Helminth infections of food animals cause significant economic losses. The effect of the infection is determined by a combination of factors of which the varying susceptibility of the host species, the pathogenecity of the parasite species, the host/parasite interaction, and the infective dose are the most important.
The economic losses are closely associated with the extend to which the pathogenic effect of helminth infections influences the production of the individual host. This may vary considerably from clinical disease including mortality to chronic production losses which may appear as eg. reduced growth rate, weight loss and/or reduced fecundity or it may go unnoticed.
The transmission success of the majority of economically important helminth
infections of animals depends almost entirely upon ingestion of the
parasites via certain food elements. Thus herbivorous and carnivorous
hosts become infected by the consumption of fodder contaminated with
infective larvae, and the continuation of the parasites life cycles is
secured by the host dissiminating pre-infective stages onto the pasture or
other food items.
Direct host-to-host transfer in helminth infections is restricted to a few parasites where prenatal infections from the mother to the growing embryo may occur and to transmission via skin penetration. Some of the filaroid worms are transmitted by vectors.
In addition to the helminth infections which cause direct economic losses due to reduced animal production yet another dimension is added by the fact that several helminth infections can be transmitted to man (zoonoses). With regard to their host range some helminth species, do not discriminate between humans and animals at all, while others have complex lifecycles which require man as either final or intermediate host in order to complete their life-cycle. Some of these diseases may be very harmful to man and a considerable amount of effort has over the years been put into the control of these through e.g. meat inspection legislation. The level of control vary from region to region and depends to a large extend upon religious and socio-economical considerations, inclusive the organisational infrastructure of the society. Although the direct pathological effects of some of the zoonotic diseases on the animal might be limited, special emphasis is directed to some of the relevant zoonotic species in this report.
A successful control of helminth diseases is highly dependent on available information on local conditions and the strength of the extension service transferring this knowledge to the farmer. In order to facilitate the utilization of existing data for planning of research and/or control programmes this report, therefore, presents the collected data on a countrywise basis.