what would happen if all parasites disappear

Parasites are organisms that live at
the expenses of another organism, which is known as host, by attaching themselves
on or in their host. They retrieve nutrients from the host while giving nothing
back to the host. There is a diverse range of parasite and each has adapted to
different hosts for survival. Based on the research data, around 50% of all
organisms on the Earth are parasitic. For example, other than the parasites
that are commonly known, fungi are also parasites. There are even bird
parasite, such as the cuckoos that lay their eggs in other birds’ nest.

The World Health Organization
declares 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 parasitic
can multiply in humans, which can cause Leishmaniasis. Helminths are larger,
multicellular organisms that can be observed by naked eye during their adult
stages. The examples of helminths include flatworms such as flukes and
tapeworms, and roundworms such as nematodes. Ectoparasites are also known as
blood-sucking arthropods, which play an important role in causing diseases by
transmitting pathogen and act as a vector.

Parasitic infections caused by
parasites is a tremendous burden for human, due to their ability to cause
illness and death. Thus, there would be a great impact on human and animals if
all parasites that cause disease disappeared. For example, malaria is one of the
common human parasitic infections in Malaysia. It is caused by the parasitic
protozoan, Plasmodium sp. and are
transmitted through the vector, the Anopheles
mosquitoes. Malaria is a life-threatening disease since it can cause organ
failure of kidneys and liver, destruction to red blood cell that results in
anemia and accumulation of fluid in the lung that causes breathing problems. It
will be a good new for those who are infected if this disease causing parasite,
the Plasmodium sp. disappear because
they would be cured immediately from this serious chronic illness.

However, this happy moment wouldn’t
last for a long period. There could be some unanticipated and unpredictable
consequences if all parasites are eradicated from this world. According to the
hygiene hypothesis proposed by David Strachan in 1989, the lack of exposure to
parasites increase the susceptibility to allergic reactions by suppressing the
natural development immune system. In 2003, Graham Rook proposed the “old
friend hypothesis” that explains the link between microbial exposures and
inflammatory disorders. He proposes that human become so dependent on the
microbes that their immune systems cannot develop properly without them and this
is thought to lead to defects in establishment of immune tolerance and may
start to attack our own body. This also explain why there is a rise of
autoimmune disease in the young in Malaysia although they are living in a clean
environment.  Gastroenterologists in the
University of Iowa had even suggested the use of helminths as treatment for
inflammatory disease. Helminths provoke a variety of anti-inflammatory
responses and awake the regulatory side of the immune system so that humans’
immune system will not overreact to those which are harmless stimuli, from the
dust and pollen to beneficial bacteria inside the body. Hence, disease-causing
parasites and microbes may be fatal to human in some cases, but they are needed
in order to help human to develop their immune system so that the autoimmune
disease and allergic cases will decrease.

            In Malaysia,
there is a large area of forests and plantation that serves important role in
the country. Parasites help to keep down and control the numbers of plant-destructing
insects and other animals that are considered as pests. Nearly all insect pests
have at least one parasite that attacks them, and most of them are parasitoid
that kills the hosts before the offspring is produced. Malaysia is a country
that hit 72% rice production of the nation’s self-sufficiency level and this
indicate that the rice production is an important field in our country. There
are some insect pests that feed on the rice, and hence cause destructive
consequences of the rice production. At this time, the parasites are useful
tools that act as biological control to these insect pests. For example, the
rice armyworm, Spodoptera mauritia in
the order Lepidoptera, is a kind of caterpillars that occur in low populations
in the rice field. The major reason of low occurrence of this species may due
to the infection of fungus and parasitoid. The presence of fungal infections
such as Paecilomyces and Metarhizium also helps to reduce the
population of the Malayan black bug, Scotinophara
coarctata, which are feed by sucking the sap of rice plants. Without the
presence of these parasites, these species will increase in numbers within
months and cause serious damage to food crops. As a result, people will have to
use chemical insecticides which would pollute the environment, to control the
population of insect pests.

            Parasites benefits
the wildlife animals by providing evolutionary adaptations to their hosts. The
host-parasite relationships are often described as co-evolutionary arm race
where the involved species mutually adapt to each other and exert selection
pressure on each other. Parasites help their hosts to increase the ability to
survive at species level. Thus, if the parasites disappear in the world one
day, there is no more selection pressure on all the organisms. The world would
be overpopulated will all types of organisms, including those with low survival
ability and low fitness. The ecosystems must have a way to regulate the
organisms’ population in order to be sustainable. When some species population
is too large due to the absence of restriction of parasites, competition and
predation are not able to limit them, and this may cause major extinction
outbreak of another species in the world.

            In
conclusion, parasites play an important role to help to balance the world
population and sustainability of the Earth. They may bring some unfavorable
disease and conditions to humans and animals, but there are always some reasons
behind the scene. Without parasites, the Earth will collapse soon since the
living organisms resides on Earth starts with a simple unicellular microbe.