**1. Introduction**

For years, man has relied on livestock for food, drought power, hides and other production activities. In less developed countries, livestock production is mostly done using traditional methods due to limited resources and these small-scale production systems accounts for most agricultural output in these countries [1]. On the other hand, companion animals are equally kept throughout the world. Dogs and cats are particularly kept as pets with increasing numbers in nations that previously did not do so but kept dogs mostly for security. Now, dogs are

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

widely used for different purposes, including companionship, life-saving actions, security as well as hunting and farming [2, 3]. Other than entertainment and sports, horses are also being kept for companionship. These livestock and companion animals are however hosts to many parasites, some of which have detrimental effects on the health and productivity of those affected. Protozoa such as *Giardia duodenalis* affect a wide range of domestic and wild animals, with serious clinical consequences especially in young animals.

*G. duodenalis* (syn. *Giardia lamblia*, *Giardia intestinalis*), a flagellate protozoan parasite, and the aetiological agent of giardiasis, is one of the most prevalent and widespread intestinal parasite in humans and several vertebrate animal species worldwide [4]. The taxonomy of the genus is mainly based on morphology and genetic evidence. According to these criteria, six species have been recognised in the genus *Giardia* and these include *G. duodenalis* in humans and other mammals, *G. agilis* in amphibians, *G. muris* and *G. microti* in rodents, *G. psittaci* and *G. ardeae* in birds. In recent years, phylogenetic analysis and enzyme electrophoresis have revealed the existence of eight assemblages A–H within the species *G. duodenalis* [5–7]. *Giardia* from humans appears to fall exclusively into Assemblage A and B while C and D are dog specific assemblages. Assemblage E is isolated from hooved animals, a characteristic of isolates from sheep, goats, cattle and pigs [8]. Cats are hosts F or Assemblage F while rats are hosts for Assemblage G [9, 10]. Assemblage H has been reported in the grey seal [11].

*G. duodenalis* is a frequently encountered intestinal parasite of domestic animals, especially livestock, dogs and cats. *Giardia* infections have been reported widely in livestock and companion animals with varying prevalence in different parts of the world, but high frequency was mostly in dairy calves [12–16]. As a parasite, *Giardia* has a broad host range, however, the adverse consequences of infection and its pathogenic potential are best recognised in humans [6]. It causes an estimated 2.8 × 10<sup>8</sup> human cases per annum [17]. In Asia, Africa and Latin America, about 200 million people have symptomatic giardiasis with some 500,000 new cases reported each year [18]. Its simple life cycle involving an environmentally resistant cyst (**Figure 1**) provides greater opportunities for the parasite to be transmitted directly from one infected individual to another, or indirectly through contamination of the environment or food [4].

**Figure 1.** *Giardia* cyst: wet smear stained with iodine (source: https://www.cdc.gov/dpdx/giardiasis/index.html).
