Impact of natural infestation of Amblyomma variegatum on the liveweight gain of male Gudali cattle in Adamawa (Cameroon)

The effect of natural tick infestation on the liveweight gain (LWG) of male Gudali zebu cattle was studied throughout a year by comparing the performances of two herds, one of which was submitted to weekly acaricidal treatment and the other was left untreated against ticks. Six species of ticks were identified on the untreated animals: Amblyomma variegatum, Boophilus decoloratus, Rhipicephalus lunulatus, Rhipicephalus turanicus, Hyalomma nitidum and Hyalomma marginatum rufipes. Most of the losses observed in the untreated herd during the rainy season were due to A. variegatum, and the loss in LWG was estimated to be 55-76 g per engorged female A. variegatum. The infestation also leads to wounds and to lesions of dermatophilosis. There was an interval between the peak infestation by A. variegatum and the appearance of weight loss owing to them. The control of ticks on the Gudali zebu in Adamawa, during the months of high infestation by A. variegatum adults, is economically profitable. On the other hand, the performances of the two herds during the dry season were similar, showing that infestation by larvae and nymphs of A. variegatum has no impact on the zebu LWG, and that tick control during that period is not profitable.     

Effects of cattle tick (Boophilus microplus) infestation on the bovine immune system

The immunosuppressive effect of experimental Boophilus microplus infestation on bovine peripheral blood lymphocytes (PBL) and on host antibody production to a protein antigen (ovalbumin) was examined. Boophilus microplus infestation caused a marginal decrease in the percentage of T lymphocytes in PBL, which was observed in both lightly (5000 larvae) and heavily (40,000 larvae) infested cattle, and began at the second infestation and continued until the end of the fourth infestation. The percentage of B lymphocytes in heavily tick-infested cattle was less than that in non-infested control cattle after the fourth infestation. The response of PBL from tick-infested cattle to phytohemagglutinin (PHA) was always less than that of tick-free cattle after the second infestation. No noteworthy differences were detected between the three stages of tick infestation, that is, 1 week before the peak of adult engorgement, the middle of the peak and 1 week after all ticks had dropped. Boophilus microplus saliva (100 microliters ml-1) suppressed 47% of the response of bovine PBL to PHA in vitro. This suppressive effect of saliva may contribute to the lower responsiveness of PBL from tick-infested cattle. Antibody production by tick-infested cattle was examined during the third and fourth heavy tick infestation. Tick-infested cattle showed a diminished response against ovalbumin after the second immunization. The immunosuppressive effects of tick infestation may play an important role in tick survival or in the transmission of tick-borne diseases in the field.     

Acquisition of resistance to the tick Amblyomma variegatum in Boran cattle, Bos indicus and the effects of Trypanosoma congolense and Babesia bigemina on host resistance

Resistance was induced in cattle to the tick Amblyomma variegatum by five consecutive infestations with nymphs and adults. Using the principal component analysis (PCA), it was found that percentage of adults engorged, percentage of adults which died, percentage of nymphs which engorged, percentage of nymphs which moulted and percentage of nymphs which died, were the main indicators of resistance against A. variegatum. The percentages of nymphs which engorged or moulted after the third infestation were significantly (P < 0.01) reduced while the percentage of nymphs which died increased significantly (P < 0.01) after the third infestation. Percentages of adults which engorged or died started to decrease significantly (P < 0.01) from the fourth infestation after an initial increase during this period. The acquisition of resistance by cattle to the adult ticks was slower than to the nymphs. Infection of cattle with Trypanosoma congolense and Babesia bigemina after the fifth infestation enhanced the acquired immunity as revealed by the significantly (P < 0.01) increased feeding period of the adult ticks and changes in other parameters.     

Factors affecting the detection of infestations of Boophilus microplus in tick control programs

Factors affecting the probability of detecting infestations of Boophilus microplus when herds of cattle are examined were studied. The probability of detecting a tick depends on the number of infested cattle in the herd, the probability of ticks being present on the areas of the beast examined, the efficiency of the examination and the proportion of the herd examined. A mathematical expression relating these factors was derived, and a range of values calculated to demonstrate the relative importance of each factor. It was evident that the efficiency of the examination should be kept better than 75%, and that it is necessary to employ a high sampling rate, preferably 100% of the herd. The probabilities of ticks being present on 6 predilection sites and 4 combinations of sites of an infested animal were determined experimentally. The tail butt, esutcheon, belly, dewlap and to a lesser degree neck and ear were all very suitable sites on which to find cattle ticks. A combination of tail butt, escutcheon and neck produced probabilities (0.58 and above) considered adequate to form the basis of an examination system. Examination systems used in New South Wales, Queensland, Argentina and at the United States-Mexico border are described. As a result of this study a new standardised system has been adopted by the Board of Tick Control for use by all New South Wales inspectors.     

Factors affecting the distributions of the ticks Amblyomma hebraeum and A. variegatum in Zimbabwe: implications of reduced acaricide usage

The ticks Amblyomma hebraeum and A. variegatum are the main vectors of heartwater, a disease of ruminants caused by Cowdria ruminantium, in the agricultural areas of Zimbabwe. At present, A. hebraeum is widely distributed in the dry southern lowveld, and occurs in at least seven foci in the higher rainfall highveld. Amblyomma variegatum occurs in the Zambezi valley and surrounding dry lowveld areas in the northwest. The distribution of A. hebraeum has changed considerably over the past 70 years, while that of A. variegatum appears to have remained fairly static. The distribution patterns of both species in Zimbabwe display anomalous features; the ticks occur in areas of lowest predicted climatic suitability for survival and development and in areas where the densities of cattle, the most important domestic host, are lowest. The only factor favouring the survival of the species in the lowveld habitats in which they occur is the presence of alternative wildlife hosts for the adult stage. Their absence from more climatically favourable highveld habitats appears to have been the result of intensive acaricide treatment of cattle over a long period and a historic absence of significant numbers of wildlife hosts. Eradication of A. hebraeum and A. variegatum by intensive acaricide treatment of cattle can be achieved in the absence of significant numbers of alternative hosts, because of the long attachment and feeding periods of the adults of these tick species. However, eradication becomes impossible when alternative hosts for the adult stage are present, because a pheromone emitted by attached males attracts the unfed nymphal and adult stages to infested hosts. The unfed ticks are not attracted to uninfested hosts, such as acaricide-treated cattle. Regular acaricide treatment of cattle is expensive and so, for economic reasons, the Government of Zimbabwe is no longer enforcing a policy of strict tick control. It is likely that reduced tick control will result in the spread of Amblyomma ticks to previously uninfested areas. Added to this, recent introductions of various wildlife species to highveld commercial farming areas have created conditions in which the ticks could become established in higher rainfall areas. Amblyomma hebraeum is more likely to spread than A. variegatum, because its adults parasitize a wider range of wildlife hosts (warthogs, medium to large-sized antelope, giraffe, buffalo and rhinoceros), whereas adults of A. variegatum appear to be largely restricted to one wildlife species (buffalo) in Zimbabwe, the distribution of which is now confined to very limited areas of the country, as part of foot and mouth disease control measures.(ABSTRACT TRUNCATED AT 400 WORDS)     

A comparison of the effect of two regimens of infestation on the development of resistance by cattle to the cattle tick, Boophilus microplus (Can.)

The development of resistance to Boophilus microplus by cattle was studied using sets of cattle twins, in stalls. One twin from each set received 3 infestations of 40,000 larvae and the other a continuous infestation of 1,000 larvae a day over the same period. Sets of twins were then challenged with 1,000 larvae a day for 40 days and 2 field infestations of 20,000 larvae. Correlations of ranking for resistance made at 40-day periods during daily infestations of 1,000 larval ticks or for corresponding intermittent infestations of 40,000 larvae were low until animals had received 120,000 larvae. Thereafter irrespective of method of infestation correlations of ranking were relatively high (r = 0.61-0.96) between periods of infestations or method of infestation including 2 field infestations. Fewer adult female ticks matured on the daily infested animals than on the intermittently infested animals during the treatment period, but animals developed a similar resistance level whether infested with either technique.     

Cytokine production by lymph node cells from mice infested with Ixodes ricinus ticks and the effect of tick salivary gland extracts on IL-2 production

In BALB/c mice repeatedly infested with nymphal Ixodes ricinus ticks, lymphocytes from axillary and brachial lymph nodes which drain the tick attachment site produced significant levels of IL-2, TNF-alpha and GM-CSF when stimulated in vitro with Con A or anti-CD3 antibodies. Cytokine production by cells from lymph nodes of the opposite flank was equivalent to that of cells from uninfested mice. Nine days after the first infestation and IL-2, GM-CSF were produced primarily by the CD4+ T cells, while some other cell types contributed also to the TNF-alpha production. In mice repeatedly infested, a gradual increase of lymph node cell production of IL-2 was observed. The IL-2 levels regularly increased from the first to the third infestation compared to TNF-alpha levels which gradually decreased. The in vitro production of GM-CSF was not affected by successive infestations. Spleen lymphocytes from naive mice produced higher levels of IL-2 than lymphocytes from axillary and brachial lymph nodes. Both tick salivary gland extracts and D-mannose inhibited IL-2 production by these lymphocytes.     

Ixodid ticks (Acari: Ixodidae) and livestock production: effect of varying acaricide treatments on ticks and productivity in east coast fever-immunized weaner and dairy cattle

In a pilot trial to evaluate cost-effective methods of acaricide application, east coast fever-immunized weaner and dairy cattle were subjected to varying tick control regimens. All experimental cattle were maintained under the same extensive system of management. Their monthly tick load, packed cell volumes, incidence of blood protozoans, weight changes, and daily milk production were noted. Apart from Rhipicephalus appendiculatus Neumann, other tick species found in the study site were R. pulchellus Gerstacker, Amblyomma gemma Donitz, Boophilus decoloratus Koch, and A. variegatum F. The control group under a weekly regimen of dipping had fewer ticks than each of the other groups for both weaner and dairy cattle. However, the percentage of increase in weight of the weaner cattle was least for the control group. The milk production of none of the groups was significantly different from that of the control group, although profit per animal for groups maintained under a monthly or six-weekly regimen of acaricide use was highest. The age of the experimental dairy cattle was found not to have any effect on their milk production. It is suggested that with successful immunization against east coast fever, both dairy and weaner cattle may be subjected to reduced dipping or spraying, the level of relaxation being dependent on the tick challenge. However, similar studies should be carried out in as many agroecological zones as possible using different breeds of cattle. Information on the level of acaricide residues in livestock products from different farming systems should also be generated. Only then can a definitive recommendation for a change from the present national intensive dipping policy be made.     

Immunization of bovines with an aspartic proteinase precursor isolated from Boophilus microplus eggs

The capacity of the Boophilus Yolk pro-Cathepsin (BYC) to induce a protective immune response in cattle against Boophilus microplus infestation was tested by vaccination experiments and by inoculation of monoclonal antibody (MAb) against BYC into fully engorged tick females. In immunization experiments the measurement of various biological parameters demonstrated a partial protection against B. microplus. A continuous decrease in the levels of specific antibodies was observed over 11 months when six bovines were maintained in field conditions. The inoculation of the MAb into tick females produced a dose-dependent decrease in oviposition and survival of the ectoparasite compared to the control.     

Effects of the sucking louse (Linognathus vituli) on the grooming behaviour of housed calves

The behaviour of cattle with and without louse infestation was studied for eight weeks. Thirty-two crossbred calves were housed in groups of four at 20 weeks old. Sixteen of the calves were artificially infested with the long-nosed cattle louse Linognathus vituli and 16 were left uninfested as controls. In infested animals the number of lice on the shoulders averaged 2.3 per 10 cm length of parted hair. The recorded frequency of irritation, manifested by rubbing and self-licking, was significantly greater in the louse-infested calves than in the uninfested controls. The infested calves spent 28 s/h rubbing and 95 s/h self-licking, compared with 8 s and 62 s/h spent by the uninfested controls. The infested calves also spent more than twice as long scratching as the controls. There were no significant effects of the infestation on social grooming.     

Financial analysis of dipping strategies for indigenous cattle under ranch conditions in Uganda

A financial analysis was performed to assess the performance of three acaricide-treatment groups of indigenous breeds (Zebu and Nganda) of cattle on a ranch in Luwero District, Uganda. The treatments were based on different frequencies: twice-a-week dipping, once-a-month dipping and no tick control. The objective was to evaluate the economic justification for intensive acaricide application for tick and tick-borne disease control in Uganda. Data were collected by monitoring cattle performance over a period of 34 months. Biological data collected included the number of cows at the beginning and end of the study, net starting liveweight, number of calves born, number of animals dying due to tick-borne diseases and other causes, number of animals sold or slaughtered and milk yield. Records of variable costs (acaricides, drugs, labour, etc.) and output prices were assembled and calculated by treatment group. Gross margin and marginal analysis were used in the financial analysis. The exchange rate in 1990-1993 was one US$ to 1200 Uganda shillings. The gross benefits obtained from animal sales, herd value and milk yield were Uganda shillings 1175, 1389 and 1311 per kg of net starting liveweight for animals dipped twice-a-week, once-a-month and not dipped, respectively. The variable costs were Ug. shs. 424, 390 and 360 per kg of net starting liveweight, respectively. Consequently, the gross margins were Ug. shs. 751, 999 and 951 per kg of net starting liveweight. Furthermore, the marginal rate of return (MRR) in changing from no tick control to once-a-month dipping was 160%, while changing from no tick control to twice-a-week dipping was negative (-313%). The above results showed that the value of increased gains in production obtained from twice-a-week dipping strategy does not offset the costs of inputs for intensive dipping. Once-a-month dipping (strategic) therefore appears to be the most-profitable tick-control strategy for the farmer. The need to conduct further studies in different livestock- production systems and to rationalise future tick control policies is discussed.     

Trials for control of ixodid ticks using pheromone acaricide tick decoys

Experimental application of Hyalomma dromedarii pheromone-impregnated in cyfluthrin (pyrethroid) decoys on experimentally infested camels revealed efficacy rate of 85.33%, while the control group showed normal pattern of tick engorgement. This study proved the rapid movement of males toward decoys and some males took the mounting position with such decoys. On the other side, the same decoys (H. dromedarii) when used on naturally infested cattle with Boophilus annulatus did not even disturb the Boophilus ticks indicating that B. annulatus contain specific pheromones which should be furtherly identified.     

Impact of pharmaceutical underutilization: a study of insurance drug claims data

From 1989 to 1992, a longitudinal study of the relationships between different tick species and domestic ungulates in the transmission and amplification of Crimean-Congo hemorrhagic fever (CCHF) virus was undertaken in the Bandia area in Senegal where the presence of the virus had been reported previously. An epizootic occurred in 1991-1992 and 22 strains of CCHF virus were isolated from Hyalomma marginatum rufipes Koch, Amblyomma variegatum (F.), Rhipicephalus guilhoni Morel & Vassiliades, and R. evertsi evertsi Neumann ticks collected from cattle and goats. No human cases were reported. Transmission of CCHF virus in the area involves a complicated pattern including many tick species and hosts. Amplicons of the S fragment (536 bp) of the CCHF genome of 12 isolates from the study were obtained by polymerase chain reaction and analyzed by restriction-length fragment polymorphism. Three different genotypes of CCHF virus were identified and present during the epizootic. One genotype was recovered from A. variegatum, R. guilhoni, and R. e. evertsi and 2 genotypes were isolated from H. m. rufipes.     

Clinical, clinico-pathological and serological studies of Babesia ovis in experimentally infected sheep

Clinical, clinico-pathological and serological studies were performed in sheep experimentally infected with Babesia ovis. Acute babesiosis occurred in all the lambs infested with adult Rhipicephalus bursa ticks and in one lamb infested with the larvae. The rate of parasitaemia and the degree of anaemia were not correlated. Decrease in the packed-cell volume ranged from 30 to 40%. Parasitized erythrocytes were not observed to block capillaries in the brain, which explained the absence of nervous symptoms in acute babesiosis. The kidneys were the most severely affected organs, exhibiting acute glomerulonephritis. The lesions observed were suggestive of vascular alteration and vascular stasis, leading to anoxia of the tissues. A disseminated intravascular coagulation (DIC) syndrome was recorded in sheep infected with babesiosis. A marked increase in the enzymes of the transaminase groups, mainly aspartate aminotransferase (AST), was observed. Enzymatic changes (increases in AST, alanine aminotransferase (ALT) and lactic dehydrogenase (LDH) and decreases in sorbitol dehydrogenase (SDH), alkaline phosphatase (ALP) and malic enzyme (MEZ)), decreases in total proteins and albumin, and increases in urea and creatinine might reflect the degree of severity of the damage to the liver and kidney tissues. Most of the lambs (85%) that were infested with larvae, and all lambs infested with adult R. bursa ticks, reacted serologically to B. ovis antigen. The serological reactions following infestation with the larvae occurred much later than those following infestation with the adult stage. The lambs which were infested with larvae showed mild clinical reactions when challenged by infected R. bursa adults, as compared with the reactions to the challenge in naive control animals. The serological findings, in addition to the fact that one splenectomized lamb reacted to larval infestation with acute ovine babesiosis, show that the preimaginal stages of R. bursa can transmit B. ovis, usually causing a sub-clinical disease. It is suggested that infections derived from preimaginal ticks in the winter can preimmunize sheep for the subsequent more severe infections derived from adult ticks in the summer. Furthermore, in the absence of a reliable vaccine against B. ovis, grazing flocks in the enzootic regions should be exposed to the preimaginal stages during their activity period (October-February) before exposure to the adult ticks in spring and summer (April-July).     

The biological basis of grooming in moose: programmed versus stimulus-driven grooming

In domestic and wild mammals, tick infestation can be a significant fitness cost. Grooming behaviour has been shown to be effective in removing ticks. We studied grooming by moose, Alces alces, infested with winter ticks, Dermacentor albipictus, to determine which of two nonexclusive models for the regulation of tick-removal grooming, programmed or stimulus driven, best fit this host-parasite relationship. The programmed grooming model states that most grooming is driven by an internal timing mechanism which periodically evokes a bout a grooming independent of peripheral stimulation from tick bites. Because programmed grooming is preventive, the model predicts that those animals that groom the most will carry the fewest ticks, and a baseline level of programmed grooming is predicted even in a tick-sparse or tick-free environment. The stimulus-driven grooming model, on the other hand, states that grooming is a direct response to cutaneous irritation caused by tick bites and other sources of irritation. This stimulus-driven model predicts that (1) animals showing the highest rate of grooming will carry the most ticks and (2) animals will groom little when tick challenge is low. Both predictions of the stimulus-driven model were supported for moose: (1) calves oral-groomed three times more than cows, and tick densities on calves were three times higher than on cows; and (2) although all moose carried high densities of immature winter ticks (larvae, nymphs) from October through to February, grooming rate was very low until adult ticks started feeding in March-April. Peak grooming rates occurred during adult tick engorgement in March-April. Because an engorging adult female tick produces far more irritation than an engorging nymphal or larval tick, moose appeared to groom in direct proportion to the degree of cutaneous irritation and did not show a baseline level of grooming. The predominance of stimulus-driven grooming and apparent absence of programmed grooming may be the result of relaxed selection pressure for grooming in the evolutionary history of moose. Because the winter tick appears to have been introduced to moose from deer relatively recently, moose may not have had the time to adapt to winter ticks. The coevolutionary relationship between moose and winter ticks may be of insufficient duration for the evolution and/or maintenance of programmed grooming. (c) 1998 The Association for the Study of Animal Behaviour.     

Studies on in vitro synthesis and secretion of human chorionic gonadtropin and its subunits

Data from cattle herds infected with brucellosis and from control (noninfected) herds were collected and analyzed using case control techniques. It appeared that herds located close to other infected herds and those herds whose owners made frequent purchases of cattle had an increased risk of acquiring brucellosis, particularly those who made purchases from other herds or from cattle dealers. Infected herds had a lower level of vaccination than noninfected herds. However, the percentage vaccinated was highly variable in each group. Vaccination per se did not appear to adversely influence the interpretation of serological test results nor did it appear to protect the individual animal. Once infected, the time required to become free of brucellosis was increased by large herd size and/or loose housing. Closed herds also took longer to become brucellosis free than more open herds. The percentage of animals removed from the herd was increased by active abortion. Those herds with multiple serological reactors (positives and questionables) at the first herd test after the imposition of quarantine had the highest percentage of cattle removed.     

Effect on herd health and productivity of controlling tsetse and trypanosomosis by applying deltamethrin to cattle

A large cattle ranch was established in 1954 in a heavily tsetse infested part of north-east Tanzania. Trypanosomosis was controlled for 30 years by prophylactic drugs but in 1988 drug resistance seemed to be developing as cases of trypanosomosis were being confirmed 4 or 5 weeks after treatment with isometamidium chloride (Samorin). Herd health had deteriorated and productivity was uneconomically low. In order to control the tsetse population the 8,000 cattle, grazing over 250 km2, were regularly dipped in the synthetic pyrethroid deltamethrin (Decatix Cattle Dip and Spray formulation). Within a year the tsetse population, as monitored by traps, had decreased by more than 90%. Disease mortality decreased by 66% and a range of productivity measures such as calving percentages and weaning weights were raised to levels above those prevailing before the decline in herd health.     

An apparent flea-allergy dermatitis in kids and lambs

Heavy infestation of lambs in two herds and kids in one herd with the cat flea, Ctenocephalides felis felis, accompanied by severe anaemia, eosinophilia and exudative dermatitis, is described. Flea infestation was more widespread during the summer months, when optimal climatic conditions for flea development prevail. The clinical and histological findings are discussed in the light of the pertinent literature. Recovery of the affected animals and normalization of the haematological values were observed after the insecticide treatment. Flea-allergic dermatitis is apparently the cause of the skin lesions in the lambs and kids.     

Eradication of a new focus of Amblyomma variegatum in Puerto Rico

In May 1992 an infestation with the tropical bont tick appeared in a small dairy heifer replacement herd in Camuy, Puerto Rico, a completely new site located near Puerto Rico's northwest coast. This finding occurred after some three years of no infestation in either Puerto Rico or the U.S. Virgin Islands and is not suspected of being associated with any previous infestations. The methods used to eradicate this tick include spray treatment at a two-week interval of all domestic livestock, with amitraz at 0.025% and permethrin at 0.055%. Dogs and chickens are also inspected. Owners are encouraged to reduce numbers of these species. All livestock on adjoining farms are inspected and treated on a frequent basis. There has been no evidence of any spread and the infestation is expected to be eliminated within 18 months.     

Influence of caecectomy and dietary protein concentration on apparent excreta amino acid digestibility in adult cockerels

Infestation with ixodid tick stimulates the immune regulatory and effector pathways of the hosts involving antigen presenting cells, T-lymphocytes, B-lymphocytes, basophils, mast cells, eosinophils and a variety of bioactive molecules like cytokines, antibodies and complement. Tick-mediated immunosuppression has been investigated using cells derived from infested animals and by exposing cells from uninfected animals to tick salivary gland molecules. Tick-induced suppression of host immune defences is characterized by reduced ability of lymphocytes from infested animals to proliferate in vitro in the presence of concanavalin A (Con A), diminished primary antibody responses to T-cell dependent antigen, and decreased elaboration of macrophage (IL-1 and TNF-alpha) and Th1-lymphocyte cytokines (IFN-gamma), whereas Th2 cytokines production (IL-4, IL-5 and IL-10) is enhanced. It is known that IL-10 inhibits Th1 cell development and also reduces the in vitro T-lymphocyte proliferative response to Con A stimulation. Proteins which inhibited T-lymphocyte in vitro responsiveness to Con A were also isolated from tick salivary glands.