Drug – bio-affecting and body treating compositions – Whole live micro-organism – cell – or virus containing – Fungus
Patent
1994-06-20
1997-07-01
Marx, Irene
Drug, bio-affecting and body treating compositions
Whole live micro-organism, cell, or virus containing
Fungus
4352341, 435911, 426 2, 426807, A01N 6300, A01N 6304, A01N 6500, C12N 114
Patent
active
056435681
DESCRIPTION:
BRIEF SUMMARY
This application was filed under 35 USA 371 as the national phase of PCT/DK92100269.
FIELD OF THE INVENTION
The present invention relates to a process for selection and isolation of nematophagous fungi to be used as biological control agents against infective larvae of parasitic nematodes such as Ostertagia ostertagi and Cooperia oncophora (Trichostrongylidae).
BACKGROUND OF THE INVENTION
Young calves which are put to pasture for the first time are susceptible to a large number of germs, i.e. threadlike small parasitic nematodes (Trichostrongylidae), which are parasites in the abomasum and intestine of cattle. These infections can cause serious diseases, such as diarrhea, indigestion, loss of weight, and death. But it is in particular the relatively mild infections which are of economic importance, since they are very widespread and result in poor growth, in particular at the end of the season.
Infected calves secrete the very small eggs of the nematodes in their faeces. FIG. 1 shows the life cycle of cattle nematode parasites. The mature parasites multiply by laying eggs in the intestinal tract of the cattle. The eggs have a size of 0.05-0.1 mm and are thin shelled. They are excreted with the dung of the animals. The larvae develop from the eggs in the cow pats on the pasture. The larvae go through three larval stages (L.sub.1, L.sub.2 and L.sub.3). The third larval stage (L.sub.3), which is infective, retain the cuticle of the second larval stage (L.sub.2) as a protective sheath until they enter their host. In the cow pat, temperature, moisture, oxygen pressure and the natural enemies of the parasites are decisive for the number of eggs that develop to the infective stage. The infective larvae, having a length of up to 1 mm, are spread from the cow pat to the surrounding grass, in particular in connection with rainy weather. Most of the larvae are present within 30 cm from the rim of the cow pats. On the grass they may be eaten by grazing animals, and then they can continue their development in the intestinal tract of the animals up to maturity.
The parasitic development starts when L.sub.3 larvae are ingested by cattle. L.sub.3 exsheath in the rumen. A few days after the infection, exsheathed L.sub.3 enter the abomasal glands, where they differentiate and increase in size. Three stages occur (L.sub.3, L.sub.4 and L.sub.5), separated by two moults. Immature adult parasites (L.sub.5) emerge from the glands around 18 days after the infection. During the next few days, they become sexually mature on the surface of the abomasal mucosa, resulting in excretion of eggs.
Since nematode parasites often cause great losses to farmers, it is very much of interest to control these parasites. Traditionally, this takes place by medical treatment, but farmers also try in various ways to protect grazing animals against eating large amount of larvae, e.g. by reducing the density of animals on the pasture so that they are not forced to graze the highly infected areas close to their own excrements. Animals can also be moved to a clean or low-infected field at the end of the summer when the danger of infection usually increases strongly.
However, these measures have a number of economic and practical drawbacks, making it desirable to find alternative methods of control. Thus, for a number of years efforts have been devoted to the development of methods for biological control of larvae of nematodes in cow pats already before they are spread as infective larvae to the grass. Biological control comprises the use of natural enemies of the nematodes, which are nematophagous fungi, also called predacious fungi, in this case.
Predacious fungi are microfungi which do not develop fruiting bodies, as is known from e.g. mushrooms, but have a growth form resembling mold. Predacious fungi are special having developed organs that are able to capture and kill small nematodes, including infective larvae of nematodes. Predacious fungi are originally terricolous fungi, but it has been found that they can also grow in cow pats. It is pre
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Gr.o slashed.nvold J.o slashed.rn
Henriksen Svend Aage
Larsen Michael
Nansen Peter
Wolstrup Jens
Larson Kristin K.
Marx Irene
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