Comparative study of sheep and buffalo isolates of Fasciola gigantica in the intermediate host Lymnaea auricularia.

A comparison was made of the biological behaviour of two isolates of Fasciola gigantica, obtained from sheep and buffalo, in the aquatic snail Lymnaea auricularia. The sheep isolate exhibited a lower rate of infection, slower larval development and the production of fewer cercariae. Larger eggs, miracidia and metacercariae were obtained from the buffalo isolate while the rediae and cercariae were smaller. Metacercariae of sheep origin were dark brown with a mortality after 80 days of storage at 4 degrees C of 30.6 per cent while those of the buffalo isolate were straw coloured and had a mortality of 10.2 per cent.

The pathogenicity of haemonchosis in sheep and goats in Iraq: 1. Clinical, parasitological and haematological findings.

The response of Awassi sheep and the local breed of Iraqi goats to primary infection with a prevalent trichostrongylid nematode, Haemonchus contortus, was compared by examining their worm burden and the pathogenic effects of the parasite on these hosts following experimental infection. The results showed that the goats had lower worm burdens and had suffered less severe clinical and haematological disturbances than the Awassi sheep. The worm counts in sheep were higher than in goats but the count of the mucosal phase of the larvae was higher in goats. These differences are possibly immunologic in origin though a genetic resistance may operate, primarily at the level of worm establishment. The pathophysiological changes are correlated with parasitological and clinical observations in the two host species.

Development and survival of Haemonchus contortus larvae on pasture in Iraq.

The survival of Haemonchus contortus infective larvae on pasture and soil was studied over a period of 12 months in the Baghdad area. Infective larvae were found on herbage and soil at all times except in the summer months. During autumn and winter infective larvae in pasture survived for periods of up to 32 weeks. Little larval migration into soil was observed during this study and larvae did not survive for long in the faecal pellets during the summer.

Gross pathology and histopathology of haemonchosis in sheep and goats in Iraq.

The response of Awassi sheep and a local breed of goats to H. contortus, the prevalent ovine and caprine strongyloid species in Iraq, was studied. A dose of 500 H. contortus (sheep origin) larvae kg-1 body wt. induced clinical and pathological changes of haemonchosis. Although the percentage recovery of worms was higher in sheep, the pathological (gross and microscopic) changes were more marked in infected goats. The extensive abomasal changes noted in goats were, in general, accompanied by a higher density or larvae in the gastric wall; the pathology did not necessarily depend upon parasite count alone and a definite relationship could not be established. The tissue changes in the goats are possibly of immunological origin, although a genetic resistance may operate, primarily at the level of worm establishment.

Effect of anthelmintic treatment on the development of resistance in sheep vaccinated or experimentally infected with Dictyocaulus filaria.

This investigation was undertaken to study the immune response of Iraqi sheep vaccinated with Dictyocaulus filaria larvae (Filiraq) and to determine the effect of tetramisole on the development of resistance to reinfection. The findings confirm the effectiveness of Filiraq in conferring protection against experimental infection with D filaria. However, the administration of anthelmintic four weeks after each vaccination interfered with the development of immunity. Termination of D filaria infection at 28 days by tetramisole treatment also prevented the immune response.

Seasonal fluctuations and hypobiosis of gastro-intestinal nematodes of Awassi lambs in Iraq.

The results of an epidemiological study involving the estimation of worm counts of gastro-intestinal nematodes of lambs, during the period December 1978 to November 1979, in the Baghdad area are reported. Ostertagia spp. and Trichostrongylus spp. were the most abundant nematodes in the weaned lambs used in this study. Ostertagia spp. infection was present throughout the period of observation, the level of infection being the highest during early summer (May-June). Trichostrongylus spp. infection, however, reached a peak during July-August. In the tracer lambs the maximum population of Ostertagia spp. was found during February-March, while that of Trichostrongylus spp. could be observed only after mid-June. Other nematodes encountered were Haemonchus contortus and Trichuris sp. but they were only present in small numbers. The proportion of inhibited larvae of Ostertagia spp. was markedly high during the dry summer months. Little inhibition was noticed during autumn and the early winter months. It appears that if the seasonal inhibition of Ostertagia spp. in Iraq is brought about by an environmental stimulus acting upon pre-parasitic larval stages, that stimulus cannot be chilling or falling temperatures, as observed in temperate northern zones.

Epidemiology of gastrointestinal parasites of Awassi sheep in Iraq.

Studies on the epidemiology of gastrointestinal nematodes of sheep, conducted at two different farms in the Baghdad area, in 1979, revealed two peaks in worm egg counts in ewes, one in spring and the other in autumn; the latter coincided with the lambing season. Similarly in lambs, two peaks of infection were apparent, but the spring peak was not so well defined. During the hot and dry summer months of Iraq, helminthic infection was at a low level. Faecal culture for larvae and their identification indicated the predominance of Haemonchus contortus infection in the ewes and that of Ostertagia and Trichostrongylus spp. in the lambs examined, Trichostrongylus infection predominating during the hot, dry period of the year. The self-cure phenomenon as well as preparturient rise in egg counts, as reported in other countries, was also observed during this study.

Study on the pathogenicity of ostertagiosis due to Ostertagia circumcincta in sheep, in Iraq.

The response of Awassi sheep to ostertagia circumcincta, the most prevalent ovine strongylid species in Iraq, was studied. A dose of 100000 larvae of O. circumcincta (Iraqi strain) induced moderate clinical symptoms of ostertagiosis. These symptoms were correlated with elevated pH of the abomasal fluid and increased plasma pepsinogen levels. There was no evidence of larval inhibition since the majority of the fourth stage larvae (L4) continued their development. No appreciable loss of worm population was observed and most of the parasites survived and exhibited a prolific egg-laying potential six months after initial infection. Assessments of the pathophysiological changes were performed and correlated with parasitological and clinical observations. The Awassi breed of sheep, the most prevalent in the Arab Middle East, seems to be more susceptible to ostertagiosis than other breeds and there was no spontaneous self-cure in this breed.

The prevalence of hydatid cysts in slaughtered animals in Iraq.

The prevalence of infection with hydatid cysts in sheep, goats, cattle and camels slaughtered at Baghdad Abattoir was recorded over a period of 18 months. The infection rates were generally lower than had been reported in previous surveys but remained high in camels. The lower prevalence rates were attributed to the destruction of stray dogs, improved standards of meat inspection and an overall improvements in socio-economic conditions. The fertility rate of the cysts was higher in camels than in sheep or goats. All the cattle cysts were sterile.

The response of Awassi sheep to re-infection with Haemonchus contortus larvae.

The response of Awassi sheep to primary infection with 10 000 Haemonchus contortus larvae and subsequent challenge with 20 000 larvae was studied. Two types of response to re-infection were observed. The first, characterized by a sharp decline in egg counts, progressive improvement in packed cell volume (PCV) and a marked loss of adult worms and challenge larvae, was considered as self-cure and protection. In the second type of response there was a temporary decline in egg counts, no improvement in PCV and necropsy findings indicated hyper-infection with challenge larvae.

Effect of anthelmintic treatment on the performance of Awassi sheep in Iraq.

Studies are reported on the effect of anthelmintic treatment on the body weight gain and wool growth of ewes with subclinical helminth infections. The parasites involved were Fasciola gigantica and Ostertagia spp., together with some Haemonchus contortus, Trichostrongylus spp., and Dictyocaulus filaria. In 1 group, 5 sheep, which were treated twice with tetramisole at an interval of 4 weeks to remove gastro-intestinal nematodes and lungworms, showed an increase of 41% in weight gain and 3.2% in wool growth compared with an untreated group. Another group, which was treated with both tetramisole and rafoxanide to remove nematode and fluke infections, had a 143% increase in weight gain and 81% in wool growth compared with the control.

The response of Awassi and Merino sheep to primary infection with Haemonchus contortus.

The possible existence of breed differences in the response of sheep to primary infection with Haemonchus contortus was examined by comparing worm establishment and pathogenic effects of the parasite in Awassi and Merino sheep of haemoglobin type B infected with 500 third stage H. contortus larvae per kg body weight. The results showed that the Merino sheep had lower faecal egg counts and worm burdens and suffered less severe clinical disturbances than sheep of the Awassi breed. This suggests that genetic resistance operates primarily at the level of worm establishment.

Genetic resistance to helminths. The influence of breed and haemoglobin type on the response of sheep to re-infection with Haemonchus contortus.

The influence of genetic factors on acquired resistance to Haemonchus contortus infections in sheep was investigated. Animals whose primary infections were terminated with an anthelmintic failed to develop any immunity against subsequent challenge as judged by worm numbers. Nevertheless, all were better able to retard the development and reduce the fecundity and haematophagic activities of their parasite populations than animals undergoing primary infections. High levels of resistance, as judged by all these parameters, were observed in most animals when the challenge larvae were superimposed on existing worm populations. The patterns of worm establishment and disease indicated that genetic factors operated in determining resistance, since fewer worms became established and less severe clinical and pathophysiological changes were observed in Scottish Blackface than in Finn Dorset sheep with the same haemoglobin type. Similar advantages were displayed by animals with haemoglobin AA and to a lesser extent those with haemoglobin AB over haemoglobin BB types. The importance of breed was further indicated by the occurrence of 'self-cure' in the majority of the Scottish Blackfaces but in only one Finn Dorset. There was no evidence that this reaction was associated with haemoglobin type.

Genetic resistance to helminths: a possible relationship between haemoglobin type and the immune responses of sheep to non-parasitic antigens.

The results of some preliminary studies on a possible association between haemoglobin type and the antibody responses of sheep to a variety of non-parasitic antigens are described. Sheep with haemoglobin AA showed a significantly better response to human serum albumin than animals of the same breed with haemoglobin BB. There was also suggestive evidence of a better response by haemoglobin AA types to rabbit red cells and horse gamma globulin. These results indicate that the greater resistance of these sheep to gastrointestinal nematodes is reflection of their superior immunological competence.

Genetic resistance to helminths. Comparison of the development of Ostertagia circumcincta infections in Scottish Blackface sheep of different haemoglobin type.

Over the years a number of investigators have reported that sheep with haemoglobin A are more resistant to Haemonchus contortus than animals of the same breed with haemoglobin B. The experiment described here was an attempt to ascertain whether a similar association might exist between haemoglobin type and resistance to non-haematophagic parasites. The results indicate that such a relationship might exist, since Scottish Blackface sheep with HbA showed milder biochemical and pathophysiological changes than their HbB counterparts and at the same time harboured smaller numbers of adult worms and more inhibited larvae when necropsied 16 days after a primary infection with 100,000 Ostertagia circumcincta third-stage larvae.

Experimental studies on the suitability of aquatic snails as intermediate hosts for Paramphistomum cervi in Iraq.

Three of the most common species of aquatic snails in Iraq were examined for their susceptibility to infection with Paramphistomum cervi. Bulinus truncatus was the only susceptible species. No development occurred in Physa acuta or Lymnaea lagotis euphratica. These findings and a previous field observation that infection of B. truncatus with amphistome larvae is not uncommon indicate that B. truncatus is an intermediate host of P. cervi in Iraq. Young snails of B. truncatus were more susceptible to infection than older ones.