oa Editorial [Hot topic: Comparative Analysis of Stage Specific Gene Regulation of Apicomplexan Parasites: Plasmodium falciparum and Toxoplasma gondii (Guest Editor: Carlos Lopez-Estrano)]

Roughly half of the entire human population is currently either at risk or already infected with a parasite [1]. Parasitic diseases do not discriminate among humans for age, sex, lifestyle, ethnic background, or socioeconomic status, which puts all humans at risk of getting infected and threaten people's life standard and social development. Human societies have long been subjected to parasite infections, most likely since the beginning of human evolution. Unfortunately, highly effective chemotherapies that are used to mitigate the effects of parasitic infections are becoming ineffective in some cases. A major contributor to this is the increase in drug resistance among many parasites [2, 3], such as Plasmodium falciparum, which makes the discovery of new drugs as well as new parasite targets highly imperative. The advent of genetic manipulation of parasites' genomes [4-8] provide the tools for the molecular dissection of drug resistance. For instance, the molecular basis of resistance to chloroquine in the malaria parasite P. falciparum has been elegantly demonstrated by Fidock and his colleagues [9]. More recently, the use of genomics, proteomics, and bioinformatic analyses have provided new critical knowledge of the biology of parasites and other organisms. Moreover, it has provided an insight into host-parasite interaction and the role of these interactions in host infections and the pathology associated with the disease. Microarrays [10-12] are commonly used to explore the effect of potential drugs on parasites gene expression. However, the outcomes of anti-parasitic compounds on gene expression profiles appear to depend on the parasite in question. An important consideration for drug development is to avoid the emergence of drug resistance [13, 14]. This could be accomplished by changing the drug's chemical composition and/or by discovering new parasite targets. In the particular case of malaria, research around sexual stage parasites in human/mosquito, hypnozoite stage of P. vivax and/or targeting the factors involved in host to host parasite transmission might prove relevant to the discovery of new and effective targets. Although genomics and bioinformatics are powerful tools, the discovery of new targets for drug development still requires a hands-on biochemical analysis of parasite biology. This will allow for a better understanding of the mechanisms involved in resistance to drugs currently used around the world to treat infectious diseases. This special issue includes two reviews on giardiasis, Giardia has been included in WHO's 'Neglected Disease Initiative' since 2004 [15]. It is estimated that of the 280 million people infected each year in Asia, Africa, and Latin America, 200 million people have symptomatic giardiasis. Two other articles focus on the virulence and RNA processing of Entamoeba histolytica, and describe different potential targets for drug development. E. histolytica infects 500 million people worldwide with 100,000 deaths each year of this disease. In addition, the last three articles deal with various aspects of malaria, toxoplasmsis, schistosomiasis, and trypanosomiasis. In this issue, I tried to incorporate a wide range of parasites and topics. I concentrated on some of the most malignant species of parasites with high morbidity and/or mortality on their susceptible population. Lastly, I would like to thank the authors and reviewers for their contribution in ensuring the quality of the manuscripts compiled in this issue.