The effects of helminth infections on the physiology of the host animal as a result of a specific host/parasite combination, are highly dependable upon the size of the infectious dose, the predilection sites of the parasite and the population density at these sites combined with its ability to evade the immune response by the host. Moreover, the physiological impact of the infection can directly or indirectly be influenced by the presence of other infectious agents such as other helminths, protozoans and/or various microbes. The immunopathological interaction between these agents are only partly understood and the attempt to explain a more than additive effect of combined infections in pathophysiological and/or energetical terms has not been successful.
For these reasons an estimation of the economic relevance of helminth infections is hard to achieve. Nevertheless, serious attemps have been made to produce reliable data.
The majority of the “impact and economy” references use condemnation figures as their starting point.
1. In cattle, buffaloes, sheep and goats most emphasis is seen in the field of losses as a result of liver condemnation. Liver condemnations as a result of helminth infections by liverflukes, schistosomes, and cestodes have been described quantitatively in:
Region 1. From Mexico (03137, 00512, 03766, 04190 and 00160), and Cuba (05873).
Region 2. Estimations are available from Peru (00244) and Brasil (05852, 03740).
Region 3. In Argentina the economic losses as a result of hydatid incidence in sheep was calculated (02980). On the base of slaughter-house results F. hepatica was only considered a serious problem in two areas.
Region 4. No condemnation figures within the “impact” subset.
Region 5. From Kenya (06194, 02447, 04460, 03154 and 08316), Nigeria (03716, 01810, 04483 and 00976), Senegal (03976) and Cameroon (00965) some data on incidence and economics are available.
Region 6. No information in the subset with regard to liver condemnation economics.
Region 7. In Turkey economic aspects concerning liver condemnations are referred to in 01058. In Iraq information is available in 05822, concerning F. gigantica infections. These data are not available for Pakistan (03519). In India for goats the economic loss was determined at 725 ruppees for a group of 448 goats.
Region 8. No information available in the data base.
Region 9. The only references in the subset are from Indonesia (01103) and the Philippines (00170).
With regard to the economic consequences of helminth infections in pigs only limited information is present in the data base.
Region 1. In Mexico because of porcine cysticercosis destruction of carcasses resulted in considerable economic losses (03701). Losses as a result of Ascaris suum infections in Mexico are mentioned in 04539 and 02664.
Region 2. In Peru losses due to porcine cysticercosis were described in an old publication (02664).
Region 3. Economic losses were described in Chile (02205).
Africa and Asia
Region 4. No information on the economics of helminth infections in pigs available.
Regions 5, 6, 7, 8 and 9 are not represented in this subset.
2. Reduced growth rates (meat and wool), reproductive performance, mortalities.
With regard to this subject two types of information have to be distinguished:
the results of field trials comparing productivity parameters in anthelmintic treatment or grazing schedules, and case descriptions;
comparative infection trials.
In this survey, apart from an evaluating study on the vaccination of cattle against Schistosoma bovis (03402) and one on experimental ovine fascioliasis (02740) only references concerning the first mentioned category came to notice.
Region 1. On Cuba a treatment schedule for the control of nematode infections in pigs was developed (02739). In the same country the impact of lungworm infections in cattle were described (05875). In Mexico the economics of Moniezia infections in sheep were analyzed (02690).
Region 2. In Venezuela economic losses from gastro-intestinal helminth infections in cattle were described (02955). In Brasil a cost/benefit analysis for the treatment of gastro- intestinal nematodes in calves was developed based on experimental chemotherapy (07060). In Colombia epidemiology studies to develop control schemes for helminth infections in cattle are a priority area (03395).
Region 3. Cost/ benefit analysis on the control of helminths in beef cattle is described (01989). In Argentina increased performance was seen following control programmes against gastro-intestinal nematodes.
Region 4. In Sudan treatment of sheep against gastro-intestinal helminth infections resulted in small but not significant rates of live weight gain (00634).
Region 5. The control of intestinal parasites increased liveweight gain and reduced mortalities in small ruminants in Kenya (01511).
Region 6. No relevant information.
Region 7. The treatment of buffaloes infected with Toxocara vitulorum showed significant economic advantages (05900). In India the economic importance of gastro-intestinal infections in sheep were analyzed (05687). In Bangladesh it was proven that treatment of calves was economically justifiable (00063), because of the negative growth effects and some mortality as a result of gastro-intestinal nematode infections. Economic analysis in cattle in India has shown that among the most prevalent and important diseases were the gastro-intestinal infections, on small and medium-sized farms in particular (01258) and the same holds for Schistosoma nasalis infections (02894). In Iraq the effects of helminth infections on liveweight gain in sheep were described (00495).
Region 8. No relevant information.
Region 9. Treatment of sheep against gastro-intestinal nematodes in Indonesia resulted in economically justified results (01218). In the Philippines the benefits of control of fascioliasis were described and estimated (05588).