1
Introduction
Back to the Future ? Solutions for Parasitic Problems

Rahime Simsek1, Aqsa Farooqui2, Salah-Ud-Din Khan3 and Shahanavaj Khan4,5,*

1 Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Hacettepe University, Ankara, Turkey
2 Department of Nursing, Indian Institute of Health and Technology (IIHT), Deoband, Saharanpur, UP, India
3 Department of Biochemistry, College of Medicine, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh, Saudi Arabia
4 Department of Medical Lab Technology, Indian Institute of Health and Technology (IIHT), Deoband, Saharanpur, Uttar Pradesh, India
5 Department of Health Sciences, Novel Global Community Educational Foundation, Australia
* Corresponding author

1.1 Introduction

Parasites are organisms that range widely in size. Parasites can be bacteria, protists, fungi, viruses, plants or animals. Parasites that live, feed, and harm the host in or on the host organism may be large enough to be visible. It is known that they infect millions of people around the world and cause thousands of deaths. In this respect, parasitic infections are an important health problem worldwide, especially in developing countries [1-3]. Today, parasitic diseases have ceased to be epidemics and have become the problem of the whole world. For example, according to the data of the World Health Organization, 1.5 billion people, in other words, 24% of the world's population, is infected with helminths transmitted from the soil (https://www.who.int/news-room/fact-sheets/detail/soil-transmitted-helminth-infections).

Diseases caused by parasites have not been adequately studied. The displacement of populations has led to the spread of regional parasitic diseases in the world and treatment and preventive health services are needed everywhere. However, the pharmaceutical industry is still not as interested in developing drugs for the treatment of parasitic infections as in other drugs. Even antiparasitic drugs discovered at the beginning of the twentieth century are still used today. This is important in terms of showing how insufficient are the efforts to develop drugs for parasitic infections. In addition, the COVID-19 pandemic we have been through has also been a risk factor for the spread of parasitic infections. Both the disease itself and the drugs used in the treatment of COVID-19 infection have caused individuals with weakened immunity have become more susceptible to opportunistic parasitic infections.

The treatment of microbial infections or tumoral diseases caused by bacteria, protozoa, fungi, parasites and viruses with drugs is called chemotherapy. In this context, the treatment of infections caused by parasites is also called chemotherapy. Difficulties such as the development of resistance in the treatment of microorganisms other than parasites are also valid for the treatment of infections caused by parasites. Moreover, natural factors such as humidity and temperature also affect the incidence, spread and treatment of some parasitic infections. Mass movements such as travels to these affected regions, and the movement of immigrants also facilitate the spread of parasitic diseases [4-6].

Parasitic infections are most common in tropical climates due to poor hygiene conditions and are less common in developed countries. However, although they affect people who are disadvantaged in many respects, they spread all over the world with mass movements. Thus, parasitic infections affect millions of people around the world every year and can cause deaths. For these reasons, parasitic infections remain current and important as the subjects of drug research and development studies.

Today, there is a need for effective antiparasitic drugs with minimized side effects. In recent years, the factors related to the diseases caused by parasites have been clarified with mechanistic studies of parasitic infections. Thus, more data are available to derive selective and active compounds. With these data, it will be possible to reach new and active drugs having less side effects and increase the success of treatment in the near future.

1.2 Parasite and the Phenomenon of Parasitism

Parasite is a word of Greek origin, and it refers to microorganisms that have evolved to living in or on another organism and feeding by damaging it. Symbiosis is a word of greek origin and means "to live together". It refers to a long-term and close relationship between two different biological organisms. Parasitism, which is a type of symbiosis, is an opportunistic relationship and expresses the relationship in which one species benefits while the other species is harmed [7-9].

1.3 Role of Parasites in Health and Diseases

The fight against parasites dates back to ancient times with the use of drugs and herbal methods being a success for humanity. According to studies, with the complete eradication of microorganisms such as viruses, bacteria and protozoa, human deaths will decrease and the quality of life will increase [10-13]. However, in a scenario where the parasites are completely destroyed, the ecological role of the parasites in the ecosystem can be better understood. The only parasite that humanity has managed to completely eradicate is variola, the smallpox parasite. Although only one parasite has been eradicated so far, intense efforts are also being made for the eradication of parasitic infections such as leprosy and Chagas disease, which are thought to be eradicated. In certain regions of the world, this eradication has been achieved [14].

In spite of the fact that they are harmful to human health, removing parasites from an ecosystem, especially from ecologically effective species, could be problematic in terms of disturbing the ecological balance. Fighting with parasites is an issue that is almost impossible to completely eradicate and needs to be evaluated in all its dimensions in terms of its consequences. The eradication of one parasite species can lead to the increase or extinction of other parasite species, as well as completely changing the balance of the ecosystem. Although it is thought that as a result of urbanization, healthier and more hygienic conditions will be created, this has not always been the case. In some cases, an increase in parasitic infections has been observed.

However, it is essential to fight parasites and to make efforts for the treatment of parasitic infections, but while doing this, they should not disturb the balance of nature, and strategies should be developed for all species in which life is possible without adversely affecting one another.

1.3.1 Ancient Information of Parasite Towards Health Problems

Medical struggles with microorganisms that cause disease in humans dates back to 3000 BCE. Parasites initially evolved long before the evolution of human beings, and early writings from Egypt mention some such as roundworms and tapeworms. Francesco Redi and Antonie van Leeuwenhoek in the seventeenth century began to research them and created an early version of the branch of parasitology. The pioneer experiments of various great scientists have helped us to understand the pathogenic mechanisms of the parasite.

Our information regarding infections of parasites extend into antiquity, and descriptions of parasites and parasitic infections are observed in the earliest writings and have been confirmed by the discovery of parasites in archaeological material. Human beings are hosts to approximately 300 different species of worms parasite and more than 70 species of various protozoans, several derived from our ancestors primate condition while others have been acquired from animals. Some parasites cause the most important diseases in the world; certainly these are parasites that have received the great attention. Since most of such parasite diseases occur in tropical regions, the parasitology field has tended to overlap with that of tropical medicine, and consequently the histories of these fields are intertwined. The organized study of parasites started with the rejection of the theory of spontaneous generation and the promulgation of the germ theory. After that, the history of human parasitology continued along two lines: the finding of a parasite and its subsequent connection with particular disease, and the identification of particular disease and the subsequent discovery that it was caused through the infection of the particular parasite.

It is known that many plants are used as chemotherapeutic treatments in Chinese medicine. Avicenna defined microbes and treated the diseases caused by microbes. Galenos tried to treat diseases by using the large plant flora of Anatolia. In the seventeenth and eighteenth centuries, plant extracts began to be used for the treatment of febrile illness. In this period, chemotherapy started with the use of Cinchona alkaloids in the treatment of malaria.

Parasites have been defined and characterized depending on a wide variety of factors, from parasite-related factors to host-related factors. Throughout history, humans have been confronted with a large number of parasites, including about 300 species of helminths, and 100 species of protozoa. These microorganisms have caused and continue to cause diseases in humans [10, 15].

1.3.2 Current Information on Parasites Causing Health Problems

Diagnostic methods of parasitic infections have been developed from the past to the present, and...