Introduction

Tropical theileriosis or  Mediterranean Coast Fever - caused by Theileria annulata - is a disease of cattle widely distributed across Southern Europe, North Africa and Central Asia. Economically, theileriosis due to T. an- nulata is one of the most important diseases of cattle in Iran, with a major potential threat to expansion and improvement of livestock production (Hashemi-Fesharaki, 1988).

The disease and its severity not only de- pend on the virulence of the causative agent, but also to a large extent on the degree of host susceptibility, which largely  depends on the breed (Osman and AlGaabary, 2007). In a stable endemic situation, there may be only mild or no clinical disease in local Zebu cattle (Constable et al., 2017). Clinical signs include marked fever, swelling of superfi- cial lymph nodes, inappetence, tachycardia, dyspnea, anemia, pale mucous membranes, and icterus. Petechiae and ecchymoses may be found on the conjunctiva and oral mucous membranes. Other clinical signs are diarrhea, weight loss, with decreased milk yield (Con- stable et al., 2017). Exotic cattle (Bos taurus) are particularly susceptible with mortalities up to 40% to 80% in some areas, whereas in indigenous cattle (Bos indicus) that general- ly suffer from much lower mortalities (about 10%) it is confined mainly to calves (Hash- emi-Fesharaki, 1988).

Theileriosis can be diagnosed by finding piroplasms in erythrocytes in Giemsa-stained thin smears from blood or lymph node biop- sies showing schizonts in lymphocytes. Bu- parvaquone is the most effective agent avail- able, and the recommended dose is 2.5 mg/  kg BW (Constable et al., 2017). In Iran, the routine treatment method for theileriosis is us- ing buparvaquone along with oxytetracycline, and control of disease relies on tick control

using acaricides and theileriosis  vaccination. It is suggested that Iranian indigenous cat-

tle in comparison with Holsteins had lower parasitemia rate, weaker response to T. annu- lata infection, milder clinical manifestations and significantly lower levels of acute phase proteins (Nazifi et al., 2010).

This study was conducted to evaluate the resistance of indigenous cattle in comparison with Holstein and crossbred cattle against

T. annulata through assessment of clinical signs and response to routine treatment.

Materials and methods

This study was conducted in the north re- gion of Iran (Gonbad-e-kavous township), where theileriosis due to T. annulata is prevalent. Historical data were collected and clinical examination was done on 51 natural- ly affected cattle with Theileria annulata (17 Holstein, 17 crossbred and 17 indigenous cows). Clinical examination included mea- suring temperature, heart rate, respiratory rate, auscultation of heart and lung, mucosal observation (for jaundice, pallor, hemorrhag- es) and palpation of prescapular, prefemoral and submandibular lymph nodes.

Examination of blood smears was used for diagnosis. Peripheral blood samples were tak- en from auricular veins and blood smears were stained by Giemsa. The slides were examined through light microscope, in which the piroplas- mic forms of the parasite were detected. The samples were divided into three groups accord- ing to their parasitemia rates by the percentage of infected erythrocytes (<33%, 33-66% and

>66%). Suspected  samples  were  confirmed by lymph node puncture and Giemsa staining which determined Theileria schizont forms.

All the cows in the three groups were treated with buparvaquone (single injection

of 2.5 mg/kg bodyweight (BW), IM) along with oxytetracycline (10 mg/kg BW, IM, q 24 h for  3 days). Their clinical signs and the results of blood smear examinations were recorded before treatment and 48 h after treatment. The severity of clinical signs, parasitemia rates and respons- es to treatment were compared among groups. Data obtained from this survey were analyzed statistically by SPSS software using Chi-square and analysis of variance (ANOVA) tests and P

Results

Clinical findings revealed that all the af- fected cows in three groups had increased re-

spiratory rate, 98% with anorexia and lymph nodes enlargement, 96.1% had fever and decreased milk yield. These clinical signs  are more prevalent than others. In the indig- enous cows the severity of fever was signifi- cantly (P<0.05) lower and the mean value of respiratory rate was significantly (P<0.001) lower than the other two groups. Abnormal lung sounds were only observed in Holstein cows (17.6%). Mucosal jaundice and pete- chiae were not seen in indigenous cattle and significant difference (P<0.05) in mucosal changes was recorded among groups. Rumi- nal hypomotility was significantly (P<0.05) lower in indigenous cattle (Table 1).

Table 1. The definite and relative frequencies of clinical signs of theileriosis according to breed of cattle

Fr (%) frequency, * P<0.05

In the present study the parasitemia rate was quantified and expressed as the per- centage of infected erythrocytes. The dif- ference in the percentage of infected eryth-

rocytes was not significant among groups (Table 2). This finding indicated that par- asitemia rate was not different in three breeds of cows.

Table 2. The percentage of infected erythrocytes according to breed of cattle

Fr (%) frequency, α=0.05

There was no significant difference among the breeds in response to treatment with buparvaquone along with oxytetracy- cline (Table 3). The data history of animals

showed that delay in treatment is a notable factor in response to treatment, in addition severity of parasitemia decreased the ef- fects of the treatment.

Table 3. The response to treatment of theileriosis according to breed of cattle

Fr (%) frequency, α=0.05

Discussion

Tropical theileriosis is an important par- asitic disease of cattle in Iran with a poten- tially great economic impact. Local breeds have tolerance to infection while exotic  and cross breeds are highly susceptible to great loss due to progression of this disease (Hashemi-Fesharaki, 1988). In this study Holstein and crossbred cows showed higher (P<0.05) fever than indigenous cows. The mean value of respiratory rate in the indig- enous cows was significantly (P<0.001)

lower than the other two groups and ab- normal lung sounds were only observed in Holstein cows. The frequencies of mucosal pallor, jaundice and petechiae were higher (P<0.05) in Holstein cows. Ruminal hypo- motility was significantly (P<0.05)  lower in indigenous cattle. These results suggest- ed that Holstein and crossbred cattle suffer more acutely from the disease than indige- nous cattle that are more resistant to thei- leriosis and exhibit milder clinical signs. The different response of various cattle breeds has been investigated in Theileria

infections. In breeds of cattle such as Bos indicus, Sahiwal is more resistant to T. an- nulata. This breed exhibited mild clinical signs and recovered from a dose of parasite which was fatal in the Holstein, B. Taurus. Holsteins showed higher fever response  and higher levels of parasitemia rate than Sahiwals. One feature of theileriosis is the production of acute phase proteins indicat- ing that the parasite induces high systemic levels of pro-inflammatory cytokines. In Holsteins, there is  prolonged  production  of the acute phase proteins, which in con- trast is only slightly elevated in the Sahi- wals (Glass and Jensen, 2007).  Nazifi  et al. (2010) reported that Iranian indigenous cattle compared with  Holsteins  had  low- er parasitemia rate, weaker response to T. annulata infection, milder clinical man- ifestations and significantly lower  levels  of acute phase proteins. Schizont-infected cells multiply in the draining lymph nodes and disseminate rapidly along with lym- phoblasts throughout the lymphoid tissues and in nonlymphoid organs, including the liver, kidney, lung, abomasum, and brain. Virulence of the disease is associated with the capacity of infected cells to disseminate inside the host. Later, schizonts differenti- ate into merozoites and invade erythrocytes (as piroplasms). The pathogenesis therefore involves proliferation of macrophages in- duced by schizonts, and anemia with icterus induced mostly by the piroplasms. Macro- phages/monocytes are the main producers of inflammatory cytokines that can induce an acute-phase protein response. The re- sponse is greater in Bos taurus Holstein breed than the Bos indicus Sahiwal breed, and this would explain the greater severity of disease in the Holstein. Infected macro- phages from taurine breeds are also more

capable of aggressive invasiveness than zebu breeds (Constable et al., 2017).

In East and Southern Africa, Zebu and Sanga cattle and their crossbreds are consid- ered to be tolerant to theileriosis (Ndung’u et al., 2005). Resistance to tick infestation varies among breeds of cattle. It is known that in many subtropical environments in Africa, indigenous breeds are highly resis- tant to ticks and theileriosis (Laisser et al., 2017). This study showed no parasitemia rate difference among the three breeds of cows.

The ability of cattle to resist ticks and tick-borne diseases such as theileriosis de- pends on the strength of their immunity to respond against the infectious sporozoites, schizonts, and piroplasm parasitic antigens. Development of a stronger immunity sys- tem comes about through exposure to such diseases (Laisser et al., 2017).

In this study there was no significant difference among the breeds in response to treatment with buparvaquone along with oxytetracycline. History of animals indi- cated that treatment is most  effective  in  the early stages of the disease and delay in treatment would have a notable impact on the animals’ response to the treatment. In addition, severity of parasitemia decreased the effects of treatment. These findings were in agreement with what was previously de- scribed by Dhar et al. (1988) and McHardy et al. (1985).

Zebu cattle survive without regular tick control methods such as dipping or spray- ing and the infected animals recover with- out treatment, using drugs (Laisser et al., 2014; Kazungu et al., 2015). This indicates that the indigenous zebu cattle in Tanzania possess genes which enable them to live and reproduce under high tick and theileri-