Parasitic diseases of camels in Iran (1931–2017) – a literature review

Parasitic diseases of camels are major causes of impaired milk and meat production, decreases in performance or even death. Some camel parasites also represent a threat to human health. About 171,500 one-humped camels (Camelus dromedarius) and 100–300 two-humped camels (Camelus bactrianus) live in Iran. Knowledge of the biodiversity of their parasites is still limited. The present review covers all information about camel parasitic diseases in Iran published as dissertations and in both Iranian and international journals from 1931 to February 2017. Ten genera of Protozoa (Trypanosoma, Eimeria, Cryptosporidium, Toxoplasma, Neospora, Sarcocystis, Besnoitia, Theileria, Babesia and Balantidium), 48 helminth species detected in the digestive system, including three species of Trematoda, four species of Cestoda, and 41 species of Nematoda, as well as helminths from other organs – Echinococcus spp., Dictyocaulus filaria, Thelazia leesei, Dipetalonema evansi and Onchocerca fasciata – have so far been described in Iranian camels. Furthermore, 13 species of hard ticks, mange mites, the myiasis flies Cephalopina titillator and Wohlfahrtia magnifica, and immature stages of the Pentastomida Linguatula serrata have also been reported from camels of Iran. Camel parasitic diseases are a major issue in Iran in terms of economics and public health. The present review offers information for an integrated control programme against economically relevant parasites of camels.


Introduction Methods
The authors checked all available documents on each of the search terms which included a combination of Iran or Iranianin Persian and English -with one of the generic names of the camel parasites as mentioned in reference books ''The Camel in Health and Diseases'' [55], ''Infectious Diseases in Camelids'', 2nd edition [171], and ''Camelid Infectious Disorders'' [172]. The databases and search engines employed for the present literature review were those of PubMed (www.pubmed. gov), Google (www.google.com), Scientific Information Database of Iran (www.sid.ir) and the collection of defended theses at all Iranian Universities (www.irandoc.ac.ir).

Protozoal infections Trypanosomosis
Trypanosoma evansi is the most pathogenic and economically important protozoan parasite of camels that causes severe disease (surra) throughout camel rearing areas of the world [19]. T. evansi is now considered as an emerging zoonotic parasite [43]. Trypanosoma was first reported in Persia in 1876 and was known to be fatal for horses, according to Haig (reviewed by Lingard [72]). After massive mortality of more than 3000 horses in 1930 in the south of Iran, Trypanosoma evansi-like parasites were diagnosed in the blood of diseased animals [26]. T. evansi infection in camels in Iran was confirmed for the first time in 1935 by Delpy and Rafyi, and experimental infections of several mammals with T. evansi isolated from an infected camel were performed [30,160]. The therapeutic and prophylactic efficacy of different dosages of Naganol Ò (suramin sodium) and antrycide methyl sulphate was studied in naturally infected camels since the dose of Naganol Ò recommended by the manufacturer was extremely expensive at that time [13,123]. Since Iran does not lie within the tsetse belt, trypomastigotes in camels have usually been assigned to T. evansi according to their morphological and morphometric features upon microscopic examination. Prevalence rates between 0 and 19.47% for Trypanosoma infections have been reported in camels. However, there are only two sequence-confirmed studies on camel T. evansi infections from Iran (Table 1). In Iran, there is also one report of a natural T. evansi infection of a two-humped camel (Camelus bactrianus) [130]. Outbreaks of Trypanosomosis in dromedary herds associated with mortalities and abortions have been documented [31,178]. Although no study has been conducted to examine infestation with known T. evansi vectors in the country, reports of natural infections with T. evansi in three dogs in Tehran [59], one horse in Shiraz [15], and one water buffalo in Ahvaz [135] with no history of travel, show that non-cyclic transmission occurs.

Eimeriosis
Coccidiosis of camels is an intestinal protozoan infection caused by apicomplexan parasites of the genus Eimeria. Disease caused by these parasites is of great economic importance because of losses due to enteritis, diarrhoea and poor weight gain [172]. Camels harbour their own species of Eimeria including E. cameli, E. rajasthani, E. bactriani, E. dromedarii, E. pellerdyi and E. leuckarti in OWC [71,172]. Data on the frequency and diversity of Eimeria species in dromedaries and Bactrian camels are limited to seven studies which were based on coproscopy, except one that reported tissue alterations caused by Eimeria spp. [68]. Overall prevalences varying between 9.51% and 63% have been reported ( Table 2). All reports concerned dromedary camels, except one that included Bactrian camels [174].

Cryptosporidiosis
Cryptosporidiosis is one of the major zoonotic infections associated with food-borne and water-borne outbreaks [25]. Cryptosporidium spp. has a faecal-oral transmission route. A broad range of hosts including humans, and domestic and wild animals can be affected by pathological changes induced by this gregarine parasite. Several polymerase chain reaction (PCR)based studies on Bactrian camels, llamas and alpacas have detected C. andersoni, C. muris, C. parvum and C. ubiquitum (reviewed by Robertson et al. [134]). However, all studies on Cryptosporidium infections in dromedary camels were based on microscopic modified Ziehl-Neelsen stained faecal smear examinations. Overall prevalences based on faecal samples from dromedaries varied between 0.5% and 37.9% (Table 3). Cryptosporidium was detected in one out of 396 [102] and 12 out of 100 [146] examined abomasum mucosa samples. Available data on clinical disease in camels are limited. A total number of 170 Iranian camel faecal samples were examined, 10% of them showed Cryptosporidium-like organisms [175]. Camel calves less than one year of age showed the highest prevalence (20%). Infected calves showed wasting, diarrhoea and debility, while older oocyst shedders showed no symptoms. Rare data on zoonotic transmission are available. In Yazd Province, 24 of 100 people in long-term contact with camels were diagnosed with Cryptosporidium spp. [146]. Infection was significantly higher in winter (32%) than in summer (16%). Several factors could contribute to seasonality. Oocyst shedding in herbivores is mostly observed during the cold months (autumn and winter). It can therefore be assumed that, on the one hand, low temperature increases oocyst viability, and on the other, during the cold months, animals usually spend more time inside the barn and the oocysts are protected from direct sunlight [25].

Toxoplasmosis
The protozoan parasite Toxoplasma gondii is an important zoonotic pathogen worldwide. Viable parasites have been isolated from edible tissues of camels [46]. Several epizootiological studies have been conducted on the detection of anti-Toxoplasma antibodies in sera of camels from Iran. The first  report was most likely from camels in Fars Province with an infection rate of 17% of 100 tested animals [103]. Antibodies against Toxoplasma were present in 4.16% of 120 tested camels from the north-eastern region of Iran using an immunofluorescence antibody test [137]. In another study, 14.57% seropositivity was reported from 254 tested camels from the centre of Iran, using the modified agglutination test based on direct agglutination of fixed parasites with sera pretreated with 2-mercaptoethanol [51]. Discrepancies in the results could be due to differences in the techniques, the initial serum dilution, age of the examined camels and different environmental conditions. There are two PCR-based publications on blood samples randomly collected from dromedaries. In the first study performed on 50 animals, Toxoplasma could not be detected [148]; however, in the other research work, the parasite was found in eight out of 122 samples (6.6%) [62]. In a comprehensive study on raw milk from various species

Neosporosis
Neosporosis is primarily a disease of cattle and dogs. Abortions caused by Neospora caninum have been reported in alpaca and llama [150]. However, despite the numerous reports on the presence of anti-N. caninum antibodies in camel sera, clinical disease has not been documented in OWCs. Antibodies against N. caninum have been reported from camels in Mashhad (5.83%) [137] and Isfahan (3.22%) [58] using an indirect fluorescent antibody test (IFAT), and also in camels in Yazd (3.94%) using a Neospora agglutination test [51].

Sarcocystiosis
There have been several cases of intestinal Sarcocystis infection in humans in Iran, but there is little information about the parasites' molecular characteristics [4]. Until very recently, there was confusion concerning Sarcocystis species in dromedary camels. However, structural investigations of S. cameli and S. ippeni microcysts by light and transmission electron microscopy in 2015 by Dubey et al. led to a reconsideration of Sarcocystis taxonomy. Sarcocystis camelicanis, S. camelocanis and S. miescheri were considered invalid. Dogs are the most likely definitive hosts as excretion of Sarcocystis sporocysts in the faeces of dogs fed camel meat was reported in several studies [33]. Recently, the first macroscopic sarcocysts from a onehumped camel were confirmed by Dubey et al. [34]. However, there are no reports of macroscopic findings of sarcocystiosis from camels in Iran. Studies on the prevalence and geographic distribution pattern of microcystic infection in the most common sites of infection (i.e. oesophagus, heart, diaphragm, limb muscle and masseter muscle) by the use of the muscle compression/squash method, pepsin/trypsin digestion method and histopathological examination revealed infection rates between 51.5% and 83.6% in at least one of the examined tissues (Table 4). In two ultrastructural and molecular characterisation studies of Sarcocystis isolated from dromedaries in Iran, S. cameli was identified, and a 600-bp specific band was amplified after PCR amplification with specific primers [36,97]. Nothing is known about Sarcocystis infection in Bactrian camels in Iran. However, in Mongolia and Kazakhstan, Sarcocystis infections have been reported in Bactrian camels but without species differentiation [172].

Besnoitiosis
Knowledge about besnoitiosis is scarce in camels and limited to only two documents reporting Besnoitia cysts in the intestine of dromedaries in India [64] and Iran [68]. In an article on camel diseases in Kenya, the authors stated that systematic besnoitiosis (which they referred to as globidiosis) occurred with clinical signs such as thickening of skin associated with hair loss, white patches on the cornea, nasal discharge, fever and acute (sometimes bloody) diarrhoea. In alimentary cases, acute (haemorrhagic) diarrhoea occurred, followed by rapid loss of condition, although no fever was reported. The fatality rate reached 10% [42]. In histopathological examination of the alimentary tract of 100 camels in Fars Province, Khodakaram Tafti et al. (2001) found Besnoitia parasites in 5% of the samples. In the mucosa of the jejunum and ileum of affected camels, a few small to large cysts with or without inflammatory reaction were seen [67].

Theileriosis
The true role of Theileria parasites as tick-borne pathogens for camels is still not confirmed. So far, DNA of Theileria equi, Theileria mutans, Theileria annulata and Theileria ovis has been detected in peripheral blood of dromedaries worldwide [73,118,143,168,177]. However, it is still not clear whether these findings result from proliferation of Theileria in camels or transmission of blood parasites at the time of a tick bite. Clinical examination of naturally infected camels revealed fever, superficial lymph node swelling, loss of appetite, a sudden loss of condition and lacrimation. The morbidity rate was high with no lethal cases. Haematological and biochemical changes in sera of infected camels indicated that the disease greatly affects hepatic, renal and muscular functions [60]. In Iran, the most prominent hard tick species infesting camels is Hyalomma dromedarii, which is presumed to be a vector of Theileria spp. (see Tick infestation section). In this country, only two studies have reported intra-erythrocytic forms of the parasite in blood smears in 15.79% and 6.20% of the examined camels, respectively [54,129]. The first report stated piroplasms in general, and did not differentiate between Theileria spp. and Babesia spp. However, in other studies, piroplasms and their developmental stages were not detected in peripheral blood or lymph nodes of the examined camels [24,85,180]. One report described successful treatment with buparvaquone in camels with Theileria piroplasms detected in blood smears and the typical signs of cattle T. annulata infection disappeared [53]. In three studies using PCR-based DNA detection and sequencing, T. equi and T. annulata were confirmed in the blood of randomly tested camels [16,143], while in another study on the blood of 310 tick-infested camels by PCR, no positive animals were found [87].

Babesiosis
Camels are not described as hosts of Babesia species and as with Theileria infection, no confirmed information is available about camel babesiosis due to the lack of experimental infections. However, typical signs of babesiosis such as fever, anaemia, haemoglobinuria, icterus and gastro-intestinal stasis have been documented in infected camels [162]. So far, the presence of DNA of Babesia caballi has been detected in camels [118], and this could have resulted from infection by infected ticks. There are only three reports on babesiosis in camels from Iran. In a light microscope study, the parasite was found in 3.54% of 113 examined blood samples [129]. In another report, Babesia DNA was found in eight out of 122 randomly tested camels in Iran, albeit without further analysis to species level [63]. Finally, based on PCR and sequencing methods, B. caballi was diagnosed in dromedaries of Iran [45]. Other investigators did not detect Babesia in the peripheral blood of tested animals, whether by light microscopy in 262, 37 and 333 samples, respectively [24,85,180] or by PCR [143] (n = 200).

Balantidiosis
Balantidium spp. are often seen in the lumen of the caecum and large intestine of several mammals, such as swine, humans and non-human primates. This ciliated protozoan may cause a zoonotic disease [149]. Occurrence of an outbreak of human balantidiasis was reported in 1948 in the south of Iran by McCarey. Due to their religious beliefs, none of the 87 patients had contact with pigs. Balantidium could not be detected in intestinal contents of sheep, cattle or goats or in river water [78]. The investigator did not suspect the numerous camels as a possible source of zoonotic infection [28]. Pathologic examination of the intestinal lesions in 100 slaughtered camels showed that one of the most frequent findings was balantidiasis of the caecum and colon with a frequency of 19% [67]. In another study, B. coli trophozoites were observed in six out of 28 smears from the mucosa of the ileocaecal junction of camels [85]. Numerous B. coli trophozoites and cysts (15,000/g) without any other parasites were observed in the faeces of an anorexic dromedary with acute diarrhoea. A therapeutic regimen, which included intramuscular antibiotic therapy (ampicillin) and anti-inflammatory drugs (flunixin meglumine), was successful [167]. It is worth noting that under certain circumstances like being under stress, camels might shed ciliate trophozoites in faeces that can be confused with Balantidium. Further research is needed to confirm the pathological significance of these ciliates in camels.

Helminthoses
Helminthoses of the digestive system The helminth fauna of the digestive tract of camelids is particularly rich with more than 50 species. Symptoms and signs of gastro-intestinal helminths in camels are numerous. The most typical ones are loss of weight, gastritis and/or enteritis, diarrhoea, anaemia and death [29]. Some of these helminths can cause zoonosis [79]. Infection rates of 78%-100% of the examined camels with at least one helminth species are reported from Iran. Camelostrongylus mentulatus, Trichostrongylus probolurus, Haemonchus contortus, Haemonchus longistipes and Stilesia globipunctata are the most common reported helminth species in different studies [10,22,37,75,84]. Reported helminths from slaughtered dromedaries and their isolation sites are listed in Table 5. There is some debate over the naming of Nematodirella longissimespiculata (syn. Nematodirus longispiculata, Nematodirus alcidis, Nematodirus alcides) in the literature but this name was kept as the most commonly used one.
In the only study on the occurrence of gastro-intestinal helminths in Bactrian camels in Iran, Tajik   Nematodirus spp., Trichuris spp. and Moniezia spp. in the faeces of 50 sampled animals [166].

Fasciolosis
Fasciolosis is a parasitic infection with global distribution, causing significant losses in domestic animal production, and it is an important food-borne trematode infection of increasing concern [107]. Both Fasciola hepatica and F. gigantica have been reported from several provinces of Iran and in different genera of snails [12]. In the sole specific study on the prevalence and pathology of Fasciola spp. in dromedaries of Iran, Eslami et al. (2003) examined the livers of 409 slaughtered camels and found that 5.3% of animals harboured F. hepatica flukes with an average number of 10.5 parasites per animal [35]. In other studies on liver infection of camels, only one out of 94 examined carcasses was infected with Fasciola [176] or no infected carcasses were found [94]. F. gigantica has also been isolated from camels in Iran [81,163].

Lungworm infection
Several nematodes are able to infect the lower respiratory tract of domestic animals, usually resulting in bronchitis or pneumonia, or both [18]. Although Dipetalonema evansi might be observed in pulmonary arteries (see Dipetalonemosis section), two species of Dictyocaulus filaria and Dictyocaulus viviparus (syn. Dictyocaulus cameli) are found in the respiratory tract and lungs of dromedaries worldwide [172]. D. filaria and D. viviparus are not camel-specific and their occurrence in camels could have resulted from cross-infection from ruminants. However, as larvae need moist conditions for survival, lungworm infections are not considered a problem in hot and dry climates. In Iran, Dictyocaulus filaria was isolated from the lungs of 3.3% and 10% of examined dromedaries in two studies [84,120].

Eyeworm infection
Helminths that affect the animals' eyes may also cause human infections and are therefore major threats to human communities [112]. So far, Thelazia leesei and T. rhodesi have been reported in OWCs [171]. In the only report on eyeworm infections in camels in Iran, Vosooghi Afshar (1976) examined 400 eyes from slaughtered dromedaries in Tehran for the presence of Thelazia parasites. In total, 70 adult T. leesei worms were isolated. The number of worms varied between three and 10 per infected eye [170].

Dipetalonemosis
Dipetalonema evansi (syn. Deraiophoronema evansi) is the sole filarioid helminth believed to cause clinical disease in camels. The mature worm is typically observed in the testicles, epididymis, spermatic cord, lungs and heart. The sheathed microfilariae can be present in the peripheral bloodstream. Moderate infections are generally asymptomatic; however, severe infections might cause respiratory symptoms, emaciation, apathy, pale mucous membranes, orchitis, aneurysm of the spermatic cord, arteriosclerosis, heart malfunction and nervous impairments [110]. Adult worms have been isolated from the lungs and testicles of camels, and pathological findings described [84,90,98,106,110,141]. Microfilariae of D. evansi were reported from blood samples in 0.88%-46.7% of the studied camels [24,61,85,98,110,124,129,141]. Recently, D. evansi was detected in the blood of 8% of 200 examined camels by PCR and sequencing methods [142]. In this study, analysis of a cytochrome C oxidase subunit I (COI) sequence of filaroid nematodes showed paraphyly of Dipetalonema evansi and Dipetalonema gracile. Further investigations on different gene loci will clarify this nematode's taxonomic position.
Onchocercosis Some filarioid species represent major threats for human and animal health and cases of zoonotic onchocercosis are increasingly being reported worldwide [113]. In camels, adult Onchocerca parasites are commonly observed in connective tissues, while microfilariae are found in the dermis and occasionally circulating in peripheral blood. Reports on the prevalence and pathology of Onchocerca fasciata infection in dromedaries indicate that 5.82%-48% of the examined camels had skin lesions due to these filarial worms [11,38,40,66,75,85,91].

Arthropod infections Tick infestation
Ectoparasites are not critical limiting factors for camel health; however, their presence can affect their productivity, which in turn has economic consequences by reducing animal weight gain and milk yield. Moreover, ticks transmit pathogens that affect animals and human populations. Ticks are abundant on camels of Iran and infestation rates of 9%-85.5% of examined dromedaries have been observed in different studies. Average numbers of 1.27-81.5 ticks per camel were recorded [27,47,95,99,101,104,128,140]. Reported tick species from dromedaries are enlisted in Table 6.

Mange mite infection
Camels are affected by a range of mites including Sarcoptes scabiei, Psoroptes spp., Chorioptes spp. and Demodex spp. [172]. Mange was a major nuisance for the camels of caravans in past times. Camel handlers used to apply tar, turpentine or ''wild rocket'' oil on the body of the animals. These treatments were repeated until the problem was resolved [164]. Sarcoptic mange is regarded as one of the most prevalent diseases of camels and can also be transmitted to humans. Although mange is common in camels of Iran  [9,85]. However, Sarcoptes scabiei var. cameli has been identified in some cases [76]. During examination of the eyelid of domestic herbivores in Iran, Rak and Rahgozar (1975) found demodectic mange infection in 23 out of 153 investigated dromedaries (15%), with no significant histological changes other than distension of the hair follicle [127].

Biting and nuisance flies
Although fly-borne parasitic diseases such as trypanosomosis and nasal bot infection are common, there is a paucity of information about the flies affecting camels. Various species of the Tabanidae and Muscidae families are observed according to a previous report [74] and also the first author's personal observations.

Myiasis
Nasopharyngeal myiasis caused by Oestridae is very common in old world camelids. The camel nasal bot, Cephalopina titillator, is usually found at necropsy or during meat inspection, and infection rates of up to 80.72% of the examined animals have been reported from Iran [74,75,85,109,111,120,126,132,152]. C. titillator was also found in the lungs of four out of 40 examined dromedaries in Iran [109]. There are also two reports of genital and gingival myiasis caused by Wohlfahrtia magnifica. Genital myiasis was recorded around the perineum and vagina of five out of 35 camels in a herd in the southwest of Iran [115]. A single case of gingival myiasis was reported in a 15-year-old camel during inspection of the teeth of slaughtered camels in Mashhad [96].

Linguatulosis
Linguatula serrata, the nose worm of canids, is a wellknown zoonotic parasite [32]. The larval stage of L. serrata has been diagnosed in mesenteric and mediastinal lymph nodes, and in the livers and lungs of dromedaries. Up to 162 nymphs were collected by Majidi Rad et al. (2015) from one infected camel [75] (Table 7). There is also one report of L. serrata nymphs in the lungs of a two-humped camel in Iran [50]. One recent paper investigated phylogenetic relationships among seven L. serrata isolates collected from camels, cattle, goats, sheep and dogs of Iran. Neither host species nor geographical location was associated with genotypes [48].

Conclusion
Camels play an important role in the epidemiology of parasitic diseases under the three aspects of animal health, transmission to other livestock and zoonoses. Parasitic infections of camels may cause reduced milk and meat production, impaired fertility and decreased calving rates. They may also lower the working efficiency or even result in death and consequently high economic losses (e.g. in camels suffering from The rank of the tick species goes from 1 (the most frequent) to 9 (least frequent).  surra). As a result, there is a need for an integrated control programme against economically important parasites of camels as well as to include parasites in health surveillance of camels. Several species of the order Strongylida can infect both camels and ruminants, and ticks with a low host specificity can be shared by several hosts (e.g. Hyalomma dromedarii) and transmit diseases between them. Consequently, deworming and tick control programmes for camels (as well as for affected livestock) are recommended to avoid cross-infections in mixed farming. Concerning the public health importance of camel parasites, several protozoa (e.g. T. evansi) and helminths (e.g. F. hepatica) may be transmitted to humans through close contact with infected camels or indirectly via invertebrate vectors in their surroundings, or via consumption of infected organs of camels. Therefore, surveillance of camel health as well as improving the community's knowledge of public health issues in this regard are necessary. The present work reflects the current state of knowledge on the parasitic fauna of camels in Iran. This knowledge is, however, probably not exhaustive because it was based on clinical and scientific reports and the experience of the authors. Other camel parasites may be present in Iran since they may not have been detected so far and included in published reports, for various reasons. This review will also serve as a reference for future research activities. Detailed epidemiological studies on the parasites of camels strongly call for molecular diagnostic tools for proper classification of species and genotypes to improve the existing diagnostic tools and give more detailed insight into the epidemiology, transmission and risk factors of camel parasites.