The Bushmeat Theorists Fail to Deliver Once Again

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The following article was originally written in December 2005, and represents the draft of a letter which I had intended to send to Emerging Infectious Diseases in response to an article published in that month's issue of the journal by a team led by doctors Nathan Wolfe and Donald Burke from Johns Hopkins University in Baltimore, Maryland, USA.

The title of the article, "Central African hunters exposed to simian immunodeficiency virus", is amusing, because what Wolfe and Burke actually demonstrate in their article is the exact opposite. Not one of the African hunters whom they tested showed any evidence of SIV exposure.

Just one of more than a thousand members of the general Cameroonian population showed some signs (by a single assay, ELISPOT) of exposure to an SIV from a colobus monkey. However, other HIV/SIV antibody assays conducted on this sample were negative, and when the researchers tried to confirm that they had found a true SIV, using PCR (polymerase chain reaction) techniques, they came up negative. There is therefore a real possibility that their one apparently positive result was actually a false positive. Even if it were a genuine positive, it would offer only very limited support to the bushmeat theory of origin of AIDS.

Doctors Wolfe and Burke and their co-authors are to be congratulated for publishing their predominantly negative findings, even if they are not to be congratulated for publishing such findings under a gratuitously misleading title!

A more appropriate title for this article might have been "Failure to detect SIV transmission from local primates to Cameroonian bushmeat hunters".

My letter of response to Emerging Infectious Diseases was never submitted, largely because its length exceeds the journal's guidelines for readers' letters. I have decided instead to make minor emendations, and to post it on this web-site.

Ed Hooper. 28/3/06


Dear Sir,

Meaningful research into simian immunodeficiency virus (SIV) infections in African primates, and into potential future zoonoses, is to be welcomed, and in many respects doctors Wolfe and Burke and their collaborators are to be commended for their ongoing efforts in this area. However, it is concerning that recent articles by these authors display a disparity between the very significant data that have been collected and the conclusions derived therefrom.

One of the earlier articles by these authors (1) was entitled "Naturally acquired simian retrovirus infections in central African hunters", and reported significant levels (10 of 1,099 = 1%) of simian foamy virus (SFV) infection among Cameroonians from nine villages sited close to natural non-human primate habitats who reported direct contact with the blood or body fluids of wild non-human primates, "mainly through hunting and butchering". The article theorised that SIVs could also be transmitted to humans in this way, but it did not report the detection of any human infections with SIVs. Subsequent enquiries about this topic to Dr Wolfe merely elicited the response that research was ongoing.

Wolfe and Burke's latest article is entitled "Central African hunters exposed to simian immunodeficiency virus" (2), but it documents the exact opposite. Just one of 1,224 Cameroonian plasma tested showed some indications of exposure to an SIV (in this case SIVcol, from Colobus guereza) by ELISPOT assay, but the plasma in question did not come from any of the "hunters", namely the 76 persons tested who reported high levels of exposure to the bodily fluids of non-human primates (NHPs) by hunting, butchery or pet-keeping. Instead, it came from one of the 1,071 members of "a general population of urban and rural areas of Cameroon, where people may handle NHP meat but are unlikely to have repeated contact with the blood or body fluids of freshly killed animals".

The ELISPOT-positive plasma showed strong humoral, but only weak cellular immune reactivity to SIVcol peptides, and the authors were unable to amplify any SIV nucleic acids by PCR. The authors proposed that this could be indicative of a virus hiding in lymphatic tissues, but a likelier explanation is that this was a false positive, or that the one human exposure to SIV that they had detected had failed to cause productive infection.

In an accompanying "Perspective" piece (3), the same authors list "some zoonotic pathogens that have emerged in the Cameroon-Congo Basin Region, 1970-2005". Nine of the ten pathogens listed are identified as causing only limited human exposure, either without replication, as single infections, or as localised outbreaks or epidemics. The tenth pathogen is HIV, and it is proposed that this arose among hunters and butchers when SIV was transmitted via "repeated single infections or localised outbreaks, followed by national then global emergence". But the first crucial step of this transmission chain (the productive SIV infection of local hunters or butchers) is precisely what the authors have thus far failed to establish. In short, Wolfe and Burke are jumping the gun, for although their data suggests that Africans may perhaps be occasionally exposed to SIVs through cutting up bushmeat, they have as yet provided no evidence that such SIVs either replicate in humans, or cause productive infections.

Few would deny the theoretical possibilities that human exposures to SIVs through bushmeat might sometimes occur, or even that such exposures might sometimes cause productive infections. What is at issue is whether such human infections with SIV (if indeed they occur), are likely to have sparked either epidemic outbreaks, or the AIDS pandemic.

There are indeed ten known examples of HIVs that seem to have derived from distinct zoonoses (HIV-1 Groups M, O and N, and HIV-2 Groups A to G, inclusive), but it seems that only five of these (HIV-1 Groups M, O and N, and HIV-2 Groups A and B) have sparked either outbreaks or epidemics, and all five of these outbreaks appear to have occurred in or around [or perhaps in the case of HIV-1(N) shortly after], the 1950s. This factor alone (the lack of evidence of any HIV infections prior to the 1950s) suggests that the hand of modern man, or, more specifically, the hand of modern medical man (ie iatrogenic factors), may have played a key role.

The most ironic aspect of this is that while advocates of the bushmeat origin of HIV seem once again to be making premature claims, another far more precisely documented theory of HIV origin, the oral polio vaccine (OPV) theory, has been repeatedly (and wrongly) described in scientific journals as "destroyed" or "refuted". Yet all five of the recognised HIV outbreaks coincide with areas where experimental polio vaccines produced in African primate cells are known (or believed) to have been administered to large populations of Africans in the late 1950s. [4] By contrast, there is only a tenuous epidemiological linkage between the hearth of HIV-1 as mooted by proponents of the bushmeat theory (which according to their latest version of events, lies in or very near south-eastern Cameroon), and the observed epicentre of pandemic (HIV-1 Group M-related) AIDS in the Democratic Republic of Congo (DRC, former Belgian Congo), Rwanda and Burundi.

Furthermore, there is to date no evidence of HIV-1(M) infection in the Cameroon/Gabon/Congo Brazzaville region to the north of the River Congo before the year 1981. This is more than 20 years after the first evidence of HIV-1(M) in Leopoldville/Kinshasa [DRC], five years after the first evidence of HIV-1(M) in Yambuku and Abumombazi (northern DRC), four years after the first evidence of the virus in Kigali, Rwanda, and a year after the first evidence of the virus in Bujumbura, Burundi.

During the 1950s, the approved standardisation procedures for polio vaccines allowed for them to be cultivated in the cells of any viable primate, and although most such vaccines were prepared in the cells of Asian monkeys such as the rhesus and cynomolgus macaques, vaccines prepared in the cells of several species of African primates were also used in a surprisingly large number of human trials. As we now know, several of these African primate species are host to their own SIVs.

Let me give just one example. From 1955 onwards the ancestral host to HIV-2, the sooty mangabey, Cercocebus atys, was one of many primates that were used for polio vaccine testing and propagation. The Pasteur Institute vaccine that was used in Europe was an inactivated polio vaccine (IPV), and was prepared mainly from the cells of Papio papio, the Guinea baboon, originating from West Africa. Large numbers of baboons were captured and held in collective pens at the Institut Pasteur facility at Pastoria, near Kindia in present-day Guinea Conakry. However, other "small monkeys" were also held in these same pens, and these included sooty mangabeys. A Guinean scientist who worked at Pastoria in the 1950s and who directed the facility from 1961 onwards has informed me that starting in 1956, Pasteur-produced polio vaccines were administered on a large scale by injection in French West Africa. (From 1955 to 1958, the Pasteur Institute's director of virology, Pierre Lepine, wrote several articles about the comparative benefits of killed and live polio vaccines, in the course of which he discussed the possibility of administering a third dose of attenuated vaccine, after establishing immunity with two prior injections of inactivated vaccine. He indicated that he and his colleagues had "conducted experiments along these lines, and we continue them, but we can only proceed with very great prudence and much deliberation.") One of the ways that Lepine proposed administering this live vaccine dose was, rather surprisingly, by injection, rather than by mouth. According to the Guinean scientist, this regime of injecting two doses of inactivated polio vaccine followed by one injection of live polio vaccine was indeed employed in French West Africa shortly after 1956.[4]

Apart from man and the sooty mangabey, it seems that the only other African primate that can be persistently infected with HIV-2-like viruses is the baboon. [5] There are therefore two potential ways in which vaccine stock used in Africa in the 1950s could have become infected with the HIV-2 precursor. A batch or batches could have been prepared direct from the cells of an SIV-infected sooty mangabey, or a batch or batches could have been prepared from baboons that had been co-caged with sooty mangabeys, and infected with SIV from the latter species via bites or scratches.

There are strong indications that the Portuguese also administered polio vaccines in their overseas territories, including Portuguese Guinea, now Guinea-Bissau, during this period. There is no record of the Portuguese having developed their own vaccine during the 1950s, but they may have used vaccine batches prepared either at the Pasteur Institute in Paris or at one of the Pasteur branches in Dakar (Senegal) or Pastoria, for during that era Pasteur scientists shared several other locally-prepared vaccines with the contiguous territory of Portuguese Guinea. [4] The earliest known appearance of HIV-2 in humans was in 1965, and West Africa (and in particular Guinea-Bissau) represents the hearth of the known HIV-2 outbreaks.[6]

Similarly the ancestral host of HIV-1, the common chimpanzee, Pan troglodytes, was among the primates that were collected in large numbers at both Franceville and at Gamaba farm (near Brazzaville), in French Equatorial Africa, in the second half of the 1950s. It is reported that cells from primates at Gamaba were used to "grow poliovirus" in the Pasteur Institute lab in Brazzaville from 1957 onwards, at a time when scientists based at that lab was conducting human trials of both IPV and OPV in French Equatorial Africa. At least one of the trials of an injected vaccine took place in 1957 at Mitzic (in the north of present-day Gabon) and in the eastern part of the contiguous territory of Spanish Guinea (now Equatorial Guinea), in an area which lies adjacent to the mooted hearths of the "minor variants of HIV-1", Groups O and N, in southern Cameroon. The earliest known infectee with HIV-1 Group O, a Norwegian sailor, appears to have become infected during a trip to Yaounde, Cameroon, in the winter of 1961-2 [7]. HIV-1 Group N was first detected in Cameroon in 1995, and the leading researcher into Group N, Francois Simon, writes that the virus may have emerged in humans some time between about 1970 and 1975, "though", he adds, "this is purely speculative".[8].

A far larger chimpanzee collection scheme based at the Laboratoire Medical de Stanleyville, in the Belgian Congo, was in operation from 1956 to 1960, and by 1958 "some 400" chimpanzees had been collected at an isolated nearby facility, Lindi camp, for the purpose of "perfecting" or "putting the finishing touches to" CHAT, an OPV developed by the Polish-American scientist, Hilary Koprowski. Officially, these chimps were merely used to "test" (ie evaluate the safety and efficacy of) Koprowski's experimental oral polio vaccines. However, personal testimonies from several Belgian and Congolese scientists and technicians, and two Belgian medical administrators, reveal that cells from the Lindi chimps were used to make tissue culture in the Stanleyville lab, and that this tissue culture was then used to prepare batches of locally-made polio vaccine. This locally-made vaccine (together with vaccine prepared in the USA) was administered in mass trials in the Belgian Congo and Ruanda-Urundi from mid-1957 (at latest) until August 1959, when CHAT vaccine was officially approved by the Belgian Congo authorities for feeding to all ages and races upon request. (Various lines of research suggest that from that month onwards, only fully safety-tested vaccine was used, in preference to locally-made batches.) In these former Belgian territories, there is a highly significant correlation between the places where this OPV (CHAT) was fed, and the first appearances of HIV-1 Group M, and of pandemic AIDS. The first evidence of HIV-1 Group M virus comes from a blood sample obtained from a male subject in Leopoldville (Kinshasa), allegedly in 1959, although the precise history of this blood sample is unclear, and it may in reality have been drawn between one to four years later. The age of the male subject is also unknown and, in contrast to previous reports, it is quite possible that he was a child at the time that his blood was tested. If so, then he would presumably have also been a CHAT vaccinee, for all Leopoldville children aged up to five years were vaccinated with CHAT between August 1958 and Aoril 1960. The earliest death from Group M-related AIDS seems to have occurred in 1962 [9].

Since the emergence of the OPV/AIDS theory, the great majority of the persons involved with these polio vaccine trials energetically deny that they ever prepared human polio vaccines from local primate tissues, but their accounts are characterised by internal contradictions and provable errors.[10] Moreover, their versions of events are contradicted by an ever-increasing number of witnesses to, and participants in, these events. However, the CHAT vaccine-makers have been supported by many present-day virologists and public health officials, even if these individuals do not have first-hand experience of the vaccine trials. Many of these individuals, however, have research interests and public health preoccupations which coincide rather closely with the disproving of the controversial or "ugly" theory of OPV/AIDS.[11] They apparently fear that if the AIDS pandemic should ever come to be directly linked to inappropriate medical experimentation, then popular faith in public health initiatives, such as vaccination campaigns, may be irrevocably shaken.

Several alleged "refutations" of the OPV theory of AIDS origin have been broadcast in science magazines and in the medical literature, but none of these refutations have been supported by any hard data. The most popular "refutations" are the following: (a) that batches of CHAT have been tested, and found to be free of HIV, SIV and chimpanzee DNA; (b) that phylogenetic dating analysis proves that the most recent common ancestor (MRCA) of HIV-1 existed in or around 1931, twenty or more years before the OPV trials, and (c) that the subspecies of chimpanzee held at Lindi camp was different from the subspecies of the mooted HIV-1 precursor host, Pan troglodytes troglodytes.

Yet on closer examination, none of these arguments hold water.

(a) The CHAT vaccine samples that were belatedly released for molecular analysis were all produced or prepared in the USA, whereas the vaccine batches that need to be released (if they still exist) and tested are those that were prepared in Africa, for instance in Stanleyville.
(b) Phylogenetic dating analysis is an inappropriate technique for measuring the evolution of a lentiretrovirus such as HIV: it measures only evolution by mutation, whereas 90% of the evolution of the HIVs occurs through recombination. Such attempts to date HIV by a molecular clock are innately bogus.
(c) The chimps at Lindi did not merely originate from "the vicinity of Stanleyville", but came from an area of 300,000 square miles of rain forest, including regions such as the Congo river below Mbandaka, where Pan troglodytes troglodytes chimps are among those that are bought and sold, and transported up-river. In short, the Lindi chimps (which were both co-caged and group-caged) are likely to have included a number of animals infected with one or more variants of "the HIV-1 precursor virus". The situation is further complicated by the chimpanzee tissue cultures that were prepared in the Stanleyville lab, which apparently used pooled chimpanzee sera as growth or maintenance medium. The Lindi camp/Laboratoire Medical de Stanleyville research thus offered multiple opportunities for recombination between different chimp SIVs, and their later dissemination into various African populations where CHAT vaccine batches were tested.[12]


It is now nearly fourteen years since Beatrice Hahn and Paul Sharp published an article entitled: "Human infection by genetically diverse SIVsm-related HIV-2 in west Africa" [13], which provided persuasive evidence that an HIV-2 infection had been acquired by a Liberian man from a sooty mangabey (while leaving open the route of cross-species transmission). For fourteen years researchers (including Hahn, Sharp, Burke and Wolfe) have been searching feverishly for similar evidence of human infection with chimpanzee SIV-related HIV-1 Group M among west central African hunters - and failing to find any such evidence. This latest article - and its deliberately misleading title - only serves to emphasise the weakness of their position.

They know what they want to find, and they are desperate to find it, come what may. Perhaps the reason why they keep failing to deliver is that their "certainties" are not certainties at all. Their long-term refusal to even countenance the OPV/AIDS hypothesis suggests that they may be in denial, and more afraid of the hypothesis than they care to admit.

Doctors Burke and Wolfe are not alone in their assumption that the AIDS pandemic virus, HIV-1 Group M, must have evolved through human contact with chimpanzee bushmeat, but their conclusions are, to say the least, premature. Any sincere approach to unravelling the origins of the HIVs must continue to examine the history of the experimental polio vaccines that were administered in the Belgian Congo, and elsewhere in sub-Saharan Africa, during the second half of the 1950s.

Edward Hooper. 28/3/06.


(1) Wolfe ND, Folks TM, Burke DS et al, "Naturally acquired simian retrovirus infections in central African hunters"; Lancet; 2004; 363; 932-937.

(2) Kalish ML, Wolfe ND, Burke DS, Folks TM et al.; "Central African hunters exposed to simian immunodeficiency virus"; Emerging Infectious Diseases; 2005; 11(12); 1928-1930.

(3) Wolfe ND, Burke DS et al.; "Bushmeat hunting, deforestation and prediction of zoonoses emergence"; Emerging Infectious Diseases; 2005; 11(12); 1822-1827.

(4) Hooper E, "The River", E. Hooper, [Boston: Little, Brown and Co, 2000 (paperback edition)]; 827-877, but especially 831-834. [Note that in the paperback edition these pages represent a completely rewritten postscript. In the Penguin UK (paperback) edition, this new postscript featured on pages 827-874, with the highlighted passage on 831-833.]

(5) Castro BA, Levy JA et al.; "Persistent infection of baboons and rhesus monkeys with different strains of HIV-2", Virology; 1991; 184; 219-226.

(6) Hooper E, "The River", [Boston: Little, Brown and Co, and London: Penguin, 2000], pages 623-643.

(?) Sharp speech

(7) Hooper E, "Sailors and starbursts, and the arrival of HIV"; British Medical Journal; 1997; 315; 1689-1691.

(8) Simon F, personal communication, March 2000.

(9) Hooper E, "The River", 259-262.

(10) Plotkin SA, "Untruths and Consequences"; Phil Trans. R. Soc. Lond. B; 2001; 356; 815-823. Plotkin SA et al., "Postscript relating to new allegations made by Edward Hooper at the Royal Society Discussion Meeting on 11 September 2000", Phil Trans. R. Soc. Lond. B; 2001; 356; 825-829. Koprowski H, "Hypotheses and Facts"; Phil Trans. R. Soc. Lond. B; 2001; 356; 831-833. Osterrieth P, "Vaccine could not have been prepared in Stanleyville", Phil Trans. R. Soc. Lond. B; 2001; 356; 839. [See also other articles by these authors, together with E. Hooper's commentaries on same, all available on this web-site.]

(11) Weiss RA, "Polio vaccines exonerated"; Nature; 2000; 416; 1035-1036.

(12) Hooper E., "Dephlogistication, imperial display, apes, angels and the return of Monsieur Emile Zola. New developments in the origins of AIDS controversy, including some observations about ways in which the scientific establishment may seek to limit open debate and flow of information on 'difficult' issues"; Atti dei Convegni Lincei; 2003; 187; 27-230.

(13) Gao F, Sharp PM, Hahn BH et al., "Human infection by genetically diverse SIVsm-related HIV-2 in west Africa"; Nature; 1992; 358; 495-499.