Getting a handle on tick control: a modern approach may be needed.
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Animals↗
Biomedical subjects
R G Pegram
Publications and source records attributed to R G Pegram.
Epidemiological observations of Zimbabwean theileriosis: disease incidence and pathogenicity in susceptible cattle during Rhipicephalus appendiculatus nymphal and adult seasonal activity.
Fifty-nine Hereford cattle susceptible to tick-borne diseases were used as tracer animals to assess the tick challenge and pathogenicity of Theileria parva under field conditions in Zimbabwe. They were moved periodically in groups of five to three commercial farms (one group consisted of four) during seasons of Rhipicephalus appendiculatus nymphal and adult activity. All tracer cattle were herded together with the farm cattle but were not dipped. The nymphal tick counts were high on two of the farms (up to 2000 per animal) but were very low on the third farm (less than ten per animal). On the three farms, 19 out of 24 (76%) tracers had patent Theileria schizonts. There was a range of clinical manifestations of theileriosis with acute and fatal infections occurring on one farm. The adult R. appendiculatus infestations during the wet season numbered 120-800 per animal on the three farms. The disease transmitted by the adults was very pathogenic on the three farms; 30 out of 35 (86%) had severe theileriosis infections. Cattle, which survived the nymphal diseases challenge, showed various degrees of immunity to subsequent T. parva challenge transmitted by adult ticks. Therefore, 13 out of 18 (72%) of these cattle had a second disease episode and the case fatality rate on the three farms was 46%. The factors which determined the epidemiological status of Theileria challenge on the farms, such as the farming systems and presence of wild animals, are discussed.
Acute Disease↗
Eradication and surveillance of the tropical bont tick in the Caribbean. An international approach.
The Caribbean Amblyomma program (CAP) is a multidonor funded effort involving several technical organizations and national governments in the eradication of the tropical bont tick. The Food and Agriculture Organization (FAO) is the lead technical agency, providing both technical and administrative support to the CAP Regional Coordination Unit (RCU) based in Barbados. All collaborating agencies, donors, and national representatives are members of the Amblyomma Program Council (APC), the overall governing body of the CAP. In addition to FAO, the other organizations involved are the Caribbean Community (CARICOM), the European Union (EU), the Inter-American Institute for Cooperation on Agriculture (IICA), the International Fund for Agricultural Development (IFAD), and the United States Department of Agriculture (USDA). Several agencies (EU, FAO, IFAD, and USDA) are also major donors. The CAP cooperates with the complementary Plan POSEIDOM Veterinaire Program in the French West Indies. The University of the West Indies (UWI), the International Institute for Biological Control (IIBC), and the Departement d'Elevage et de Medecine Veterinaire des Pays Tropicaux (EM-VT) in Guadeloupe are other collaborators.
Agriculture↗
Past and present national tick control programs. Why they succeed or fail.
The historical reasons for the introduction of tick control during the nineteenth century are reviewed. Background and concepts for the choice between long-term tick control and tick eradication are compared. Case studies of large-scale tick control or eradication programs in Africa, Australia, the United States, and the Caribbean are used to highlight successes and failures. The main reasons for lack of sustainability, or failure, of programs are discussed. These include the economic constraints that were faced in several African countries, or technical shortcomings such as were perceived as a major problem in Puerto Rico. The successes are generally associated with enforcement of appropriate legislation and good management, such as occurred in Zimbabwe. These case studies are analyzed to identify features that may assist in the implementation of the ongoing tropical bont tick eradication program in the Caribbean. The paper concludes with some practical suggestions for the future, and the need to reassess the economics of control and the potential additional animal health benefits derived from tick control programs.
Animal Husbandry↗
The CARICOM/FAO/IICA Caribbean Amblyomma Program.
The objective of the Caribbean Amblyomma Program is to eradicate the tropical bont tick (TBT), Amblyomma variegatum, from the Caribbean. Field activities directed to eradication of the TBT were initiated in May 1995 commencing in northern Caribbean islands. Plans have been finalized for the remaining islands to the south to start eradication activities in early 1997. The components of the program include tick control and surveillance, adaptive research, training, communications, and extension. Despite uncertain financial support, substantial progress has been made so far with strong participation by farmers and livestock owners who have been made responsible for the compulsory treatment of all ruminant livestock.
Animal Husbandry↗
Immunisation of cattle in Zimbabwe using Theileria parva (Boleni) without concurrent tetracycline therapy.
Five hundred and ten cattle were immunised using the Theileria parva (Boleni) stock without concurrent chemotherapy with tetracycline on 2 farms in Zimbabwe, both of which had a history of theileriosis. The stabilate had been titrated in Friesian calves to determine a 50% protective dose (PD50) and 2 or 3 (PD50s) were used to immunise the cattle. None of the cattle showed a clinical reaction following the immunisation procedure. However, the cattle were shown to have responded immunologically on testing for antibodies to a T. parva antigen in an indirect fluorescent antibody test. The immunised cattle were then exposed to a natural field challenge causing severe theileriosis in control cattle. Immunisation against theileriosis without the need for concurrent chemotherapy is much less expensive than the infection and treatment method (US $2.72) compared to US $10.23 in the first year) and would be much more attractive to commercial and traditional farmers.
Animals↗
Long-term studies on the economic impact of ticks on Sanga cattle in Zambia.
Three different tick control policies were tested in groups of traditionally managed Sanga cattle in the Central Province of Zambia over a period of 3 years. One group was given strategic tick control using 12 pyrethroid acaricide spray applications between the onset and the end of the wet season (October to March). The productivity of this herd was compared with that of a group with no tick control and a group under an intensive tick control regimen of spraying every week in the wet season and every 2 weeks in the dry season (36 applications per year). The highest output was associated with intensive tick control, followed by strategic control and then no tick control policies. However, when the costs of tick control were taken into account, the strategic tick control policy produced the best economic result, followed by the intensive and then the no tick control policies. Neither the strategic nor the intensive tick control policy was sufficient to prevent the transmission of East Coast fever (ECF) infection when this disease was introduced to the area.
Animals↗
Effects of immunisation against Theileria parva on beef cattle productivity and economics of control options.
Over 500 cattle of all age groups on 2 farms in Zimbabwe were immunised against theileriosis using the "infection and treatment" method and disease prevalence and their productivity assessed during a period of 18 months. The immunising stock, Theileria parva (Boleni) was isolated in Zimbabwe. None of the immunised cattle suffered from theileriosis upon natural exposure whereas 22 unimmunised cattle died of theileriosis and a further 48 required treatment for theileriosis. In the first year, some immunised cattle were maintained with minimal threshold dipping (once or twice during the rainy season). During periods of very high tick challenge of 100 to 1,000 Rhipicephalus appendiculatus per animal from January to March, a transient decrease in liveweight gain was observed particularly in cows. However, by the end of the period of observation, the weights had recovered so that intensively dipped and immunised and threshold or strategically dipped groups of cattle showed no significant differences. From the results it was estimated that each engorging female R. appendiculatus caused a temporary depression in weight gain of 8 grams. In young stock the weight loss was exacerbated by the presence of screw worm (Chrysomya bezziana) infestation. It was then possible to define an economically attractive integrated tick and theileriosis control strategy based on these findings, whereby immunised cattle were dipped 6 times between mid-December and mid-March. In this regimen, no weight loss occurred and no cases of screw worm were observed. For each of 3 herd sizes of 250, 500 and 1,000 cattle, comparisons were made of the costs of 4 different control options: (i) Intensive dipping (40 times/year) (ii) Intensive pour-on acaricide treatments (18 times/year) (iii) Theileria immunisation with strategic dipping (6 times/year) (iv) Theileria immunisation with pour-on treatment (4 times/year) It is concluded from these studies that, on farms where theileriosis is a serious problem, immunisation coupled with a strategic dipping programme is economically very attractive. In the year in which immunisation is carried out, costs will be higher than for intensive dipping, but from the second year on, the costs are decreased to approximately 50% of those for intensive dipping.
Animals↗
An assessment of host resistance to ticks on cross-bred cattle in Burundi.
Groups of cattle of four different cross-breeds (Ankole x Friesian, Ankole x Brown-Swiss, Ankole x Guernsey, Ankole x Sahiwal) plus a group of pure Ankole cattle were immunized against tick-borne diseases: East Coast Fever, using a Theileria parva trivalent vaccine, and anaplasmosis, babesiosis and, subsequently, heartwater. With the exception of two small subgroups of Ankole and Ankole x Sahiwal which were treated by weekly spraying using Delnav, all the groups were exposed to natural field challenge of ticks to quantify the development of host resistance to ticks. The results indicate resistance to the most abundant species, Rhipicephalus appendiculatus, as follows: Ankole > Ankole x Sahiwal > Ankole x Brown Swiss > Ankole x Friesian > Ankole x Guernsey. In both Amblyomma variegatum and Rhipicephalus evertsi evertsi, the manifestation of different levels of resistance between breeds is inapparent. Correlations between total ticks and standard female ticks were good for R.appendiculatus (r = 0.73) and R.evertsi (r = 0.51) but poor for A.variegatum (r = 0.31). Correlations between species were reasonably consistent (r = 0.43-0.59). There was no significant correlation between tick burdens and daily liveweight gain (DLWG) over the whole period of the study. Of the cross-bred groups, Ankole x Sahiwal, which had the highest level of resistance, had the highest DLWG. In contrast, the Ankole x Guernsey which developed the lowest level of resistance had only marginally lower DLWG, the difference being only 8 g/day. During the first period of exposure to ticks, however, the untreated Ankole x Sahiwal group had markedly lower DLWG, which may indicate that the development and manifestation of resistance is at the expense of productivity.
Animals↗
Challenge of Theileria parva (Boleni) immunised cattle with selected east African Theileria stocks.
Theileria parva (Boleni) stock from Zimbabwe was used to immunise 24 susceptible Friesian calves by infection and treatment with oxytetracycline. Twenty-eight days after immunisation the animals in groups of 6 plus 2 susceptible controls were subjected to challenge: 3 groups with heterologous stocks and one group with the immunising stock. Theileria parva (Boleni) gave good protection against homologous challenge, the T. parva (Muguga, Kenya) and buffalo-derived T. parva (Serengeti transformed, Tanzania) parasite stocks. It did not protect against the T. parva (Kasoba, Malawi) stock and 3 out of 6 immunised cattle died and the remaining 3 had to be treated with parvaquone. In a second experiment, the 6 T. parva (Boleni) immunised animals which had received homologous challenge, together with the 2 controls which had recovered without treatment from T. parva (Boleni) infection, were challenged with the T. parva (Kasoba) stock. Four out of 6 of the immunised animals resisted the challenge with mild to moderate reactions. The other 2 animals had severe reactions and one died. The 2 control animals which recovered from T. parva (Boleni) infection resisted the T. parva (Kasoba) challenge and both had mild reactions. It is suggested that oxytetracycline used in the first experiment may have interfered with the expression of the full protective capacity against the virulent T. parva (Kasoba) stock. Further studies on the use of the T. parva (Boleni) stock without oxytetracycline treatment could identify a more broadly immunising effect and a more economical vaccination method.
Animals↗
A study of the diapausing behaviour of Rhipicephalus appendiculatus and R. zambeziensis under quasi-natural conditions in Zambia.
The diapausing behaviour of Rhipicephalus appendiculatus was studied under quasi-natural conditions in the Eastern Province of Zambia. Newly-moulted adults of ticks indigenous to the study area entered a behavioural diapause when exposed to daylengths below a critical photoperiod, provisionally a daylength between 11 h 20 min and 11 h 45 min. In the Eastern Province of Zambia the diapause was apparently not terminated by a long-day signal, but by a weakening of the photoperiodic maintenance of the diapause because of increasing age of the ticks. Adults of a reference stock indigenous to Kenya also entered a diapause when exposed to daylengths below the same threshold and maintained this diapause for the same length of time. Adults of a reference stock of Rhipicephalus zambeziensis indigenous to Zimbabwe did not enter a diapause when exposed to the same daylengths. The relevance of the findings is discussed in relation to the distributions of the two species.
Adaptation, Physiological↗
Tick control: a standardized terminology.
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Animals↗
Rhipicephalus interventus sp. nov. (Acari: Ixodidae), a new tick species closely related to Rhipicephalus tricuspis Dönitz, 1906 and Rhipicephalus Iunulatus Neumann, 1907, from east and central Africa.
Descriptions of the adults of this new species are given, together with information on its hosts and distribution. Previously it was referred to briefly by Walker, Keirans, pegram & Clifford (1988), who noted that in many respects it is intermediate in appearance between R. tricuspis and R. Iunulatus.
Africa, Central↗
Rhipicephalus aquatilis sp. nov. (Acari: Ixodidae), a new tick species parasitic mainly on the sitatunga, Tragelaphus spekei, in east and central Africa.
This tick, originally referred to as Rhipicephalus species III by Yeoman & Walker (1967), was first collected from a sitatunga, Tragelaphus spekei, and then occasionally from cattle, in Tanzania. Further collections, mostly from sitatunga, have since been seen from Uganda and Zambia. Descriptions of the adults of this species are given, together with information on their hosts and their distribution.
Africa, Central↗
Patterns of Rift Valley fever activity in Zambia.
An hypothesis that there was an annual emergence of Rift Valley fever virus in Zambia, during or after the seasonal rains, was examined with the aid of sentinel cattle. Serum samples taken during 1974 and 1978 showed evidence of epizootic Rift Valley fever in Zambia, with more than 80% positive. A sentinel herd exposed from 1982 to 1986 showed that some Rift Valley fever occurred each year. This was usually at a low level, with 3-8% of the susceptible cattle seroconverting. In 1985-6 more than 20% of the animals seroconverted, and this greater activity was associated with vegetational changes--which could be detected by remote-sensing satellite imagery--which have also been associated with greater virus activity in Kenya.
Animals↗
Studies on the economics of ticks in Zambia.
Two herds of experimental Sanga cattle were maintained under traditional savanna grazing management for three years in the Central Province of Zambia. One herd was kept free of ticks by regular acaricide treatment, while the other was given no tick control. Milk production, growth rate, fertility and mortality were monitored throughout the trial. The tick-free herd performed significantly better than the tick-infested herd, but the value of the additional production was much less than the cost of the acaricide used. It is concluded that there is no economic justification for intensive tick control under these conditions. However, strategic tick control would be justified if the quantity of acaricide used could be reduced by 50% without any major reduction in benefits. The results indicate that treating calves below 45 days of age reduces their performance, as does treating cows during periods of very low tick challenge. Therefore, it seems likely that economically beneficial strategic tick control policies could be developed.
Animals↗
Comparison of the calf suckling technique and milk oxytocin test for estimation of milk yields.
The calf suckling technique and milk oxytocin test were compared as methods to quantify lactation yields in Sanga-type cows in the multi-purpose livestock sector of central Zambia. There was no significant difference between the overall means derived from 154 observations. The oxytocin method interferes less with the multi-purpose system of management, is less time consuming and does not require expensive calf weight scales.
Analysis of Variance↗
Effect of dry season supplementation of Sanga cattle in Zambia.
Supplementation of lactating Sanga cows in central Zambia with low cost crop residues and urea-mineral licks resulted in significant increases in milk offtake (79%), total daily milk (86%), and daily liveweight gain of their calves (86%). At 1988 market prices the value of the additional milk (ZK54.00) and of liveweight of both cow and calf (ZK189.00) over the 13 weeks exceeded the estimated costs of inputs by ZK180.00.
Animal Feed↗