AIDS and Insects

One of us (PJ) got malaria twice in his life, once in Zaire, because he had stopped taking quinine as a prophylactic, and another time in Papua-New Guinea, in the highlands, after collapsing of car on a road and a full night passed there under the stars. PJ was badly bitten by mosquitoes, one of which was infected, but fortunately his wife and kids escaped getting the infection. In both the instances nivaquine promptly put things in order, since it was a benign form of the disease. Then again in New Guinea, PJ got the dengue, a disease transmitted by a day-biting mosquito (A^edes), which attacked him in a hotel room, full of those insects without any way to exterminate them. The hotel owners were playing golf and the shops were closed after 4 pm! No insecticide available anywhere. The dengue, this one, close to Murray encephalitis, gives a high fever, skin rash and several bad side effects. Mosquitoes, Simuium, fleas, lice and many other insects transmit to man and to animals a fairly large number of diseases, some dreadful and often fatal (Jolivet, 1980).

About 25-30 years ago, AIDS or Sida did not exist or had just started, but the fact was ignored by most people. It started its insidious progress in America and Africa before invading the rest of the planet. At present, we are still powerless, without a vaccine or a real cure against this terrible invader. Antibiotics have effectively controlled sexually transmitted diseases, but they are not effective against the terrible virus HIV. There are no effective vaccines against AIDS, as also against malaria, leishmaniasis, trypanosomiasis, onchocercosis and practically against any protozoan and nematode disease. Tetracyclines, however, seem to work well against Rickettsiae, mycoplasmas and several bacteria-like pathogens.

Several years ago, people hypothesised possible transmission of the HIV by mosquitoes (Jolivet, 1991). Can arthropods really carry retroviruses? We all know that many viruses are transmitted by Diptera or flies, namely arboviruses, and viruses causing yellow fever, dengue haemorrhagic or not, various types of encephalitis (Japanese, equine, St Louis, Nile, Venezolana etc.), and to this list may be added non viral diseases such as malaria, due to a parasitic protozoan, Plasmodium, various nematodes, etc. Let us note that, in the case of yellow fever for instance, the virus does not undergo any developmental change inside the mosquito, but simply multiplies itself as in a test tube filled with a culture medium. Bedbugs do not seem to transmit diseases, but Diptera, like Ceratopogonidae or Simulium, transmit viruses and worms to man and to various mammals. And lice, fleas and many other insects are also disease carriers.

People thought that, if many viruses multiply in a mosquito and are reinjected into man, why it would not be the same with the HIV? Since many Diptera transmit many viruses, why those insects and many other blood sucking insects, as bedbugs and Reduviidae should not be able to carry and transmit AIDS?

In 1986 a rumour started from Belle Glade, in Florida, that mosquitoes could carry the disease. From 1980 to 1985, 76 inhabitants of this small town (16,500 heads) developed the disease. It amounted to the rate of 461 for 100,000 inhabitants, which at that time seemed substantial. This rate was comparable to other high risk areas, like San Francisco, New York or Key West. Several specialists immediately suspected the mosquitoes to be the carrier of the disease, but inspectors from Atlanta CDC (Communicable Diseases Center) were able to prove that use of drugs intravenously, prostitution and promiscuity were very common in that town. Many Belle Glade inhabitants came from Haiti, the country where seropositive people were numerous. Moreover, most of the cases were found among younger people, and there was no case among young children and among old persons. If the mosquitoes were involved, then persons from all age groups would have been suffering from HIV infection.

Insects (mosquitoes, bugs, fleas, lice) can transmit a virus, a bacterium or any other parasite in two ways, namely mechanical transfer, as with a soiled needle, i.e. without any further development, or biological transfer when the virus or the nonviral pathogen multiplies in mosquito's viscera and then migrates to its salivary glands. However, it does not seem likely that HIV viruses are able to multiply within mosquitoes.

Two other retroviruses, those causing infectious equine anemia and bovine leucosis, are mechanically transmitted by bugs. But in both cases, the donor blood contains the virus at a very high density. AIDS carrier's blood contains not more than 10 viral particles per milliliter, exactly 100,000 times less than in the two aforesaid retroviral diseases. Also, the volume of blood transmitted by a bug is very small. It has been calculated that nurses wounded by a contaminated needle are infected in a very small percentage of cases, around 3 per thousand, and there is 140 times more blood in a syringe needle than that in the proboscis of a bedbug or of a mosquito.

It has been proven that HIV, responsible for AIDS, can remain alive for two or three days inside the gut of a mosquito, but it seems that the probability of a mechanical transmission is practically zero. It may also be pointed out that the virus has had only a recent association with mosquitoes, and it has not so far developed an adaptation to the insect's physiology.

Frequency of AIDS cases, similar to Florida or Haiti, has been found also in Democratic Congo Republic (Zaire). It seems that in the cases there too, it is difficult to attribute the transmission of the disease to mosquitoes. It seems more reasonable to attribute it to promiscuity and prostitution. Until recently, AIDS transmission by a mosquito, though theoretically not impossible, seems highly improbable. We cannot plan experiments on man.

— Fig. 15.1. A: Tabanus (Tabanidae), adult. B: Stomoxys (Muscidae), adult (after Itard, 1973; Jolivet, 1980).

The only way to make sure about transmission by mosquitoes would be to put under the same tent HIv positive people and healthy people, and to introduce Anopheles, Culex and Aedes mosquitoes. We could find out if the healthy people get the infection without any contact except through mosquitoes. But such an experiment is unthinkable.

Most of the AIDS specialists reject the hypothesis of mosquito transmission of the disease from man to man. Drug and sex seem to be the main ways of transmission, and yet a recent paper raises some questions (Eigen et al, 2002), and according to it, AIDS in some cases is perhaps horizontally transferred like other arthropod-borne diseases!

The primate Pan troglodytes troglodytes, a chimpanzee, has been recently defined as a natural animal host and a reservoir of the human immunodeficiency virus (HIv), not only SIv. Apes are hunted in Africa and sold on open markets. The carcasses are covered with blood-feeding flies, among them the stable fly (Stomoxys calatrans), a biting fly common also in Europe. This fly has been proven to be an effective vector for the retrovirus causing equine leukemia (see above). According to laboratory experiments, the infectivity of ingested HIv virus is not reduced in the regurgitates of this fly. That could explain in Africa a possible primary transmission of HIv from ape to man, through this blood sucking fly.

In view of the dreaded nature of AIDS, it is necessary to investigate further a possible role of blood sucking insects in transmission of the disease.

References

Eigen, M., Kloft, W J. Ad Brandner, G. 2002. Transferability of HIV by arthropods supports the hypothesis about transmission of the virus from apes to man. Naturwissenchaften 89: 185-186. Itard, J. 1973. Epidémiologie des trypanosomiases animales africaines. Maisons-Alfort : 102 pp.

Jolivet, P. 1980. Les Insectes et l'Homme. Presses Universitaires de France, Paris. 128 pp.

Jolivet, P. 1991. Curiosités Entomologiques. Chabaud publs., Paris. 171 pp.

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