PARASITES
Parasites are typically small organisms that live at least partly, if not entirely, at the expense of another species of living organism, called the host. They may live externally on the body of the host (ectoparasites) or inside the host (endoparasites). Both kinds obtain nutrition, shelter and other requirements from the host, but contribute nothing to the latter's welfare. The adverse effects of parasitism on the host range from almost none to eventual death.
A well-adapted and successful parasite is one which easily infects a host or reinfects another host to carry out its life processes without causing undue or serious harmful effects to its host. The success of any parasite is dependent upon the continued existence of its host.
Some parasites can live in a broad range of hosts, while others can develop in only one particular host species. Indeed, host specificity varies enormously. Human infections acquired from animals are known as zoonoses. Just as the host specificity is highly variable, the parasitic fauna includes a wide range of organisms, from single-celled protozoa to helminths, arthropods and vertebrates. Nearly every phylum has parasitic members. However, the magnitude of the problem and the importance of parasites have not always been given sufficient attention.
Although parasites of humans and animals are often pathogenic (disease-producing), some parasites are of immense potential value in the biological control of pests of agricultural importance.
Bedbugs do not carry diseases, but are merely annoying as they rely on humans for their blood meal. Malaysia has one of the worldÕs two bedbug species—parasites which get their name from their fondness for biting people in bed.
In the past, lice were associated with the transmission of diseases, but this is no longer the case. They are an indicator of poor hygiene and, like bedbugs, are no more than a nuisance.
In contrast, fleas have been the carriers of diseases which have caused many deaths over the centuries. The most serious of these diseases was bubonic plague (the Black Death), which is carried by the oriental rat flea or plague flea (Xenopsylla cheopis); an outbreak of this disease occurred in Malaysia as recently as 1928. The other common fleas in Malaysia live on cats and dogs.
Mosquitoes are hosts to both the protozoans, which transmit malaria, and nematode worms, which are the cause of filariasis. Both of these diseases affect wildlife as well as humans. Wildlife are also affected by ticks, which can then be transmitted to both people and domestic animals. Heavy economic losses can be caused to livestock herds in Malaysia affected by tick infestation. However, vaccines are being developed to prevent such losses.
Mites are found on agricultural crops and in houses as well as on wild birds. Those on crops and birds can transmit diseases to humans, who can also be affected by dust mites in houses. Susceptible people can suffer allergic reactions from such mites.
Roundworms, tapeworms and flukes are all found in animals which are eaten by humans. Thus, people are easily infected if such food is not thoroughly cooked. Roundworms also live in soil and on plants, and so the eggs can be easily ingested from dirty hands.
