activity of three anihelmintics against mixed infections...

228 PROCEEDINGS OF THE [VOL . 34, No. 2

Activity of Three Anihelmintics Against Mixed Infections ofTwo Trichostrongylus Species in Gerhils, Sheep, and Goats

K. C. KATES AND D. E. THOMPSON 1

In any screening program to test anthel-mintics, a suitable host-parasite system is ofprimary importance. Since this laboratory-plans to conduct such a screening program ona long-range basis, we tried to determine thebest host—parasite system for that purpose.

In connection with gastrointestinal nema-todes, Standen (1963) listed three naturalhost-parasite systems involving small labora-tory animals, which were then employed asprimary anthelmintic screens, viz. the rat—Nippostrongylus brasiliensis, mouse—Nemato-spiroides dubious, and rabbit—Trichostron-gylus retortaeformis. According to the liter-ature, improved primary screens that aid inthe discovery of new anthelmintics may bedeveloped by using species of Trichostrongylus,normally parasitic in domestic animals, in sus-ceptible small laboratory animals. Such speciesare useful because of their low host specificity,high pathogenic potential, and because certainspecies occur in both the stomach and smallintestine of susceptible hosts.

Drudge et al. (1955) and Leland andDrudge (1957) reported that rabbits couldbe infected with Trichostrongylus axei fromruminants and equines, and possibly also withTrichostrongylus colubriformis. Wood (1958)standardized infections of T. colubriformis inrabbits, and concluded that this system wassatisfactory for evaluating potential livestockanthelmintics. However, in this system pheno-thiazine and Trolene (Ronnel) were inactive,whereas carbon tetrachloride and diethylcar-bamazine were active. Cauthen (1958) re-ported that in the rabbit-T. axei system, pheno-thiazine, piperazine citrate, and "Cu-nic"(1.75% copper sulfate plus 0.8% Black Leaf40) showed only minimal activity.

1 This work was done while the authors were employedby the Division of Veterinary Research, Bureau of Veter-inary Medicine, Food and Drug Administration, Departmentof Health, Education, and Welfare, Beltsville, Maryland.Present address: Beltsville Parasitological Laboratory, Ani-mal Disease and Parasite Research Division, ARS, USDA,Beltsville, Maryland.

2 Division of Veterinary Research Laboratory7, BVM, U. S.Department of Health, Education, and Welfare, Beltsville,Maryland.

Although guinea pigs can be infected experi-mentally with T. colubriformis (Herlich et al.,1956; Herlich, 1958; Gordon et al., I960;Sturrock, 1963; Williams and Palmer, 1964),and apparently with T. axei (El-Rawi, 1961),their susceptibility seems to vary widely andthe system may be of limited value.

Leland (1961, 1963a) reported that Mon-golian gerbils (Meriones unguicukrtus) couldbe infected with T. axei and that the systemshowed promise as a primary anthelminticscreen (1963b). It successfully detected ac-tivit y of thiabendazole at 200 ing/kg, but notat 12.5 to 100 ing/kg; however, certain otheranthelmintics showed no activity.

Williams and Palmer (1964) used T. colu-briformis infections in rats, mice, guinea pigs,and rabbits for primary anthelmintic screens.They found that young male rats (50 g) andmice (20 g) were satisfactory hosts for T.colubriformis, and that Libyan gerbils (Meri-ones libycus) could be infected with T. axeiand T. colubriformis.

The reports of Leland (1961, 1963a, b)stimulated us to investigate further the utilit yof the gerbil—trichostrongyle system in anthel-mintic research. We found that Mongoliangerbils could be infected with both T. axeiand T. colubriformis. Data are reported inthis paper on mixed infections of these twonematodes. Limited trials were also conductedwith similar experimental infections in sheepand goats, primarily to check the efficiency ofthe anthelmintics used. We have also reportedsome unexpected changes that occurred overabout 17 months in the main Trichostrongylusspp. isolate used in this work. Part of thiswork was previously reported by the authors inabstract (1965).

MATERIAL S AND METHODS

ANIMAL S EMPLOYED: Young gerbils (Meri-ones unguiculatus) of both sexes were pur-chased from Tumblebrook Farm, Brant Lake,New York. The gerbils were kept in smallwire cages and given a standard pelleted feed

Copyright © 2011, The Helminthological Society of Washington

JULY, 1967] HELMINTHOLOGICAL SOCIETY 229

and water ad lib. At the start of the tests thegerbils were 6 to 12 months old, and the meanweight of 112 gerbils was 77 g. However, themean weights of 26 experimental groups ofgerbils varied from 70 to 96 g. Most of theexperimental groups comprised equal numbersof both sexes.

The 6 goats and 18 sheep used in thiswork were raised helminth free and were 1to 2 years old when infected. In Test 5 themean weight of the animals varied from 31 to50 kg per group. The sheep and goats werefemales and wethers, and were assigned to thetest groups without regard to sex.

ORIGIN, CULTURE, AND ENUMERATION OFINFECTIVE LARVAE: Two isolates of Tricho-strongylus spp. were used, viz., KH (KentuckyHorse) and BB (Beltsville Burro).

KH ISOLATE: This was supplied by Dr. S. E.Leland, then of the University of Kentucky.It consisted of several thousand T. axei larvaeof Equine Isolate "A" (Leland, 1963a), butDr. Leland informed us that he was not surethis isolate was pure T. axei. About 2,000 ofthese larvae were inoculated orally into eachof several rabbits, and larvae from the rabbitfecal cultures were inoculated in Lamb 85(Table 1). Only T. axei adults were recoveredat necropsy from the rabbits originally inoc-ulated with the KH isolate, but a small num-ber (0.4%) of T. colubriformis were recoveredfrom the small intestines of gerbils in Test 1.Thereafter, the KH isolate was transferredsuccessively to two goats and another lamb(207) to obtain enough larvae for later tests.Table 1 shows that by January 1965 the spe-cies configuration of the KH isolate hadchanged from the supposedly pure T. axeito an isolate with only about 36% T. axei,the remainder being T. colubriformis. Theorigin of the latter species and the cause ofthis quantitative shift in numbers of the twospecies are obscure, but the T. colubriformismay have been present in the original isolate.Nevertheless, because this isolate consisted ofboth a stomach and an intestinal species ofTrichostrongylus, it was feasible to test anthel-mintics against both species in gerbils and indomestic ruminants.

BB ISOLATE: We attempted to obtain a pureT. axei isolate by inoculating a helminth-freelamb (221, Table 1) with infective larvae

obtained from culture of burro (Eqiius asinus)feces containing trichostrongyle eggs. Uponnecropsy, the same two species were recoveredas the two which comprised the KH isolate.The reaction of the two trichostrongyle isolates,consisting of the same two species, to threeanthelmintics in gerbils was compared (Test 8,Tables 1, 2).

Infective larvae for the tests were obtainedfrom fecal cultures of stock animals (see Table1). The larvae per ml of stock suspension wereestimated by averaging counts of four 1 mlsamples. Because the gerbil stomach is small,each stock suspension was adjusted so that theappropriate number of larvae was delivered in0.5 ml or less of the suspension. Larvae forsheep and goat inoculations were cultured andenumerated similarly, except that much largerdoses were used.

LARVA L INOCULATION OF ANIMALS : Ninedifferent larval suspensions were used: Oneeach for Tests 1 to 7 and one each for Tests8A and 8B. For each gerbil, 0.5 ml or lesswas quickly removed from the continuouslystirred bulk suspension with a 0.5 ml tuber-culin syringe. To the syringe was attached a#18 hypodermic needle, modified by cuttingoff the sharp tip and adding a small globuleof solder, to prevent injury to the esophagusduring inoculation. In various tests, 997 to1,500 larvae were inoculated per gerbil (Tables2-3).

Sheep and goats were infected with singledoses of larvae in small gelatin capsules byoral inoculation with a balling gun. Thesecapsules were prepared as follows: Individualdoses of 41,000 or 50,000 larvae (Table 4)were removed from the stock suspensions witha calibrated pipette and placed on a small filterpaper laid over a piece of blotting paper; theexcess water was allowed to blot off and thefilter paper was folded with the larvae on theinner surface and inserted in the gelatincapsule.

ANTHELMINTIC S EMPLOYED, THEIR ADMINIS-TRATION, AND DOSAGES: Three anthelminticswere used; these and details concerning themwere supplied by the manufacturers as indi-cated below:

1. Phenothiazine (Atomic Basic ChemicalCo.)a. N.F. product; 7 ^ average particle



TABL E 1. T. axei and T. colubriformis in two isolates recovered at necropsy from various experimen-tally infected, nnmedicated animals (controls) over the 17-month period of the anthelmintic tests re-ported herein.

number1

12345678A

8B

Month/Year

8/6310/6310/633/642/648/641/651/65

7/641/65

infected

54442325

15

A. Kentuckv-HorseGerbilsGerbilsGerbilsGerbilsGoatsSheepSheepGerbils

B. Beltsville-BurroLamb (#221)Gerbils

animals

( K H ) IsolateRabbit-Lamb 85Lamb 85Lamb 85Goat 90Lamb 85, Goat 90Lamb 207̂Lamb 207Lamb 207

(BB) IsolateBurroLamb 221

Per cent of each speciesat necropsy

T. aexi

99.697.997.897.468.228.127.636.1

95.896.9

T. colubriformifi

0.42.1•-> o2.6

31.871.972.463.9

4.23.1

See Tables 2-4 for further details.Lamb 207 was infected with larvae from 2nd stock goat.

size; 95% pure; wetting agent 1%lecithin; 1960 batch.

b. Purified product; 6.9 ̂ average par-ticle size; 99.9% pure; wetting agent1% lecithin; 1960 batch.

c. Purified product; 2-3 ̂ average par-ticle size; 99.9% pure; wetting agent1% lecithin; 1963 batch.

Thiabendazole (Merck Institute forTherapeutic Research). Pure chemicaland water dispersable powder.Ruelene as "Ruelene Wormer Drench"(Dow Chemical Co.). This product wasprepared as a sheep drench for investiga-tional use only, and consisted of the fol-lowing ingredients:

On printed labelRuelene—21%Propylene glycol—79%

Dow Chemical Co. assayRuelene—21.3%Propylene glycol—78.7%

The phenothiazine and thiabendazole pow-ders were prepared as water suspensions foruse as drenches. The flui d Ruelene WormerDrench was used as supplied by the manu-facturer; the doses were calculated on thebasis of the Ruelene content determined fromthe assay.

The drenches were administered to gerbilsby the same technique used for larval inocula-tions. The phenothiazine and thiabendazoledrenches were prepared so that not more than0.5 ml was administered at one time. Theplanned anthelmintic doses were given togerbils in two parts, one-half in the morning

and one-half in the afternoon of the same day,and to the sheep and goats as single doses witha dosing syringe equipped with a Whitlocknozzle.

The anthelmintic closes were given to gerbilson the basis that each gerbil treated weighed100 g, rather than as mg./kg (Tables 2, 3).As the mean weight of the gerbil test groupsvaried from 70 to 96 g, the mg/kg dosesactually given were 4-30% higher than thoselisted in the tables. Because of the smallquantities of drugs used per gerbil, we do notbelieve this method of calculating doses ma-terially affected the results. The doses wereabout the normal therapeutic dose, double thenormal dose, and (thiabendazole only) quad-ruple the normal dose.

The doses were given to the sheep and goats(Table 4) as mg/kg of body weight, and alldoses were within the recommended thera-peutic range.

In all tests except one, the drugs were ad-ministered 24 to 36 days postinfection, whenthe nematodes were mature. In one test withgerbils (Test 3, Table 3) the drugs were given12 days postinfection, when the nematodeswere immature.

NECROPSY AND WORM COUNT PKOCKDUKES;EFFICACY CALCULATIONS: Al l animals werekilled 5 days posttreatment. At necropsy, thestomachs and small intestines of the gerbilswere removed; each organ was cut into smallpieces and placed in 50 ml of artificial pepsindigestion flui d (0.5% scale pepsin and 0.5%


JULY, 1967] HELMIiNTHOLOGICA L SOCIETY

TABLE 2. Activity of three anthelmintics on experimentally induced, mixed trichostrongyle infectionsinvolving two isolates and two species (T. axei and T. colubriformis) in gerbils. (Test 8A, B; also seeTable 1).

Drug and dose1( Divided dose,Vi AM, V> PM )

None( Controls )Phenothia/.inePurif ied, 2—3 fj.

1,200 mg/kgThiabendazole

100 mg/kRRuelene

400 mg/kg

None( Controls )PhenothiazinePurified, 2-3 /*

1,200 mg/kgThiabendax.ole

100 mg/kgRuelene

400 mg/kg

No. larvaeinoculatedper gerbil

1,500

1,500

1,500

1,500

1,400

1,400

1,400

1,400

No. gerbilsper group

A. Kentuckv-Horse

5

5

5

5

B. Beltsville-Burro

5

5

5

5

Avg no. nematodes pergerbil at necropsy

T. a. T. c.

Isolate

150 264

99 173

44 5

85 14

Isolate

279 9^

240 4

134 0

135 0

Per cent efficacy

T. a. T. c.

34 35

71 98

43 95

14 5fi»

52 100"

52 100"

3 Treatment 24 days postinfection; necropsy 5 days later." Only about 3% of T. colubriformis in BB isolate; see Table 1 for details.:1 Numbers of T. c. too small for these efficacy calculations to be meaningful.

HCl) in a 100 ml wide-mouthed bottle, andthe bottle was capped. The digests were in-cubated at 37 C for 14 hours; formalin wasthen added to preserve the nematodes forcounting and identification. Total wormcounts were made from all gerbils.

At necropsy of the sheep and goats, theabomasums were quickly tied off with stringfrom the small intestines at the pyloric valve,and the two organs removed separately forworm recovery. Each organ was then openedand its contents were recovered; the remainingtissues were then separately subjected to arti-ficial peptic digestion as for gerbils. Both thecontents of the organs and the separate digestswere made up to 2,000 ml with water and two100 ml samples were removed while the bulkmaterial was continuously stirred. Total wormsper animal were calculated from these samples.

Efficacy of the anthelmintic treatments wascalculated on the basis of postmortem wormcounts by using the following formula:

Avg worms in controls— avg worms in treated animals

Avg worms in controls X 100 = % efficacy.

RESULTSANTHELMINTI C STUDIES: The results ob-

tained with the gerbil-Trichostrongylus spp.system are summarized in Tables 2 and 3.The three phenothiazines showed very lowgrade or no activity against T. axei and T.colubriformis in gerbils, even when the puri-fied product of 2-3 p, average particle sizewas given at about double (1,200 mg/kg) thenormal therapeutic dose recommended fordomestic ruminants (Tests 4 and 8). How-ever, the purified, 2-3 ^ phenothiazine at 600mg/kg was highly efficacious against the samenematode species in sheep and goats (Table 4).

Anthelmintic activity of thiabendazole andRuelene was readily detected in this system.In Test 1 (Table 3), as the dose of thiabenda-zole increased (50, 100, and 200 mg/kg) theefficacy against the predominant T. axei infec-tions also increased (40, 83, and 97%, respec-tively). In Tests 1 to 4, 200 mg/kg of thia-bendazole gave consistent results (97, 94, 93,and 89%, respectively) against T. axei. InTest 3, thiabendazole was about as effectiveagainst immature T. axei (mainly 4th andearly 5th stages) as against adult T. axei inthe other tests. In Test 4, about double thenormal dose of Ruelene showed only low gradeactivity against T. axei.


232 [VOL. 34, No. 2

TABL E 3. Activity of three anthelmintics on experimentally induced, mixed trichostrongyle infectionsin gerbils. Kentucky-horse isolate used, which consisted mainly of T. axei (T. a.) in these tests; onlysmall numbers of T. colubriformis (T. c.) were present.

Avg no. nematodes perTest no.;1Time of

treatment

1

36 clayspostinfection

2

35 dayspostinfection

3


4


Drug and dose-

None( Controls )Thiabendazole

50 mg/kgThiabendazole


200 mg/kg

None( Controls )PhenathiazineNF, 7 A

600 mg/kgPhenothiazinePurified, 6.9 A

600 mg/kgPhenothiazinePurified, 2-3 /j.


200 mg/kg

None( Controls )PhenothiazineNF, 7 A

600 mg/kgPhenothiazinePurified, 6.9 /i

600 mg/kgPhenothiazinePurified, 2-3 /JL


200 mg/kg

None( Controls )PhenothiazinePurified, 2-3 ft

1,200 mg/kgThiabendazole

200 mg/kgRuelene

400 mg/kg

No. larvaeinoculatedper gerbil

1,090

1,090

1,090

1,090

997

997

997

997

997

1,055

1,055

1,055

1,055

1,055

1,200

1,200

1,200

1,200

.r\o. geroilsper group

5

4

4

4

4

3

4

4

4

4

4

4

4

4

4

4

4

4

gerbil at

T. a.

215

130

37

6

214

162

253

216

13

347

283

213

220

26

267

279

29

196

necropsy:;

T. c.

1

1

0

0

5

0

3

4

0

8

0

17

5

0

7

14

0

1

Per centefficacy

T. a. only

—

40

83

97

—

25

0

0

94

—

18

39

37

93

—

0

89

27

1 See Table 1 for further details.- Divided dose; M> AM and Vs PM.;1 Necropsy 5 days posttreatment.

Test 8 (Table 2) was a comparison of theeffectiveness of the three anthelmintics, atabout double the normal therapeutic dose,against both the KH and BB isolates of Tricho-strongylus spp. in gerbils. Phenothiazine hadonly low grade efficacy against the KH isolate,which at the time of this test consisted of about36% T. axei and 64% T. colubriformis. How-ever, a difference in efficacy appeared withthe thiabendazole and Ruelene against thetwo species. Both drugs were more efficacious

against T. colubriformis (98 and 95%) thanagainst T. axei (71 and 43%); this was con-firmed with the BB isolate, although the num-bers of T. colubriformis involved were small.Thus, sensitivity of the KH and the BB isolatesto these three anthelmintics seemed to beabout the same.

In the potency tests with these three anthel-mintics against similar experimental Tricho-strongylus spp. infections in sheep and goats(Table 4), all the larval cultures used had



TABL E 4. Activity of three anthelmintics on experimentally induced, mixed infections of T. axei andT. colubriformis in sheep and goats.

Test no.;1Time of

treatment

5

31 daysposttreatment

6


7


Drug and dose

None( Controls )PhenothiazinePurified, 2—3 /JL


100 mg/kK

None( Controls )PhenothiazinePurified, 2—3 p,

600 mg/kKThiabendazole

100 mg/kKRuelene

200 mg/kK

None( Controls )Thiabendazole

50 mK/kgRuelene

100 mg/kg

No. larvae-inoculatedper animal

41,000

41,000

41,000

50,000

50,000

50,000

50,000

50,000

50,000

50,000

No. animalsper group

2

2

2

3

3

3

3

2

o

2

Goats

Goats

Goats

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep

Avg no. nematodes peranimal at necropsy

T. a.

7,697

912

0

9,813

3

0

0

4,330

0

1,290s

T. c.

3,515

5

0

25,023

50

0

3

11,545

5

0

Per centefficacy

T. a. T. c.

88 99.9

100 100

_

90.9 99.9

100 100

100 99.9

_

100 100

70 100

1 See Table 1 for further details.- Kentucky-Horse isolate used." One sheep had almost all worms.

substantial numbers of both T. axei and T.colubriformis (Table 1). These limited testsshow that our preparations of the three drugswere of normal potency against these speciesof nematodes in two of their normal hosts.However, 200 mg/kg of Ruelene was superiorto 100 mg/kg against T. axei; both levels ofthis drug removed practically all of the T.colubriformis.

OBSERVATIONS ON Trichostrongylus SPP. ISO-LATES: Table 1 summarizes the history of ourexperience with the KH isolate of Tricho-strongylus spp. Although this isolate appearedto be pure T. axei when received, either itbecame mixed with small numbers of T. colu-briformis or some T. colubriformis was presentin the original shipment. The necropsy datafrom the untreated (control) animals showedthat T. colubriformis in this isolate graduallyincreased through transfer to stock sheep 85and goat 90, increased substantially when itwas transferred from goat 90 to a second stockgoat, and again increased proportionatelythrough transfer from the second stock goatto Lamb 207. Subsequent infections of 5sheep and 5 gerbils (Tests 6, 7, 8A) withlarvae cultured from the feces of Lamb 207

over a period of 5 months maintained ratiosof about 1 to 3, or 1 to 2, T. axei to T. colubri-formis. About the same ratios of the two spe-cies were obtained from 5 lambs as from 5gerbils. Thus, on a proportional basis, gerbilsare about as susceptible as sheep to infectionwith these two species. In further support ofthis conclusion, approximately similar percent-ages of the two species were recovered from5 girbils infected with the BB isolate fromLamb 221 as from Lamb 221 itself.

UNIFORMITY OF INFECTIONS IN UNTREATED,CONTROL GERBILS: In using this gerbil-tricho-strongyle system to screen the anthelminticpotential of chemicals, the range of infectionsestablished is an important consideration. Theinfections in control gerbils in 6 tests indicatethat substantial numbers of both species wereestablished (Table 5). In Test 8A, one gerbilhad only 37 T. colubriformis at necropsy,whereas the other four had reasonably uniforminfections of this species; all five had quiteuniform infection of T. axei (135-166). Themost uniform infections of the combined spe-cies (241-333) were established in the gerbilsin Test 8B. In general, the infections were



TABL E 5. Ranges in necropsy worm counts ofT. axei and T. colubriformis in individual gerbilsin untreated, control groups.

T. axci T. coliibriformi.v Both species

Test 1Test 2Test 3Test 4Test 8ATest 8B

138-298146-299248-463135-446135-166227-333

0-50-110-300-17

37-4510-17

138-2981146-299248-493139-451172-594241-333

1 The ranges of T. a. and T. c. are not simply additive,as the T. c. did not always occur in the gerbils whichhad the highest and lowest T. a. worm counts.

uniform enough to make this a reliable testsystem.

DISCUSSION

Our results show that the gerbil-Tn'c/io-strongylus spp. system is satisfaetory to screennew chemicals for treating nematode infectionsin animals. We have confirmed and extendedLeland's (1963b) preliminary observations thatthe gerbil-T. axei system showed promise asa primary anthelmintic screen. Our results forthiabendazole activity against Trichostrongylusspp. below the 200 rng/kg level differ some-what from those of Leland. He stated thatthiabendazole at 100 mg/kg and below showedno activity against T. axei; we observed 40%activity at the 50 mg/kg dose, and 52, 72,and 83% activity in different tests at the 100mg/kg dose. However, we used divided dosesof the drug, whereas Leland vised single doses,and also based our drug doses on gerbilweights of 100 g each, although the meanweight of the gerbils was 77 g. In our tests atthe 100 mg/kg level thiabendazole apparentlyremoved 98% of the T. colubriformis. Thetwo species-gerbil system may be more sensi-tive to anthelmintic activity than the one-species-gerbil system. Thus, T. axei in gerbilsmay be more sensitive to some chemicals andT. colubriformis to others.

Leland's (1963b) work and ours show thatphenothiazine preparations have littl e or noactivity in the gerbil-T. axei and the gerbil-Trichostrongnlus spp. systems. This is prob-ably due to the fact that the digestive tractsof gerbils and domestic herbivores, particularlyruminants, differ anatomically and physio-logically. The activity of both thiabendazoleand Ruelene in the gerbil-trichostrongyle

system justifies further investigation of thesystem as a primary anthelmintic screen.

One advantage of this host-parasite systemas a primary screen is its manipulative sim-plicity. Gerbils are easily infected with mixedlarvae of T. axei and T. colubriformis by oralinoculation of small numbers of larvae. Be-cause of the small size of gerbils, only verysmall quantities of test drugs are needed, andthese are easily administered to these docileanimals. Furthermore, breeding colonies areeasily established following the procedures ofSchwentker (1963), Ringle and Dellenback(1963), Kramer (1964), and Marston andChang (1965).

Our limited data on controlled anthelmintictests with sheep and goats experimentally in-fected with Trichostrongylus spp. and treatedwith phenothiazine, thiabendazole, and Rue-lene can be compared with data reported byDrudge et al. (1964) on these three anthel-mintics for removal of natural infections ofTrichostrongylus spp. from sheep. The follow-ing tabulation and efficacy calculations per-tain only to Trichostrongylus spp., based ondata reported by Drudge et al. (1964).

DrugandDose

None ( controls )

PhenothiazinePurified, 2-3 n550 mg/kg

Thiaben/.adole44 mg/kg

Ruelene125 mg/kg

Nematodes at necropsyAvg/lamb1

T.a. T.e.

2,564 4,520

32 2,032

4 0

448 675

T.v.

2,048

496

0

8

; Per centefficacy

T.a. T.c.

-

99 55

99.9 100

82 75

T.v.

-

80

100

99.9

1 Five lambs per group (T.a.—T. axai; T.e.—T. colubri-formis; T.v.—T. vitrimts).

These results of Drudge et al. for thiaben-dazole at 44 mg/kg are similar to our resultswith 50 mg/kg (Table 4, Test 7). Resultsare also similar for phenothiazine and Ruelene,except that we obtained somewhat higher ef-ficacies against T. colubriformis with 600 mg/kg of phenothiazine and 100 mg/kg of Ruelenethan they obtained with 550 mg/kg and 125mg/kg of the same drugs, respectively.

Although the cause of the quantitative spe-cies change of our KH isolate of Trichostron-gylus spp. is obscure (Table 1), certain factorsmay have been involved: (a) differences inegg productivity of the two species, (b) dif -



ferences in susceptibility of the stock animalsused, (c) differences in time of peak egg pro-duction of the two species in mixed infections,(d) the effect of culture conditions on thedifferential development of infective larvae ofthe two species (Ciordia et al., 1966). Theinteraction of these two closely related spe-cies in mixed infections warrants furtherinvestigation.

The BB isolate was obtained from a burrowhich had grazed for several months on apasture formerly grazed by sheep. The burroprobably became infected with one or bothof the two trichostrongyle species as a resultof sheep contamination of the pasture. Wewere not able to follow this isolate throughseveral transfers in stock animals to deter-mine if the two species would undergo thesame quantitative change as in the KH isolate.However, our work indicates that when tricho-strongyle isolates are obtained from equines,such isolates may contain more than one spe-cies of Trichostrongylus.

SUMMARY

Experiments were conducted to evaluategerbils simultaneously infected with T. axeiand T. colubriformis as a host-parasite systemfor vise as a primary screen for new chemicalsof possible anthelmintic activity. Three pheno-thiazine products, thiabendazole, and Ruelenewere used in this evaluation. This system de-tected activity of both thiabendazole andRuelene, but not of the three phenothiazines.T. colubriformis in gerbils appeared to be moresensitive to thiabendazole and Ruelene thanT. axei. Al l preparations of anthelmintics usedin the gerbil tests showed normal activityagainst similar mixed trichostrongyle infec-tions in sheep and goats. Quantitative changesthat occurred over a period of about 17 monthsin one mixed isolate of T. axei and T. colubri-formis are described, and the possible factorsinfluencing these changes are discussed.

LITERATURE CITED

CAUTHEN, C. E. 1958. Inefficiency of rabbitsfor testing anthelmintics to he used againstgastro-intestinal nematocles of ruminants. J.Parasit. 44: 246.

CIORDIA, H., W. E. BIZZELL, D. A. PORTER, ANDC. F. DIXON. 1966. The effect of culturetemperature and age on the infectivity of the

larvae of Trichostrongylus axei and T. colu-briformis in rabbits and guinea pigs. I. Parasit.52: 866-870.

DRUDGE, J. H., S. E. LELAND, Z, N. WYANT , ANDC. W. ELAM . 1955. Studies on Tricho-fitrongulus axei (Cobbold, 1879). I. Someexperimental host relationships. I. Parasit.41: 505-511.

, J. SZANTO, Z. N. WYANT , AND G. ELAM .1964. Field studies on parasite control insheep: Comparison of thiabendazole, ruelenc,and phenothiaxine. Am. J. Vet. Res. 25: 1512-1518.

EL-RAWI, B. M. 1961. Adaptation of Tricho-strongylus colubriformis and T. axei in do-mestic rabbits and guinea pigs. Diss. Abstr.21: 3201.

GORDON, H. McL., W. MULLIGAN , AND R. K.REINECKE. 1960. Trichostrongylus colubri-formis in the guinea pig. Austral. Vet. J. 36:466-471.

HERLICH, H. 1958. Further observations on theexperimental host-parasite relations of theguinea pig and ruminant parasite, Tricho-strongylus colubriformis. J. Parasit. 44: 602.

, F. W. DOUVHES, AND R. S. ISENSTEIN.

1956. Experimental infections of guineapigs with Trichostrongylus colubriformis, aparasite of ruminants. Proc. Helm. Soc. Wash.23: 104-105.

KATES, K. C., AND D. E. THOMPSON. 1965. Com-parative studies of some commercial anthel-mintics against ruminant trichostrongyle nem-atodes in rabbits, sheep and goats. J. Parasit.51(2, sec. 2 ): 33.

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LELAND , S. E. 1961. Some aspects of experi-mental infection of the mongolian gerbil(Meriones ungiricitlatus) with Trichostron-gylus axei, J. Parasit. 47(4, sec. 2 ): 19.

. 1963a. Studies on Trichostrongylus axei(Cobbold, 1879). VIII . Some quantitativeaspects of experimental infection of the mon-golian gerbil (Meriones unguiculatus). ] .Parasit. 49: 617-622.

. 1963b. Preliminary evaluation of Trich-ostrongylus axei in the mongolian gerbil as ascreening system for anthelmintics of domesticanimals. J. Parasit. 49(5, see. 2): 15-16.

-, AND J. H. DRUDGE. 1957. Studies onTrichostrongylus axei (Cobbold, 1879). II .Some quantiative aspects of experimental in-fection in rabbits. J. Parasit. 43: 160-166.

MARSTON, J. H., AND M. C. CHANG. 1965. Thebreeding, management and reproductive physi-ology of the mongolian gerbil (Meriones un-guicukctus). Lab. Animal Care 15: 34-48.


236 PROCEEDINGS OF THE [VOL. 34, No. 2

RlNGLE, D. A., AND R. J. DELLENBACK. 1963.

Age changes in plasma proteins of the mon-golian gerbil. Am. J. Physiol. 204: 275-278.

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infections of guinea pigs for laboratory experi-ments. Parasitology 53: 189-199.

WILLIAMS , G. A. H., AND B. H. PALMER. 1964.Trichostrongylus colubriformis (a nematodeparasite of sheep and other ruminants) as atest organism in screening for sheep anthel-mintics in the laboratory. Nature 203: 1399-1400.

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Zoological Nomenclature in the Jet Age1

CURTIS W. SABROSKYEntomology Research Division, Agricultural Research Service, USDA

In this age of molecular biology and spacescience, there are those who regard taxonomyin general, and nomenclature in particular, ashorse-and-buggy biology. So here I am, askedto speak on a subject, zoological nomenclature,that would be, I am sure, at the very bottomof any Gallup poll rating in biology. I did thebest I could by dressing up the title, and hencemy talk is called "Zoological Nomenclature inthe Jet Age." With jets, of course, you canexpect a blast of hot air and a lot of noise, butthe trip wil l be fast.

With reference to modern science, it strikesme that there is a strange phenomenon today.The wider the horizons, the narrower the view-point of some scientists on the older areas ofknowledge. But as a taxonomist I know thatall wil l come home to roost some day. Whenmen land on the moon, they wil l collect sam-ples. Then they wil l ask the elementary ques-tion in taxonomy: "What is it?" And thenthey wil l submit it for identification to sometaxonomist!

However, I did not come here to wring myhands. I came to talk about some problems inzoological nomenclature. I shall not review thehistory of nomenclature, or Codes, or Inter-national Congresses of Zoology. That has been

1 Presented as part of an after-dinner program at the56th anniversary meeting of the Helminthological Societyof Washington, 19 October 1966.

done often, and ad nauseam, frequently byme. Rather I shall concentrate on present andfuture general problems. We simply cannotescape nomenclature of some kind because wemust have names, or symbols, or some meansof referring to objects and concepts, of record-ing information concerning them, and of com-municating with others about them. Nomen-clature may be derided as old fashioned, butlike eating and sex, it is basic, and it won'tgo away. And it has problems, even in modernsophisticated science, and sometimes becauseof that sophistication. I am seriously concernedabout some of these problems. I think they arcmatters with which the International Com-mission and taxonomists in general must cometo grips in this jet age. I may not have patanswers, but at least I wish to discuss theproblems. I want to think out loud for a while.

WHAT Is PUBLICATION?

My first problem is an old one, but recentlyit has hit me in the face: What is publication?This problem transcends nomenclature andtaxonomy, but it is more acute in taxonomybecause we use date of publication as an ob-jective, factual criterion of priority.

Recently, during the meeting of the Amer-ican Institute of Biological Sciences on thecampus of the University of Maryland, I at-


activity of three anihelmintics against mixed infections...

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