Studies on Filariasis in Small Mammals in Northeast Thailand · Studies on Filariasis in Small Mammals in Northeast Thailand Markpol Tingpalapong, DVM, LL.B. Richard E. Whitmire,

Studies on Filariasis in Small Mammals in

Northeast Thailand

Markpol Tingpalapong, DVM, LL.B.Richard E. Whitmire, LTC, VCBruce A. Harrison» MAJ, MSCPranee Hansukjariya~ B.Sc.

Principal Investigators:

Dr.

Mak Joon-Wah*Bumrung ChaikwangPakdee Chuenchom

Associated Investigators:

OBJECTIVE: To establish a consistently reproducible, readily available, gene-ticall.y controlled laboratory animal model for the study of infection withnematodes of the Superfamily FiLaPiaidea.

BACKGROUND: The need for a consistently reproducible laboratory animal modelfor studies of infect'ionwith nematodes of the Superfamily Fi~ariaidea has beenexpressed (1). A mosquito-transmitted filaria-laboratory rat system would ful-fil this requirement and is the ultimate goal of these studies. Attempts totransmit Brugia tupaia through mosquitoes to various laboratory animals were madeat the SEATO Medical Research Laboratory (SMRL) in 1969 and 1970 (2, 3) but wereunsuccessful.

One mosquito-transmitted filarial parasite, BrienZia booZiati.,has been reported in Malaysia and laboratory rats have been successfully infectedwith this nematode at the University of Singapore (4, 5). Additionally, onereport of mosquito transmission of Brugia pahangi to mice using Aedes togoi at

the University of Singapore is reported (6).

A preliminary study in which 1,694 wild rodents in Thailand were trappedand screened for microfilaria was undertaken by Dill, et alo (7). Results ofthis study revealed the presence of unreported filarial nematodes of severalspecies 0 Mosquito transmission studies utilizing these new species of micro-filaria were unsuccessful. Subsequent to this study, one of the new species ofmicrofilaria has been described and named Dunnifilaria dillio (8)0

Tb.is study is modeled after the earlier study by Dill, et aZ. (7).

METHODS: Small mammals were live-trapped in the area of Pak Chong, using ba-"Clanas as bait. The animals were screened in the field by examining blood filmsfor the presence of microfilaria. Blood was obtained by either orbital bleedingor by cardiac puncture. The number of each species trapped and the number ofpositive for microfilaria (regardless of species) is seen in Table I.

Head, Filariasis Divis~on, Institute for Medical Research, Kuala Lumpur,

Malaysia 0

*

62

Thirty-three of the positive animals were transported to our laboratory fordefinitive identification of the microfilaria and further studies. Four animalsdied either during the trip to the laboratory or soon after arrival. Bloodsmears from twenty nine of the animals were sent to Dr. Mak Joon Wah for identi-fication of the microfilaria. The results of these identifications are seen inTable II.

Periodicity studies were undertaken to determine the optimum time to feedmosquitoes for transmission studies. Microfilaria counts were performed everytwo hours for twenty-four hours using the method of Ramachandran (9). The fol-lowing species of animals (with the number of animals of each species in paren-theses) were used in the'periodicity studies: Rattus koPatensis (2), Rattusrattus (1), Rattus sabanus (2), Rattus surifer (1), Menetes berdmorei (1),Tupaia glis (2).

RESULTS: Results of the microfilaria counts of the periodicity studies areseen in Table III. Numbers of animals used in this study are not sufficient toestablish a definite cyclic pattern. Periodicity studies involving more animalswill be conducted in the coming year.

Efforts in the future will concentrate on DunnifiZaria diZZi and DunnifiZa-ria ramachandrani. Studies will be directed at description of the life cycle ofthese filarids and trials using initially Aedes togoi and Aedes aZbopiatus formosquito infectivity and transmission studies.

REFERENCES

1.

WHO Expert Committee on Filariasis 2nd Report, WHO Tech. Report, 1967 Non359.

2. Manning, G.S., Harrison, B.A., piggs, C.L., and Wooding, W.L.,Brugia tupaia. SMRL Annual Report 1969.

Studies on

3. Manning, G.S., Wooding, W.L., Diggs, C.L., Harrison, B.A., Susceptibilityof Laboratory Animals to Brugia tupaia, SMRL Annual Report" 1970.

4.

Singh, M., Ho, B., BrienZia booZiati. A Filaria of the Malayan Forest Rat,Rattus sabanU8.~ Jpur. of He1. 77:127-133, 1973.

5. Singh, M., Ro, B. and Lim, B.L.~ Preliminary Results on ExperimentalTransmission of a New Filarial Parasite, BrienZia b~oZiati from Malayan WildRats to Laboratory Albino Rat. S.E.A.J.T.M. & P.R. 3:622, 1972.

6. Ewert, A., Ho, B.C.. The Fate of Brugia pahangi Larvae Immediately AfterFeeding by Infective Vector Mosquitoes., Trans. of the Royal Soc. of Trap.Med. Hyg.. 6l:No. 5, pp. 659-662.

7.. Dill, G.S., Tingpalapong, M., Gould, D.J., Weaver, R.E.1975.

SMRL Annual Report

63

8. Mak, J.W., Weaver, RoE., DunnifiZaPia diZZi sp. n. (Nematoda: Filaroidea)from Rattus koratensis in Thailand, Jour. of Hel.

9. Ramachandran, C.P. A Guide to Methods and Techniques in FilariasisInvestigations. Pusat Penylidelean Perubatan, Bulletin No. 15: p. 10, 1970.

64

Table I.

Species Number Caught Number Positive

31026151

332

191

1531

37159

90

00300005050

197

25

Bandiaota savi LeiHy7-omys sui7-usMenetes berdmoreiMenetes aervio7-7-orRattus berdmoreiRattus bukit bukitRattus exu 7-ansRattus korotensisRattus 7-oseaRattus rattusRattus mpid orbusRattus sabanusRattus sU1'iferTupaia g Us

Total 550 64

Table II.

Microfilaria SpeciesDunni!i!~ DunnifiZaria O1ougia Brien!iaramachandrani di Z U tupaia sergenti

Animal Species

Rattus sabanus * 10 4 0 0

Rattus surifer 0 3 0 0

Rattuskoratensis*

4 2 0 0

Rattus rattus 1 0 0 0

Menetes be2"dmo2"ei 0 0 0 1

Tupaia gUs 00 0 6

Total is more than 100% because both species of mic~ofi1ariapresent in the same animal in some cases.

*

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