Publisher Summary This chapter discusses the epidemiology and control of nematode infections of grazing animals. The disease resulting from nematode infections is the consequence of exposing insufficiently resistant animals to grazing that is too heavily infected so that they pick up infective larvae at an excessive rate. The disease producing infection is acquired over a relatively short space of time, in some cases because the animals quickly become refractory to infection, in others because worm numbers are regulated in the host to maintain a level proportional to the rate at which new infection is acquired. The number of generations of the parasites involved in the process of auto-infestation is always small. This is either because of the rapid development by the host of a resistance to reinfection or because of the long time taken for the free living phase of the life cycle to be completed. In some cases both factors operate. Disease because of the simple transmission of infections can be avoided by withholding groups of susceptible animals from pasture contaminated by other groups. The choice of control measures where disease is because of auto-infestation depends on how the number of generations involved is normally limited.

The epidemiology and control of some nematode infections of grazing animals.

The epidemiology of helminth disease in farm animals.

Farm management and systems of helminth control.

Publisher Summary This chapter discusses the meteorological factors and the forecasts of helminthic disease. With some helminthic diseases, for example parasitic gastroenteritis in sheep, several different species of nematodes may be involved. These are unlikely to show identical responses to changes in weather or host. Even where single species are involved, different stages in the life cycle may respond differently to changes in weather and, for example, the nematode egg is usually more resistant to desiccation than the larva. Assessing the role of climate on helminth parasites requires the important disease-free years when, seemingly, the parasite population is reduced to an innocuous level. It is important to recognize that the level of the parasite population is determined by the interaction between the high reproductive potential of the parasite and the variable limiting factors (mainly meteorological) in the environment. Normally, these limiting factors maintain a high environmental pressure on the parasite, high mortality ensues and the population is maintained in check.

Meteorological factors and forecasts of helminthic disease.

Back to the future: developing hypotheses on the effects of climate change on ovine parasitic gastroenteritis from historical data.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0031182000072413

G. Everett

Papers

The ecology of the free-living stages of Trichostrongylus colubriformis.