Sains Ma1aysiana 28: 1-8 (1999)                                                                                                                    Sains Hayat/

                                                                                                                                                                                Life Science

Jangkitan Trypanosoma lewisi Pada Tikus Liar

(Infection of Trypanosoma lewisi in wild rats)

Zainal-Abidin Bin Abu Hasan & Noor Azmi Ahmad

Jabatan Zoologi, Fakulti Sains Hayat

43600 UKM Bangi, Selangor D. E. Malaysia

ABSTRAK

Sejumlah 23 ekor tikus liar Rattus rattus diardii yang diperolehi dari kawasan Bandaraya Kuala Lumpur telah digunakan bagi menentukan beberapa aspek jangkitan parasit Trypanosoma lewisi pada tikus ini. Caletan darah segar, caletan darah nipis terwarna dan teknik lapisan darah berbuih berkuantitatif (QBC) telah dilakukan untuk menentukan parasitemia dan prevalens jangkitan parasit. Serum tikus juga telah diperolehi bagi menentukan titer antibodi IgM dan IgG menggunakan teknik antibodi berpendar imun. Adalah didapati bahawa prevalens jangkitan parasit adalah 21.7% (5/23) dan parasitemia keseluruhan pada tikus yang terjangkit adalah rendah dan puncak parasitemia tidak melebihi lima peratus. Bilangan parasit berkurangan secara perlahan-perlahan dan parasit lenyap dari edaran darah pada minggu kelapan. Sepanjang tempoh jangkitan, peringkat-peringkat parasit berikut telah muncul dan dikenalpasti iaitu metasiklik tripomastigot awal yang diikuti dengan peringkat pra-pembahagian epimastigot, peringkat pembahagian belahan-dua tak sekata epimastigot, peringkat pembahagian belahan-berganda tak sekata epimastigot dan peringkat 'rosette', peringkat perantara dan diakhiri dengan peringkat dewasa. Semua tikus yang terjangkit dan beberapa yang lain yang tidak terjangkit mempunyai IgM dan IgG terhadap parasit ini. Apabila tikus-tikus ini diberikan jangkitan cabaran dengan parasit T. evansi yang lebih ganas, titer IgM dan IgG didapati meningkat tetapi walau bagaimanapun, peningkatan titer ini tidak menghalang kematian tikus. Didapati juga antiserum terhadap T. lewisi menunjukkan gerakbalas silang yang nyata terhadap antigen T. evansi. Hasil kajian ini menunjukkan bahawa corak jangkitan alamiah T. lewisi pada tikus liar R. rattus diardii adalah tidak patogenik namun begitu ia melibatkan gerakabalas keimunan yang membawa kepada pembentukan IgM dan IgG. Antibodi yang terbentuk terhadap T. lewisi adalah bersifat spesifik dan tidak dapat memberi perlindungan terhadap jangkitan T. evansi.

ABSTRACT

A total of 23 wild rats, Rattus rattus diardii obtained from Kuala Lumpur City area was used to study some parasitological aspects of the infection of  Trypanosoma lewisi in these animals. Fresh blood smears, stained thin blood smears and quantitative buffy coat analysis (QBC) were prepared to determine parasitaemia and the prevalence of the infection. Serum samples were also collected to determine IgM and IgG antibody titres using the immunofluorescence antibody technique. It was found that the prevalence rate of the infection was 21.7% (5/23) and the parasitaemias of all infected rats were low throughout the period of the observation and that the peaks never exceeded five percent. The number of the parasites decreased slowly and the parasites completely disappeared from the blood by the eighth week. Developmental stages of the parasite were observed and identified during the period of the infection starting with the early metacyclic trypomastigote form and followed by pre-divisional epimastigote, unequal binary epimastigote, unequal multiple epimastigote, rosette form, intermediate form and terminated with the adult forms. All infected and some uninfected rats showed they had considerable IgM and IgG titres to T. lewisi. When these animals were challenged with a more virulence parasite T. evansi, they were not protected and all succumbed to infection although they had elevated antibody titres following challenge and that antisera to T. lewisi showed good cross-reactions with T. evansi antigens. These results seem to suggest that in nature, T. lewisi causes a non-pathogenic type of infection in the wild rats. Nonetheless, this non-pathogenic infection proved to involve some immunological responses in particular in the production of IgM and IgG antibodies. These antibodies are species specific and can not protect the rats

from T. evansi infection.

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