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Development of sero-diagnostic and molecular tools for the control of important tick-borne pathogens of cattle in Africa.

Tick-borne diseases (TBDs) are a major economic constraint to livestock production in sub-Saharan Africa. ILRI is focussing on developing a range of products, such as vaccines, diagnostics and decision support services to underpin improved control programmes against these diseases. We have developed three highly sensitive and specific enzyme linked immuno-assays (ELISAs), which allow precise diagnosis of Theileria parva, Babesia bigemina and Anaplasma marginale. These tests have been standardised and validated using defined experimental and field infection sera. Parasite specific recombinant antigens and monoclonal antibodies against bovine immunoglobulins as secondary antibodies have played an important role in in enhancing the sensitivity and specificity of the assays. They have been further evaluated in on-farm longitudinal sero-epidemiological studies to define infection dynamics and disease risks in various farming systems in Kenya and Uganda. In addition, DNA-based tests for differentiation of Theileria species and characterisation of Theileria parva stocks have been developed. These tests have been derived through physical mapping and sequencing of key elements of the T. parva genome, which include repetitive and telomeric regions, minisatellite sequences, antigen genes and a number of random DNA sequences. These tools are currently being deployed in conjunction with field immunisation programmes to determine the biological impact of introducing live vaccines of T. parva on population dynamics.

Africa↗

The history of the cattle tick Boophilus microplus in Australia and achievements in its control.

For more than 100 years, tick fever and the cattle tick have caused tremendous financial loss to cattle producers around the world. Since Australia became infected with the disease and infested with its tick vector in the mid-19th century, a great deal of research effort has been directed towards their effective control by Australian farmers, administrators and scientists. Such research has yielded information which has facilitated the development of various control strategies that have equal application in other countries afflicted with the same problem. It has been demonstrated that integration of a variety of these strategies is necessary for long-lasting control.

Animals↗

A controlled trial of tick-borne encephalitis vaccination in patients with multiple sclerosis.

The aim of this study was to investigate a possible link between a single vaccination against tick-borne encephalitis (TBE) and the appearance of one or more new cerebral lesions in magnetic resonance imaging (MRI) and/or a clinical relapse of MS. Fifteen MS patients with documented history of MS relapses living in a TBE endemic area were matched with 15 patients selected from a patient database containing 500 cases of MS. Three patients in each group were unvaccinated while all others had basic immunisation and regular booster vaccinations. Patients of the vaccination group received a single dose (3.3 microg) of a TBE vaccine. TBE antibodies were detected by ELISA and confirmed by neutralisation test. MRI was used as marker for disease activity and progression in addition to the clinical neurological examination. No association was seen between TBE vaccination and MRI detected disease activity, clinical relapse or disease progression of MS.

Antibodies, Viral↗

Dogmas and misunderstandings in East Coast fever.

East Coast fever (ECF) is the most important tick-borne disease in eastern, central and southern Africa and caused an estimated loss of US $186 million in 1989 in the 11 countries where it occurs. It was brought to southern Africa with cattle from Tanzania in 1901 and, over the next 3 years, devastated the cattle that had survived the rinderpest pandemic of the 1890s. Chemical control of ticks using arsenical compounds was introduced in the early 1900s and became the main control measure for both ticks and the diseases they transmit. This method of control has become less reliable over the last 30 years for many reasons, including reduced government spending on livestock and extension, the cost of acaricides, acaricide resistance, poor management of dips and spray races, and poor application of cattle movement control and quarantine. Significant advances in immunization and treatment have been made in the last 30 years, and more robust integrated strategies combining immunization, reduced frequency of chemical control and treatment are being adopted or considered. Throughout its history, ECF has been a source of great anxiety and cost to farmers, and of intense interest to research workers. Many dogmas and misconceptions have become established, some of which still flourish while others took years to demolish. This paper briefly reviews these as well as the history of the disease and explores recent epidemiological findings and their relevance to applying effective control.

Africa↗

Entomopathogenic nematodes as control agents of developmental stages of the black-legged tick, Ixodes scapularis.

Thirteen species or strains of entomopathogenic nematodes of the genera Steinernema and Heterorhabditis were tested in vitro against unfed and engorged larvae, nymphs, and adults of the black-legged tick, Ixodes scapularis. Nematodes were pathogenic to engorged female ticks, but not to unfed or engorged larvae, nymphs, males, and unfed females. Steinernema riobravis (355) and Heterorhabditis megidis (M145) killed ticks most rapidly, with mean day of death postinfection of 2.5 and 3.5 days, respectively. However, all nematode strains and species were lethal to engorged female ticks within 7.5 days. Development of juveniles and reproduction of nematodes did not occur inside the tick cadavers, because no infective juveniles (IJs) emerged from cadavers after 40 days, and no nematode life-cycle stages other than the primary IJs could be isolated from cadavers. Egg masses were produced by 4 of 702 nematode-infected, engorged females. Egg masses produced were not significantly smaller than masses produced by control ticks; however, only 1 of the 4 egg masses hatched, whereas all of the egg masses produced by the control ticks hatched. Entomopathogenic nematodes may be useful as an alternative management method for I. scapularis populations, and may be more acceptable than acaricidal chemicals for use in infested areas.

Animals↗

Effectiveness of carbaryl applications for the control of Ixodes dammini (Acari: Ixodidae) nymphs in an endemic residential area.

Ground applications of carbaryl in early June 1989 reduced populations of nymphal Ixodes dammini Spielman, Clifford, Piesman & Corwin by 100% in five 0.4-ha residential sites 72 h after application. High levels of control (greater than 90%) persisted for almost 2 mo. Five nymphs were recovered at the periphery of the sprayed plots at two sites 2 wk after spraying and nine nymphs were collected at the periphery of the sprayed plots at three of the sites 4-5 wk after application. At 8 wk after application, I. dammini nymphs were recovered within three of the sprayed plots. Chemical control of nymphal I. dammini may be a viable management practice for homeowners living in endemic areas to reduce the chances of acquiring Lyme disease.

Animals↗

Population regulation in ticks: the effect of delayed mating on fertility in Ixodes trianguliceps (Acarina: Ixodidae).

The paper describes an experimental investigation of the effects of delayed mating on both the time course of engorgement and the reproductive output by female Ixodes trianguliceps Birula. Males apparently do not mate with females off the host prior to the female's blood meal, and successful mating is less likely to occur within the first 3 to 4 days of the blood meal. If mating is delayed beyond day 7 of the blood meal, the rate of engorgement decreases sharply from day 7 or 8 onwards, until mating has occurred, after which engorgement is completed rapidly. Female ticks subject to delayed mating show a markedly reduced reproductive output, caused either by a complete failure to lay eggs or by a lower engorged weight and consequent lower egg production. The ecological significance of these observations is that they may reveal an example of inverse density dependent fertility, which, because of the destabilizing effect on the tick population, might be exploited in the control of ticks.

Animals↗

Field evaluation of two formulations of cyfluthrin for control of Ixodes dammini and Amblyomma americanum (Acari: Ixodidae).

Liquid or granular cyfluthrin was applied in the spring and fall to different test plots at a rate of 0.41 (AI) kg/ha to control Ixodes dammini Spielman, Clifford, Piesman & Corwin and Amblyomma americanum (L.). Spring application of liquid cyfluthrin showed the most significant decreases of both species. I. dammini nymphs were reduced 97% at 10 d, 100% at 2 mo, and 100% at 1 yr; and A. americanum adults and nymphs were reduced 91-93% at 10 d and 100% at 2 mo posttreatment. Granular cyfluthrin applied in the spring gave 97 and 87% control of nymphal I. dammini 10 d and 2 mo posttreatment, respectively.

Animals↗

Efficacy of tags impregnated with pheromone and acaricide for control of Amblyomma variegatum.

The efficacy of tags impregnated with pheromone and acaricide for control of Amblyomma variegatum on cattle in Guadeloupe was determined for a 13-week trial. Comparisons were made between untreated cattle and cattle with tags containing either pheromones alone (o-nitrophenol, methyl salicylate, 2,6-dichlorophenol and phenylacetaldehyde), pheromones plus acaricide (cyfluthrin or deltamethrin), or acaricide alone. Tags were fastened to cattle both on collars on the neck and with adhesive to tail hairs, with over 98 and 90% of tags retained, respectively, during the trial. By the end of the trial, tick infestations increased on untreated cattle (311.7%) and cattle with pheromone tags (154.8%) but decreased on cattle with pheromone/ cyfluthrin (-45.0%), cyfluthrin (-42.8%), pheromone/deltamethrin (-68.7%) and deltamethrin tags (-87.6%). Cattle with pheromone tags had greater proportions of ticks on the hind regions (81%) compared to untreated cattle (62.5%) and on the front regions (18.2%) compared to untreated cattle (8.2%) indicating that ticks aggregated in response to pheromones. Analysis of hair samples by gas chromatography indicated that, within 2 days of placement, cyfluthrin spread rapidly over the body from the tags. Both cyfluthrin and deltamethrin were present in detectable levels on all eight body regions examined throughout the trial. Analysis of the tags indicated that they all still contained pheromone components after 13 weeks under field conditions.

Animals↗

Tickcidal effect of monoclonal antibodies against hemocytes, Om21, in an adult female tick, Ornithodoros moubata (Acari: Argasidae).

In the present study, monoclonal antibodies (mAbs) against adult Ornithodoros moubata hemocytes were established. Afterward, artificial feeding was performed to assess the tickcidal effect of fetal bovine serum meal containing each mAb. As a result, Om21 showed the strongest tickcidal effect on adult female O. moubata. The reactivity of various tick cells and organs, including the hemocyte, midgut, trachea, ovary, fat body, and muscle, to Om21 was then examined by an indirect immunofluorescent antibody test and by immunoelectron microscopy. Om21 reacted with not only hemocytes but also with fat body cells, epidermis, cuticle of the trachea, connective tissue of the muscle, and the basement membrane of the midgut, trachea, fat body, oocyte, and epidermis. These results suggest that Om21 passing through the midgut epithelium induced a tickcidal effect on hemocytes or various organs. However, the target of Om21 could not be identified in the present study. The antihemocyte mAb produced in this study, Om21, may be useful for the immunological control of ticks.

Animals↗

Effectiveness of host-targeted permethrin in the control of Ixodes dammini (Acari: Ixodidae)

Tubes of commercially available permethrin-treated cotton balls were distributed twice each year in 1989 and 1990 at five sites in a Lyme disease endemic area in Connecticut. Five additional sites were not treated. At each application, 48 tubes, sufficient to treat 0.4 ha, were dispersed at 10-m intervals through woodlands, around ornamental plantings, and along rockwalls. The cotton was collected by white-footed mice (Peromyscus leucopus) from the majority of the tubes, which resulted in a decrease (37.2% in 1989 and 91.5% in 1990) in the number of subadult Ixodes dammini Spielman, Clifford, Piesman, and Corwin on the mice in the treated areas. There were no significant decreases in the number of host-seeking nymphs or adults of I. dammini in 1989 or 1990 between the treated and untreated sites. The rates of infection in the host-seeking nymphs with Borrelia burgdorferi, the etiological agent of Lyme disease, at the treated sites (13.0 and 14.6% for 1989 and 1990, respectively) were comparable to those at the untreated sites (16.9 and 13.2% for 1989 and 1990, respectively). The distribution of permethrin-treated cotton around individual residences significantly reduced the number of ticks on P. leucopus but was not sufficient to reduce the risk of exposure to infected host-seeking nymphs and adults of I. dammini after two seasons of treatment.

Animals↗

Effects of combining the fungi Beauveria bassiana and Metarhizium anisopliae on the mortality of the tick Amblyomma variegatum (ixodidae) in relation to seasonal changes.

The effect of formulation, fungal concentration, type and seasonal changes on the mortality of the tick Amblyomma variegatum was investigated. A previous study demonstrated high pathogenicity of strains of the fungi Beauveria bassiana and Metarhizium anisopliae against the ticks Rhipicephalus appendiculatus and Amblyomma variegatum (Kaaya et al. J Invertebr Pathol 1996; 67: 15-20). The present study was undertaken to explore possible additive or synergistic effects of the two fungi on A. variegatum. The effects of oil and water formulations at different concentrations of each fungus and combination of the two on the mortality of A. variegatum in the laboratory and in the field during the wet and dry seasons were determined and compared. The oil formulation performed better in all assays, with highest tick mortality of 92% occurring during the wet season at conidia concentration of 1 x 10(10) conidia/ml of the mixed fungi compared to 49% for the water formulation at similar conidia concentration. However, at the same conidial concentration during the dry season, mortalities in the field were relatively low with the mixture of the fungi recording 24% and 17% tick mortality for the oil and water formulation respectively. The effect of infecting the ticks with a cocktail of the two fungi was inconclusive under more controlled conditions in the laboratory but field results under both wet and dry seasons indicated significant differences between the separate and mixed fungi infections. The results demonstrate a potential of cocktail formulations in the control of ticks and possibly of other arthropod pests.

Animals↗

Recent developments in ectoparasiticides.

The sales and use of ectoparasiticides for the control of arthropod parasites of domestic animals constitute a major sector of the global animal health market. Animals are infected by a number of parasitic insect and acarine species causing major economic losses in production livestock, intense irritation and skin disease in companion animals, or public health issues, including bites of humans or zoonotic disease transmission. Dog and cat fleas, for example, can be a serious source of both animal and human irritation, which has led to a rapid expansion in the development of flea control products. The control of ectoparasite infections of veterinary importance still relies heavily on the use of chemicals that target the arthropod nervous system. Such compounds have suffered from a number of drawbacks, including the development of resistance and concerns over human and environmental safety. The search for safer technologies has, however, been hindered by the limited number of active target sites present in arthropods and, to some degree, by the ever-increasing costs of research and development of compounds with novel modes of action.This review provides a background to the currently available groups of ectoparasiticide compounds used in veterinary medicine and highlights some of the more recent developments including the introduction of insect growth regulators and new and improved methods of product application.

Animals↗

Third-year evaluation of host-targeted permethrin for the control of Ixodes dammini (Acari: Ixodidae) in southeastern Connecticut.

The impact of commercially available permethrin-treated cotton balls targeted at Ixodes dammini Spielman, Clifford, Piesman & Corwin on white-footed mice, Peromyscus leucopus, was evaluated for a third year at five residential sites in south-central Connecticut. Each site had been treated twice each year from 1989 through 1991 with sufficient product to treat 0.4 ha of mouse habitat, and results were compared with five untreated sites. There were no significant differences in the number of host-seeking nymphs or adults of I. dammini, the vector of the Lyme disease spirochete, Borrelia burgdorferi, in 1991 between the treated and untreated sites. The rate of infection in host-seeking nymphs by B. burgdorferi at the treated sites (15.3% of 600) was comparable with that at the untreated sites (16.5% of 454). Only 16.3% of 86 P. leucopus captured at the treated sites were infested with I. dammini subadults compared with 66.9% of 118 from the mice at the untreated sites. The impact of permethrin-treated cotton during the third year of treatment was similar to that observed for the first 2 yr and did not reduce the risk of exposure to spirochete-infected, host-seeking nymphs and adults of I. dammini.

Animals↗