Veterinary Parasitology 92 (2000) 261–267

Interaction betweenTrypanosoma evansiandHaemonchus contortusinfection in goats

D.K. Sharma∗,1, P.P.S. Chauhan2, R.D. Agrawal3

Department of Parasitology, College of Veterinary Science and A.H. Chandra Shekhar Azad University ofAgriculture and Technology, Mathura Campus, Mathura 281001 (UP), India

Received 18 January 2000; received in revised form 31 May 2000; accepted 4 June 2000

Abstract

An experimental study on interaction betweenTrypanosoma evansiandHaemonchus contortusinfections was conducted in 42 male Barbari goats of 6–9 months age. Parasitological observationslike prepatent period, faecal egg count, worm burden and mortality were made in animals infectedwith H. contortusfollowed 1 week later withT. evansiand vice versa. These parameters were alsoexamined in animals with single infection with each of these parasites.

It was revealed thatT. evansiinfection in goats lowered the normal resistance toH. contortus.The prepatent period was markedly reduced to 16–18 days in cases whereT. evansiprecededH. contortusas compared to 21–25 and 21–23 days in singleH. contortusand in aH. contortusprecedingT. evansiinfection, respectively. The rate of L3 establishment was significantly enhancedin infection whereT. evansiprecededH. contortus. A higher rate of mortality and more pronouncedpathological effects were observed in combined infections than in single ones. © 2000 ElsevierScience B.V. All rights reserved.

Keywords:Goat;Haemonchus contortus; Trypanosoma evansi; Interaction

1. Introduction

Though single parasitic infections in a host are not uncommon in nature, mixed infec-tions with various species or with several different types of parasites is the rule. In mixedinfections, the presence of a pathogen may enhance the effect of the other in the host. This

∗ Corresponding author. Tel.:+91-565-7632-44; fax:+91-565-7632-46.E-mail address:dinesh@cirg.up.nic.in (D.K. Sharma).

1 Senior Scientist, CIRG Makhdoom, P.O. Farah 28122, Mathura (UP), India.2 Ex Professor and Head, Dept. Parasitology, Veterinary College Mathura (UP), India.3 Professor and Head, Dept. Parasitology, Veterinary College Mathura (UP), India.

0304-4017/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0304-4017(00)00310-1

262 D.K. Sharma et al. / Veterinary Parasitology 92 (2000) 261–267

is more likely to occur when the first infection has an immunosuppressive effect on the hostthus making the latter more vulnerable to other parasites to which it was otherwise resistant.The interaction between two or more parasites is an inevitable situation which may lead tosignificant physiological and biochemical changes in body tissue and fluids which couldnot be attributed to either of these parasites individually.

In view of the severe immunosuppressive effects of trypanosomosis in affected animals(Holmes et al., 1974; Scott et al., 1977) the present study was envisaged to evaluate the pos-sible impact of concurrent infections ofT. evansiandH. contortusin goats on parasitologicalparameters.

2. Materials and methods

The experiment was carried out at the Department of Veterinary Parasitology, Collegeof Veterinary Science and A.H. Mathura, U.P. (India). Barbari male goats of 6–9 monthsage having approximately same weight and health status were used for the study. All theselected goats were screened for haemoprotozoan along with other internal and externalparasitic infections. Irrespective of infection or otherwise, all animals were treated withtrypanocidal drug (Berenil, 4 mg/kg) and a broad spectrum anthelmintic (Valbazine, as permanufacturer’s recommendation). Ectoparasites were removed by dipping the animals in0.8% Malathion, an acaricide. All the animals in different groups including controls werefurther maintained separately in complete hygienic conditions and provided with fresh greentree toppings and concentrate with no grazing to avoid the risk of unwanted infection. Theanimals were watered from trough.

2.1. Experimental design

The design of experiment is tabulated (Table 1). The total 42 experimental animals weredivided into four groups. The first two groups A and B, consisting of 12 animals in each,were further subdivided in two groups and designated as infected and controls, with eightand four animals each, respectively. Animals in groups A and B were used for pure infectionand were givenH. contortusandT. evansiinfections. Group C involved a total of 18 animalscomprising 14 and 4 animals as infected and control, respectively. Of the 14 goats in this

Table 1Experimental design and infection regimen

Groups No. of animals Infection regimen on

Infected Control 0 day 7 day

A 8 4 5000 L3 of H. contortusorally/animal –B 8 4 106 T. evansi/animalC (T+H)a 8 4 106 T. evansi/animal 5000 L3 of H. contortusorally/animalC (H+T)b 6 5000 L3 of H. contortusorally/animal 106 T. evansi/animal

a (T+H) represents group whereT. evansiinfection precededH. contortusinfection.b (H+T) represents group whereH. contortusinfection precedesT. evansiinfection.

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group, eight had double infection withT. EvansiprecedingH. contortusand six had doubleinfections but in reverse order. Every infected group had its own control (4 animals).

Laboratory strain ofT. evansi(Bubaline) was procured from Indian Veterinary ResearchInstitute, Izatnagar (UP) and maintained in laboratory raised albino mice before its inoc-ulation in experimental goats. Blood collected from mice at teeming/peak parasitaemiawas mixed with Alsevier solution for preparation of inoculation with 1×106 trypanosomes,subcutaneously.

For H. contortusinfection of goats, L3 were obtained in large numbers through copro-culture of faeces of donor sheep which was infected L3 (H. contortus)of goat origin.

Standard Mac Master egg counting technique was followed for estimating the numberof eggs per gram (EPG) of faeces. For the total worm count, in animals naturally died orslaughtered at the end of experiment, abomasum was ligated and cut off at the time ofautopsy. Total abomasal content was poured in a enamel tray after opening it. It was washedthrough decantation under tap water till all the debris was removed. Counting was mademanually through picking individual worm.

Analysis of data was made using the studentt-test.

3. Results

All the goats in group A infected withH. contortuslarvae (L3) developed patent infection.Initially, 25% of the animals started passing eggs on day 21 post infection (PI). Thereafter,the proportion increased and on 25 day PI faecal samples of all the animals were positive forH. contortuseggs. In infected animals EPG rate picked up slowly from 2.5±0.35 (×200)on day 21 PI, attained peak of 31.42±1.21 (×200) on day 35 PI and it was 13.71±(×200)on 42 day PI.

In group C (T+H), having dual infections, the infected animals developed patent infectionof H. contortusgradually as revealed by faecal examination. The voiding of eggs in faecescommenced on 16 day PI when 37.5% of the animals were found to containH. contortuseggs in faeces which were later confirmed by coproculture. Number of infected animalswent up next day, i.e. day 17 PI to reach 87.5%. By day 18 PI all the animals were founddischargingH. contortuseggs in the faeces. Mean EPG figures of 2.00±0.00 (×200) on16 day PI, gradually reached a peak value of 26.60±11.56 (×200) day PI. Thereafter, itdeclined on day 42 to 9.66±0.98 (×200) (Fig. 1).

In animals of group C (H+T), where L3 (H. contortus)preceded theT. evansiinfection1 week after, 33.3% of the animals, started discharging eggs on day 21 PI and by day 23PI, faecal sample examination showed all the animals (5) positive forH. contortuseggs.Mean EPG of 2.00±0.70 (×200) observed on day 21 PI rose gradually to reach peak of27.40±1.34 (×200) on day 36 PI. Thereafter, it declined to 13.25±0.73 (×200) on 42 dayPI (Fig. 1).

Mean weekly EPG figures in different groups of infected animals are given in Table 2.Weekly mean EPG of 5.62±0.77(×200) observed in group A in week 4 was statisticallysimilar to EPG of group C (T+H). However, this value was significantly lower than meanEPG seen in group C (H+T). Though weekly mean EPG of 9.95±1.65 (×200) in group C(H+T) was highest in 4 week PI, all the three groups were statistically similar in 5 week.

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Fig. 1. EPG pattern in pure and concurrent infections.

In 6 week the mean EPG observed in group A and C (H+T) were similar, but these weresignificantly higher than the EPG in group C (T+H).

The abomasal worm load encountered in slaughtered and post-mortem cases in groupC (T+H), having double infections whereT. evansiprecededH. contortusinfection wassignificantly more than the worm population in other two groups A and C (H+T) (Table 2).

All the experimental animals in groups B and C which were inoculated withT. evansi(106) became trypanosome positive within a week of inoculation. However, techniqueslike wet film and thick stained film examinations, failed to detect parasitaemia in blood.Microhaematocrit capillary tube was found to be the most suitable laboratory method todetect the low level parasitaemia. The level of parasitaemia in experimentally infected goatswas found to be extremely low to be quantified.

During the course of experimental study, different infected groups encountered mortality.However, no causality was observed in any of the goats of control groups during experi-mentation. Group C (T+H) experienced highest mortality starting with two deaths during4th week, and by the end of 6th week five of the eight animals died. In group C (H+T),

Table 2Pre-patent period, worm burden and EPG ofH. contortusin pure and concurrent infections

Groups Incubation period (days) Abomasal worm infection EPG (×200) (weeks PI)

4th 5th 6th

A 21–25 475.57±18.25 5.62±0.77 23.75±2.62 22.28±2.33C (T+H)a 16–18 554.75±27.23 7.74±2.01 20.19±0.51 13.89±1.28C (H+T)b 21–23 450.20±22.64 9.95±1.65 21.14±160 22.07±1.60

a (T+H) represents group whereT. evansiinfection precededH. contortusinfection.b (H+T) represents group whereH. contortusinfection precedesT. evansiinfection.

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only two deaths were encountered during 6 week study when one goat died immediatelyafter 1st week, while the second mortality was observed after 5th week. In group A, havingH. contortusinfection singly, two goats died in the course of experimentation. First mor-tality in this group occurred just after the 1st week and the second goat died after 5th week.In trypanosomal infection in group B, only one goat died after the 2nd week.

4. Discussion

Observations in the present study indicated that concurrent infection ofT. evansiin goatslowered down the body resistance toH. contortusinfection and making the animals moresusceptible to it. The prepatent period ofH. contortuswas cut short significantly as a resultof concurrentT. evansiinfection. The rate of L3 establishment was significantly enhancedwhereT. evansiinfection precededH. contortus. Higher mortality was seen in concurrentinfections than in single infection and pronounced pathological effects were visible due toimmunosuppression byT. evansiinfection.

Though interaction ofTrypanosomaand Haemonchussp. had been studied in goats(Griffin et al., 1981), camel (Yaguob, 1989), cattle (Kaufman et al., 1992) and in sheep(Goosens et al., 1997), but all these usedT. congolenseexcept Yaguob (1989) who usedT. evansi. Prepatent period in the present study, in Group A, i.e. withH. contortusalone,ranged from 21 to 25 days whereas in Group C (T+H) it was reduced to 16–18 days as allthe animals in this group started discharging eggs during the 3rd week PI. Results agreedwith Griffin et al. (1981), Kaufman et al. (1992) and Goosens et al. (1997) who reportedreduction in prepatent period ofH. contortusin goats, cattle and sheep respectively havingprior trypanosomal infection. In the present study, in Group C (H+T) whereH. contortusinfection was super imposed byT. evansiafter 1 week, the prepatent period (21–23 days)remained unaffected.

Reduction of the prepatent period in group C (T+H), showed that prior infection ofT. evansifacilitated the growth ofH. contortusworms and led them to early maturity whichmight be due to the suppression of IgE production byT. evansi(Griffin et al., 1981) whichotherwise normally produced in quantity by the gut in response to parasites of alimen-tary canal (Ogilvie and Parrott, 1974) and was responsible for nematode rejection by itsimmediate hypersensitivity effect.

Higher EPG mean in 4th week (PI) or 1st week of patency in either type of doubleinfections over single infection, in present study, was similar to Kaufman et al. (1992).Nevertheless, present results on egg output disagreed with Griffin et al. (1981) who observedpersistently lower faecal eggs count in goats with double infections.

The higher egg output, though not significant, in 4th week afterH. contortusinfectionin group C (T+H), may be attributed to large number of worms being established and theirearly maturity in this group than in pure infection, i.e. group A. But statistically similarEPG means in 5th week in all the groups, were perhaps due to lower rate of egg producedfrom larger number of worms in Group C (T+H) because of intense competition withinabomasum leading to reduced fecundity (Ratcliffe and Le Jambre, 1971). This view wasfurther supported when egg output mean in pureH. contortusinfection superseded thecorresponding value in double infections in group C(T+H). Similarly, significant higher

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egg output mean in group C (H+T) in H. contortussuperimposed byT. evansiin 4th weekas compared to pureH. contortusinfection was in conformity to studies made by Kaufmanet al. (1992) in cattle but the difference was cut down in next 2 weeks by sudden increase ineggs output in pure infection. The phenomenon could be explained on the basis of slightlyearly maturation of worms in group C(H+T), as 100% of the animals infected in this groupstarted discharging eggs at 23 day PI as against 25 day PI in group A and superior rate offecundity in lowly populated infection.

Higher abomasal worm population mean in animals with double infections in groupC(T+H) was similar to Griffin et al. (1981) in goats. Higher worm load in group C (T+H)over A and C (H+T) might be due to immunosuppressive effect ofT. evansiinfection ingroup C which lowered down the host resistance againstH. contortus. Statistically, similarworm population in groups A and C (H+T) might be explained as animals in group C(H+T) had already been infected withH. contortusfor 1 week before they receivedT.evansiinfection. It was quite possible that L3 of H. contortushad already been establishedby that period and so late immunosuppression effect exerted by trypanosomal infectioncould not had appreciable impact in group C (H+T) animals.

All the animals infected withT. evansi(106/inoculum) either singly or in associationwith H. contortusshowed parasitaemia within 7 days of infection similar to Kaufmanet al. (1992). Present observation slightly differed from Griffin et al. (1981) who recordedparasitaemia after 10 days of infection. Again unlike Griffin et al. (1981) the parasitaemialevel in all the groups was too low to be detected by wet film and thick stained film ex-amination. However, present study confirms that buffy coat technique by microhaematocritcentrifugation technique (Woo, 1969) should be used for detection of trypanosomes in goats.

5. Conclusion

Observations emphasize the importance of concurrent infections in goats especially inendemic areas where strategic changes in parasitic control measures might be required fortheir successful worm control.

Acknowledgements

Thanks are due to the Dean, College of Veterinary Science and A.H., Mathura, and theDirector, CIRG, Makhdoom for their co-operation in the completion of this work.

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