**3. Types of internal parasites in chickens**

## **3.1 Blood parasites of chickens**

Birds may be hosts for a number of blood-inhabiting protozoan species and nematode worms which are transmitted by haematophagous arthropods [13]. Protozoan parasites include haemosporidia which belong to several genera such as *Plasmodium*, *Haemoproteus*, *Leucocytozoon*, *Hepatozoon*, *Babesia*, and *haemoflagellates* that belong to the genus *Trypanosoma*. Most of the birds are susceptible to being infected with blood parasites and the prevalence rate, especially in the tropics, maybe more than 30%. Blood parasites vary in their host, both for the arthropod vectors and the vertebrate host, specificity. While some are restricted to a small number of host species, others can survive and reproduce in a wide variety of birds and arthropods [14]. Internal parasites are mainly classified into two groups (Protozoa and Helminthes). Protozoa include gastrointestinal and blood protozoans while helminths include three groups: Trematodes, Cestodes and Nematodes [15].

Many recent studies have focused on avian blood parasites as a model system for host–parasite interactions in evolutionary and ecological aspects. Extensive laboratory studies have been conducted describing their pathologies, especially for species of Leucocytozoon). Based on the current taxonomy, three species of Leucocytozoon and three species of *Trypanosoma* are found in the domestic chicken *Gallus gallus domesticus*, mainly in tropical and subtropical regions worldwide [16].

These are: *Leucocytozoon macleani. Leucocytozoon caulleryi. Leucocytozoon schoutedeni. Trypanosoma numidae. Trypanosoma calmettei. Trypanosoma gallinarum.*

All of these species are well distinguished based on the morphology of their blood stages and/or laboratory experiments documenting their transmission and life cycles. The pathogenicity of many species of Leucocytozoidae (Sporozoa, Haemosporida) in wild birds is unclear, many cases of mortality have been reported in domestic chickens and other poultry. The most common vectors of avian trypanosomes are arthropods that belong to the families Hippoboscidae, Culicidae, Ceratopogonidae, and Simuliidae [17]. In addition, dermanyssid mites have been identified as avian trypanosome vectors. Little is known concerning the pathogenic effects of trypanosomes in chickens although artificial infection with *Trypanosoma brucei* showed no obvious impairment of health. Previous accounts of blood parasites in chickens in Africa are relatively rare. In a study in Zimbabwe, 4 of 94 examined chickens harbored *Leucocytozoon sabrazesi*, and 5 of the 94 examined chickens harbored *L. macleani* in Ghana; however, no Leucocytozoon or *Trypanosoma* infections were detected [18]. Earlier studies showed Leucocytozoon species infected 55 of 163 (34%) examined chickens in Ibadan, Nigeria. In a study of 110 chickens observed in Anambra, and Nigeria, none was infected with blood

parasites. In Tanzania, it is reported that out of 150 chickens tested, more than 50% were infected with *L. schoutedeni* [19].

### **3.2 Helminthes of chickens**

The name "helminths" is derived from the Greek word helmins or helminthos, a worm, and is usually applied only to the parasitic and non-parasitic species belonging to the phyla Platyhelminthes (flukes, tapeworms and other flatworms) and roundworms (Nemathelminthes). The helminths are invertebrates characterized by elongated, flat or round bodies. The flatworms or platyhelminths (platy from the Greek root meaning flat) include flukes and tapeworms [20]. Round worms are nematodes (nemato from the Greek root meaning thread which includes helminths have similar anatomic features that reflect common physiologic requirements and functions. The outer covering of helminthes is the cuticle or tegument; nutrients must be absorbed through the tegument. A helminths also has a head and tail end, and its tissues are differentiated into three distinct tissue layers: - ectoderm, mesoderm and endoderm [21]. Parasitic helminths of chickens are commonly divided into three main groups:
