UNIVERSITI PUTRA MALAYSIA

A STUDY OF CANINE DIROFILARIASIS IN KUALA LUMPUR

GURMEET KAUR DHALIWAL

FPV 1988 4

It is hereby certified that ...,/e have read this thesis entitled "A Study of Canine Dirofilariasis in Kuala Lumpur" by Gurmeet Kaur Dhaliwal, and in our opinion it is satisfactory in terms of scope, quality, and presentation as partial fulfilment of the requirements for the degree of Master of Science

. ����::tt.�i .

SULAIMAN HAJI MOHD. YASSIN, Ph.D. Professor/Dean of Graduate School

Universiti Pertanian Malaysia (Chairman Board of Examiners)

C.J. GASKELL, Ph.D. Professor

Small Animal Hospital Crown Street, Liverpool

United Kingdom (External Examiner)

.. ��?:!.� MOHD. FADZIL HJ. YAHAYA,

Associate Professor Faculty of Veterinary Medicine and Animal Science

Universiti Pertanian Malaysia (Internal Examiner)

CK(�� REHANA·ABD�i: Ph.D.

Faculty of Veterinary Medicine and Animal Science Universiti Pertanian Malaysia

(Supervisor/Internal Examiner)

This thesis was submitted to the Senate of Universiti Pertanian Malaysia and was accepted as partial fulfilment of the requirements for the degree of Master of Science.

Date: '1} '$ Jrii �,r'!£8 fa'�. � .. li � j:!'Jo}

, / ,

'*�J� . • • • • : • • • • c�� • • • • • J' • • • •

SULAIMAN M. YASSIN, Ph.D. Professor� Dean of Graduate Studies.

A STUDY OF CANINE DIROFI LARIASIS IN KUALA LUMPUR

By

Gurmeet Kaur Dhal iwal

D . V . M .

A thesis submitted i n partial ful fi lment o f the require �ents fo r the degree of Ma ster of Science in the

Faculty of Veterinary Medicine and Anima l S cience , Uni versiti Pe rtanian Ma lays ia .

June 1988

ACKNOWLEDGEMENT

I would like to express my sincere gratitude and appreciation to the following people :

( i ) Dr . Rehana Abdul lah Sani , my supervisor , for her invaluable advice , guidance and encouragement throughout this study�

( ii ) Professor M . R . Jainudeen and Dr . Sharifuddin Wahab for their encouragement, support and concern throughout the s tudy .

( iii ) Dr . G�orge Abraham and the Committee member s of the Society of Prevention of Cruelty to Animal s ( S . P . C . A . ) , for their patience , help and kind cooperation , without which this study would not have been pos sible .

( iv ) The Climatic division of Department of Petaling Jaya furnishing the required data .

the Meteorological for efficiently

( v ) Private practitioners for unselfishly sharing their time and informa tion required .

(vi ) The Faculty of Veterinary Medicine and Animal Science for providing the financial s upport for this pro ject .

( vii ) Ms . Josephine Low manuscript .

for diligently typing the

( viii ) My famil y and friends for a l ways being there for me.

iii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TABLE OF CONTENTS . . . ... . .. .. . ... . ... . .. . . .. ... . . . . . . . . . . . . .. . .. ..

LIST OF TABLES . ... .. .. .. .. ... . . .. .. .. . . . ... . . . . . . . . . . .. .. G .. . . . .. .. .. .

LIST OF FIGURES ... .. . ... . ... ... . . .. ... . . . . . . . . .. . ... .. ... .. . . .. ... .. .

ABSTRACT .. .. .. -. . ... .. . .. . . . ... . ' . . .. . . . . .. . . . . . . . .. .. .. ... .. . .. . .. .. .. .. .. ..

CHAPTER 1 - INTRODUCTION

CHAPTER 2 - LITERATURE REVIEW . •• . ••••••••••••••••••• . .

Final and Intermediate Hosts

Life Cycle

Morphology .. .. ' . .. .. .. . . .. . . .. .. .. .. .. .. .. .. . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..

Prevalence

Host Risk Factors • • •••••• • • • ••••••••••••••••••• • •••

Diagnostic Tests • • • ••••• • •• • ••••••••••• •••••••••••

Enzyme -Linked Immunosorbent Assay

CHAPTER 3 - MATERIALS AND METHODS

Ani mals

Study period

Blood samples

Necropsy

Enzyme-Linked Immunosorbent Assay

iv

PAGE

iii

iv

vii

ix

x

1

4

4

5

6

7

9

11

13

20

20

20

20

21

21

PAGE

Data on Pet Dogs ••••••••••••• • •••••••••••••••••••• 25

Cl imatic Daj:a ... . . . . . . . . . . . . . . . . . . ,til •••• • ••••••• • •••• 2 5

Survey of Private Practitioners . . . . . . . . . . . . . . ... . . . . 25

CHAPTER 4 - RESULTS •••••••••••• • •••• • ••••••••••••••••• 26

Prevalence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Monthly Prevalence of Q. immitis Infection •••••• • • 26

Influence :of Rainfall and Temperature on the Preva�ence of D . immi tis Infection

Influence of Hos t Factors on the

31

Prevalence of D. immitis Infection • • •••••••••••••• 31

Lengths o f Adul t D. immi ti s and Mal e to Female Ratios •••••• • ••••••• • • . •••• . • •• . . . . •••••• . • 3 5

The S pecificities , Sensiti vities and Accuracies of the Direct Smear, Modified Knott ' s Concentration Technique ( K . C . T . ) and the ELISA.- ••• .

-••••• •••••••••••••••••••••••• • e, . • 36

De velopment ·of the ELISA • • •••••••••••• • ••••••••••• 3 7

Survey of Private Practi tioners 4 3

Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Therapy 4 3

Prophylaxis 46

Problems Encountered 48

CHAPTER 5 - DISCUSSION •••••••••• • ••••••••••••••••••••• 50

CHAPTER 6 - SUMMARY AND CONCLUS IONS 70

v

PAGE

BIBLIOGRAPHY 7 4

APPENDICES 7 9

Appendix A : Data on Dog, Pos t Mortem and Diagnostic Tests •••••••••••••••••• 7 9

Appendix B : Questionnaire 88

vi

'IABLE NO.

1

LIS'I OF 'IABLES

PREVALENCE OF D. immitis IN 'IHE S'IRAY DOG POPULA'IION

INFEC'IION

2 PREVALENCE OF D. immitis IN 'IHE

PAGE

2 7

OWNED DOG POPULATION ••••• • • • • • • • • • • •• • • • • • 2 7

3 NUMBER OF STRAY DOGS HAVING ADUL'I WORMS AND MICROFILARIAE, MICROFILARIAE ALONE, ADULT WORMS ALONE AND NEGATIVE FOR BOTH ADULT WORMS AND MICROFILARIAE • ••••••• • • • • • •• • • • • 28

4 NUMBER OF MICROFILARAEMIC AND OCCUL'I ( DUAL' SEX OR S INGLE S EX ) INFECTIONS IN STRAY DOGS •••••••••• • • • • • - . . . . . . . .. .. . . . . 28

5 MONTHLY PREVALENCE OF D. immitis INFECTION BAS ED ON NECROPSY IN 'IHE STRAY DOG POPULATION •••••••••••••••••••••• 29

6 RELATIONSHIP BETWEEN PREVALENCE OF D. i ffimitis I NFECTION AND HOS'I AGE IN S'IRAY DOGS e- . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 33

7 RELATIONSHIP BETWEEN PREVALENCE OF D. immitis INFECTION AND HOST SEX IN STRAY DOGS • • • • • ••• ••••••• . - . . . . . . . . . . . . . . . . . 3 3

8 RELATIONSHIP BETWEEN 'IHE PREVALENCE OF D. immi tis I NFECTION AND HOST COAT COLOUR IN S'IRAY DOGS ••••• • •••• • • ••••••

9 RELATIONSHIP BETWEEN THE PREVALENCE OF D. immitis INFECTION AND HOST

34

BODY WEIGHT IN S'IRAY DOGS. . . . . . . . . . . . . . . . . . 34

10 AVERAGE L ENG'IHS AND RANGE OF LENG'IHS OB'IAINED FOR ADUL'I MALE AND FEMALE

11

D. immitis

NUMBER FEMALE )

OF DUAL AND S INGLE ( MALE OR SEX INFEC'IIONS AND 'IHE

AVERAGE RA'IIOS OF MALE TO FEMALE

35

WORMS • • • • • .• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 36

1 2 RESUL'IS OF 'IHE D.S., K.C.T. AND ELISA • • • • • 3 8

Vll

TABLE NO. PAGE

13 THE SENSITIVITIES, SPECIFICITIES AND ACCURACIES OF THE D . S. , K . C.T . AND ELI SA • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 38

14

15

1 6

1 7

1 8

1 9

ABSORBANCE VALUES USING DYNATECH IMMULON MICROTITRE PLATE AND PLAIN MICROTITRE PLATE AT ANTIGEN CONCENT­RATION OF 2 UG/ML, CONJUGATE DILUTI ON AT 1 /1 000 AND TWOFOLD SERA DILUTI ONS OF i/200, 1 /400 , 1/800, 1/1600 AND 1/3200 • • • • • • • • • • • • • • • • • • • • • • • • • 42

DIAGNOSTIC TESTS FOR INFECTI ON USED BY PRACTITIONERS IN KUALA PETALING JAYA

D . imrnitis 1 2 PRIVATE

LUMPUR AND

TREATMENT USED BY

OF CANINE DIROFILARIASI S 1 2 PRIVATE PRACTI ONERS

44

IN KUALA LUMPUR AND PETALING JAYA • • • • • • • • • 45

MICROF I LARICIDES INFECTI ON USED

FOR D . BY 1 2

immi tis PRIVATE

PRACTITIONERS IN KU�LA LUMPUR AND PETALING JAYA

SUPPORTIVE DRUGS TREATMENT OF CANINE

USED IN . THE DIROF I LARIASIS

BY 1 2 PRIVATE PRACTITIONERS IN KUALA LUMPUR AND PETALING JAyA • • • • • • • • • • • • •

NUMBER OF B LOOD EXAMINATI ONS CONDUCTED AFTER TREATMENT OF D . immitis INFECTI ON BY 1 2 PRI VATE PRACTITIONERS IN KUALA LUMPUR AND PETALING JAYA • • • . • • • • • • • • • . • • • • • • . • . • • • • • .

45

47

47

20 DRUGS AND SCHEDULES USED FOR THE PROPHYLAXI S OF CANINE DIROFI LARIASI S BY 12 PRIVATE PRACTITIONERS IN KUALA

2 1

2 2

LUMPUR AND PETALING JAYA • • • • • • • • • • • •

PROPHY LAXIS COMMENCEMENT FOR D . immi tis PREVENTION BY 12 PRIVATE PRACTITI ONERS IN KUALA LUMPUR AND PETALING JAYA • • • • • • • • • • • . • • • • • • . • . • . . • • • • •

DATA ON DOGS, DIAGNOST I C TESTS

POST MORTEM AND

v i i i

48

49

79

LIST OF FIGURES

FIGURE NO. PAGE

1 THE MONTHLY PREVALENCE OF D . immitis I NFECTION IN 200 STRAY DOGS AROUND KUALA LUMPUR FROM FEBRUARY 1 986 TO JANUARY 1987

2 MEAN MONTHLY RAINFALL AND PREVALENCE OF D . immitis I NFECTION I N STRAY DOGS AROUND KUALA LUMPUR FROM FEBRUARY 1986 TO JANUARY 1987 ••••••••••••

3 T ITRATION OF FOUR CONCENTRTIONS OF

4

5

AGAINST POS ITIVE AND ANTIGEN NEGATIVE 1/400

DOG SERA AT DILUTION OF AND CONJUGATE DILUTION AT

1/1000 •••••••••••••••••••••••••••••••••••

'I I 'IRA'I I ON OF SIX DILU'II ONS OF POS I'IIVE AND NEGATIVE DOG SERA AGAINST ANTIGEN CONCENTRATI ON A'I 2 UG/ML AND CONJUGATE DILU'IION AT 1/1000 •••••••••••••••••••••••••••••••••••

T ITRA'IION OF FOUR DILU'IIONS OF CONJUGA'IE AGAINS'I POSITIVE AND NEGATIVE DOG S ERA A'I DILU'II ON OF 1/400 AND AN'I IGEN CONCENTRTI ON A'I 1 UG/ML e- • • •••••••••••••••••••••••••••••••

ix

30

32

3 9

4 0

4 1

An abs tract of the thesis presented to the Senate of Universiti Malaysia in partial fulfi lment of the requi rements

fo r the degree of Master of S cience .

A STUDY OF CANINE DIROFI LARIASIS I N KUALA LUMPUR

by

Gurmeet Kaur Dhaliwal

June 1988

Supervisor Dr. Rehana binti Abdul lah Sani

Faculty Veterina ry Medi cine and Animal S cience

Although much importance has been placed on human

filari as i s , work on canine filariasis is limited in this

country . This s tudy was carried out to obtain a general

overview on the status of canine di rofi lariasis in Kuala

Lumpur. Throughout a one year s tudy , parasitologica l records �

were s tudied and blood samples were col le cted f rom stray dogs

whi ch we re later necropsied . Blood samples were subjected to

the modified Knott's concentration technique, the direct smear

and the enzyme-linked immunosorbent assay whi ch was developed

using the adult worm antigen . Information was obtained from

private practitioners by the use of questionaires . The period

prevalence of canine dirofilariasis was 42. 0 percent and 1 0 . 0

pe rcent within the stray dog and owned dog populations

re specti vely . The monthly pre valence indicated that

dirofi larisis was prevalent throughout the year and was not

x

significantly infl ue nced by rainfal l and tempe rature changes i n

this area . Pre vale nce was significantly highe r i n dogs above

f i ve years of age ( p < 0 . 001 ) and dogs of body weights above

15 kg ( p < 0 . 05 ) . Host sex a nd coat colour did not i nflue nce

the distribution of dirofilariasis . Occult cases comprised 4 7

pe rcent of the positi ve cases of dirofilariasis. Of these , the

percentages of single-sex and dual -sex i nfections were 2 9

pe rcent and 1 8 percent respe ctively. The range of l e ngth of

the female D. immiti s was 1 2 . 3 cm to 31 . 5 cm, while that for

the male was 8. 7 cm to 1 9 . 5 cm . The a ccura cies of the modified

Knott's concentration technique , the dire ct smear a nd the

e nzyme-l i nked immunosorbent as say were 80 . 5 pe rcent , 7 7 . 5

percent and 53 . 0 percent respe cti vel y . The s urvey of private

practitioners i ndicates that the mai n adulticide ,

mi crofilari cide and prophylacti c drugs currentl y being used are

thia cetarsamide , l evamisole a nd diethy l carbamazine . The di re ct

smear a nd the fi ltration tech nique are the mos t freque nt ly used

diagnostic tests . Side-effects of drugs used, client ' s

wi l li ngness to bear cos t of treatment and the lack of cli ent

compl ia nce i n completing the course of medi cation are the mai n

problems faced. b y pri vate practitioners i n the treatme nt of

ca ni ne di rofilariasis ."

xi

Abstrak tesis yang dikemukakan J\.<:!VOUO u<:!llat Univers iti Pe rtanian Malaysia bagi memenuhi sebahagian da ripada syarat­

syarat untuk ijazah Maste r Sains

KAJIAN DIROFILARIASIS ANJING DI KUALA LUMPUR

oleh

Gurmeet Kaur Dha l iwal

Jun 1988

Penyel ia Dr. Rehana binti Abdullah Sani

Fakulti Kedoktoran veterinar dan Sains Peternakan

Walaupun banyak kerja-kerja telah dijalankan ke atas

filarias is manusia , k erja-kerja filarias is anj ing adalah terhad

di nege ra ini. Kaj ian ini telah dijalankan untuk mendapatkan

pandangan menyeluruh mengenai s tatus d irofilarias is anj ing di

Kuala Lumpur . Dalam mas a setahun , rekod parasit dikaj i dan

sampel- sampel darah telah d iambil dari a njing-an j ing l iar yang

kemudiannya dibedah s iasat . Teknik ' Modif ied Knott's

concentration', smear terus dan 'enzyme-l inked immunosorbent

as say' telah dijalankan ke atas sampe l darah .

telah digunakan sebaga i antigen dal am

Cacing dewasa

'enzyme-l inked

immunosorbent assay . ' Maklumat telah didapati dari k l inik-

k l inik swasta me lalui ka j i sel idik . Prevalen tahunan

dirofila riasis an j ing l iar ia lah 42 peratus manakala prevalen

ke atas anjing be rtuan ialah 10.0 pe ratus . Dari prevalen

xii

bulanan, di rofi lariasis adalah pre valen sepan j ang tahun dan

tidak dipengaruhi secara keertian oleh pe rtukuran hujan dan

s uhu di kawasan ini . Keertian pre valen adalah lebih tinggi

pada an j ing yang berumur lebih lima tahun ( p < 0 . 001 ) dan

an j ing

Jantina

yang

dan

berat

warna

badan lebih dari 1 5 kg ( p < 0 . 05) .

bulu tidak mempengaruhi taburan

di rofi lariasi s . Empat pul uh tujuh peratus daripada kes-kes

dirofilariasis adalah kes ' occult ' . Dari 47 peratus ini , 29

peratus adalah infeksi ' single-sex ' dan 1 8 peratus adalah

infeksi ' dual -sex ' . Pan jang purata D . immitis betina ialah

1 2 . 3 cm ke 3 1 . 5 cm, manakala pan j ang purata j antan adalah 8 . 7

cm ke 1 9 . 5 cm . Ketepatan teknik ' modi fied Knott ' s

concentration ' adalah 80 . 3 peratus , smear terus , 7 7 . 5 peratus

dan ' enzyme-linked immunosorbent a ssay ' , 5 3 . 0 peratus . Kaj i

selidik dari klinik-klinik swasta menun jukkan ubat untuk

membunuh cacing dewasa, mikrofi laria dan ubat prophylaktik yang

sering digunakan ialah thiacetarsamide , levami sole dan

diethylcarbamazine . Smear terus dan teknik turas adalah

u j ika j i diagnostik yang biasa digunakan . Kesan sampingan ubat

yang digunakan, kerelaan tuanpunya anj ing untuk menanggung kos

perubatan yang tinggi dan kesanggupan mereka untuk menghabiskan

jangkamasa perubatan adalah masalah-masalah utama yang d ihadapi

oleh klinik-klinik swasta dalam pengubatan dirofi lariasis

an j ing .

xiii

CHAPTER 1

INTRODUCTI ON

In Malaysia, only a few s pecies of fi larial worms have

been known to infect dogs . Brugia pahangi has been recorded

from dogs in East Pahang ( Reid and Laing , 1 95 7 ) , while the

s ubperiodi c Brugia malayi has been establi shed in dogs

experimentally with resulting mi crofilaraemia ( Reid and Laing,

1959 ) . Among all the filarial infections here , the most

commonly re�uLLed canine filarial worm is Dirofilaria immitis .

This is also the mos t pathogenic filarial worm in dogs as the

infection may ca use cardiopulmonary insuffi ciencies whi ch can

eventually result in the death of the infected animal . The

pre valence rate of Dirofilaria repens has been reported to be

5 . 6 percent in cats in this country ( Mak, 1984 ) and a lthough

this filarial worm i s known to infect dogs , no s uch canine

infections have been reported . Infections by other fi larial

worms s uch as Dipetalonema reconditum, D . grassi and D .

dracunculoides have not been reported to occur in dogs in this

co untry .

There have been a few reports on t he pre valence rate

of Dirofilaria

Retnasabapathy

and Lee , 1 981 ;

immi tis infection ( Mul lin,

and Khoo , 1 9 76 ; Kan et a l . , 19 7 7 ;

Ra jamanickam et a l . , 1981 ) .

1

1970;

Faridah

However,

2

there is no information avai lable on the current status of the

drugs being used for prophylaxis and t reatment, diagnostic

tests employed and problems faced by priva te practitioners with

regard to .dirofilarias is in this country . The diagnostic tests

widel y used in Malaysia rely upon the detection of circulating

microfilariae . Thus , cases of occul t dirofi lariasi s , that is ,

heartworm infected dogs without circulating microfilariae , are

a problem for diagnosis . Serological tests such as the indirect

fluorescent antibody test ( Ellsworth and Johnson , 197 3 ; Wong

and Suter, 197 9 ; Dawe et al . , 1 980) and more recently, the

enzyme-linked immunosorbent assay ( Scholtens and Patton , 198 3 ;

Wagner et al . , 1984; Grieve et al . , 198 6 ) have been empl'oyed

and show promising results in helping to diagnose cases of

occult d irofilariasis .

In view o f the current si tuation of d irofilariasis in thi s

country, thi s study was undertaken to establish the following : -

i) The period prevalence of the disease in the s tray and

owned canine population .

ii) The trend of the prevalence of canine dirofi lariasis

monthly for the period o f one year .

iii ) The influence of weather such as rainfal l

temperature o n the pre val ence o f the disease .

and

iv ) Influence of host factors n amely sex, age, coat

colour and body weight on the prevalence of disease.

3

v ) The length o f the adult worm and its sex ratio .

vi ) The sensiti vity, specificity and accuracy of the

dire ct smear a nd the modified Knott ' s concentration

technique in detecting dirofilariasis .

vii ) The de velopment of the e nzyme-l inked immunosorbent

assay as a diagnostic tool .

vii i ) The current s tatus o f drugs used for prophylaxis and

treatment , diagnostic tests employed a nd problems

bei ng faced by pri vate practitioners i n Kuala Lumpur

a nd Peta l i ng Jaya with regard to canine

dirofilariasis .

CHAPTER 2

LITERATURE REVIEW

FINAL AND INTERMEDIATE HOSTS

Dirofilaria immitis i s a fi larial parasite which has been

reported to infect a wide range of mammalian hos ts such as

dogs , cats , bears , horses , orang utans and even humans .

Howe ver, patent infections only occur i n dogs , cats , wi ld

feline s , Californian sea lions and ferret s (otto , 1975) . Among

tnese, only the dog acts as the main reservoir of infection as

well a s being the main hos t . Once infected , the canine hos t can

develop polysystemic disorders with cardiopulmonary signs

occuring most frequently . Congestive heart failure e ventually

develops, some times accompanied with as sociated organ

malfunction ( namely the kidney and l i ver ) , thus ultimately

resulting i n the death of the i nfected animal ( Rawlings, 1981).

The transmis sion of the infection depends sole ly upon the

mosquito which acts a s the intermediate hos t . Thi s i s because

part o f the development o f the parasite occurs within the

mosquito itse l f . Approximately 70 species (Ludlam e t al . ,

1 9 70 ) of the many known species of mosqui toes in the world

have been reported to allow devel opment of Q. immitis larvae .

In Malaysia, l i mited i nformation i s avai lable on the species of

mosqui toe s that act as the i ntermediate host . Cheong e t a l . ,

4

5

( 1981 ) confirmed Armigere s suba lbatus to be a primary vector of

D. immiti s . Mansonia species have bee n known to harbour the

infection but has been sugge sted to play a less important role

in the transmi ssion of Q. immi tis because they are uncommon in

the city. A . subalbatus however, is a common urban mosqui to in

Malaysia which breeds in septic tanks and feeds readily on man

and domestic anima l s such as dogs and birds ( Cheong et al . ,

1981). In Singapore , Culex fatigans , Aedes aegypti and Aedes

albopictus were found to support the development of

D . immi t i s . �hese species are also found i n Peta l i ng Jaya and

Kuala Lumpur and may also act as intermediate hosts here

( Chel lapah and Chel lapah , 1968 ) .

LIFE CYCLE

The adult worm resides in the pulmonary artery and the

right ventricle of the hear t . Occas ionally the 'worms may be

found in the left s ide of the heart, the anterior and poste rior

vena cavae and in ectopic sites such as the peritoneal cavity

( Kelly, 1978 ) . The viviparous female releases the unsheathed

larvae, the microfilariae , which circulate in the bloods tream .

These microfi lariae have a l so been reported to cross the

placenta and i nfect the foetus i n pregnant bitches ( Mantovani

and Jackson, 1 9 66 ) . �hus, circulati ng microfilariae of

D. immitis may be found in puppies less than s ix months of age .

Howe ver , these microfi lariae cannot develop into adul t

heartworms since the mosquito i s required to complete the 1ife-

6

cycle .. Therefore the microfi lariae is an end-stage unless

i ngested by a mosquito, and can circulate for as l ong as two

years ( Newton , 1968) .

After ingestion by a female m osquito, the microfilaria

undergoes two moul ts after which it becomes the i nfecti ve third

stage . This takes about 14 to 21 days under optimal temperature

and humidity ( Kelly, 1978) . The third s tage larva i s deposited

on the s kin of the d og when the mosquito feeds . I t acti vely

mi grates to a resting site in the s ubcutaneous , s ubserosal

tis s ue s , muscles or fat . Here i t moul ts t o the f ourth stage

larva ( 18 mm ) long at nine to 12 days after infection and to

the fi fth stage larva ( 80 mm ) long at 70 to 80 days after

infection . At approximately three months after infection , the

immature adult begins migrating to the right ventricle and

adjacent vesse l s . Microfi lariae are present in the uterus of

the. worm six months after infection by the mosquito and appears

s hortly in the peripheral blood ( Kume and Itagaki , 1955). These

adul t worms have a long biotic l ife and infections have been

reported to be patent up to seven years ( Newton, 1968) .

MORPHOLOGY

The adul t worms are l ong and s l e nder and pos sess a thick

c uticle . The ma les are relatively shorter tha n the females and

possess a distinct spiral ·tail . Ma les mea s ure from 1 2 cm to

18 cm ( Webber, 1955; Kel l y , 1978 ) . Sou l sby ( 1976 ) reported a

ra nge of le ngth of 1 2 cm to 16 cm. The fema le wh ich i s

7

viviparous, has the vulva s ituated at the anterior end just

caudal to the oesophagu s . Female worms mea sure between 25 cm to

30 em ( Soulsby , 1976; Kel l � 1978), whi l e Webber ( 1955)

reported lengths of 1 5 . 1 em to 30 . 0 cm .

The microfi lariae found in circul ation measure 290p to

340 p ( Ke l l y , 1 9 78 ) . Mak et a l e ( 1 980 ) reported an average

length of 234 . 8p and a width of 8 p. The microfi laria of

D . immitis can be di fferentiated from that of Dipetalonema

reconditum a s the former has a tapered head and a straight

tai l , whi l e the l atter has a blunt anterior end and a button

hooked tail ( Lindsey, 196�) . However , these characteristics are

not always eas i l y recognised and frequently a misdiagnosis can

be made . More recent l y , these species may be differentiated by

demons trating the acid phosphatase activity via the

precipitation of a pink dye ( Chaul ifaux and Hunt, 1971 ) . The

D . immitis microfi laria wil l take the pink dye at t he anterior

excretory pore and anus while the entire microfilaria of

D . reconditum stains pink.

PREVALENCE

A wide range of prevalence rates for dirofi lariasis has

been reported in Malays ia . Mul l in ( 1970) reported a preva lence

of 30 . 4 percent . In hi s study , 101 s tray dogs from Kuala Lumpur

and Petal ing Jaya were screened for circulating microfi l ariae

us ing the thick blood film technique. Necropsy revealed that 28

dogs had D. immiti s i nfection , whil e the thick blood film

8

technique detected only 2 2 of these infected dogs . In another

study, necropsy upon 764 stray dogs from Kua la Lumpur and

Petaling Jaya over a six year period , revealed a pre valence of

2 5. 8 percent ( Retnasabapathy and Khoo , 1 9 76 ) . �he study also

revealed that there was an i ncreasing trend i n the prevalence

of D . immitis i nfection f rom 1 968 to 1972 . Followi ng thi s , i n

1 9 7 3 and 1 9 7 4 , the pre vale nce rates dropped b y almost eight

percent a nd 10 percent respectively compared to the figure i n

1 97 2 ( 36 . 6 percent ) . �hey attributed this t o be d ue t o the

des truction of a large n umber of stray dogs i n response to a

case of rabies in March 1 973 . Kan et a l e ( 1977 ) reported a

prevalence rate of 32 . 4 percent . In his study , a total of 340

pet dogs in a nd around Seremban were s creened usi ng the thick

blood film technique , the chamber method and the mi l l ipore

fi l te r method. Faridah and Lee ( 1981 ) conducted a pre valence

s tudy of dirofi lariasi s in pet dogs which were brought to the

Small Animal C l i nic of the Faculty of Veteri nary Medici ne and

Animal Science , Uni versiti Pertanian Malaysia. �he direct smear

and modified Knott ' s concentra tio n technique were emplo yed i n

the screeni ng of dogs for the presence of circulat i ng

microfilariae . Of 4 30 dogs s creened , 1 8 . 1 percent were found

to be positive for circulating microfilariae . �hi s figure is

comparatively lower tha n those reported by other workers

( M ul l i n , 1 970 ; Ka n et al . , 1977 ) and it was s uggested that this

was due to a s i ngle blood sampl i ng where undetected

mi crofilaraemia may have exi sted . �he lowe st prevale nce rate

of D. immi ti s.i nfection reported was 1 2 . 0 percent ( Ra j ama nickam

9

et al . , 1981 ) . In this s tudy , 2 3 3 dogs were examined for

circulating microfilariae usi ng the direct smear , the modified

Knott ' s concentration technique and the mi l l ipore fi lter method

( ' Difil ' test-kit, EVSCO Pharma, U. S . A . ) . The dogs studied were

pet dogs from various veterinary clinics in Kuala Lumpur ,

Petaling Jaya and Klang .

HOST RISK FACTORS

In a s tudy by Kan et al . ( 19 7 7 ), the prevalence rates of

D . immitis infection among pedigree and non-pedigree dogs were

compared . Of a total of 3 70 dogs , pedigree dogs had a

significantly higher pre va lence rate ( 39 . 2 percent ) than the

mongrel s ( 2 7 .4 percent ) . Among the pedigree dogs , the Boxers

had the highes t incidence of infection followed by the

Dobermans . , Daschunds and Alsations . I t was also apparent from

this study that short haired dogs were more prone to infection

than the l ong haired breeds . Thi s was similarly reported by

stewart e t al. ( 1979 ) . Kan e t a l . ( 197 7 ) a lso noted that there

was no signi ficant difference in the distribution of infection

between males and females . This is in agreeme nt with the

findings of Gli ckman et al e ( 1 984 ) and Martin and Collins

(1985 ) . Selby et al . (1980 ) noted a higher prevalence of

heartworm i nfection in hunti ng and sport ing dogs . He attributed

thi s fi nding to the dogs be i ng more exposed to the infected

mosquitoes duri ng hunti ng and trai ning. Selby et al . ( l 980 ) a l s o

found that l arger dogs (body we ight >22 kg ) had a higher

10

pre valence compared to smaller dogs ( body weight <1 4 kg ) and

s tressed that the breed of the dog should a lways be taken i nto

account . However , contradictory findings were reported by

Martin and Col l i ns ( 1 985 ) who reported that there was no

correlation between the body we ight of the dog and the

prevale nce of the dirofilarias i s . It was summarised by Selby

et ale ( 1 980 ) �hat the i ntact, large male hound, four to seven

years of age , has the highes t risk of bei ng i nfected while dogs

of smaller breeds , less than two years old, spayed females and

castrated males have the lowest risk of being infected. S tewart

et ale ( 19 7 9 ) screened a total of 8 1 dogs i n North �exas and

\

reported a pre valence of 7 . 4 perce nt . Adult heartworms were

recovered from a s ignificantly higher percentage of male dogs

than females and the male dogs harboured significantly greater

number of adult worms than female dogs . Similar findings of the

prevalence of infection being higher i n males was reported by

Faridah and Lee ( 1 981 ) .

�he pre valence o f infection with D . immit i s was reported

to increase with the age of the host ( Stewart et al . , 1979 ) .

�hi s i s probabl y becaus e , the older the dog, the greater the

chances of it being bitten by i n fected mosqui toes . �his f i nding

was also reported by Faridah and Lee ( 1 981 ) who noted a

significantly higher i ncidence among older dogs ( >4 years ) .

In a study conducted i n Aus tralia, 3 3 1 greyhounds were

scree ned for D. immi tis using the fi l tration technique

( Martin and Col lins , 1985 ) . The results of t h i s s tudy s howed