enzootiology of trypanosoma evansi in pantanal, brazil

Enzootiology of Trypanosoma evansi in

Pantanal, Brazil

H.M. Herreraa,*, A.M.R. Davilab, A. Noreka, U.G. Abreuc,S.S. Souzab, P.S. D’Andread, A.M. Jansena

aLaboratorio de Biologia de Tripanosomatıdeos, Departamento de Protozoologia, FIOCRUZ/RJ,

Pavilhao Carlos Chagas 3 Andar, Av Brasil 4365, CEP 21045-900, Rio de Janeiro, BrazilbLaboratorio de Biologia Molecular de Tripanosomatıdeos, Departamento de Bioquımica e

Biologia Molecular, FIOCRUZ/RJ, Pavilhao Carlos Chagas 3 Andar,

Av Brasil 4365, CEP 21045-900, Rio de Janeiro, BrazilcCentro de Pesquisa Agropecuaria do Pantanal, EMBRAPA/Pantanal, Rua 21 de Setembro,

1880, CEP 79320-900, Corumba, MS, BrazildLaboratorio de Doencas Endemicas, Departamento de Medicina Tropical, FIOCRUZ/RJ, Pavilhao

Carlos Chagas 3 Andar, Av Brasil 4365, CEP 21045-900, Rio de Janeiro, Brazil

Received 4 July 2004; accepted 26 July 2004

Abstract

In order to better understand the enzootiology of trypanosomiasis caused by Trypanosoma evansi

in the Brazilian Pantanal we examined domestic and wild mammals by microhematocrit centrifuge

technique (MHCT), immunofluorescence antibody test (IFAT) and polymerase chain reaction (PCR).

T. evansi infection was detected in all species sampled with exception of the sheep and the feral pig.

High parasitemias were observed in capybaras (5/24), coatis (18/115), horses (31/321) and dogs (3/

112). Among these species, only the capybaras did not develop anemia. Low parasitemias, only

detected by PCR, were found in buffaloes (18/43), bovines (29/331), marsupials (1/4), small rodents

(14/67), bats (7/18), and one armadillo (1/8). The highest prevalence of T. evansi infection was

recorded in horses (73%), although no neurological signs in infected horses were observed. Diagnosis

through standard parasitological tests and IFAT should be used with caution since they may overlook

comprovedly infected horses. The relationship between ranch management and T. evansi infection in

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Veterinary Parasitology 125 (2004) 263–275

* Corresponding author. Tel.: +55 21 2598 4324; fax: +55 21 2560 6572.

E-mail address: [email protected] (H.M. Herrera).

0304-4017/$ – see front matter # 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.vetpar.2004.07.013

horse was investigated. The importance of other transmission mechanisms apart from the tabanids

and reservoir hosts are discussed.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Trypanosoma evansi; Natural infection; Reservoir; Diagnosis; Pantanal; Brazil

1. Introduction

Among the pathogenic trypanosome species, Trypanosoma evansi (Trypanosomatidae,

Kinetoplastida) is known to have a large diversity of mammalian hosts and is the most

important disease producing agent throughout the tropical and subtropical areas of the

world. The main difference with other trypanosomatids is the lack of maxicircles kDNA.

Consequently there is no development of T. evansi in the vector. Indeed, this parasite is

adapted to mechanical transmission and has a broad host range in a wide geographical

distribution (Hoare, 1972; Lun and Desser, 1995).

This flagellate is transmitted by hematophagous flies, mainly Tabanus sp., through oral

infection by ingestion of meat or blood from infected animals and by vampire bats

(Desmodus rotundus) in South America (Hoare, 1965, 1972; Losos, 1986).

In spite of being considered a hemoflagellate, T. evansi (Salivaria, Trypanozoon) is a

protozoan parasite of both intra and extra vascular fluids (Sudarto et al., 1990). One of the

most interesting aspects of T. evansi is its ability to periodically switch its major variant

surface glycoprotein (VSG), producing relapses of parasitemias. Parasitemic waves have

been reported with Brazilian T. evansi isolates in experimental infections (Aquino et al.,

1999; Queiroz et al., 2000; Herrera et al., 2001).

There are considerable differences in the severity of syndromes caused by T. evansi

infections in the different geographical areas of its occurrence, depending on the virulence

of the strain and the susceptibility of the host. Anemia is the main outcome of infection.

Consequently, it has been suggested that the resistance to developing anemia, as well as

control of parasitemia, reflect the degree of tolerance to infection by the hosts (Trail et al.,

1990). Sick animals may display fever, general loss of condition and immunosupression

(Hoare, 1972; Holland et al., 2001).

The diagnosis of T. evansi infection is still difficult because the clinical signs are varied

and non-specific and, in enzootic areas, the natural hosts frequently present mild chronic

forms of the disease (Losos, 1986; Franke et al., 1994a; Arias et al., 1997).

The routine of T. evansi diagnosis is mainly based on finding the flagellates in wet films,

smears or by the michrohematocrit test. These methods are specific but less sensitive,

principally in detecting parasites during low levels of parasitemia (Woo, 1970; Murray et

al., 1981; Monzon et al., 1986).

Serological methods have been used for mass screening, however, antibodies may be

missing due to serological latency (Franke et al., 1994b; Aquino et al., 1999; Herrera et al.,

2001; Wernery et al., 2001). The amplification of repetitive DNA satellite regions of

Trypanozoon have shown to be very specific and sensitive and has been used in large

trypanosomiasis epidemiological approaches in both animals and humans (Moser et al.,

1989; Masiga et al., 1992; Kanmogne et al., 1996; Katakura et al., 1997).

H.M. Herrera et al. / Veterinary Parasitology 125 (2004) 263–275264

In the Brazilian Pantanal, T. evansi is enzootic, infecting domestic and wild animals

(Nunes et al., 1993). This parasite causes a severe disease in horses locally called ‘‘Mal de

Cadeiras’’ due to the nervous symptomatology characterized by hind limbs paresis,

resulting in a staggering gait (Silva et al., 1995a). Two forms of the disease are described in

Brazil due to T. evansi infections: acute syndrome that produces early death in horses and

dogs if untreated (Silva et al., 1995c, 1996; Aquino et al., 1999), and chronic, affecting

mainly capybaras (Hydrochaeris hydrochaeris) and coatis (Nasua nasua) (Franke et al.,

1994b; Herrera et al., 2002).

Outbreaks of ‘‘Mal de Cadeiras’’ have occurred periodically among Pantanal livestock

since the beginning of the 19th century (Wilcox, 1992). This disease is a problem of great

economic importance due to high cost of treatment and death of sick animals (Silva et al.,

1995b; Seidl et al., 1998, 2001).

The large seasonal floodplain called Pantanal covers about 140,000 km2. It is located

near the geographical center of South America and its economic activities are mainly based

on cattle ranches. The livestock population is estimated in 4,000,000 cattle, 5000 buffaloes

and 140,000 horses. In spite of not being considered of economic importance, sheep are

also raised in the region (Cadavid Garcia, 1986). Wildlife is abundant in this region

(Lourival and Fonseca, 1997).

The Pantanal wetlands contain 10 sub-regions (Fig. 1) that differ in degree of vegetation,

flooding and physiognomy. During the wet season most of the grasslands are flooded and

during the dry season water remains only in a few pools. The length and severity of flooding

and drought in the Pantanal vary, not only from year to year, but also from sub-region to sub-

region (Adamoli, 1987). Outbreaks of disease caused by T. evansi have been reported in the

last two decades in the study area and are associated mainly with the rainy season, when

tabanids are abundant (Silva et al., 1995b; Davila et al., 1999; Barros and Foil, 1999).

Capybaras and coatis have been considered the main wild reservoirs for ‘‘Mal de Cadeiras’’

(Nunes et al., 1993; Silva et al., 1999). Nevertheless nothing is known about the importance of

other species concerning the T. evansi enzootiology in this area.

In this scenario, many aspects concerning the epizootiology of ‘‘Mal de Cadeiras’’ in the

Pantanal region are still unknown. The aim of this research was to improve the knowledge

of the variables that are involved in the transmission cycle of T. evansi in the southern

Pantanal. The possible role of infected wild and domestic animals as reservoir hosts and the

importance of ranch management in the epidemiology of ‘‘Mal de Cadeiras’’ is discussed.

2. Material and methods

2.1. Study area

The sampled area covered approximately 1000 km2 and is located at the Nhecolandia sub-

region, 100 km west of Corumba city (Fig. 1). In this region, livestock shares the same habitat

with wild animals. During the rainy season a large part of the area is flooded and much of the

non-flooded higher ground (‘‘cordilheira’’) is interspersed throughout the region. The

vegetation includes mixed scrub with grassland (woodland savannah), open grass fields and

‘‘cordilheiras’’, which is are covered by deciduous forests (Adamoli, 1987).

H.M. Herrera et al. / Veterinary Parasitology 125 (2004) 263–275 265

2.2. Field procedures

Blood samples were collected during four excursions between February 2000 and

March 2001. Samples from domestic animals (horses, dogs, cows, buffaloes and sheep)

were collected from the jugular vein. Wild mammals were trapped under government


Fig. 1. Map showing the Pantanal, sub-regions and location of the study area.

authorization of the Brazilian Environment Institute (licenses no. 229/2000 and 228/2000),

immobilized with zolazepan and tiletamina cloridrat (Zoletil1 50), venipunctured

and immediately released after blood sampling and recovery from anesthesia. Blood

was collected into vacutainer tubes or microhematocrit containing ethylenediaminete-

traacetic acid (EDTA) as the anticoagulant, kept on ice and processed on the same day of

collection.

Each animal was sampled on only one occasion. In the field, T. evansi was detected by

microhematocrit centrifuge technique (MHCT) (Woo, 1970). The hematocrit value was

estimated by the packed cell volume (PCV), using the standard microhematocrit method

according to Schalm et al. (1975). Samples for the molecular diagnosis (PCR) were

obtained from 10 ml of whole blood dropped on a filter paper confetti. Samples for

serological test (IFAT) were stored at �4 8C until used.

2.3. Anemia

Packed cell volume (PCV) values were used as an index of anemia. The mean PCV

values of T. evansi for negative animals in the serological, parasitological and molecular

tests were considered as normal values.

2.4. Parasitemia

Animals with positive MHCT tests were considered as having high parasitemias, since

positive MHCT test only detects parasitemias from 104 parasites/ml (Woo, 1970). Animals

of MCHT test negative that displayed positive PCR test were considered as displaying low

parasitemias.

2.5. DNA extraction

DNA extraction was performed with Chelex-1001 1% according to Walsh et al. (1991)

with minor modifications by De Almeida et al. (1997), in brief: 500 ml of Milli-Q water

was used for the initial wash of the confetti during 30 min. After 15 min the tubes were

inverted 2–3 times, then, after 10 min of centrifugation at 12,000 rpm in an eppendorf

centrifuge, supernatant was discarded and 100 ml Chelex-1001 1% added. The tubes were

shaked manually, incubated at 56 8C during 30 min, boiled for 8 min and vortexed for

2 min. After a final 5 min centrifugation at 12,000 rpm, 80 ml of supernatant was placed in

a fresh tube and stored at �20 8C.

2.6. DNA amplification

A polymerase chain reaction (PCR) was performed with primer sets (TBR1 and TBR2)

specific for Trypanozoon satellite DNA regions, according to Masiga et al. (1992).

The PCR assay showed to be sensitive enough to detect 10 fg of T. evansi DNA. The

primer sets TBR1 and TBR2 were tested using T. rangeli, T. cruzi, Leishmania braziliensis,

Crithidia fasciculata and Herpetomonas muscarum as controls. The results showed a

single band expected (164 bp) only for T. evansi (paper in preparation).


PCR was performed in Perkin Elmer 96001 PCR machines and for each set of

amplification reactions genomic DNA of T. evansi (10–20 ng) was used as positive control

and double distilled water was used as negative control. Standard PCR amplification was

carried out in 10 ml reaction mixtures, each containing 1 ml of DNA as template, 1.5 mM

MgCl2, 1 mM of each primer, 200 mM of each dNTP, 0.5 unit Taq polymerase, and 5%

DMSO. Amplification conditions were as follows: 95 8C for 5 min (initial denaturation),

then 35 cycles of 95 8C for 1 min (denaturation), followed by 55 8C for 1 min (annealing)

and 72 8C for 1 min (extension), with a final extension step of 10 min at 72 8C. Finally, all

the 10 ml of each amplified sample were analyzed by electrophoresis in 2% agarose gel

containing ethidium bromide 0.5 mg/ml and photographed under ultraviolet light.

2.7. Serological test

Immunofluorescence antibody test (IFAT) for detecting IgG was performed for horses,

dogs and coatis. The IFAT reaction was conducted according to the protocol utilized by

Camargo (1964). Negative control serum samples were obtained from animals located

in areas where T. evansi does not occur and positive serum samples were obtained from

the parasitological positive field animals. Standardization of the protocol was undertaken

in order to establish suitable working dilutions for each specific fluorescein antibody

conjugate. The following conjugates were used: anti-horse IgG (Sigma1) for horses,

anti-dog IgG for dogs and anti-raccoon IgG (Kirkegaard & Perry Laboratories1) for

coatis.

The cut off for each animal species was considered as the lower titer of serum samples in

which parasites could be detected by MHCT or PCR. The reaction was taken as being

positive when the dilution of serum was respectively � 1:10 for horses and � 1:40 for dogs

and coatis. The reaction was performed in twofold dilutions starting from 1:5 to 1: 2560.

2.8. Statistical analysis

To compare between MHCT and PCR positive results for every species sampled the chi-

square (x2) test was employed. The t-test (equivalent variances) was used to evaluate a

possible correlation between high parasitemias, assayed by MHCT, and anemia, evidenced

by the PCV values. The comparison of equine IFAT results with their respective values of

PCV was performed by means of t-test.

3. Results

T. evansi infection was detected by at least one of the three methods employed in all

species sampled, except for feral pigs and sheep. The pattern and prevalence of infection

differed according to the animal species (Table 1).

Infection with low parasitemias as detected by positive PCR test and negative MHCT

test, was noticed in bovines, buffaloes, bats, small mammals and one armadillo. It

is noteworthy that buffaloes displayed high T. evansi prevalence as detected by PCR

(Table 1).


Parasitemias by positive MHCT test were observed in capybaras, coatis, horses and

dogs (Table 1). Coatis and capybaras showed the higher parasitemias since the number of

animals positive by MHCT and number of animals positive by PCR was not significantly

different (P < 0.05).

Horses presented the highest prevalence of T. evansi infection among all species

sampled. The higher equine seroprevalence levels with parasitemias assayed by MHCT

were observed in farms where no control of equine infectious anemia (EIA) was performed

(Table 2). A strong relationship between horse management and high parasitemias could be

established since animals from ranches where a program of EIA control is conducted, did

not present positive MHCT test and displayed the lower seroprevalence rates (Table 2).

Moreover, means of hematocrit values were significantly different (P < 0.05) in horses

derived from farms that control IEA (33.4%) than horses derived from farms that not

control IEA (30.2%), to anyone of MHCT positive and negative animals.

All infected coatis and capybaras even those with positive with MHCT were in apparent

good health condition. No neurological signs were observed in horses, even in animals that

displayed high parasitemias. Dogs with high parasitemias presented severe clinical

symptoms such as emaciation, conjunctivitis and facial edema.


Table 1

Prevalence of T. evansi infection in mammals in the Nhecolandia sub-region, Pantanal

Species Total sampled Number of positives/percentual of positivity

MHCT PCR IFAT

Horse 321 31/9.6 112/34.9 236/73.5

Dog 112 3/2.7 11/9.8 26/23.2

Coati 115 18/15.6 22/19.1 35/30.4

Capybara 24 5/20.8 7/29.2 4/33.3

Cattle 331 0 29/8.8 nd

Buffalo 43 0 18/41.9 nd

Small mammals

Thrichomys sp. 46 0 7/15.2 nd

Clyomys sp. 11 0 2/18.2 nd

Oecomys sp. 7 0 3/42.8 nd

Dasyprocta sp. 3 0 2/66.7 nd

Marsupials

Gracilinanus sp. 2 0 0 nd

Monodelphis sp. 2 0 1/50.0 nd

Bats

Artibeus sp. 6 0 3/50.0 nd

Platyrrhinus sp. 5 0 1/20.0 nd

Carollia sp. 3 0 1/33.3 nd

Myotis sp. 2 0 2/100.0 nd

Noctilio sp. 2 0 0 nd

Armadillos

Euphractus sp. 8 0 1/12.5 nd

Feral pigs

Sus scorfa feral 10 0 0 nd

Sheep 40 0 0 nd

MHCT: microhematocrit centrifuge technique; PCR: polymerase chain reaction; IFAT: immunofluorescence

antibody test; nd: not done.

Anemia, as proved by low PCV values, was observed in all examined dogs independent

of the presence of T. evansi, probably as a consequence of the bad conditions in which they

were maintained. Anemia was not recorded in capybaras since no significative difference

(P < 0.05) was observed between means of hematocrit values from MHCT negatives and

positives animals. A direct correlation between high parasitemias and anemia was observed

in horses and coatis since we found significative difference (P < 0.05) between means of

hematocrit values from MHCT negatives and positives animals. It is important to note that

no correlation between anemia and serum positivity in horses was observed (P < 0.05).

IFAT serological titers ranged from 1:10 to 1:1280 in horses and from 1:40 to 1:640 in

coatis and dogs. Serological negative animals with PCR positive results were observed in

horses (13%), dogs (3%) and coatis (4%) (Fig. 2). Nevertheless, we found serological

positive results with PCR negative in horses (55%), dogs (55%) and coatis (44%) (Fig. 3).


Table 2

Prevalence of T. evansi infection in horses in the Nhecolandia sub-region, Pantanal

Ranch Total sampled Number of positives/percentual of positivity

MHCT PCR IFAT

R1 48 0 1/2.1 21/43.7

R2 18 0 0 8/44.4

R3 119 26/21.8 68/57.1 85/71.4

R4 47 1/2.1 16/34.0 43/91.5

R5 40 3/7.5 23/57.5 36/90.0

R6 49 0 4/8.2 43/87.7

Total 321 31/9.6 112/34.9 236/73.5

R1 and R2 are ranches that control EIA while R3, R4, R5 and R6 do not control EIA.

Fig. 2. Infections observed by positive PCR tests in serologically negative samples. PCR: polymerase chain

reaction; IFAT: immunofluorescence antibody test.

Fig. 3. Low parasitemias as proved by PCR negatives in serological positive samples. PCR: polymerase chain

reaction; IFAT: immunofluorescence antibody test.

Infection by T. evansi was observed in equines, dogs, coatis, capybaras and small

mammals in both the rainy and dry season.

4. Discussion

Our results showed that in the Pantanal region T. evansi infects a wide range of host

species of domestic and wild mammals and causes various degree of parasitemia and

clinical signs. The distinct habitats and behavior patterns of small rodents, bats and

armadillo suggest that there are still unknown factors underlying the transmission cycles.

Low and cryptic parasitemias observed in animals of all T. evansi infected species

suggest their importance in the maintenance of the parasite in nature. Sub-patent

parasitemias have been widely described in T. evansi enzootic areas and some factors were

associated to this feature: difference in virulence of strains, host susceptibility, chronic

phase or even individual nutritional status (Monzon et al., 1986; Aquino et al., 1999;

Herrera et al., 2001). Considering that stress may result in weakness of the infected animals

and consequently low immunity and exacerbation of parasitemia (Luckins et al., 1979;

Payne et al., 1991), the presented data suggest that all T. evansi infected species may be

involved in the transmission cycle of the parasite.

The higher seroprevalence observed in horses suggests that they are more exposed to T.

evansi infection than the other species sampled. The higher prevalence assessed by IFAT in

comparison with the other two tests employed was expected. Horses that presented IFAT

positive test and negative results by PCR and MHCT probably reflect animals submitted to

chemotherapy. High horse seroprevalence rates have also been reported in other areas of

the Pantanal and South America reinforcing the importance of the enzooty in continent

(Franke et al., 1994a; Monzon et al., 1995; Reyna-Bello et al., 1998).

The high number of infected horses with low parasitemias, only detected by PCR reflect

cryptic infections probably as the result of incorrect treatment or the consequence of a mild

course of infection. These low parasitemias explain why no correlation between low PCV

values (anemia) and serological positive horses was found. In addition, the presented data

showed that treatment of T. evansi infected animals based only on screening of animals

with low hematocrit values will certainly overlook infected animals.

Negative IFAT tests in PCR positive testing animals may reflect serological latency or

false negative results. Indeed, IgG plasmatic concentration reach high titer after 3 weeks

(Reyna-Bello et al., 1998; Aquino et al., 1999; Wernery et al., 2001) and has an important

role in the control of ‘‘Mal de Cadeiras’’ because animals with recent infections are not

detected by serological screening. These findings showed the importance of using a more

sensitive and precocious test such as PCR.

The high prevalence rate of horse infection in all periods of sampling suggest two

situations: these animals may become infected during the winter or they may be developing

a long lasting course of T. evansi infection. These data associated with the absence of

nervous symptomatology of ‘‘Mal de Cadeiras’’ in this study support the importance of

horses themselves as reservoir for T. evansi.

The higher equine prevalences of T. evansi infection in farms without control for EIA,

associated to MHCT positive results uniquely evident in these areas, suggest a synergism


between these two immunosuppressive diseases. Consequently, it is evident that a good

horse management is fundamental for ‘‘Mal de Cadeiras’’ control.

Although the importance of wild mammals in the maintenance of T. evansi in the natural

environment is recognized, a relationship between equine trypanosomiasis prevalence and

proximity of infected wild mammals was not established. We found low horse

seroprevalences with negative MHCT and PCR in areas where coatis and capybaras

displayed high T. evansi prevalence rates and parasitemias. Similar data were recorded in

the northern Pantanal (Franke et al., 1994a). These data point that overlapping T. evansi

transmission cycles may not occur in the Pantanal.

The rapid death of T. evansi infected dogs may explain the low prevalence rates found

during this study. Indeed, these dogs are stray animals and when sick they are not treated.

Our data concerning coatis indicate that animals with high parasitemias develop

anemia. Anemia, biochemical and pathologic changes have been reported in coatis

naturally and experimentally infected with T. evansi (Silva et al., 1999; Herrera et al., 2001,

2002). Therefore, since high prevalences rates were found in the Pantanal region, this

parasite may be acting as an important agent of selection and density control of the free-

living coatis populations.

The high prevalence of T. evansi infection found in capybaras and coatis during the dry

season suggests that these species indeed develop a long lasting course of infection in

nature. However, transmission due to other mechanisms other than bloodsucking flies

should not be ruled out.

Concerning capybaras, we concluded that this caviomorph rodent plays an important

role in the dispersion and maintenance of T. evansi in the Pantanal environment due to: (a)

high T. evansi prevalence rates; (b) the degree of tolerance to infection due to resistance to

develop anemia associated to high parasitemias; (c) the great population density in the

Pantanal region; (d) long lasting patent parasitemia and (e) the absence of clinical

symptoms. Infected but apparently healthy capybaras were also recorded in the Pantanal

and in Venezuela (Morales et al., 1976; Franke et al., 1994a; Arias et al., 1997).

Furthermore, anemia as evaluated by hematocrit values, was not reported in experimentally

infected capybaras (Franke et al., 1994b).

The oral route may be important in the dispersion of T. evansi infection in dogs, coatis

and capybaras. They may become infected as a consequence of their frequent fights.

Moreover, gregarious species such as coatis and capybaras have an aggressive behavior and

may transmit T. evansi among themselves by the oral route, maintaining the infection in the

social group. Therefore, since dogs remain close to the horseman, during the vector season

they can act as a link between wild and domestic animals playing an important role in the

epizootiology of ‘‘Mal de Cadeiras’’.

The parasitemias detected only by PCR in bovines and buffaloes demonstrate that these

species also play a role in the maintenance of T. evansi in the Pantanal due to their high

population density. These species may serve as source of infection for vampire bats and

therefore should be diagnosed and treated. Low parasitemias in bovines seem to be

common in the Pantanal region since negative MHCT test was also observed in

seropositive bovines in the northern Pantanal (Franke et al., 1994a).

The detection of T. evansi infection in small rodents, marsupials, non-hematophagous

bats and armadillo is puzzling and places new questions concerning the transmission of this


flagellate in the Pantanal region. Since nocturnal species spend the day in their holes and

Tabanidae has diurnal/crepuscular activity, it is possible that other vectors may be involved

in the transmission of T. evansi.

Considering that natural infection was reported for pigs and sheep in South America and

Asia (Lun et al., 1993; Vokaty et al., 1993), our negative results concerning these species

show that transmission cycle of T. evansi is peculiar for the different enzootic areas.

The present data suggest that for the T. evansi epidemiological survey in the Pantanal

region two or more techniques should be used to diagnose reservoir hosts. Diagnosis

through standard parasitological tests should be used with caution when it is impossible

perform PCR and seronegatives animals shall be re-tested after 30 days due to serology

latency.

In spite of the recent trend in not considering virulence and pathogenicity as a parameter

to evaluate a sign of an ancient host–parasite interaction, the observation of pathogenic

features of T. evansi infection in capybaras and coatis associated with prehistoric

biogeographical events, made us to speculate about the time-scale of their relationships.

African rodent caviomorphs (primitive capybara ancestor), that probably have an

ancient coevolution history with T. evansi, reached the South American continent 37

million years ago (mya). Placental carnivores arrived in South America about 3–3.5 mya

(Flynn and Wyss, 1998). Therefore, the T. evansi association with coatis is probably more

recent than with capybaras and, although these two wildlife species develop chronic

infections, coatis display anemia and pathological changes while infected capybaras do not

have clinical signs and anemia, withstanding high parasitemias (Franke et al., 1994b;

Herrera et al., 2001, 2002). This propose that T. evansi infection in Neotropical mammals

precedes the South American colonization by the Spanish Settlers.

Acknowledgements

To ranches and local people for field assistance. Supported by Conselho Nacional de

Pesquisa e Desenvolvimento; Instituto Oswaldo Cruz/Fiocruz; Programa de Apoio a

Pesquisa Estrategica em Saude/Fiocruz and Conservation Internacional do Brasil.

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enzootiology of trypanosoma evansi in pantanal, brazil

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