Malaria is a severe disease caused by parasites of the genus Plasmodium, which is transmitted to humans by a bite of an infected female mosquito of the species Anopheles. Malaria remains the leading cause of mortality around the world, and early diagnosis and fast-acting treatment prevent unwanted outcomes. It is the most common disease in Africa and some countries of Asia, while in the developed world malaria occurs as imported from endemic areas. The sweet sagewort plant was used as early as the second century BC to treat malaria fever in China. Much later, quinine started being used as an antimalaria drug. A global battle against malaria started in 1955. The World Health Organization carries out a malaria control program on a global scale, focusing on local strengthening of primary health care, early diagnosis of the disease, timely treatment, and disease prevention. Globally, the burden of malaria is lower than ten years ago. However, in the last few years, there has been an increase in the number of malaria cases around the world. It is moving towards targets established by the WHO, but that progress has slowed down.
Plasmodium
Plasmodium
Plasmodium
Plasmodium
P. malariae, P. falciparum, P. vivax, P. ovale
P. knowlesi
P. knowlesi
Plasmodium
Malus aer
Plasmodium
Anopheles
Plasmodium
Plasmodium
P. vivax
P. malariae
P. falciparum
14].
Plasmodium
species, and it consists of several subspecies [14].
].P. vivax
andovale
infections, the persistence of the merozoites in the blood or hypnozoites in hepatocytes can cause relapse months or years after the initial infection. Additionally, relapse of vivax malaria is common afterP. falciparum
infection in Southeast Asia. Relapse cases were observed inP. falciparum
infections, which can lead to a rapid high parasitemia with subsequent destruction of erythrocytes [,]. Children, pregnant women, immunocompromised and splenectomized patients are especially vulnerable to malaria infection, as well as healthy people without prior contact withPlasmodium
. A laboratory test for malaria should always confirm clinical findings. The proving of malaria is carried out by direct methods such as evidence of parasites or parts of parasites, and indirect methods that prove the antibodies to the causative agents () [,,].| Advantages | Disadvantages | |
|---|---|---|
| Direct methods | ||
| Microscopic analysis | Fast test, cheap | Required much experience as well as equipment |
| Rapid diagnostic tests | Quick and simple | Less sensitive and accurate, price |
| Molecular tests | Correct determination of type, highly sensitive and accurate | Price, long-term in a large number of cases |
| Indirect methods | ||
| Indirect immunofluorescence | Specific, sensitive | Long time to perform, subjective evaluation of results |
| ELISA | Correct determination of type, specific, sensitive | Long time to perform, price |
P. falciparum
orP. vivax
infections or both []. False-positive rates ofP. vivax
were typically small, between 5% and 15%. On the other hand, the false-positive rates ofP. falciparum
range from 3–32% [,]. Good RDTs might occasionally give false-negative results if the parasite density is low, or if variations in the production of parasite antigen reduce the ability of the RDT to detect the parasite. False negative results of the RDT test forP. falciparum
ranged between 1% and 11% [,,,]. The overall sensitivity of RDTs is 82% (range 81–99%), and specificity is 89% (range 88–99%) []. Polymerase chain reaction (PCR) is another method in the detection of malaria. This method is more sensitive and more specific than all conventional methods in the detection of malaria. It can detect below one parasite/μL. PCR test confirms the presence of parasitic nucleic acid [,]. PCR results are often not available fast enough to be useful in malaria diagnosis in endemic areas. However, this method is most helpful in identifyingPlasmodium
species after diagnosis by microscopy or RDT test in laboratories that might not have microscopic experts. Additionally, PCR is useful for the monitoring of patients receiving antimalaria treatment [,]. Indirect methods are used to demonstrate antibodies to malaria-causing agents. Such methods are used in testing people who have been or might be at risk of malaria, such as blood donors and pregnant women. The method is based on an indirect immunofluorescence assay (IFA) or an ELISA test. The IFA is specific and sensitive but not suitable for a large number of samples, and the results are subjective evaluations. For serological testing, ELISA tests are more commonly used [26].
]. Rapid and accurate diagnosis of malaria is an integral part of appropriate treatment for the affected person and the prevention of the further spread of the infection in the community.Rapid and accurate diagnosis of malaria is an integral part of appropriate treatment for the affected person and the prevention of the further spread of the infection in the community.
Artemisia annua
) was used for the treatment of malaria in China []. Much later, in the 16th century, the Spanish invaders in Peru took over the cinchona medication against malaria obtained from the bark of the Cinchona tree (LatinCinchona succirubra
). From this plant in 1820 the French chemists, Pierre Joseph Pelletier, and Joseph Bienaimé Caventou isolated the active ingredient quinine, which had been used for many years in the chemoprophylaxis and treatment of malaria. In 1970, a group of Chinese scientists led by Dr. Youyou Tu isolated the active substance artemisinin from the plantArtemisia annua
, an antimalarial that has proved to be very useful in treating malaria. For that discovery, Youyou Tu received the Nobel Prize for Physiology and Medicine in 2015 [,,]. Most of the artemisinin-related drugs used today are prodrugs, which are activated by hydrolysis to the metabolite dihydroartemisinin. Artemisinin drugs exhibit its antimalarial activity by forming the radical via a peroxide linkage []. WHO recommends the use of artemisinin-based combination therapies (ACT) to ensure a high cure rate ofP. falciparum
malaria and reduce the spread of drug resistance. ACT therapies are used due to high resistance to chloroquine, sulfadoxine-pyrimethamine, and amodiaquine []. Due to the unique structure of artemisinins, there is much space for further research. Extensive efforts are devoted to clarification of drug targets and mechanisms of action, the improvement of pharmacokinetic properties, and identifying a new generation of artemisinins against resistantPlasmodium
strains []. The German chemist Othmer Zeidler synthesized dichlorodiphenyltrichloroethane (DDT) in 1874 during his Ph.D. At that time, no uses of DDT was found, and it just became a useless chemical []. The insecticide property of DDT was discovered in 1939 by Paul Müller in Switzerland. DDT began to be used to control malaria at the end of the Second World War []. During the Second World War, the success of DDT quickly led to the introduction of other chlorinated hydrocarbons which were used in large amounts for the control of diseases transmitted by mosquito []. From the late Middle Ages until 1940, when DDT began to be applied, two-thirds of the world’s population had been exposed to malaria, a fact that represented a severe health, demographic, and economic problem [,,,,]. DDT is an organochlorine pesticide which was applied in liquid and powder form against the insects. During the Second World War, people were sprayed with DDT. After the war, DDT became a powerful way of fighting malaria by attacking the vector []. Five Nobel Prizes associated with malaria were awarded: Youyou Tu in 2015. Ronald Ross received the Nobel Prize in 1902 for the discovery and significance of mosquitoes in the biology of the causative agents in malaria. In 1907, the Nobel was awarded to the already-mentioned Charles Louis Alphonse Laveran for the discovery of the causative agent. Julius Wagner-Jauregg received it in 1927 for the induction of malaria as a pyrotherapy procedure in the treatment of paralytic dementia. In 1947 Paul Müller received it for the synthetic pesticide formula dichlorodiphenyltrichloroethane. Attempts to produce an effective antimalarial vaccine and its clinical trials are underway. Over the past several decades’ numerous efforts have been made to develop effective and affordable preventive antimalaria vaccines. Numerous clinical trials are completed in the past few years. Nowadays are ongoing clinical trials for the development of next-generation malaria vaccines. The main issue isP. vivax
vaccine, whose research requires further investigations to identify novel vaccine candidates [,,]. Despite decades of research in vaccine development, an effective antimalaria vaccine has not yet been developed (i.e., with efficacy higher than 50%) [,,]. The European Union Clinical Trials Register currently displays 48 clinical trials with a EudraCT protocol for malaria, of which 13 are still ongoing clinical trials []. The malaria parasite is a complex organism with a complex life cycle which can avoid the immune system, making it very difficult to create a vaccine. During the different stages of thePlasmodium
life cycle, it undergoes morphological changes and exhibits antigenic variations.Plasmodium
proteins are highly polymorphic, and its functions are redundant. Also, the development of malaria disease depends on thePlasmodium
species. That way, a combination of different adjuvants type into antigen-specific formulations would achieve a higher efficacy [,]. Drugs that underwent clinical trials proved to be mostly ineffective [,,]. However, many scientists around the world are working on the development of an effective vaccine [,,]. Since other methods of suppressing malaria, including medication, insecticides, and bed nets treated with pesticides, have failed to eradicate the disease, and the search for a vaccine is considered to be one of the most important research projects in public health by World Health Organization (WHO). The best way to fight malaria is to prevent insect bites. Malaria therapy is administered using antimalarial drugs that have evolved from quinine. According to its primary effect, malarial vaccines are divided into pre-erythrocytic (sporozoite and liver-stage), blood-stage, and transmission-blocking vaccines [,]. Most medications used in the treatment are active against parasitic forms in the blood (the type that causes disease) () []. The two crucial antimalarial medications currently used are derived from plants whose medical importance has been known for centuries: artemisinin from the plant Qinghao (Artemisia annua
L, China, 4th century) and quinine fromCinchona
(South America, 17th century). Side-by-side with artemisinin, quinine is one of the most effective antimalarial drugs available today [,,]. Doxycycline is indicated for malaria chemoprophylaxis for travel in endemic areas. It is also used in combination with the quinine or artesunate for malaria treatment when ACT is unavailable or when the treatment of severe malaria with artesunate fails. The disadvantage of doxycycline is that children and pregnant women cannot use it []. Due to the global resistance ofP. falciparum
to chloroquine, ACTs are recommended for the treatment of malaria, except in the first trimester of pregnancy. ACTs consist of a combination of an artemisinin derivative that fast decreases parasitemia and a partner drug that eliminates remaining parasites over a more extended period. The most common ACTs in use are artemether-lumefantrine, artesunate-amodiaquine, dihydroartemisinin-piperaquine, artesunate-mefloquine, and artesunate with sulfadoxine-pyrimethamine. The ACTs were very efficient against allP. falciparum
until recently when numbers of treatment failures raised in parts of Southeast Asia. Atovaquone-proguanil is an option non-artemisinin-based treatment that is helpful for individual cases which have failed therapy with usual ACTs. Although, it is not approved for comprehensive implementation in endemic countries because of the ability for the rapid development of atovaquone resistance. Quinine remains efficient, although it needs a long course of treatment, is poorly tolerated, especially by children, and must be combined with another drug, such as doxycycline or clindamycin. Uncomplicated vivax, malariae, and ovale malaria are handled with chloroquine except in case of chloroquine-resistantP. vivax
when an ACT is used [,,,,].| Medication Name | Year of Discovery/Synthesis | Origin | Usage | Mechanism of Action | Side Effects | Advantages/Disadvantages | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Quinine | 1600 | Cinchona | tree, South America | Resistance to chloroquine, prophylaxis, and treatment of malaria | Inhibition of DNA and RNA synthesis | Headache, abortion, or congenital malformations if taken during pregnancy | Toxic, less effective than other medication | |||||||
| Chloroquine | 1934 | Synthesized by German scientist Hans Andersag | A most powerful remedy for the prophylaxis and treatment of malaria | Inhibition of DNA and RNA synthesis | Gastrointestinal disturbances, headache, skin irritation | Developed resistance of most strains | of P. falciparum | to the medication | ||||||
| Primaquine | 1953 | The 8-aminoquinoline derivative | Infections with | P. vivax | and | P. ovale | , prophylaxis and treatment of malaria | Interferes in transport chain of electrons and destroys parasite mitochondria | Anorexia, nausea, anemia, headaches, contraindicated in pregnancy and children under 4 years of age | Prevent relapse in | P. vivax | and | P. ovale | infection |
| Doxycycline | 1960 | Pfizer Inc. New York | Prophylaxis in areas with chloroquine resistance and against mefloquine-resistant | P. falciparum | Inhibition of protein synthesis by binding to 30S ribosomal subunit | Gastrointestinal disorders, nausea, vomiting, photosensitivity | Effective and cheap, use for treatment and prophylaxis in all malarious areas | |||||||
| Mefloquine | 1971 | USA army and WHO | Multiresistant | P. falciparum | strains, prophylaxis, and treatment of malaria | Damage to parasite membrane | Gastrointestinal disorders, CNS disorder, contraindicated in pregnancy and patients with epilepsy | Partial resistance, brain damage | ||||||
| Proguanil (chloroguanide) | 1953 | Biguanide derivate | Prophylaxis in infections with | P. falciparum | Inhibition of DNA synthesis | Digestive problems only in large doses | The least toxic antimalarial drug | |||||||
| Pyrimethamine | 1953 | Pyrimidine derivatives | For tissue parasites, prophylaxis, and treatment of malaria | Folic acid antagonist | Gastrointestinal disorders, neuropathy, in high doses also megaloblastic anemia | The rapid development of resistance | ||||||||
| Atovaquone/proguanil | 2000 | Ubiquinone analog | For the prophylaxis and treatment of malaria | Inhibition of cytochrome bc1 in | Plasmodium | Nausea, vomiting, diarrhea, headache, dizziness, anxiety, difficulty falling asleep, rash, fever | Most commonly used, fewer side effects and more expensive than mefloquine, | P. falciparum resistance |
Anopheles
Gambusia holbrooki
73]. In 1930 legislation was passed to enforce village sanitation, which included the construction of water infrastructure and safe wells, contributing to the prevention of malaria. Regular mosquito fogging with arsenic green (copper acetoarsenite) was introduced, and larvicidal disinfection of stagnant water was carried out.
79].
81].
Plasmodium


Anopheles, which means that the conditions of transmission of the imported malaria from the endemic areas still exist. The risk of malaria recrudesce is determined by the presence of the vector, but also by the number of infected people in the area. Due to climate change, it is necessary to monitor the vectors and people at risk of malaria. Naturally- and artificially-created catastrophes, such as wars and mass people migration from endemic areas, could favor recrudescing of malaria. Once achieved, eradication would be maintained if the vector capacities are low and prevention measures are implemented. The increased number of malaria cases worldwide, the recrudesce of indigenous malaria cases in the countries where the disease has been eradicated, the existence of mosquitoes that transmit malaria and the number of imported malaria cases in Croatia are alarming facts. Health surveillance, including obligatory and appropriate prophylaxis for travelers to endemic areas, remains a necessary public health care measure pointed at managing malaria in Croatia.

vivax
knowlesi
7]
References