Malarial parasites in pakistan

Malaria is caused by protozoan parasites of the genus Plasmodium – single-celled organisms that cannot survive outside of their host(s). As the malaria parasites enter the blood stream they infect and destroy red blood cells. Destruction of these essential cells leads to fever and flu-like symptoms, such as chills, headache, muscle aches, tiredness, nausea, vomiting and diarrhea. These initial symptoms are non-specific: in other words, they are self-reported symptoms that do not indicate a specific disease process. Plasmodium falciparum is responsible for the majority of malaria deaths globally and is the most prevalent species in Pakistan. The remaining species are not typically as life threatening as P. falciparum. Plasmodium vivax, is the second most significant species and is prevalent in Pakistan. P. vivax and Plasmodium ovale have the added complication of a dormant liver stage, which can be reactivated in the absence of a mosquito bite, leading to clinical symptoms. rasite lifecycle Parasite lifecycle Malaria parasites spread by successively infecting two types of hosts: female Anopheles mosquitoes and humans. At the same time she takes a blood meal to nourish her eggs, the female Anopheles mosquito injects sporozoites into the blood stream of malaria’s next victim. The sporozoites are rapidly taken up by the liver cells. In all species of Plasmodium, these parasites develop to form schizonts (the multinucleate stage of the cell during asexual reproduction), from which several thousand merozoites develop. In Plasmodium vivax and Plasmodium ovale only, a proportion of the liver-stage parasites (known as hypnozoites) remain dormant in the hepatocytes. In this stage the parasite can remain dormant for months or several years. These two species of parasite can therefore initiate a cycle of asexual reproduction causing clinical symptoms in the absence of a new mosquito bite, giving P. vivax infection the name relapsing malaria. When the liver cells rupture, the merozoites are released into the bloodstream where they rapidly invade the red blood cells. These blood-stage parasites replicate asexually – rapidly attaining a high parasite burden and destroying each red blood cell they infect, leading to the clinical symptoms of malaria. The trigger is as yet unknown, but a small percentage of merozoites, differentiate into male and female gametocytes, which are taken up by the mosquito in her blood meal. It is these gametocytes that cause the cycle of transmission to continue back to the mosquito. Male and female gametocytes fuse within the mosquito forming diploid zygotes, which in turn become ookinetes. These ookinetes migrate to the midgut of the insect, pass through the gut wall and form the oocysts. Meiotic division of the oocysts occur and sporozoites are formed, which then migrate to the salivary glands of the female Anopheles mosquito ready to continue the cycle of transmission back to man. Treatment milestones Background Two important currently used antimalarial drugs are derived from plants whose medicinal values had been noted for centuries: artemisinin from the Qinghao plant Malaria treatment milestones Quinine Quinine comes from the bark of a tree native to South America. According to legend it was first brought to Europe by a Countess who had been treated with it in Peru in the 1600s. The bark was named cinchona in 1742 by Linnaeus. In 1820, two French chemists isolated quinine from the cinchona bark and quinine became a treatment of reference for intermittent fever throughout the world. Quinine remains an important and effective treatment for malaria today, despite sporadic observations of quinine resistance.(1) Chloroquine Research by German scientists to discover a substitute for quinine led to the synthesis in 1934 of Resochin (chloroquine) and Sontochin (3-methyl-chloroquine). These compounds belonged to a new class of antimalarials, the four-amino quinolines. The German research went no further and the formula for Resochin was passed to a US sister company. During World War II, French soldiers happened upon a stash of German-manufactured Sontochin in Tunis and handed it over to the Americans. American researchers made slight adjustments to the captured drug to enhance its efficacy. The new formulation was called chloroquine. Only after comparing chloroquine to the older and supposedly toxic Resochin, did they realize that the two chemical compounds were identical.(1) Following the war, chloroquine and DDT emerged as the two principal weapons in WHO’s global eradication malaria campaign. Subsequently, chloroquine resistant P. falciparum probably arose in four separate locations starting with the Thai-Cambodian border around 1957; in Venezuela and parts of Colombia around 1960; in Papua New Guinea in the mid-1970s and in Africa starting in 1978 in Kenya and Tanzania and spreading by 1983 to Sudan, Uganda, Zambia and Malawi.(1) Sulfadoxine/Pyrimethamine A pyrimidine derivative, proguanil, also emerged from the antimalarial pipeline during World War II. Proguanil’s success in treating humans led to further study of its chemical class and to the development of pyrimethamine. Resistance to the two monotherapies appeared quickly (within one year in the case of proguanil). Sulfones and sulfonamides were then combined with proguanil or pyrimethamine in hopes of increasing efficacy and forestalling or preventing resistance. By 1953, P. falciparum resistance had already been noted in Tanzania. When Sulfadoxine/Pyrimethamine (SP) was introduced in Thailand in 1967, resistance appeared that same year and resistance spread quickly throughout South-East Asia. Resistance to SP in Africa remained low until the late 1990s but since then it has spread rapidly.(1) Mefloquine The development of mefloquine was a collaborative achievement of the US Army Medical Research and Development Command, WHO/TDR and Hoffman-La Roche, Inc. Mefloquine’s efficacy in preventing falciparum malaria when taken regularly was shown in 1974 and its potential as a successful treatment agent was shown soon after. Resistance to mefloquine began to appear in Asia in 1985, around the time the drug became generally available.(1) Artemisinin Artemisinin was isolated by Chinese scientists in 1972 from Artemisia annua (sweet wormwood), better known to Chinese herbalists for more than 2000 years as Qinghao. In the early 1970s, initial testing by Chinese scientists of Qinghao extracts in mice infected with malaria showed it to be as effective as chloroquine and quinine in clearing the parasite. Mao Tse Tung’s scientists then began testing in humans and in 1979 published their findings in the Chinese Medical Journal.(1) Artemisinin and other artemether-group drugs have been the main line of defense against drug resistant malaria in many parts of South-East Asia. Artemisinin has been a very potent and effective antimalarial drug, especially when used in combination with other malaria medicines.(3) Combining an artemisinin drug with a partner drug that has a longer half-life was found to improve the efficacy of the artemisinin. It also reduced treatment duration with the artemisinin and appeared to reduce the likelihood of development of resistance to the partner drug. In the early part of this century, Artemisinin-based combination therapy (ACT) had been shown to improve treatment efficacy and was thought to be a key to containing resistance in Southeast Asia. Read more about the MMV artemisinin programme. Tackling resistance However, in 2009, evidence of resistance to artemisinin-based combination therapy (ACT) was reported. Initially in the Thai-Cambodia border region, and now increasingly in Southeast Asia, ACTs are taking longer and longer to clear the parasite from patients. MMV’s first step is to determine whether resistance is only to artemisinin, or whether all artemisinin-like molecules (i.e. endoperoxides) in our pipeline are compromised.