Cameroon And The Origin Of HIV

By Alan Thevenet N. Tita, MD, Ph.D and Denis M. Tebit, Ph.D

Widespread international press reports of a recent study published in a prestigious medical journal (Science) attributing the origin of the human immunodeficiency virus (HIV), the virus that causes AIDS, to chimpanzees in Cameroon generated uproar within the Cameroonian community.

Many raised concerns about an agenda to label Africa as the origin of everything bad and emphasised alternative theories for the advent of HIV, including conspiracies.

One vital ingredient of scientific critique is to go beyond press reports and conduct direct reviews of the actual research publication. To inform and educate those who like ourselves are interested in this controversy, we prepared a summary of the published article with an accompanying commentary.

Summary Of Research

Background: Molecular studies indicate that HIV-1 is a descendant of the simian immunodeficiency virus (SIV) found in certain captive chimpanzees, suggesting chimpanzees as an animal origin for HIV. For this reason, HIV has been classified as a zoonotic infection (transmitted from animals to humans).

However, to be tenable, the virus must also be found in non-captive (wild-living) chimpanzees in their natural habitat. The purpose of the reported study was, therefore, to examine whether wild living chimpanzees identical to the captive ones, also harbor SIV.

Methods

The chimpanzee sub-species that carry the HIV-1 ancestor virus (SIV) are known to be wild-living in South Cameroon, Gabon and Congo with extensions into Equatorial Guinea and Central African Republic.

The study was set in Cameroon (possibly for logistic reasons) and 10 forest sites were covered. Chimpanzees being reclusive were not directly accessible for specimen collection.

Therefore, researchers utilised serologic, molecular, genetic and epidemiologic methods to a) identify the HIV-1 ancestor virus from fecal specimens collected from the surface of the soil in forest habitats, b) confirm that these fecal specimens were from the specific type of chimpanzee in question, c) identify fecal specimens that came from each individual chimpanzee, and d) determine the gender of each chimpanzee.

Results

423 (70.6 percent) out of 599 fecal samples were from the chimpanzee type known to harbour HIV-1 ancestor virus (the remaining samples were either from a different type of chimpanzee or from gorillas, or were too degraded to yield reliable results).

These 423 fecal samples were from a total of 108 individual chimpanzees. 34 of those fecal samples (8%) tested positive for the HIV-1 ancestor virus (SIV), representing 16 individual chimpanzees (14.8 percent) including 7 males and 9 females.

Infected fecal samples, (and therefore infected individual chimpanzees), where found in only 5 of the 10 forest sites and the sero-positive rate in chimpanzees in these sites ranged from 4.4 percent to 35.3 percent.

Additional studies to determine if HIV-1 could have evolved from the 16 identified ancestor viruses were all positive for 2 of 3 HIV-1 subgroups (M and N) but not for subgroup O (which is traced primarily to Cameroon but is also prevalent in Gabon and Equatorial Guinea).

Viruses from forest sites deep to the southeast of Cameroon were most closely related to HIV-1 subgroup M, while viruses from a more central site were related to subgroup N.
As expected, none of the fecal samples from gorillas or from other chimpanzee types were positive for the HIV-1 ancestor virus.

Conclusion: Chimpanzees found in the south of Cameroon are natural reservoirs for the HIV-1 ancestor virus (SIV).

Commentary

Investing in deciphering the origin of HIV/AIDS is certainly a worthwhile effort. This can help tailor effective preventive interventions (especially a vaccine), and optimize therapy against the current epidemic. It can also help forestall the emergence of a similar epidemic from another virus. Unfortunately, there is the unproductive risk of attributing blame.

There is evidence and consensus among experts that a chimpanzee species (captive or habituated) from Central Africa harbour an HIV-1 ancestor virus. Recent disagreement has centered on the mechanism of transmission between humans and chimpanzees.

One theory is the natural transmission theory, which proposes that the ancestor virus was transmitted to humans through the hunting and handling of chimpanzees. Certainly, alternative theories abound including conspiracies and medical accidents.

Prominent among these is the theory that human infection originated from widespread testing between 1957-1960 of an oral polio vaccine in Africa [Democratic Republic of Congo (DRC), Rwanda and Burundi] by a U.S. researcher.

Supporters believe that the vaccine was contaminated with the HIV-precursor through a production process that involved chimpanzees. However, the lead researcher and other collaborators in the polio study have maintained that chimpanzees were not used in the production process.

This polio vaccine theory has been brought into further disrepute by several studies on old samples of the vaccine, which yielded neither chimpanzee DNA, nor HIV or its precursor. Furthermore, genetic evolutionary studies of HIV suggest the transmission to man might have occurred earlier than 1950s when the polio vaccine trial took place.

The researchers in the current study reviewed here, support the predominant natural transmission theory, which is further strengthened by their unquestionable finding that the HIV-1 precursor has a natural habitat in wild living chimpanzees in southern Cameroon.

However, contrary to some press reports, it is our estimation that the finding is not the "smoking gun" evidence supporting the natural transmission theory. It firmly establishes that chimpanzees were involved in the origination of the HIV/AIDS pandemic but it does not dispel reasonable doubts about the veracity of the natural transmission theory. Less compelling is any suggestion that findings establish an exclusive geographic origin of HIV/AIDS.

It is not proven that these chimpanzee reservoirs are exclusive to Cameroon. In fact, the same chimpanzee species are found in Gabon and Congo as well as Equatorial Guinea and Central African Republic. One would expect chimpanzees in the other countries to also harbor the HIV-1 precursor, seriously confounding any speculation about HIV/AIDS originating in Cameroon.

Additionally, the findings do not completely exclude the likelihood that chimpanzees may not be the original or only host of the HIV-1 precursor. Thus, press declarations that "the jump between chimps and humans occurred in southeastern Cameroon" should be prefaced as speculation, albeit informed.

1Center for Research in Women's Health, Division of Maternal-Fetal Medicine, Dep't of Obstetrics and Gynecology, University of Alabama at Birmingham. 2Division of Infectious Diseases, Case Western Reserve University Cleveland, Ohio

Comments

[LILIAN]

Let's say it originated from the chimpanzees in Cameroon, how long had the chimpanzees carried the virus? How did it affect Cameroonians before being discovered in the U. S. A.?