Vet Parasitol. 2014 Aug 29;204(3-4):153-7. doi: 10.1016/j.vetpar.2014.05.004.

Control and eventual eradication of Trypanosoma evansi infection in dromedary camels after an episodic outbreak in mainland Spain: an example in a non-endemic area.

Gutiérrez C1, Tamarit A2, González-Martín M3, Tejedor-Junco MT3.

  • 1Department of Animal Medicine and Surgery, Veterinary Faculty, University of Las Palmas de Gran Canaria, 35416 Arucas, Las Palmas, Canary Islands, Spain. Electronic address: cgutierrez@dpat.ulpgc.es.
  • 2Animal Health Laboratory, Conselleria of Agriculture, Fishing and Nourishment, Av. Manuel Soto 18, 46024 Valencia, Spain.
  • 3Department of Clinical Sciences, University of Las Palmas de Gran Canaria, P.O. Box 550, 35080 Las Palmas de Gran Canaria, Canary Islands, Spain.

Abstract

In 2008, Trypanosoma evansi was detected on a camel farm in mainland Spain. The animals were isolated, confined in a closed stable, and treated twice with melarsamine (Cymelarsan(®), Merial, Lyon, France) with an interval of 1 month. Clinical and laboratory examinations by means of parasitological, serological, and molecular procedures (polymerase chain reaction (PCR)) were carried out regularly for 6 years. After the treatment, all parasitemic camels were cleared of parasites, and in the seropositive camels a progressive decrease in antibody levels was observed, with complete disappearance of antibodies between 15 and 21 months, except in one animal which showed doubtful Ag-Ab reaction at 21 months post treatment. In the next assessment, 6 months later, the diagnostic tests conducted on all animals had a negative result. The diagnostic and therapeutic tools recently developed against T. evansi will evidence new and alternative approaches after the parasite is detected, particularly if outbreak occurs in geographically localized areas in territories free of the disease. Copyright © 2014 Elsevier B.V.

KEYWORDS: Camel; Control; Mainland Spain; Melarsamine; Trypanosoma evansi

PMID: 24933467

 

SUPPLEMENTS:

Trypanosoma evansi is the most widely distributed of the pathogenic African trypanosomes of animals, affecting domestic livestock and wildlife in Asia, Africa and Latin America. This parasite causes a disease known as surra, and is mechanically transmitted by biting flies, although vampire bats would act as vectors in South America. It affects a number of domestic animals and the principal host species varies according to geographical location. Thus, buffalo, cattle, camels and horses are particularly susceptible, but other animals, including wildlife, can also be affected (OIE, 2008).

Dromedary camels were introduced into the Canary Islands at the beginning of the XV century and they have been used since then for labour and transport. With a population of over 10,000 camels in the middle XVIII century, the camel census suffered a drastic decrease during XX century due to the development of modern machines and instruments for agriculture and transport. In fact, the Canarian camel population was about to disappear at the end of the 60’s of the last century, but tourism-related activities increased the population in special in the 80’s and 90’s importing animals from the near West African coast. Nowadays, the Canary Islands harbour the most important camel population in Europe (about 2000 camels) and they are the most important source for exporting to Europe and South America. However, at the time of imports, some diseases were not included into the import health conditions, and accidental introduction of Trypanosoma evansi through camels coming from Africa, was detected in 1997 (Gutierrez et al., 2000). Despite this finding, Canarian dromedaries were afterwards exported to continental Europe, and as a result, outbreaks of T. evansi were detected on mainland France and Spain (Gutiérrez et al., 2010)

In February 2008, Trypanosoma evansi was first identified on mainland Spain on an equine and camel farm located in the Alicante province after the introduction of a dromedary imported from the Canary Islands about 6 months earlier. The farm contained 21 dromedaries y 67 equines, of which 12 camels and 2 equines showed circulating trypanosomes and 4 more camels showed specific antibodies. The real status about the disease had just been established; however, how we must face this outbreak was unknown for us. In this sense, it is very important to remark that there are no sanitary measures or recommendations provided by any international animal health institutions to fight against this parasite when it is detected in any region, endemic or not. In our opinion, the choice of the sanitary measures would heavily depend on the outbreak geographical location (in particular if the disease is endemic or not) and could include drastic actions (euthanizing the infected animals) or more conventional procedures (treating the infected animals and assessing the evolution of the disease). Given the scarce census of camels and their high commercial value on mainland Spain, we decided in collaboration with the Official Veterinary Services the isolation of all serological or parasitological positive animals and their treatment irrespective their positive or negative parasitological/serological status. Thus, all those animals were treated twice with melarsamine (Cymelarsan®, Merial, France) at a dose of 0.5 mg/kg b.w., by IM route, with an interval of one month between the two administrations.

Once the treatment was administered, the animals had to be monitored in order to evaluate the efficacy of the drug against this T. evansi strain. We really expected that the trypanosomes were killed by using melarsamine at double dose recommended by manufacturers (although indicated by many authors and organizations) and used twice. Periodical clinical and laboratory evaluations were then established for both, positive and negative camels and for the infected equines, although these latter were finally euthanized by the decision of the owner. The question now centred on how many months or years would be required to consider the outbreak as controlled and, finally, as eradicated. In this respect, we considered the longest period of time that the chronic form of the disease takes in a camel. In the available literature, the longest period has been reported to be 3-4 years in dromedaries which would show clinical signs related with the chronic form of the disease. Thus, we decided to monitor the animals for a period of 6 years, which included detecting any diseased animal during a 2 years period extended the longest chronic form. The following monitoring schedule was then established: Seven days post-treatment, once a month for the first 3 months, once every 2 months for the next 6 months, every 3 months for the next 9 months, every 6 months for the next 18 months and annually for the next 3 years (36 months). We expected negative results by parasitological and molecular procedures (absence of the parasite in blood) and a progressive decrease of the specific antibodies, which was bound to occur if the animals had not been in contact with the parasite. The next question was what we would do if an animal showed parasitemia again and/or increases of circulating antibodies, but fortunately it never occurred.

Throughout the study the animals showed absence of circulating trypanosomes as well as a progressive decrease of antibodies until their seroconversion, which occurred in all seropositive animals.

The occasional introduction of T. evansi into countries free of the parasite has most often resulted in the parasite becoming endemic, except in the outbreaks occurred in Australia (1907), USA (1909) or Bulgaria (1939) where the animals were sacrificed. These episodic T. evansi outbreaks have been good examples of the disease eradication until now, but they occurred over a century ago. The improvement in diagnostic methods including parasitological, serological and molecular tests and that of new trypanocide agents, which were not available at the beginning of the past century, would point out that there are in place new strategies to fight against this parasite in new territories.

In our example, we decided to face the outbreak isolating and treating the animals mainly for two reasons: the outbreak was located on an isolated farm and the dromedary camels have a high commercial value in Europe. However, the risk of dissemination of the disease could have been high given the presence of potential vectors in the area, particularly Tabanus spp and Stomoxys calcitrans (Tamarit et al., 2010). On the other hand, the lack of efficacy of the melarsamine would have been catastrophic for the animal status in that Spanish region. If the treatment had been unsuccessful the animals would have been euthanized. For that reason, the most important aspect in the control of a T. evansi outbreak is the trypanocide to use, particularly in those non endemic areas, which there are not reservoirs of T. evansi in the surroundings. The progressive resistance of the different T. evansi strains to the commercially available trypanocides requires the development of new drugs in order to avoid the progressive extension of this tropical disease.

 

References

Gutiérrez C, Juste MC, Corbera JA, Magnus E, Verloo D, Montoya JA. Camel Trypanosomosis in the Canary Islands: assessment of seroprevalence and infection rates using the card agglutination test (CATT/T. evansi) and parasite detection tests. Vet Parasitol 2000; 90: 155-159.

Gutiérrez C, Desquesnes M, Touratier L, Büscher P. Trypanosoma evansi: recent outbreaks in Europe. Vet Parasitol 2010; 174, 26–29.

OIE, 2008. Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. On line: www.oie.int

Tamarit, A., Gutiérrez, C., Arroyo, R., Jimenez, V., Zagalá, G., Bosch, I., Sirvent, J., Alberola, J., Alonso, I., Caballero, C.. Trypanosoma evansi infection in mainland Spain. Vet Parasitol 2010; 167, 74–76.

 

Figures

Figure 1. Blood smear from an infected camel in which T. evansi can be detected by its movement (movie). P1010011

 

Figure 2

Figure 2.  A trypanosome detected in a stained blood smear. Anisocytosis and hypochromic erythrocytes (regenerative anemia) are also evident.

 

Figure 3

Figure 3. Lymph node aspirates showing one trypanosome. This technique can be used in the field when parasites have not been detected in blood.

 

Figure 4

Figure 4. A picture of the first T evansi infected camel showing the chronic form of the disease in the Canary Islands (1997). Clinical signs related to the disease such as emaciation or atrophy of the hump are clearly visible.

 

Figure 5

Figure 5. Edemas of the lower parts are also common in camels affected by T. evansi. In this dromedary camel, preputial edema was observed.

 

The authorDr. Carlos Gutiérrez
Department of Animal Medicine and Surgery, Veterinary Faculty,
University of Las Palmas de Gran Canaria,
35416 Arucas, Las Palmas, Canary Islands, Spain.
Electronic address: cgutierrez@dpat.ulpgc.es.

 

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