Haemoparasitism was investigated among 108 captured wild grass cutters (Thryonomys swinderianus) in Kogi State, north central Guinea savannah zone of Nigeria. Examination of thick and thin smears prepared using blood obtained from the tail veins of the investigated rats, was used for the detection of the presence of infection. Anaplasma marginale was the only haemoparasite encountered in the study. An overall infection rate of (5.55%) was recorded among the investigated rats. The distribution of the parasite among the investigated rats based on sex shows that 2(5.88%) of the 34 female rats were positive, while 4(5.40%) of the 74 males were infected with the Anaplasma marginale. On the basis of the age of the rats examined, 6 of them were youngs below 6 months of age with no infection recorded among them, while the remaining 102 adults had 6(5.88%) of them infected with the Anaplasma marginale.There was no statistical significant variation in the prevalence of Anaplasma marginale based on sex and age of the examined grass cutters (P˃0.05). This report further reiterates the occurrence of anaplasmosis among rodent population and represents the first report from the study area and one of the few among grass cutters(Thryonomys swinderianus).The finding is of great epidemiological significance in view of the potentials of grass cutters(Thryonomys swinderianus) to serve as reservoir host of anaplamosis in Nigeria.
Greater cane rats scientifically called Thryonomys swinderianus are widely distributed throughout Africa’s semi-humid regions and are found in forests and savannahs but do not inhabit rainforest, dry scrub, or desert (Mensah and Okeyo, 2005).They are the largest grass eating rodents found over much of the sub Saharan Africa (Oboegbulem and Okoronkwo, 1990) and are regarded as the second biggest wild rodent after the porcupine in Africa.
An estimated 40,000 tonnes of the meat of grass cutters is consumed yearly in West Africa (Mensah and Okeyo, 2005) with the meat said to be similar to the one of piglets, a reason for its high appreciation in West and Central Africa (Adjanohoun, 1988).The meat is in fact the most expensive meat in West Africa including Nigeria, Togo, Benin, Ghana and Coted’voire (Martins 1985, Baptist and Mensah, 1986; Asibey and Addo, 2000).
Tremendous progress has been made towards the domestication of grass cutters in West African countries of Nigeria, Togo, and Benin where they are kept on small holder farms. They have also been an increase in the number of demonstration farms owned by Governments and individuals in recent times particularly in the Republics of Benin and Togo.
In Nigeria, cane rats are mostly found in the predominant southern forest and the North central savannah with few or none in the Sahel regions of the North western and north eastern parts of the country. Accompanying the intensification of domestication is the rapidity with which causative agents of diseases may be transmitted among domesticated animals. Prominent among disease causing agents that have been associated with cane rats are bacteria (Oboegbulem and Okoronkwo, 1990) and parasites (Adejinmi and Emikpe, 2011) with gastrointestinal parasites, the most widely studied (Opara, 2010; Okeke et al., 2008; Futagbi et al., 2010; Olayemi et al., 2011; Opara and Fagbemi, 2008)
Incidences of occurrences of haemoparasites under natural conditions have earlier been reported in wild and captive reared cane rats (Opara and Fagbemi, 2008) and other rodents (Ajayi et al., 2006).Also haemoparasites (Trypanosome) has been successfully established in cane rats under experimental condition (Opara and Fagbemi, 2010aαb).Trypanasoma, plasmodium and Babesia were the haemoprotozoans reported among the wild and captive reared grass cutters by (Opara and Fagbemi, 2008) while (Ajayi et al., 2006) reported 63.08% prevalence among one hundred and thirty rodents distributed across nine different species including Thryonomys swinderianus.Plasmodium,Trypanasoma,Babesia and Anaplasma were the haemoparasites identified in that study. Similarly polymerase chain reaction integrated with sequence analysis was used by (Wu-Chun et al., 2006) for the determination of natural Anaplasma phagocytpphilum infections among ticks and rodents in the forest area of Jilin Province in China. The study revealed 8.8% infection rate among the 102 rodents examined. The current study was designed to determine the haemoparasites that are associated with wild grass cutters in kogi state, North Central Nigeria.
Materials and Methods
Ofu, the headquarters of Ofu local Government area of Kogi State is located on 7 0 14 ‘ 9 0 N and 6 0 55 ‘ 32 0 E co.ordinates.It is situated close to Lokoja, the administrative headquarters of Kogi State in North central Nigeria. The climate is characterised by wet and dry season with an annual rainfall range of between 1016mm and 1524mm and mean temperature not falling below 27.70C(Ifatimehin and Ufuah, 2006;Wikipedia 2012).
108 wild grass cutters were captured alive by local hunters between July and December, 2011 at five different villages in Ofu Local Government Area of Kogi State, Guinea savannah zone of North central Nigeria. The rats were kept for different periods of time (2-3 weeks) prior to sale. They consisted of 74 males and 34 females, 6 Youngs and 102 adults. Sexing and age estimation were done according to (Asibey, 1974; Adu, 1999; Addo et al., 2001) where the ano-genital distance was the principal criterion used in assigning an animal to a group. Also the sizes of the animals were used as complimentary features in classification as described by (Opara, 2010).Ticks were found on seventy three (73) out of the one hundred and eight (108) examined rats and were identified to be species belonging to the Genus Boophilus at the Parasitology Laboratory of the Department of Veterinary Microbiology and Parasitology, University of Maiduguri.
The experiment was carried out according to the care and use of experimental animals’ protocol (Ochei and Kolkatar, 2000) .Three (3) mls of blood from the tail vein was collected by cutting the tail using scissors and draining the blood into an ethylene diamine tetracetic acid (EDTA) tube. The blood was immediately transported on ice pack to the Haematology Laboratory of Government owned Kogi State Specialist Hospital Lokoja. Thick and thin blood smears were prepared as described by (Eberhand and lammie, 1991; Houwen, 2000) and analysis on the 108 blood specimen carried out according to the methods of (Ajayi et al., 2006; Bhatia et al., 2006).Briefly, thin smear was prepared by putting a drop of blood at one end of a slide and touching with one end of a spreader at an angle of 300. The spreader was drawn smoothly and steadily so that small amount of blood was drawn and the thin smear made. The smear was air dried and fixed by immersion in methyl alcohol for 3 minutes after which it was air dried in an up right position and stained using Giemsa.Meanwhile, thick smear was made by putting a small drop of blood on a centre of a grease free slide and the blood spread in about 10mm diameter of the original drop using a glass rod. It was then air dried for ten (10) minutes and dehaemoglobinised and stained. Both slides were examined under the microscope and Anaplasma marginale identified according to the taxonomic key of (Radunz, 2008).
Results obtained were subjected to Chi-Square analysis for test of significance. P<0.05 were Considered significant at 95% confidence limit (Maed and Curnow, 1983).
Results obtained from this study are recorded in Tables 1 and 2. Table 1 presents the distribution of Anaplasma marginale based on age groups and their respective infection rates. 6(5.55%) of the 108 investigated cane rats were positive for Anaplasma marginale, the only haemoparasite encountered in the study .All the six positive samples were among the one hundred and two(102) adults investigated while no parasite was recorded among the six young rats examined. Similarly, Table 2 shows the distribution of the parasites based on different sex groups, 4(5.40%) out of the seventy four (74) male rats sampled were positive while two 2(5.88%) of the thirty four (34) females were positive for Anaplasma marginale.
|Table 1:Distribution of Haemoparasite (Anaplasma marginale) in cane rats based on age|
|Grass cutter||Number examined||Number(%) infected|
|Table 2: Prevalence of Haemoparasite (Anaplasma marginale) in cane rats based on sex|
|Grass cutter(sex)||Number examined||Number(%) infected|
Haemoparasitism is an important infection affecting several animals including rodents where they are responsible for production losses ranging from loss of body condition to outright death of animal. The occurrence of haemoparasites among rodents especially grass cutters have earlier been reported (Ajayi et al, 2006; Opara and Fagbemi, 2008; Opara and Fagbemi 2010aαb).Dipeolu et al., (1981) demonstrated the natural occurrence of Anaplasma marginale in wild African giant rat (Cricetomys gambianus), a rodent belonging to the family Cricetomyidae.Similarly,(1.3%) infection rate for Anaplasma phagocytophilum was reported by (Bray et al.,2007) among common shrews(Sorex araneus),a rodent belonging to the family Soricidae in northwest England. In the current study, the occurrence of Anaplasma marginale, the only parasite encountered among the 108 examined grass cutters was 5.55% using both thick and thin smear examinations. All of the six identified parasites were seen both on thin and thick smear film. The prevalence of 5.55% of anaplasmosis in this study is higher than the 1.54% earlier reported by (Ajayi et al, 2006) among nine different species of rodents including Thryonomys swinderianus in Jos, North central Nigeria and also higher than the (1.3%) reported for Anaplasma phagocytophilum infection among common shrews(Sorex araneus) in northwest England. There was no statistical significant variation in the prevalence of Anaplasma marginale among the examined grass cutters based on the sex and age (P˃0.05).The finding in this study further reiterates the earlier report by (Dipeolu et al., 1981) who reported the natural occurrence of Anaplasma marginale among wild African giant rats. The close association among rodents especially in the wild may aid in the transmission of the parasites in the presence of capable vectors. The high presence of ticks (Boophilus spp), a known vector for the transmission of anaplasmosis on the body of the cane rats may be a reason for the relative high prevalence of the infection when compared to (Ajayi et al., 2006; Bray et al., 2007).Also animals in the wild are known to have unhindered access to one another, thereby increasing the possibility of sharing vectors of diseases once present. Similarly, rats sampled in this study were captured from the wild unlike those used by Ajayi et al., 2006 who sampled rats from around human dwellings. The vegetation cover and the environmental fauna in the two areas of study are similar since both of them are located in the Guinea Savannah climatic zones. This report is the first report on the occurrence of anaplasmosis in cane rats (Thryonomys swinderianus) in the study area and one of the few reported in the literatures. The epidemiological significance of this finding in relation to other rodents needs to be investigated since cane rats may be found in association with other rodents. The potentials for grass cutters (Thryonomys swinderianus) serving as reservoir host for anaplasmosis in Nigeria is also of great concern.
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