness and storing it in the 'standard memory banks' (D, 185). During any prolonged suspension or minute lapse of consciousness, from trauma to picnolepsy, the reactive mind is busy doing its own recording, causing further problems for the analytic mind. Assuming that anything short of epiphany has a dose of dim-wittedness about it, then it is clear that the reactive mind is likely to be ever-present. This evil phantom is the 'Other Half' from The Ticket That Exploded passage cited above. The Other Half could, of course, be language itself as an entity preceding any one individual, dictating its own conditions upon an individual's fundamental ability to exist socially, acquired contagiously in youth long before any prophylactic possibility of critical self-consciousness. Most persuasively, language is a virus in that both are dead until they find life within a human host: '... the evilest of them all are the viruses ... So bone lazy they aren't even hardly alive yet. Fuckin' transitional bastards'.  But language in this sense has no body, nor is it solipsistically bounded by a single body. The Other Half could also be the hallucinated body set askew during sensory deprivation, the kinaesthetic body, the astral body, the imago, the phantom body that makes its appearance felt when limbs are amputated, but none of these bodies have language and none have the agency, let alone a subaltern one, that could work the line between symbiosis and parasitism, let alone take over the whole show. The reactive mind has both a concrete corporeal existence and language. The Other Half mimics the submerged presence of the reactive mind in the modulated symmetry of consciousness and unconsciousness, as both exist in order to record. With respect to agency, that both record experience into their respective banks (as though in a proprietary ritual of capitalism) should account for the move to parasitism and beyond.
The reactive mind meets the virus in Hubbard's assertion that 'it is fairly well accepted in these times that life in all forms evolved from the basic building blocks: the virus and the cell' (D, 73). Viruses may in fact have played a part in the electrical and cognitive functioning of an individual because 'even neurons exist in embryo in the zygote, and neurons do not themselves divide but are like organisms (and may have the virus as their basic building block)' (D, 185). Burroughs' version simply reverses the order; neurons do not have a virus in their collective past but instead the healthy neural cell mutates into the virus that is language. The evolutionary development toward language proposed by Burroughs was aided by Hubbard in at least two ways: first, the reactive mind was already equipped with its own voice engramically recorded and played back - the Dianetic demon - and second, there was a radio station available to transmit the recordings.
Hubbard, through a very familiar process, derived his demon by pathologising the Socratic daemon which in contrast more resembles a best friend. In fact, what looks like premonition of 'language as a virus' by Burroughs in 1955 - 'It's almost like automatic writing produced by a hostile, independent entity who is saying in effect, "I will write what I please"'  - is actually a melding of traditional muse, Surrealist automatism and Socratic daemon, and is too beneficial for Burroughs, too insufficiently pathogenic, to be Dianetic and viral. The Dianetic demon is, according to Hubbard, a demon 'who gives thoughts voice or echoes the spoken word interiorly or who gives all sorts of complicated advice like a real, live voice exteriorly'; yet it should not be confused with psychotic voices: '(People who hear voices have exterior vocal demons - circuits have tied up their imagination circuits)' (D, 126). Hubbard equates its form and function:
A Dianetic demon is a parasitic circuit. It has an action in the mind which approximates another entity than self. And it is derived entirely from words contained in engrams (D, 124).
This other-entity-than-self is wired in between an individual's analytical consciousness and the standard data banks of memory. When the consciousness asks for data pure and simple, an exchange that usually transpires in silence, it is given some other data by a voice. That voice eventually insinuates itself more and more until it effectively takes over, leaving the '"I" on a tiny and forlorn shelf' (D, 125). This is not a hydraulic condition caused by what Korzybski would call a 'semantogenic blockage'; instead it is a electronic flow redirected within circuitry fed with a nefarious source of countermanding engramic voice from the coexistent body of mind which is the reactive mind. Here, Hubbard gives wiring instructions; the 'analyser' belongs to the analytical mind of consciousness and self-identification and 'got to listen to me, by God' are words, in this case, inscribed as an engram:
An electronics engineer can set up demons in a radio circuit to his heart's content. In human terms, it is as if one ran a line from the standard banks toward the analyser but before it got there he put in a speaker and a microphone and then continued the line to the plane of consciousness. Between the speaker and the microphone would be a section of the analyser which was an ordinary, working section but compartmented off from the remainder of the analyser. 'I' on a conscious plane wants data. It should come straight from the standard bank, compute on a sublevel and arrive just as data. Not spoken data. Just data.
With the portion of the analyser compartmented off and the speaker-microphone installation and the engram containing the above words 'got to listen to me, by God' in chronic restimulation, another thing happens. The 'I' in the upper-level attention units wants data. He starts to scan the standard banks with a sublevel. The data comes to him spoken. Like a voice inside his head (D, 124 - 125).
It might sound a bit disconcerting (although you know where to get help) that something as commonplace as inner speech might constitute an aberration caused by other voices interceding upon the self-contained self, yet
It is a safe assumption that almost every aberree contains a demon circuit ... A Clear does not have any 'mental voices'! He does not think vocally. He thinks without articulation of his thoughts and his thoughts are not in voice terms (D, 125).
Of course, this inner biologic is what Burroughs describes above in his rhetorical imperative to 'Try halting your sub-vocal speech. Try to achieve even ten seconds of inner silence. You will encounter a resisting organism that forces you to talk'. This resisting organism - the virus, word, language - has become widespread and naturalised by not calling untoward attention to itself and by not destroying its host, although it has the capability to exile the self to a 'tiny and forlorn shelf'; thus, bearing the strategical acumen of other viruses, the word virus joins both Hubbard and Burroughs who also extol the existential role of survival. For Hubbard, survival is no less than the Goal of Man, and for Burroughs, 'I am primarily concerned with the question of survival - with Nova conspiracies, Nova criminals, and Nova police. A new mythology is possible in the Space Age'. 
1. William S. Burroughs, The Ticket That Exploded, New York: Grove Press, 1962, pp. 49 - 50.
2. William S. Burroughs, Nova Express, New York: Grove Press, 1964, pp. 48 - 49.
3. The following passage best typifies the usurper virus: 'The end result of complete cellular representation is cancer. Democracy is cancerous, and bureaus are its cancer. A bureau takes root anywhere in the state, turns malignant like the Narcotic Bureau, and grows and grows, always reproducing more of its own kind, until it chokes the host if not controlled or excised. Bureaus cannot live without a host, being true parasitic organisms ... Bureaucracy is wrong as a cancer, a turning away from the human evolutionary direction of infinite potentials and differentiation and independent spontaneous action, to the complete parasitism of a virus.' William S. Burroughs, Naked Lunch, New York: Grove Press, 1959, pp. 133 - 134.
4. On Burroughs' audiotape experiments see Robin Lydenberg, 'Sound Identity Fading Out: William Burroughs' Tape Experiments', in Wireless Imagination: Sound, Radio and the Avant-garde, eds. Douglas Kahn and Gregory Whitehead, Cambridge, Massachusetts: MIT Press, 1992, pp. 409 - 437.
5. Early mention (7 October 1959) of Dianetics in The Letters of William S. Burroughs: 1945 - 1959, ed. Oliver Harris, New York: Viking Penguin, 1993, p. 429. This edition was L. Ron Hubbard, Dianetics, New York: Hermitage House, 1950. Henceforth cited as D.
6. Letter to Allen Ginsberg (27 October 1959), Letters, ibid., p. 431.
7.Richard Semon, The Mneme, London: George Allen & Unwin, 1921. Henceforth cited as M.
8. Letter to Allen Ginsberg (13 October 1956), Letters, op. cit., p. 335.
9. Letter to Allen Ginsberg (7 February 1955), ibid., p. 262. The Socratic daemon relates also to Burroughs' suspicious attitude toward the Buddhist attempts of some of his peers to quell the inner voice, such as Ginsberg, who sought to rid the voice by vibrating his brain pan with chant. Such attempts might, after all, create a 'cured writer'. Naked Lunch, op. cit., p. 138.
10. Victor Bockris, A Report from the Bunker with William Burroughs, London: Vermillion, 1982, p. 2.