Wild Rats as Reservoir of Trypanosoma Lewisi in Northwest India

Research Article

Austin J Pathol Lab Med. 2014;1(2): 3.

Wild Rats as Reservoir of Trypanosoma Lewisi in Northwest India

Rayat CS* and Vasishta RK

Department of Histopathology, Postgraduate Institute of Medical Education and Research, India

*Corresponding author: Rayat CS, Department of Histopathology, Postgraduate Institute of Medical Education & Research, Chandigarh-160012, India

Received: September 01, 2014; Accepted: October 09, 2014; Published: October 13, 2014


Trypanosomiasis is a drowsy condition caused by parasitization by extracellular hemoflagellate protozoa known as trypanosome. Pathogenic and nonpathogenic species of trypanosomes occur in a wide range of vertebrate hosts, ranging from fish to mammals. The host and vector happen together in the same habitat but their interaction could be influenced by feeding preferences of the vector due to variable climatic conditions. Trypanosoma lewisi is a natural hemoflagellate of rats (Rattus species) and other rodents in all areas of the world and considered to be nonpathogenic for human beings, however, in the recent past three reports of T. lewisi infection in infants had appeared form the coastal states located in the Southwest India. Anthropozoonosis has been well documented in trypanosomiasis and is a point of caution as animal reservoirs of a variety trypanosomes are around. Suppressed immune status of human hosts and changing feeding preferences of the vectors may complicate the scenario. A case report of Trypanosoma evansi infection in human adult from India could be considered as a flip in the vector behavior and pathogenicity of T. evansi, relatively due to over exposure to vectors and sub-optimal immune status of infected person. We could cite only single report about the detection of T. lewisi in the blood of wild rat (Rattus norvegicus) from India. Changing scenario of T. lewisi pathogenicity in infants, through the last few years in India, prompted us to conduct this study to detect the natural reservoir of T. lewisi in Northwest India. In this study we figure out the detection of T. lewisi infection in wild rats at Chandigarh; geographically located in northwest India.


DNA: Deoxyribonucleic Acid; fps: Frames per Second; cm: Centimeter; μm: Micrometer; g: Gram


Trypanosomiasis is popularly known as sleeping sickness. It is a somnolent condition, resulting from parasitization of blood by extracellular hemoflagellate protozoa known as trypanosome. This protozoan belongs to the order kinetoplastida and members of this order are recognized by the possession of kinetoplast, a DNA containing particle close to the flagellar basal body [1]. Pathogenic and nonpathogenic species of Trypanosoma occur in a wide range of vertebrate hosts, ranging from fish to mammals and are transmitted by blood sucking insects and other vectors [2].

Trypomastigote and epimastigote stages are common to nearly all trypanosome life cycles. There is considerable difference between the specific infections in different mammals and transmitting vectors [2]. Major species of the hemoflagellate pathogenic to man are: Trypanosoma gambiense and T. rhodesiense, which cause African sleeping sickness, and T. cruzi causing South American Trypanosomiasis or Chagas's disease. Trypanosoma lewisi is a nonpathogenic, natural blood parasite of the common black and brown rats in all parts of the world. In men the disease is transmitted by bites of the insect vector, tsetse fly (Glossina species), but T. lewisi is transmitted by rat fleas [2-4]. American trypanosomiasis can be transmitted to humans by blood sucking insects of the genra Tratoma, Rhodium and Panstrongylus [5]. Some trypanosomes of animals are pathogenic and cause morbidity and mortality in livestock. Trypanosoma brucei is found in wild game and domestic animals in tropical Africa. Trypanosoma evansi causes 'surra' in horses. Blood feeding tabanids are responsible for the transmission of T. evansi in horses and cattle. Trypanosoma vivax and T. congolense cause disease in domesticated and wild cattle and are transmitted by tsetse flies. Tsetse flies become infected by feeding on the blood of an infected man or animal. Trypanosomes taken up in blood meal by tsetse fly migrate to the cavity between peritrophic membrane and gut wall and multiply there. The life cycle in tsetse fly takes about three weeks. Trypanosoma lewisi is the natural parasite of rats (Rattus species) transmitted by rat fleas; by Nosopsyllus fasciatus in temperate regions and Xenopsylla cheopis in the warmer areas of the world [2]. Trypanosoma lewisi belongs to stercorarian group of trypanosomes and its trypomastigotes possess typically elongate slender body with pointed posterior end. Saxena and Miyata documented an unusual type of T. lewisi in the blood of Rattus norvegicus from New Delhi, India in 1993[6].

The aim of the present study was to screen the peripheral blood films of wild rats trapped around human dwellings at Chandigarh, India to detect the infection of T. lewisi to establish the existence of reservoir of this hemoflagellate parasite as we foresee an approaching danger of zoonotic infection to infants and immune suppressed patients in the light of most recent reports of T. lewisi infection in infants from the Southwest India [8-10]. Feeding preferences of vectors like Xenopsylla cheopis and tabanids have definitely changed in India as the reports of zoonotic infections are pouring in. Here we construe the evidence of the presence of T. lewisi infected rats at Chandigarh; geographically located in Northwest India. Our report could probably be an evidence of wild reservoir of Trypanosoma from this part of India and accentuate a need to be alert while investigating febrile patients with drowsiness. Similar studies by other researchers could be helpful to further establish the geographical migration of infected animals and possible risk of the disease to infants with poor innate immunity with/without primary immunodeficiency. Patients with acquired or therapeutic immunosuppression may also be considered at potent risk of zoonotic infections and investigated with alertness. There is a need to be extra vigilant while examining blood films from infants and immune compromised patients.

Materials and Methods

Three peripheral blood films each were prepared by tail prick of each of the ten wild rats trapped around human dwellings at Chandigarh, India during the last eight months. Giemsa stained peripheral blood films were screened microscopically using '40x' objective lens to detect any Trypomastigote of Trypanosoma species. Two of the ten rats were found to be positive for trypanosomes. Photomicrography was done using '100x' oil immersion lens. Olympus BX51 compound microscope (Olympus Corporation, Japan) was used for photomicrography and images were captured using Olympus DP20 Digital Camera (Olympus Corporation, Japan). Olympus DP20 is a 2 megapixel Camera with high color fidelity and transfers images at 15 fps. The camera control unit has been loaded with image capture software which displays images at 1600 x 1200 pixel size. Temporary image files were stored at 'Compact- Flash Memory Card' of the camera controller and downloaded to the attached PC. Images were accurately cropped without altering pixel values. Morphometry was done to determine the length of trypomastigotes through interactive procedure using Qwin-550 image analysis software (Leica Corporation, UK).

Results and Discussion

Two of the ten trapped wild rats weighing between 200 to 250 g were found positive for trypanosomes on thorough microscopic examination of Giemsa stained peripheral blood films. The composite photomicrograph presented as Figure 1, shows four extracellular hemoflagellate found in approximately 1 cm2 area of blood film towards tail. Essential morphological features of the hemoflagellate are well exhibited in Figure 2. Total length of trypomastigotes, including flagellum was measured to be 35-42 μm. The parasite could be T. lewisi as the species has already been documented to cause infection in wild rats and other rodents. However, molecular study was not done to establish the species of the trypanosome as the parasites were detected in its natural host. Extracellular hemoflagellate illustrated in the composite photomicrograph Figure 1 has slender bodies with oval shaped nuclei placed internally at anterior-posterior junction of the body. There were no granular inclusions in the parasites and the morphological features conform to the features of T. lewisi, as documented in literature by various researchers [1-6].

Citation: Rayat CS and Vasishta RK. Wild Rats as Reservoir of Trypanosoma Lewisi in Northwest India. Austin J Pathol Lab Med. 2014;1(2): 3. ISSN:2471-0156