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• Translation

3. The Scientific Steering Committee’s five examples of diseases of concern

Posted: 13 July 2007

(b) Malaria

SSC: “The relationship between the parasite and the host is quite specific”.

ADI Response:

ADI agrees with the Scientific Steering Committee that the relationship between the parasite that causes malaria, and the host species infected with the disease, is very specific – each parasite has its own host species.

• Differences exist not only between the host species but the strains of malaria plasmodium that they contract are also distinct and specific to the host species46:

Natural host-------------Malaria species
Human ------------------P. falciparum, P.vivax, P.malariae, P.ovale
Chimpanzee-----------P.reichenowi
Gibbons-----------------P.hylobati
Old world monkeys--P cynomolgi, P.knowlesi, P.simiovale, P.gonderi

This makes research using NHP even more complex, because a different parasite and a different host species are being studied. Furthermore, when success is achieved in infecting a NHP with a human malaria parasite, the differences in response to the parasite, combined with the fundamental differences between human and non-human primates, will affect the outcome of the research.

SSC: “[human malaria parasites]..do… infect some non-human primate species…”.

ADI Response: use of primates is unnecessary, as advanced scientific techniques are available; use of primates opens the research to misleading results:

• Although chimpanzees are susceptible to experimental P. falciparum, it causes only brief and moderate parasitization and no severe infection47.
• Guyanese and Bolivian squirrel monkeys used to test malaria vaccine, differ in their antigens that act as receptors to Plasmodia (parasite) antigens, so one sub-species is susceptible and the other is not48.

SSC: “….the parasite has obligatory intra-hepatic developmental phases that are not amenable to in vitro cultivation”.

ADI Response: This is no longer correct.

• A human liver cell culture has been produced recently, which supports two of the human malaria strains and allows the study of the biology of the liver stage parasite which is needed for the development of drugs and vaccines49.

SSC: “…well-characterised models with similar immune responses to humans (such as macaques) are essential in vaccine development”.

ADI Response:

• Human malaria plasmodium was mixed with vaccinated macaque blood in vitro because of the inability of the monkey to contract the human malaria parasite. In tests to assess safety for humans, and potential to predict likely immune response, it was found that the rhesus immune response was higher than in humans, as well as other species differences50.
• As mentioned earlier, in the ‘alternatives’ section, there are many advanced technology systems that replace the use of animals, including in vitro; human volunteers; epidemiological studies of the disease in the environment; studies of human and parasite genetic diversity, as well as large scale literature reviews of malaria research.
• Environmental solutions can be found in order to reduce the risk factors involved in malaria infection. Human activities associated with different social groups for example have been seen to have an impact on malaria exposure and consequently immunity51. The use of insecticide treated nets as a means of reducing the transmission to humans from malaria mosquitos, has been seen to reduce the deaths of young children by an average of 20%52.

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