Susceptibility of Amblyomma variegatum ticks to acaricides in Ghana.

Abstract. The susceptibility of unfed and fed stages of larvae, nymphs and adult females of Amblyomma variegatum ticks were tested using Shaw's filter paper dip method against four acaricides; chlorfenvinphos and dioxathion, chlorfenvinphos, gamma benzene hexachloride and amitraz at four different concentrations including the recommended dose rates. Based on their lethal concentrations (LC50 & LC90) chlorfenvinphos and dioxathion combined and chlorfenvinphos alone placed first and second, respectively, in all stages except at the unfed nymphal stage where gamma benzene hexachloride topped with a LC50 of 0.001629, while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone had LC50 of 0.001794 and 0.002258, respectively. Amitraz appeared to have a quick knock-down effect on larvae and nymphs but at the recommended dose rate, showed no mortality of the ticks at that stage. However, at a concentration of 0.040%, amitraz showed a 100% inhibition of oviposition and hatching of laid eggs. Gamma benzene hexachloride produced only 66% inhibition of oviposition while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone produced 100% inhibition of oviposition at their recommended dose rates. Fed nymphs were more susceptible than the unfed nymphs. Eggs laid by engorged female ovipositing ticks, applied with gamma benzene hexachloride, hatched.

Epidemiological studies on gastrointestinal parasitic infections of lambs in the Coastal Savanna regions of Ghana.

The types of gastrointestinal parasites (Eimeria and helminths) encountered by 70 lambs and the seasonal pattern of both Eimeria and strongylate infections in these lambs in the derived Coastal Savanna were followed for three years. Eimeria oocysts and helminth eggs were detected in the faeces of lambs at the same time, indicating the concurrence of both Eimeria and helminth infections. Eimeria oocysts were first seen in the lambs 20 days after birth (DAB) and the level of oocyst output increased by the fourth week. Eimeria species identified in the lambs were E. parva, E. pallida, E. faurei, E. ahsata, E. bakuensis, E. intricata, E. granulosa, E. ovinoidalis and, occasionally, E. marsica, E. ovinoidalis, the most pathogenic species, dominated the oocyst output during the early part of the life of the lambs. Strongyloides papillosus eggs appeared at 46 DAB, preceding strongylate nematode eggs, which were seen at 57 DAB and those of Moniezia at 69 DAB. The pattern of Eimeria oocyst output paralleled that of the worm egg output, and high oocyst and strongylate worm egg counts corresponded with the period of high rainfall during the study period. Although oocyst and worm egg output fluctuated, high Eimeria oocyst counts were seen again in the lambs when they were 1 and 2 years old. Haemonchus species formed 71% of the infective larvae revealed by larval culture.

A study on the time of ovicidal effect of some anthelmintics in Djallonke sheep and its implication for the control of parasitic helminth infections.

The time lag between the administration of five different anthelmintics and the exertion of their ovicidal effect on worm eggs was monitored in five groups of Djallonke sheep. In this experiment, all the animals in all treated groups and an untreated control group were grazed together. Worm egg output and the number of infective strongylate nematode larvae (L3s) recovered from fecal cultures from each group were observed every four hours for 72 h. The earliest time observed for the occurrence of ovicidal effect resulting in the absence of L3s in fecal cultures was 8 h after the administration of the anthelmintics. However, this time was not the same for all the anthelmintics. The implication of the results are discussed in relation to its application for worm control.

Oocyst counts in crossbred ewes under tree-crop plantation in the forest zone of Ghana.

In this paper, the Eimeria oocyst output of two groups, pregnant ewes (group 1) and non-pregnant controls (group 2), which were followed from September 1993 to August 1994, is described. In both groups of animals the level of oocyst output was high during the minor rainy season. However, during the periparturient period the pregnant ewes showed the higher oocyst output. The oocyst output in both group fell to similar levels after weaning of the lambs in March 1994. The species of Eimeria identified in order of dominance were Eimeria parva, E. pallida, E. faurei, E. ahsata, E. ovina, E. intricata, E. granulosa and E. ninakohlyakimovae. There were no differences in the species composition of oocysts in both groups of animals.

Seasonal changes in the level of infective strongylate nematode larvae on pasture in the coastal savanna regions of Ghana.

The level and type of infective strongylate nematode larvae on pasture were followed from March 1994 to April 1995 in the coastal savanna regions of Ghana. The number of infective larvae on pasture was high, reaching 2458 kg-1 dry matter of grass during the period of and soon after the rains, and very low or none in the absence of rainfall. The number of infective larvae on pasture was directly related to the pattern of rainfall, but it was also influenced by the number of raindays in the period. The following genera were found in order of prevalence: Haemonchus, Oesophagostomum, Trichostrongylus, Cooperia. The mean total adult worm burdens of tracer lambs released monthly were related to the levels of herbage infective larvae.

Studies on the morphological changes in the midguts of two ixodid tick species Boophilus microplus and Rhipicephalus appendiculatus during digestion of the blood meal.

Light and electron microscopy were used to study the morphological changes which accompanied feeding and digestion of the blood meal in the midgut epithelium of two ixodid tick species Boophilus microplus and Rhipicephalus appendiculatus. In unfed ticks of both species, the midgut epithelium was lined by stem cells and empty digest cells in which haematin accumulated with starvation. On attachment to its hosts, differentiation of the stem cells and the loss of haematin from the midgut epithelium, seemed to be synchronous. Digestive activity with the appearance of the digest cell series started in the anterior end of the midgut when it came in contact with the blood meal. Although various stages can be distinguished, it would appear that these are in reality phases of activity of a single cell type--the digest cell. No additional evidence was obtained on other cell types.

Histochemical changes in the midgut of two ixodid tick species Boophilus microplus and Rhipicephalus appendiculatus during digestion of the blood meal.

The changes in the midgut epithelia of two ixodid tick species, Boophilus microplus and Rhipicephalus appendiculatus, have been studied using several histochemical techniques. It was revealed that there is an accumulation of RNA at the time of tick attachment to the host and prior to the arrival of the blood meal, indicating that the midgut digest cell is furnished with the machinery characteristic of a synthetic cell. There appears to be a synchrony in the appearance of granules with peroxidase activity and the uptake of haemoglobin into the midgut digest cells. Alkaline phosphatase activity was observed in the midgut epithelia of all ticks except in a few of the long-starved ticks, and was concentrated in the apical plasma membrane regions of those digest cells involved in absorption and the intracellular digestion of haemoglobin. The presence of these enzymes suggests that the midgut digest cell is a multifunctional cell capable of both secretory and digestive activities. The colloidal material in the midgut lumen was found to result from the accretion of several products both secreted and excreted by the midgut epithelial cells and exhibited different staining reactions depending on which component dominated. The nature of the material suggests that in addition to its its digestive function it may serve as a sink to bind all the by-products of digestion and thereby facilitate their excretion.

Epidemiological observations on helminth infections of calves in southern Ghana.

This paper describes helminth infections in three groups of calves of different ages grazing naturally infested pastures from March 1987 to May 1988. Calves in which the faecal egg output was followed from birth showed Toxocara vitulorum eggs as early as two days after birth and maximum patency occurred after two months. The fall in Toxocara egg output coincided with a rise in that of the strongylates; Haemonchus spp., Trichostrongylus spp. and Oesophagostumum spp. The influence of rainfall in dictating strongylate nematode infection was clear with high egg output during high rainfall and low egg counts when the rainfall was lower. There was an indication that calves carry the infection from the end of the minor rainy season in November to the beginning of the next rains in March and then contribute to pasture contamination. However, calves born in December may remain uninfected until the onset of the rains.

Periparturient rise in faecal nematode egg counts in west African dwarf sheep in southern Ghana in the absence of arrested strongyle larvae.

The nematode egg output of two groups of ewes, a pregnant test group (2-3 years of age) mated between March and April and a non-pregnant control group (5-6 years of age) was followed. The worm burdens acquired by worm-free 'tracer' lambs were also followed on the same pasture from March 1988 to February 1989. There was a significant difference (P less than 0.05) in the magnitude of the egg output in the test group compared with the control group. In the test ewes, an initial rise in egg production occurred 2 weeks after lambing and was maintained for five consecutive months. Necropsy worm counts from the 'tracer' lambs revealed that pasture larval levels were directly related to the levels of rainfall. Adult nematodes (Trichostrongylus colubriformis, Trichostrongylus axei, Haemonchus contortus, Oesophagostomum venulosum and Trichuris ovis), and some Moniezia expansa were present in almost all the lambs throughout the year, with the exception of January and February 1989. The absence of immature larvae in these lambs indicates that arrested development is not a feature of the life cycle of these species in Southern Ghana. The occurrence of a periparturient rise of nematode eggs in West African Dwarf ewes, a year-round breeder, means that susceptible lambs could be open to infection throughout the year. Control should, therefore, be conducted by treating ewes after lambing and restricting the breeding season to particular periods of the year.

Histochemical localisation of acid phosphatase and non-specific esterase in the midguts of two species of tick, Boophilus microplus and Rhipicephalus appendiculatus, as determined by light microscopy.

Serial sections of glycol methacrylate-embedded and frozen midguts of Boophilus microplus and Rhipicephalus appendiculatus were studied histochemically by light microscopy. The use of the naphthol AS-TR phosphate technique combined with glycol methacrylate embedding enabled the precise localisation of lysosomal enzyme activity, despite the ubiquity of haematin granules in tick midgut epithelia. The presence of acid phosphatase and non-specific esterase activity in the same cells was observed in all of the various developmental stages and feeding phases of the ticks. The pattern of appearance of these cells paralleled the reported level of protease activity in the midgut lumen. The cells were found to be solitary, particularly during the slow digestive phases, and appeared to move into the lumen, where they eventually disintegrated. The cells therefore appear to function as holocrine secretory cells. This is the first report indicating the presence of such secretory cells in the midgut of unfed ticks. The disintegration of these cells in the lumen suggests that lumenal digestion may be more important than hitherto realised.