Haematological changes in experimental trypanosomiasis
in Barbari goats
D.K. Sharma
a,*, P.P.S. Chauhan
b, V.K. Saxena
c, R.D. Agrawal
b aCentral Institute for Research on Goats, Makhdoom, Farah, Mathura 281122, UP, IndiabDepartment of Parasitology, College of Veterinary Science and A.H., C.S. Azad University of Agriculture and Technology,
Campus Mathura 281001, UP, India
cCentral Avian Research Institute, Izatnagar 243122, UP, India
Received 6 December 1999; accepted 11 April 2000
Abstract
Haematological changes due toTrypanosoma evansiinfection were studied in 12 Barbari male goats of 6±9 months of age. These were divided in two groups, A and B, consisting of eight infected and four control animals, respectively. The animals were kept in strict hygienic conditions and on a zero grazing schedule. Animals of group A were exposed to 1106T. evansi
subcutaneously. Animals of both the groups were bled weekly and blood samples were examined for different haematological parameters including PCV, Hgb and total RBC count, and erythrocytic indexes of MCV, MCH and MCHC were calculated. Analysis of data revealed signi®cant changes in all these parameters and erythrocytic indexes in infected goats when compared with controls. Observations showed macrocytic anaemia with reticulocytosis in response to early haemolysis.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Goats; Trypanosomiasis; Haematology
1. Introduction
Trypanosomiasis ranks high in importance amongst protozoan infections of animals and man. It occurs in tropical and subtropical regions of the world and affects different species of animals like horse, camel, dog, cattle, sheep and goats. Realising its endemic nature, Urquhart (1974) regarded trypanosomiasis as the biggest factor which limits the number and pro-ductivity of the cattle, sheep and goats.
In India, trypanosomiasis or `surra' is caused by
Trypanosoma evansi in different categories of live-stock. Outbreaks of surra leading to high mortality have been frequently recorded in equines and bovines
including buffaloes in different states of the country. However, barring a few reports (Samaddar et al., 1962; Jatkar and Purohit, 1971)T. evansiinfection in goats in India had not been studied comprehensively and a wide gap in our understanding of the course of this infection still existed.
Unlike in horses, camels and dogs,T. evansi infec-tion in goats, follows a subclinical or chronic course with very low levels of parasitaemia that are dif®cult to detect by common laboratory methods. Several reports of experimental infection of goats were avail-able, but generally, goats are considered to be resistant to trypanosomal infection, showing only a mild or subclinical manifestation of disease (Stephen, 1970; Boyt, 1971). However, Boid et al. (1981) report high anti-trypanosomal antibody titres in a sizeable
*Corresponding author.
proportion of goats in endemic areas, and such goats may act as reservoirs for this infection.
Trypanosoma evansi, being a member of thebrucei
group, occurs in blood plasma, intercellular tissue, and body cavity ¯uid. Anaemia associated with Trypano-soma bruceiis characterised by macrocytosis, reticu-locytosis, hyperplasia of bone marrow and spleen and increased haemosiderin deposits. A shortened circu-lating half-life of Cr labelled RBCs indicated anaemia of haemolytic origin (Jenning, 1976). However, the picture of T. evansi infection in goats has not been elucidated fully, particularly in the presence of con-current infections. The present experimental study in local but widely distributed Barbari goats, was con-ducted with an objective to study the haematological changes inT. evansiinfection in zero grazing condi-tions.
2. Materials and methods
The experimental study was conducted in the Department of Parasitology, Veterinary College, Mathura. A total of 12 Barbari male goats of 9±12 months of age, or similar weight, and in good health, were used for the present study. Selected goats were screened for haemoprotozoans along with internal and external parasites. All the goats, irrespective of infec-tion, were treated with a trypanocidal drug (Barenil) and a broad spectrum anthelmintic (Valbazen). Ecto-parasitic infection was ruled out by dipping of all the selected goats in 0.8% Malathion.
After 30 days post treatment (PT), the goats were divided in two groups A and B consisting of eight and four goats and designated as infected and control groups, respectively. Animals of both groups were housed in two different pens under a zero grazing system. They were fed with tree toppings from Peepal (Ficus religiosa) and/or Ber (Zizephus zuzuba) to avoid any unwanted infection from the ground. Restricted amount of concentrate in the form of crushed barley with suf®cient quantity of mineral mixture was also provided. Drinking water was avail-able ad libitum in water troughs.
Laboratory strain ofT. evansi(Bubaline) was pro-cured from Indian Veterinary Research Institute, Izat-nagar (UP) and maintained in laboratory raised albino mice before its inoculation into experimental goats.
Blood collected from mice at teeming/peak parasitae-mia was mixed with Alsevier solution for trypanoso-mal counting and preparation of inoculum. Anitrypanoso-mals of group A were inoculated with 1106trypanosomes, subcutaneously.
Animals of both the groups were bled in the morn-ing at a weekly interval post infection (PI) up to 6 weeks and detection of parasite was made through direct blood, thin and thick stained blood smears and microhaematocrit centrifugation technique, i.e. the Woo method (Woo, 1969). Blood for haematology was processed with EDTA 20% (0.05 ml/ml of blood). PCV, Hgb and total RBC count were recorded in both the groups and erythrocyte indexes of mean corpus-cular volume (MCV), mean corpuscorpus-cular haemoglobin (MCH) and mean corpuscular haemoglobin concen-tration (MCHC) were calculated. Data obtained were compiled, tabulated and analysed statistically using Harvey (1975) analysis for studying the effects of weeks, group and interaction (groupweek). The subclass means were compared using Duncan's multi-ple range test (DMRT) as modi®ed by Kramer (1957).
3. Results
Within 7 days PI all the experimental goats in group A, inoculated with T. evansi, were tested trypano-some-positive. But only the Woo method could detect parasites and all other methods like wet and dry, thick and thin stained smears failed to detect parasitaemia at any stage of infection. The animals remained trypano-some-positive throughout the study, i.e. 6 weeks. The analysis of variance for haematological parameters in
T. evansiinfected and control goats are given in Table 1 and least squares means are presented in Table 2.
Mean PCV of animals of group A, infected withT. evansi, was signi®cantly (p<0.01) less than in control in group B (Table 1). Weekly mean PCV in group A fell rapidly in the very ®rst week when compared with control and reached its minimum value observed on sixth week PI. In group B, the mean PCV remained steady with no signi®cant variation. Highest weekly mean PCV in infected animals was observed in the ®rst week.
less than the corresponding ®gure observed in group B. The highest weekly mean Hgb concentration in group A was observed in ®rst week while the lowest among the two groups was found in the sixth week (Table 2).
Mean RBC count in group A was signi®cantly (p<0.01) less than that of group B. The fall in RBC count in infected animals was progressive and
con-tinued until the fourth week. Thereafter, the RBC level remained steady during the last 2 weeks (Table 2). Variations due to infections and interaction between week and group for erythrocytes count were signi®cant (p<0.01). The RBC level in group B was almost steady showing no signi®cant change throughout the study.
Mean MCV index in infected goats showed sig-ni®cant variations (Table 1). Weekly mean MCV index Table 1
Analysis of variance for haematological parameters inTrypanosoma evansiinfection in goats
Source of variations d.f. Mean squares
PCV Hgb RBC MCV MCH MCHC
Infection 1 1537.87** 91.73** 378.41** 163.23** 46.44** 117.43**
Weeks 5 5.63 0.23 8.60** 61.04** 6.45** 7.49
Infectionweeks 5 16.86* 1.43 6.50** 26.32** 2.87** 9.37
Remainder 56 4.59 0.61 0.38 4.46 0.59 4.62
*Indicates level of signi®cance which is at 5% level (p>0.05). **Indicates level of signi®cance which is at 1% level (p>0.01).
Table 2
Factor-wise least squares means of various haematological parameters inTrypanosoma evansiinfection in goatsa
No. of observations
PCV (%) Hgb (g/dl) RBC
(millions/mm3)
MCV (fl) MCH (pcg) MCHC (g/dl)
Overall 68 26.680.27 8.360.09 10.460.07 26.120.26 8.280.09 30.640.27
Groups
A 44 21.700.32 7.150.11 7.990.09 27.750.31 9.140.11 33.020.32
B 24 31.660.43 9.580.16 12.930.12 24.500.43 7.410.15 30.270.43
Weeks
I 12 27.060.65 8.560.24 12.12A0.18 22.31A0.64 7.08A0.23 31.780.65
II 12 26.680.65 8.210.24 10.87B0.18 24.46B0.64 7.53A0.23 30.660.65
III 11 27.620.67 8.480.24 10.12C0.19 28.09C0.66 8.67B0.24 30.830.67
IV 11 27.850.67 8.41C0.24 9.720.19 28.84C0.66 9.09B0.24 31.440.67
V 11 26.500.67 8.340.24 10.06C0.19 28.88CD0.66 8.67B0.24 32.260.67
VI 11 25.390.67 8.180.24 9.88C
0.19 26.15BD
0.66 8.62B
0.24 32.890.67
Groupsweeks
AI 8 24.12b0.75 8.070.27 11.01c0.21 21.95a0.74 7.33b0.27 33.410.76
BI 4 30.00c1.07 9.050.39 13.23d0.30 22.68a1.05 6.84b0.38 30.161.07
AII 8 22.12ab0.75 6.970.27 8.92b0.21 24.54ab0.74 7.69b0.27 31.080.76
BII 4 31.25c1.07 9.450.39 12.82d0.30 24.37ab1.05 7.37b0.38 30.231.07
AIII 7 23.00b0.80 7.220.29 7.43a0.23 30.98de0.79 9.73b0.29 31.410.81
BIII 4 32.25c1.07 9.750.39 12.81d0.30 25.20ab1.05 7.62b0.38 30.251.07
AIV 7 21.71ab
0.80 6.970.29 6.65a
0.23 32.63e
0.79 10.48b
0.29 32.100.81
BIV 4 32.00c
1.07 9.850.39 12.79d
0.30 25.06ab
1.05 7.71b
0.38 30.781.71
AV 7 20.00a
0.80 6.880.29 7.01a
0.23 28.61cd
0.79 9.88b
0.29 34.830.81
BV 4 33.00c
1.07 9.800.39 13.12d
0.30 25.16ab
1.05 7.47a
0.38 29.701.07
AVI 7 19.28a
0.80 6.770.29 6.94a
0.23 27.76bc
0.79 9.75b
0.29 35.280.81
BVI 4 31.50c
1.07 9.600.39 12.83d
0.30 24.55ab
1.05 7.48a
0.38 30.501.07
value in group A increased gradually by the fourth week, showing signi®cant change in initial value and then receded in the following weeks. Variations in weekly mean MCV and interaction between groups and weeks were signi®cant (Table 1).
Mean MCH and MCHC indexes of infected animals were found to be signi®cantly greater than the corre-sponding value observed in control group. Variations over the period in weekly mean MCH values and interaction between groupsweeks were also signi®-cant (p<0.01). Weekly MCH index in infected animals increased gradually during the initial weeks to show a signi®cant rise in the third week with highest index value in the fourth week. Thereafter, the index values remained steady but signi®cantly higher than the control in the following weeks.
4. Discussion
Pathogenesis of anaemia in trypanosomal infection seems to be variable in nature. Haemodilution, osmo-tic and mechanical fragility of RBCs, extravascular haemolysis, decrease life span of RBCs and dyshae-mopoiesis all have been discussed by various research workers as pathogenic mechanisms in different ani-mals (Clarkson, 1968; Jatkar and Purohit, 1971; Anosa and Isoun, 1976; Dargie et al., 1979; Murray, 1979; Cox and Sale, 1983; Singh and Mishra, 1986). Goats are supposed to be resistant to trypanosomal infection (Stephen, 1970; Boyt, 1971) and develop a very low level of parasitaemia which remains almost unde-tected by common laboratory techniques. Experimen-tal trypanosomal infection in goats have been discussed by a few workers (Grif®n and Allonby, 1979; Masake, 1980; Saror, 1980; Ngeranwa et al., 1993). However, haematological changes in goats due to trypanosomal infection should be visualised in the light of the fact expressed by Murray (1979) that the onset and severity of anaemia in trypanosomiasis is directly related to the appearance of the parasite in blood and the level of parasitaemia. Grif®n and Allonby (1979) reported a drop in PCV in Trypano-soma congolenseinfected goats irrespective of acute, subacute and chronic disease. Dargie et al. (1979) noted a decline in PCV in sheep with increase in parasitaemia and its recovery with disappearance of parasite. Ngeranwa et al. (1993) reported a drop in
PCV in goats by the twelfth week inT.evansi infec-tion.
Results of the present study, showing signi®cant decline in PCV, Hgb and erythrocyte counts, were in agreement with Dargie et al. (1979) and Grif®n and Allonby (1979). The drop in mean PCV of 31.5% in infected goats against controls was lower as compared to 50.8 and 41.5% PCV drops reported by Anosa and Isoun (1976) and Ngeranwa et al. (1993), respectively. However, the fall in the present study was sharp and encountered in 6 weeks as against 12 weeks of Nger-anwa et al. (1993). Results also con®rmed the ®ndings of Samaddar et al. (1962) in Indian goats that there was fall of erythrocytes in trypanosomal infection. But, the fall encountered here was gradual as against steep fall in their study. Our ®ndings disagreed with those of Otieno and Gachanja (1976) who recorded no perceptible change in any of the three blood para-meters.
Present haematological changes in PCV and ery-throcytes seems characteristically to be due to hae-modilution and haemolysis. The increase of weekly mean MCV in the ®rst 4 weeks, which characterised reticulocytosis, was not suf®cient to compensate hae-molysis. Lowering of mean MCV value in last 2 weeks marked by increase in PCV and RBCs showed a haemopoietic response to the loss of RBC through haemolysis.
Signi®cantly, the high mean MCV in infected goats observed in the present study, is in contrast to the low MCV (Samaddar et al., 1962) and unchanged MVC observed by Ngeranwa et al. (1993) in T. evansi
infection. Signi®cant increases in mean MCH and MCHC were in agreement with observations of Samaddar et al. (1962). The higher MCH index may be attributed to a compensatory mechanism in response to haemoglobin loss. MCHC values though signi®cantly higher (p<0.01) than control, fell within the normal range of Schalm et al. (1975).
haemolysis and dishaemopoeisis (Richardson and Kendall, 1963; Jatkar and Purohit, 1971; Naylor, 1971; Dargie et al., 1979).
Changes in all haematological parameters in the present study seems to point out a macrocytic anaemia showing reticulocytosis in response to early haemo-lysis and depressed haemopoeisis response. Further studies based on advanced haematological techniques might help to explain the mechanisms underlying this caprine response and why goats seem generally resis-tant toT. evansiinfection.
Acknowledgements
Thanks are due to the Dean, College of Veterinary Science and A.H, C.S. Azad University of Agriculture and Technology, Campus Mathura, UP and the Direc-tor CIRG, Makhdoom, P.O. Farah, Mathura, UP for extending necessary support for the study.
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