A review on the diagnosis of animal trypanosomoses

Abstract

This review focuses on the most reliable and up-to-date methods for diagnosing trypanosomoses, a group of diseases of wild and domestic mammals, caused by trypanosomes, parasitic zooflagellate protozoans mainly transmitted by insects. In Africa, the Americas and Asia, these diseases, which in some cases affect humans, result in significant illness in animals and cause major economic losses in livestock. A number of pathogens are described in this review, including several Salivarian trypanosomes, such as Trypanosoma brucei sspp. (among which are the agents of sleeping sickness, the human African trypanosomiasis [HAT]), Trypanosoma congolense and Trypanosoma vivax (causing "Nagana" or animal African trypanosomosis [AAT]), Trypanosoma evansi ("Surra") and Trypanosoma equiperdum ("Dourine"), and Trypanosoma cruzi, a Stercorarian trypanosome, etiological agent of the American trypanosomiasis (Chagas disease). Diagnostic methods for detecting zoonotic trypanosomes causing Chagas disease and HAT in animals, as well as a diagnostic method for detecting animal trypanosomes in humans (the so-called "atypical human infections by animal trypanosomes" [a-HT]), including T. evansi and Trypanosoma lewisi (a rat parasite), are also reviewed. Our goal is to present an integrated view of the various diagnostic methods and techniques, including those for: (i) parasite detection; (ii) DNA detection; and (iii) antibody detection. The discussion covers various other factors that need to be considered, such as the sensitivity and specificity of the various diagnostic methods, critical cross-reactions that may be expected among Trypanosomatidae, additional complementary information, such as clinical observations and epizootiological context, scale of study and logistic and cost constraints. The suitability of examining multiple specimens and samples using several techniques is discussed, as well as risks to technicians, in the context of specific geographical regions and settings. This overview also addresses the challenge of diagnosing mixed infections with different Trypanosoma species and/or kinetoplastid parasites. Improving and strengthening procedures for diagnosing animal trypanosomoses throughout the world will result in a better control of infections and will significantly impact on "One Health," by advancing and preserving animal, human and environmental health.

Keywords: Antibody-detection; Cross-reactions; DNA detection; Microscope examination; Trypanosome; Undetected infection.

Fig. 1

Geographical distribution of the “Nagana” disease complex (Trypanosoma congolense, T. vivax and T. brucei) [–36]

Fig. 2

Geographical distribution of Trypanosoma vivax [, –34, 36, 42]

Fig. 3

Geographical distribution of Trypanosoma evansi (“Surra”) [6, 33, 43, 50]

Fig. 4

Geographical distribution of Trypanosoma cruzi [6, 69, 76]

Fig. 5

Geographical distribution of pathogenic mammal trypanosomes [, –36, 42, 43, 50, 69, 76]

Fig. 6

Main morphological features of four subgenera of mammal trypanosomes on Giemsa-stained thin blood smears. a Microscopic image of Trypanosoma brucei brucei in mice blood; morphology of the subgenus Trypanozoon: large-sized trypomastigote (17–30 µm), slender form, free flagellum, small sub-terminal kinetoplast, sharp posterior extremity, central nucleus and large undulating membrane; b Microscopic image of Trypanosoma congolense-type savanna in mice blood; morphology of the subgenus Nannomonas: small-sized trypomastigote (8–22 µm), no free flagellum, terminal sub-lateral kinetoplast, round posterior extremity, central nucleus and no undulating membrane. c Microscopic image of Trypanosoma vivax in cattle blood; morphology of the subgenus Duttonella: large-sized trypomastigote (20–27 µm), slender form, free flagellum, large terminal kinetoplast, round posterior extremity, central nucleus and large undulating membrane. d Microscopic image of Trypanosoma lewisi in rat blood; morphology of the subgenus Herpetosoma: very large-sized trypomastigote (21–36 µm), slender form, free flagellum, very large sub-terminal kinetoplast, very long sharp posterior extremity, anterior nucleus and large undulating membrane. Scale bar: 10 µm

Fig. 7

Molecular and serological tests for the detection of trypanosomes and trypanosomoses: a Ethidium bromide-stained electrophoresis gel of a monospecific PCR; the result can be considered to be positive when a visible PCR product exhibits the specific weight expected (here: lanes 2, 3, 6–10, 12, 14, 16); otherwise, when the product is non-specific (lane 17) or non-visible (lanes 1, 4, 5, 11, 13, 15), the PCR is negative. Lane 18 is the DNA ladder. b Ethidium bromide-stained electrophoresis gel of a multi-specific PCR based on the amplification of the internal transcribed spacer 1 (ITS1); species-specific results are deduced from the weight of the visible PCR products obtained (here: lanes 1, 12 are the DNA ladder; lanes 2–4 are T. congolense; lanes 5–7 are Trypanozoon; lane 8 is T. theileri; lane 9 is T. simiae; lanes 10, 11 are T. vivax. c Trypanosoma vivax antibody detection ELISA plate; first 2 rows are blanks (A, B), positive controls (C, E, G) and negative controls (D, F, H); all samples are tested in duplicate and appear to be positive, doubtful or negative, according to their mean optical density. d Picture of the card of a CATT/T. evansi exhibiting parasite agglutinations in the positive control and samples 163 and 017; other samples are considered to be negative