AbstractNematodes are structurally simple animals known commonly as roundworms or thread worms. They are cylindrical non-segmented cigar shaped organisms distinguishing them from other types of worm. However, despite this simplicity these helminths are the most ubiquitous animals on earth and have successfully managed to colonise almost every environmental niche imaginable. The majority of nematodes are free living and are found within soil and water on every continent on earth. However, many have also adapted to parasitize a host or in some cases a range of hosts. The diversity of these invertebrates is amazing with species having evolved to feed on such a wide platter of food as bacteria, algae, fungi, invertebrates (including nematodes) and cellular components of both plants and animals.
However, as amazing and intriguing as these creatures are, they possess a more sinister side which expresses itself mainly in the form of those parasitic species which affect man. Either in a humanitarian nature through direct infection and disease or indirectly as an economical burden on agricultural productivity. The parasitic nematodes such as hookworms (Necator americanus), whipworms (Trichuris trichess) and roundworm (Ascaris lumbricoides) are all highly prevalent within the global population with approximately 4.5 billion helminth infections estimated in a world population of some 6 billion (UNICEF, 1998). Although not all of these infections will result in mortality, morbidity as a result of infection is very common that unfortunately like so many other sicknesses is more prevalent and exacerbated in developing countries.
Other parasitic worms of importance are those that have detrimental effects on agricultural output, whether of a veterinary or arable nature, forestry and horticulture. Nematodes such as the intestinal parasite Ascaris suum, the barber-pole worm Haemonchus contortus or the lung worm Dictyocaulus
vivipams all impose parasitic burdens upon important agricultural livestock. Infection leads to a loss of production through decreased weight gain and in the worst cases can result in death of the host if not treated. Many species also parasitize companion animals often causing emotional stress to both pet and owner.
However, of greater significance and more important in terms of monetary value is the economic burden elicited by the phytoparasitic nematodes (those which infect plants). These nematodes infect plants from a wide range of species including those used in the production of fiber. For example, Rotylenchulus reniformis infects cotton plants and Globodera tabacum infects tobacco plants, as well as a wide range of species infecting crops for consumer consumption. A few examples of these are Globodera pallida which infects potato plants, Heterodera glycines which infects soya beans and the Meloidogyne genus which can infect a number of plant species including tomatoes. The majority of plant parasites infect the roots of the host plant although a number will also infect above ground level (Jagdale and Grewal, 2002; Munn and Munn, 2002).
The extent to which our lives are affected by these apparently insignificant organisms is only now becoming apparent with attention turning to the arduous task of controlling these pests particularly in light of nematicide restrictions. The two main methods of control currently used involve the manipulation of the environmental conditions in a deleterious way to the nematodes, and/or combined with the use of chemical compounds of a specific nature in the form of nematicides (anthelmintic therapeutics) (Conder, 2002) or general toxins in the form of a pesticide (Atkinson, 2002).
Unfortunately, the effectiveness of both approaches are somewhat hampered by the resilience of nematodes against control methodologies and the developing resistance among animal parasitic species (Kaplan, 2004). The increased awareness, of potential environmental damage caused by pesticides has further limited nematode control (Atkinson, 2002). As a result of these developments, continued research is essential to understand the intricate biological processes that enable these worms to function despite our best attempts to disrupt fundamental biological processes. This may lead to the identification of more efficient and effective means of control before the defences currently in place have been rendered ineffective.
|Date of Award||2006|
|Supervisor||Gerard Brennan (Supervisor), Nikki Marks (Supervisor) & Colin Fleming (Supervisor)|