The use of enzyme linked immunosorbent assays to investigate the prevalence of Trypanosoma equiperdum in Ethiopian horses

Histopathological lesions in reproductive organs, distal spinal cord and peripheral nerves of horses naturally infected with Trypanosoma equiperdum

Background

Dourine, a venereal transmitted trypanosomosis caused by Trypanosoma equiperdum, has different clinical signs related to the reproductive and nervous system. Pathologic tissue changes associated with the disease are poorly described. The present study describes the histopathological lesions in naturally T. equiperdum-infected horses in the chronical stage of dourine.

Results

Four chronically dourine diseased horses underwent a post-mortem examination. They were Woo test negative, but CATT/T. evansi positive, had a low packed cell volume (PCV) and exhibited obvious clinical signs of dourine. Post-mortem examination did not reveal gross lesions in the organs assumed to be responsible for the symptomatology. On histopathology, genital organs were affected, with mononuclear cell infiltration and erosions and degeneration of seminiferous tubules and perivascular lymphoplasmacytic cuffing in the uterus. In the nervous system, mononuclear cell infiltration was located in peripheral nerves, ganglia and in the spinal cord, leading to axonal degeneration. Real-time PCR using ITS primer revealed the presence of trypanosomes in these organs and conventional PCRs using maxicircle and RoTat1.2 primers further confirmed the involvement of T. equiperdum since the DNAs from the vagina, testicle, distal spinal cord, sciatic and obturator nerves found to be positive for maxicircle and negative for RoTat 1.2.

Conclusions

The histopathological lesions in the spinal cord and peripheral nerves explain the incoordination of the hind legs in T. equiperdum-infected horses, whilst its presence in the genital tract exemplifies the venereal transmission.

Tissue (re)distribution of Trypanosoma equiperdum in venereal infected and blood transfused horses

Dourine, caused by Trypanosoma equiperdum, is a life-threatening venereal disease in equidae. So far, there is no clear evidence on how and when stallions become infectious, nor which tissues are affected by the parasite in diseased animals. Post-infection, after a transient, temporary phase of parasitaemia, the parasite disperses to different tissues in an unknown distribution pattern. This study describes the distribution of the parasite after infection by artificial insemination (AI) or blood transfusion. Mares (N = 4) were artificially inseminated with T. equiperdum spiked semen whereas stallions (N = 4) were infected by blood transfusion. The course of the disease was monitored by parasitological (Woo) and molecular (PCR) tests and clinical signs and haematological parameters were recorded. At 120 days post infection, horses had a full necropsy, histopathology and PCR. A similar pattern of parasitaemia, disease progression and tissue distribution were seen in all horses. Ejaculated semen in the preclinical stage and epididymal semen in the chronic stage of the disease was positive on PCR and caused infection in mice. Cymelarsan^® treatment in the chronic stage did not result in a clinico-haematological or histopathological improvement. At necropsy, lesions were observed in the nervous and reproductive system. Histopathological lesions were most severe in the peripheral nerves and associated ganglia, the testicles and genital mucosae with multifocal infiltration of lymphocytes, plasma cells and histocytes. The parasites disseminated to several tissues including the nervous system, testicles and semen. The results indicate that transmission of T. equiperdum is possible through semen even from symptomless stallions post-treatment.

Dourine: a neglected disease of equids

Dourine is a venereal transmitted trypanosomosis causing a major health problem threatening equines worldwide. The origin and identification of Trypanosoma equiperdum within the subgenus Trypanozoon is still a subject of debate. Unlike other trypanosomal infections, dourine is transmitted almost exclusively by coitus. Diagnosis of dourine has continued to be a challenge, due to limited knowledge about the parasite and host-parasite interaction following infection. The pathological lesions caused by the diseases are poorly described and are observed mainly in the reproductive organs, in the nervous system, and on the skin. Dourine has been neglected by research and current knowledge on the disease, and the parasite is very deficient despite its considerably high burden. This paper looks in to the challenges in identification of T. equiperdum and diagnosis techniques with the aim to update our current knowledge of the disease.

Infectious diseases of working equids

Most working equids reside in low-income countries where they have an essential role in the livelihoods of their owners. Numerous infectious diseases negatively impact the health and productivity of these animals. There are considerable technical, social-behavioral, and institutional impediments globally to reducing the burden of infectious diseases on working equids. One the greatest remaining challenges is the lack of funding for research, resulting from the low priority assigned to working equids by funding bodies. Changing the attitudes of decision makers will require data-driven advocacy, and global networks of collaborators have a vital role in building this more robust evidence base.

Serological and parasitological survey of dourine in the Arsi-Bale highlands of Ethiopia

This study was conducted from August 2005 to January 2007 to determine prevalence and distribution of dourine in horses and to investigate the occurrence of clinical and carrier cases in donkeys and mules in the Arsi-Bale highlands. Study methodology was based on questionnaire, serological, clinical and parasitological survey. The questionnaire indicated that dourine is a major health problem of equines in the Arsi-Bale highlands. Though dourine is commonly observed throughout the year, it has a seasonal character and occurs mostly during the breeding season from June to late September. Serological screening of 646 horses showed a seroprevalence of 184 (28%), 161 (25%) and 125 (19%) for card agglutination test for trypanosomosis, LATEX and enzyme-linked immunosorbent assay, respectively. Risk factors were parity number, previous history of abortion and body condition score. No trypanosomes could be detected by Giemsa staining or by haematocrit centrifugation technique. Ten puppies inoculated with blood samples, genital washes and oedematous fluids remained parasitologically negative. Different characteristic signs of dourine were observed. During the genital stage, mares showed vaginal oedema, discharge and presence of depigmented scars over the external genitalia. In stallions, oedema of the scrotum and prepuce, prepucial and urethral discharge, and ulceration of the genital mucosae mainly of the penile were observed. In both sexes, lameness in one or both legs, partial dragging and stiffness of the hind legs and incoordination were the dominant signs observed as nervous form of the disease.

Comparative diagnosis of parasitological, serological, and molecular tests in dourine-suspected horses

Study on comparative sensitivity of parasitological, serological, and molecular tests on 237 horses originating from two dourine-suspected districts of Arsi-Bale highlands of Ethiopia was conducted to determine the prevalence of the disease and degree of agreement of the diagnostic tests. Accordingly, the prevalence of the disease was found to be 4.6%, 36.7%, and 47.6% by parasitological Woo test, RoTat 1.2 and 18S PCR tests, respectively. The seroprevalence of the disease was 27.6% in CATT/Trypanosoma evansi test. In Ethiopia, it was for the first time that trypanosomes from dourine suspected horses were demonstrated in 4.6% of the animals using Woo test. The findings of the present study disclosed that dourine is highly prevalent and one of the major diseases of horses in the area. There was no statistically significant difference (P>0.05) in prevalence of the disease between districts, sexes, and age groups of the animals. However, there was a statistically significant difference (P<0.05) in the prevalence of the disease between emaciated and animals with good body condition. Assessment of the degree of agreement of the diagnostic tests employed revealed low to fair (k = 0·1 - 0·4) with significantly higher sensitivity by PCR than other tests.

Efficacy of Cymelarsan and Diminasan against Trypanosoma equiperdum infections in mice and horses

Trypanocidal sensitivity studies were conducted to assess the efficacy of Diminazene diaceturate (Diminasan) and Bis (aminoethylthio) 4-melaminophenylarsine dihydrochloride (Cymelarsan) against Trypanosoma equiperdum (isolated from two mares with chronic cases of dourine) 713/943 and 834/940 Dodola strains in experimentally infected mice and horses. Diminasan at doses from 3.5 mg/kg to 28 mg/kg and Cymelarsan at doses of 0.25 mg/kg and 0.5 mg/kg body weight failed to cure any of the mice, indicating a clear dose dependent relationship in the mean time of relapse observed in mice. Indeed, mice treated with lower doses relapsed after a shorter time than mice treated with higher doses. However, mice treated with Cymelarsan at doses of 1.0 mg/kg and 2.0 mg/kg body weight were cured and no parasitemia was observed for 60 days. The efficacy of Cymelarsan was also tested in horses. Two groups of horses containing two animals each were infected with T. equiperdum 834/940 Dodola strain and treated with Cymelarsan at a dose rate of 0.25 mg/kg and 0.5 mg/kg, respectively. Cymelarsan at 0.25 mg/kg and 0.5 mg/kg body weight cleared parasitemia within 24 h post treatment and none of the animals were found to show relapse throughout the 320 days of observation. The sensitivity of the particular trypanosome strain to Cymelarsan was also supported by the relative improvement in the mean PCV levels of horses following treatment. A statistically significant difference (p<0.01) in the mean PCV levels of horses treated with Cymelarsan was observed between day 20 at peak parasitemia and days 40 as well as 60 of observation. The mean PCV levels of horses in the control group progressively decreased within the first 60 days of post infection. Two of the horses in the control group developed chronic form of dourine manifested by genital as well as nervous signs with progressive loss of body condition within 320 days post infection. The efficacy of Cymelarsan against the chronic form of dourine was confirmed after treatment of one of the control horses with Cymelarsan at a dose rate of 0.25 mg/kg body weight at day 282 post infection. It was noted that the treated horse improved overall body condition and clinical signs such as incoordination of hind legs, weakness and ventral oedema disappeared within 10 days of treatment. Thus, Cymelarsan was found to be quite effective in curing horses in acute as well as chronic form of dourine. The results obtained from the present study will be important for designing effective control measures against dourine.

Trypanosoma equiperdum: master of disguise or historical mistake?

After 100 years of research, only a small number of laboratory strains of Trypanosoma equiperdum exists, and the history of most of the strains is unknown. No definitive diagnosis of dourine can be made at the serological or molecular level. Only clinical signs are pathognomonic and international screening relies on an outdated cross-reactive serological test (the complement-fixation test) from 1915, resulting in serious consequences at the practical level. Despite many characterization attempts, no clear picture has emerged of the position of T. equiperdum within the Trypanozoon group. In this article, we highlight the controversies that exist regarding T. equiperdum, and the overlap that occurs with Trypanosoma evansi and Trypanosoma brucei brucei. By revisiting the published data, from the early decades of discovery to the recent serological- and molecular-characterization studies, a new hypothesis arises in which T. equiperdum no longer exists as a separate species and in which current strains can be divided into T. evansi (the historical mistake) and Trypanosoma brucei equiperdum (the master of disguise). Hence, dourine is a disease caused by specific host immune responses to a T. b. equiperdum or T. evansi infection.

A field study to estimate the prevalence of Trypanosoma equiperdum in Mongolian horses

From May to July 2000, a cross-sectional study was conducted to estimate the prevalence of Trypanosoma equiperdum in the horse population of the central province (Tuv aimag) of Mongolia. On average, four herds were selected from each of the 29 aimag subdivisions (119 herds). From each herd, 10 horses were sampled in proportion to sex and age categories in the respective herds (1190 horses). Sera from 1122 horses were analysed for T. equiperdum antibodies using two serological assays, the complement fixation test (CFT) and the enzyme-linked immunosorbent assay (ELISA). The crude estimate of the CFT and the ELISA seroprevalence was 7.6 and 6.7%, respectively. Concordance between the CFT and ELISA results was high (96%). The highest number of CFT positive animals was detected in one herd in Möngönmorit (6/10), followed by herds in Bayandelger (5/10) and in Bayantsagaan (5/10). Poor body condition was significantly correlated with positive serological status in both CFT and ELISA. A history of abortion appeared to be a risk factor for both CFT and ELISA seropositivity. Blood samples of all horses belonging to herds with at least three (3/10) seropositive animals (CFT and/or ELISA) were analysed by light microscopy and by PCR using a Trypanosoma (Trypanozoon) brucei specific primer pair. No trypanosomes or any other haemoparasites could be detected in Giemsa stained thin blood smears. Eight out of the 130 samples (6.2%) analysed by PCR gave positive signals. Seven out of the eight PCR positive horses were also serologically positive. One PCR (and ELISA) positive stallion from Möngönmorit showed emaciation, scrotal and preputial oedema and an oedematous skin plaque. From the serological and DNA-based results it is concluded, that trypanosome infections occur in horses in the Tuv aimag of Mongolia. Since at present neither serological nor DNA-based tests allow a subspecies specific identification within the subgenus Trypanozoon, no definitive diagnosis can be given for T. equiperdum. Whether the examined herds are infected with T. equiperdum or with T. evansi, the causative agent of surra, remains an open question. However, based on the clinical findings, the negative parasitological results and the concentration of conspicuous seroprevalences in single herds, circumstantial evidence supports the existence of infections with the causative agent of dourine.

Animal trypanosomiasis in South America. Current status, partnership, and information technology

Animal trypanosome species of economical importance in South America include T. vivax and T. evansi. Both species are described in Brazil, Bolivia, Colombia, French Guyana, Peru, Suriname, and Venezuela. In Argentina and Guyana, only T. evansi and T. vivax are found, respectively. Our studies on T. vivax indicated that the parasite was spreading around 1.3 km per day in Bolivia. We found severe leukopenia in bovines from Pantanal (Brazil) and the Department of Santa Cruz (Bolivia). Because it can cause immunosuppression, the importance of trypanosomiasis control in ensuring success of vaccination campaigns against foot and mouth disease (FMD) in the Pantanal and Bolivia should be considered. The use of one needle for several animals during FMD campaigns in Brazil and Bolivia could also contribute to the spread of T. vivax. The anticipated losses due to T. vivax could exceed $160 million, assuming there are 11 million head of cattle in the Brazilian Pantanal and Bolivian lowlands. International collaboration among research institutes is needed to deal with these diseases and parasites. Previous efforts using information technologies resulted in the creation of two discussion lists (Tryplink and Trypan), the edition of the on-line version of Trypnews and Internet conferences.

Trypanosoma evansi and T. equiperdum: distribution, biology, treatment and phylogenetic relationship (a review)

Trypanosoma evansi and T. equiperdum were compared regarding their ultrastructure, their mammalian hosts, way of transmission, pathogenicity, diagnosis and treatment, and biochemical and molecular characteristics. Electron microscopic investigation revealed no ultrastructural differences between the two species except that there were more coated vesicles in the flagellar pocket of T. equiperdum. Biological, biochemical and molecular studies were reviewed and exhibited many similarities between T. evansi and T. equiperdum. The most prominent differences between the two species are the presence of maxicircles in T. equiperdum, which are missing in T. evansi, and the route of transmission. While T. evansi is transmitted by biting flies, T. equiperdum is transmitted from one equine host to another during copulation when mucous membranes come into contact. Otherwise the two species are remarkably similar. The phylogenetic relationship between the two species and T. b. brucei is being discussed, and the hypothesis is proposed that T. evansi arose from a clone of T. equiperdum which lost its maxicircles.