The Role of Cryptosporidiosis in Sheep Welfare

Welfare in animal production has been defined as the optimal mental and physiological state of the animals. It has been recently redefined according to ani-mals’ freedoms. As systems, individual sheep and herds are dynamic with constant interaction with each other and the environment. In this interaction, diseases play a fundamental role in welfare. Parasitism is common in sheep, and several manage-ment practices have been established to maintain the herds healthy. Cryptosporidium represents a special case, because it is a highly resistant environmental parasite, that can easily infect lambs, producing weakening diarrheas and even death. In this chapter, the role of cryptosporidiosis in sheep welfare and economic loss will be analyzed, as means of providing information on how to minimize and deal with the infection.


Introduction
Animal welfare and health status in herds go hand in hand. When pathogens are present, disease may develop and will be reflected on decreased productivity. Parasites are pathogens which may be found in the environment as well as in the hosts, some of them as opportunists that can cause disease. Such is the case of Cryptosporidium spp., a ubiquitous parasite with worldwide distribution, which causes diarrhea in newborn lambs that can lead to death or self-limiting diarrheas in immunocompetent hosts. In this chapter, welfare and cryptosporidiosis is discussed in an attempt to provide information on how to prevent and control the disease.

Species and life cycle
There are more than 38 species of Cryptosporidium, but only three main species are reported in small ruminants: C. parvum, C. xiaoi and C. ubiquitum [11]. Cryptosporidium spp. oocysts size ranges from 4 to 4.5 μm, with spherical to ovoid shape, and four sporozoites per oocyst. They can be identified through Ziehl-Neelsen stain, where oocysts are shown as bright pink round bodies. The transmission of the infection happens by direct ingestion of oocysts present in food and water. Once in the host, oocysts excyst in the gut and sporozoites are released, entering the intestinal epithelial cells through the brush border [12]. After excystation, sporozoites are found in the extracytoplasmatic The Role of Cryptosporidiosis in Sheep Welfare DOI: http://dx.doi.org /10.5772/intechopen.99876 parasitophorus vacuole, where the parasite reproduces either asexually or by schizogony, leading to 8 merozoites within a type I meront. Merozoites are capable of invading neighboring epithelial cells and other sites of the intestine, where they either reproduce asexually forming thin-wall oocysts that cause autoinfection or a sexually forming type II meronts differentiating into microgametocytes and macrogametocytes, which will unite to form the zygote. This zygote will form 4 sporozoites in thick or thin-walled oocysts, by a process called sporogony. The ones with the thick wall are released to the environment through feces [13] (Figure 1). Up to 1X10 6 -2X10 6 oocysts/g of feces can be excreted by the host (which are immediately infectious) becoming a source of infection to susceptible lambs [15]. Oocysts can survive in water and in the environment several months, as soon as cool temperatures and suitable moisture exists, and can be easily transported through air and water [16].

Prevalence
Cryptosporidium was incidentally discovered by Tyzzer in 1907, but until 1978 oocyst identification in feces samples was confirmed through microscopy, making it the diagnostic method. Several stains have been proven, but the most common is modified Ziehl-Neelsen. Next came immunological tests which are more sensitive and specific for the detection of antigens, giving rise to immunofluorescent tests. These are specially used in water samples. Finally, genetic tools such as PCR were developed to identify the species [17,18]. Nevertheless, microscopy using stains still remains as the simplest, cheapest and the most common way for detection.
Ever since it was first detected and confirmed as pathogen, there have been many studies regarding prevalence in sheep from different geographical regions, in which its presence may be attributed to either infectivity or the contamination of the environment [19]. In an attempt trying to explain the wide variation in prevalence, it is shown in tables according to Koeppen's climate classification (Tables 1-5).

Figure 1.
Cryptosporidium spp. life cycle [14].     Results show that it can be found in all different climates. One important factor is the high resistance of the oocysts when shed to the environment. Whenever there are conditions in which the parasite can survive (protection from desiccation or avoidance of direct sunlight) it will be present, even in zones with low humidity [87]. As cryptosporidiosis is multifactorial, it is also very important to take into account the immune status of the host. Immunocompetency varies with age, therefore making lambs the most susceptible. When sheep are immunocompetent, they develop the disease with weakening diarrhea and excrete high loads of the parasite, but it is self-limiting. They remain as healthy carriers, still excreting infective oocysts to the environment. Therefore, it is also important to analyze the prevalence results according to the health status of the host. In some countries, such as Iran, where studies with different climates have been undertaken ( Table 5)

Economic loss
Economic loss is reflected not only in mortality, but in retarded growth rates, decreased feed conversion rate, poor carcass quality, veterinary assistance and increased costs due to extra care. Moreover, healthy sheep can shed oocysts, specially periparturient ewes, with the possibility of maintaining the infection within the flock [88] and contaminate the environment [73].
Cryptosporidium causes diarrheas in developing countries, and it has been found that in developed countries it has become a serious problem, due to the limited number of parasitic protozoa in their surveillance programmes, as well as being a neglected disease caused by high confidence in hygiene, municipal sanitization services and good agriculture and livestock practices [18].
The model GloWPa-Crypto was used in [89] and differences were found in oocyst load in extensive and intensive systems, in which intensive ones provided a higher load directly on land.

Prevention, control and treatment
Transmission of Cryptosporidium spp. is influenced by reservoirs and environmental characteristics. Oocysts are sensible to high temperature and desication. Direct sunlight for several hours entirely inactivates oocysts [90]. To prevent and protect lambs from cryptosporidiosis, colostrum is fundamental. Hygiene measures are very important to destroy the parasite and prevent its transmission in between animals and from the environment. Cleaning and disinfecting pens and buildings, the use of clean straw beds, avoiding high number of ewes in the parturition area and separating healthy from ill animals during diarrhea outbreaks, as well as an appropriate and in time administration of colostrum to lambs, aid in the prevention of cryptosporidial outbreaks and decreases the morbidity and mortality in sheep herds [91].
There are three main ways for treating cryptosporidiosis in farms: using drugs (most of them have been proven at laboratory level), fluid therapy and reducing the quantity of oocysts excreted to the environment [92].
There is no specific drug targeted against cryptosporidiosis, although more than 140 active principles have been tested in vivo and in vitro but none of them have been useful for eliminating cryptospodiosis from the infected animal. This can be explained because of its particular intracellular but extracytoplasmatic location in the intestine, making it resistant to antimicrobials as well as a difficult drug target. The first attempts to cure cryptosporidiosis were based on using the same drugs as the ones for genetically related pathogens (Apicomplexa) such as Toxoplasma and Plasmodium, but are not suitable against Cryptosporidium because of differences in its cell biology and biochemistry: it has no apicoplast organelle, neither citiric acid cycle nor cytochrome respiratory chain. Due to the fact that cryptosporidiosis has had a higher impact in underdeveloped countries, the strategy for treatment has been the use of existing medications [14].
Significant results have been found when using halofuginone lactate [93], which is the only one licensed treatment for cryptosporidiosis in calves, thought to interfere with the merozoite and sporozoite stages of Cryptosporidium and proven effective in the control of oocyst shedding [94]. It is an antiprotozoal drug for Eimeria and Theileria, derivative of quinazolinone [95], used both for prevention and treatment [96]. Other drugs that have also reduced the excreted number of oocysts [40] are: paramomycin, (an aminoglycoside broad-spectrum antibiotic, poorly absorbed in the gut, remaining active in the lumen [97]), metronidazole (a nitroimidazole used against giardiasis [95]), benzoxaborole (a synthetic boronheterocyclic compound that inhibits essential enzymes, used an antimalarial) and occidiofungin (a broad-spectrum glycolipopeptide with antifungal activity) [98,99]. Nitazoxanide (nitratiazole benzamide derivative, licensed in humans as treatment for cryptosporidiosis [95]), beta-cyclodextrin (a cyclic oligosaccharide made up of glucose residues [100], used as pharmaceutical excipient [101]) as well as colostrum preparations, probiotics and decoquinate (coccidiostat quinolone derivative [102]) have also been used [103]. Therefore, the following sanitary and breeding recommendations are essential: sectioning of age groups, assurance of sufficient colostrum supply and intake, isolation of sick animals from the healthy ones, avoiding over-population, cleanliness and dryness of the environment, disinfection of premises and daily cleaning of equipment [93].
As alternative treatments, experiments in mice using watery and alcoholic extracts from Curcuma longa and Coriandrum sativum have been effective in reducing the number of excysted oocysts [104]. Peganum harmala, Artemisea herb-alba and Olea europea have shown similar results [105].
The most important measure to lessen the clinical signs of cryptosporidiosis is oral or intravenous fluid therapy. To decrease the spread of the disease, it is imperative to avoid oocyst shedding to the environment. For decontamination of surfaces, over 35 disinfectants have been tested, but only 5 are effective: 50% ammonia, 3% hydrogen peroxide, 10% formalin, Exspor and Oo-cide. Formaldehyde or ammonia gas used for steam heat sterilization and fumigation are also recommended [103]. UV radiation and ethylene oxide have been reported to be effective [106]. Not only lambs may be infected through the fecal-oral route, but they can also get infected by drinking contaminated water. This may happen due to the high number of oocysts released to the environment and their resistance to chlorine and other conventional disinfectants used in water treatment processes. Oocyst concentrations of more than 150/L of surface water have been found in agricultural run-off water [15]. Therefore, another effective way of preventing Cryptosporidium spread into the environment and watersheds is using vegetation buffers, which aid in the retention of oocysts (Figure 2) [107].
Proper composting of manure (>60°C) inactivates oocysts and reduces the risk of their viability. Slurry storage produces ammonia and low pH, and anaerobic digestion using mesophilic and thermophilic bacteria also helps reducing oocyst viability. Fencing sheep away form water sources prevents water contamination with feces [108].
Even though many antigenic target candidates have been characterized, there is still no vaccine with proven effectiveness or ideal cost-benefit ratio [109].

Conclusion
Cryptosporidium spp. is a ubiquitous parasite that directly affects animal welfare by producing self-limiting diarrheas in immunocompetent hosts. In lambs, it is capable of producing a weakening diarrhea which may lead to death. The disease may be complicated by the interaction of other pathogens such as E. coli or Salmonella spp. Asymptomatic sheep may excrete oocysts, becoming a source of infection and contaminating the environment. Prevalence worldwide in sheep herds may be up to 100%. To prevent the disease, hygiene measures should be taken to avoid environmental contamination. Pregnant ewes should be separated from the herd during and after parturition. If lambs get infected, they should be treated in the same way as with any other diarrheic disease, with fluid therapy. Many active principles have been tested, as well as alternative natural remedies such as plant extracts in an attempt to cure cryptosporidiosis which have only shown to reduce the number of oocysts excreted, mildening the disease in lambs and reducing environmental contamination, but none of them cures the disease. Vaccines are still in development as means of prevention. Even though there is neither a specific treatment for curing cryptosporidiosis nor a vaccine, manure should be properly composted and to avoid water contamination, vegetation buffers may be used.
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