Parasites are organisms that live atthe expenses of another organism, which is known as host, by attaching themselveson or in their host.
They retrieve nutrients from the host while giving nothingback to the host. There is a diverse range of parasite and each has adapted todifferent hosts for survival. Based on the research data, around 50% of allorganisms on the Earth are parasitic.
For example, other than the parasitesthat are commonly known, fungi are also parasites. There are even birdparasite, such as the cuckoos that lay their eggs in other birds’ nest. The World Health Organizationdeclares that parasites cause nearly 20% of all infectious disease. Generally,there are 3 main types of parasites that cause diseases, which includes the protozoa,helminths and ectoparasite. The microscopic size protozoa that are parasiticcan multiply in humans, which can cause Leishmaniasis. Helminths are larger,multicellular organisms that can be observed by naked eye during their adultstages. The examples of helminths include flatworms such as flukes andtapeworms, and roundworms such as nematodes.
Ectoparasites are also known asblood-sucking arthropods, which play an important role in causing diseases bytransmitting pathogen and act as a vector.Parasitic infections caused byparasites is a tremendous burden for human, due to their ability to causeillness and death. Thus, there would be a great impact on human and animals ifall parasites that cause disease disappeared. For example, malaria is one of thecommon human parasitic infections in Malaysia.
It is caused by the parasiticprotozoan, Plasmodium sp. and aretransmitted through the vector, the Anophelesmosquitoes. Malaria is a life-threatening disease since it can cause organfailure of kidneys and liver, destruction to red blood cell that results inanemia and accumulation of fluid in the lung that causes breathing problems. Itwill be a good new for those who are infected if this disease causing parasite,the Plasmodium sp.
disappear becausethey would be cured immediately from this serious chronic illness.However, this happy moment wouldn’tlast for a long period. There could be some unanticipated and unpredictableconsequences if all parasites are eradicated from this world. According to thehygiene hypothesis proposed by David Strachan in 1989, the lack of exposure toparasites increase the susceptibility to allergic reactions by suppressing thenatural development immune system. In 2003, Graham Rook proposed the “oldfriend hypothesis” that explains the link between microbial exposures andinflammatory disorders.
He proposes that human become so dependent on themicrobes that their immune systems cannot develop properly without them and thisis thought to lead to defects in establishment of immune tolerance and maystart to attack our own body. This also explain why there is a rise ofautoimmune disease in the young in Malaysia although they are living in a cleanenvironment. Gastroenterologists in theUniversity of Iowa had even suggested the use of helminths as treatment forinflammatory disease. Helminths provoke a variety of anti-inflammatoryresponses and awake the regulatory side of the immune system so that humans’immune system will not overreact to those which are harmless stimuli, from thedust and pollen to beneficial bacteria inside the body. Hence, disease-causingparasites and microbes may be fatal to human in some cases, but they are neededin order to help human to develop their immune system so that the autoimmunedisease and allergic cases will decrease. In Malaysia,there is a large area of forests and plantation that serves important role inthe country.
Parasites help to keep down and control the numbers of plant-destructinginsects and other animals that are considered as pests. Nearly all insect pestshave at least one parasite that attacks them, and most of them are parasitoidthat kills the hosts before the offspring is produced. Malaysia is a countrythat hit 72% rice production of the nation’s self-sufficiency level and thisindicate that the rice production is an important field in our country. Thereare some insect pests that feed on the rice, and hence cause destructiveconsequences of the rice production. At this time, the parasites are usefultools that act as biological control to these insect pests. For example, therice armyworm, Spodoptera mauritia inthe order Lepidoptera, is a kind of caterpillars that occur in low populationsin the rice field. The major reason of low occurrence of this species may dueto the infection of fungus and parasitoid. The presence of fungal infectionssuch as Paecilomyces and Metarhizium also helps to reduce thepopulation of the Malayan black bug, Scotinopharacoarctata, which are feed by sucking the sap of rice plants.
Without thepresence of these parasites, these species will increase in numbers withinmonths and cause serious damage to food crops. As a result, people will have touse chemical insecticides which would pollute the environment, to control thepopulation of insect pests. Parasites benefitsthe wildlife animals by providing evolutionary adaptations to their hosts. Thehost-parasite relationships are often described as co-evolutionary arm racewhere the involved species mutually adapt to each other and exert selectionpressure on each other. Parasites help their hosts to increase the ability tosurvive at species level. Thus, if the parasites disappear in the world oneday, there is no more selection pressure on all the organisms.
The world wouldbe overpopulated will all types of organisms, including those with low survivalability and low fitness. The ecosystems must have a way to regulate theorganisms’ population in order to be sustainable. When some species populationis too large due to the absence of restriction of parasites, competition andpredation are not able to limit them, and this may cause major extinctionoutbreak of another species in the world. Inconclusion, parasites play an important role to help to balance the worldpopulation and sustainability of the Earth. They may bring some unfavorabledisease and conditions to humans and animals, but there are always some reasonsbehind the scene.
Without parasites, the Earth will collapse soon since theliving organisms resides on Earth starts with a simple unicellular microbe.