Pathogenesis and Transmission

As well as in blood plasma, Trypanosoma brucei and T. congolense can also be detected in intercellular fluid of tissue. Thus, besides anaemia, they can also cause degenerative, inflammatory and necrotic lesions in diverse organs due to an intensive invasion of lymphocytes, macrophages and plasma cells. The pathogenicity and virulence of the different trypanosomes infecting dogs is generally variable and dependent on the species, the transmitting Tsetse flies, environmental factors and co-infections.

T. brucei and T. congolense are two of three pathogenic agents of the so-called Nagana in cattle and horses. The pathogens are usually transmitted by tsetse flies (Glossina spp.) during blood feeding. The trypomastigote form is inoculated by the insect. Within the vector the parasite multiplies in a different form and finally is transmitted to a new host during feeding of the fly. Apart from this cyclic development and transmission, the pathogens can also be transferred mechanically through tabanids and biting flies.

T. evansi is the pathogenic agent of the so-called Surra or Mal de Cadeiras in camels, equines and other animals. It is transmitted mechanically by tabanids and stable flies (Stomoxys spp.), and in South America by vampire bats. Additionally, dogs can also be infected by consumption of affected meat from T. envansi-infected herbivores.

T. cruzi and T. rangeli are both transmitted by triatomines, also known as kissing bugs. T. cruzi is transmitted to a definitive host through the vector’s excrement. Metacyclic trypanosomes penetrate the organism either through normal healthy mucosa or broken skin, often caused by scratching. Ingestion of T. cruzi-infected bugs may also cause infection of the definitive host. Although T. rangeli can also be transmitted through the vector’s faeces, the main route of transmission is via saliva, through the bite of an infected triatomine.

Attempts to infect triatomines with T. caninum were unsuccessful. The mode of transmission of this little-known trypanosome species remains unclear (Madeira et al., 2009).


Further information

  • Madeira MF, Sousa MA, Barros JH, et al.: Trypanosoma caninum n. sp. (Protozoa: Kinetoplastida) isolated from intact skin of a domestic dog (Canis familiaris) captured in Rio de Janeiro, Brazil. Parasitol. 2009, 136, 411-23

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