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The cattle industry faces a substantial risk from haemoprotozoan parasites, which can lead to decreased productivity and increased mortality in dairy animals. Key haemoprotozoa affecting dairy cattle include Babesia, Theileria, and Trypanosoma. Although the precise financial losses caused by haemoprotozoan infections in dairy animals have not been fully quantified, it is reported that the annual losses attributed to Theileria parva alone exceed USD 300 million. Furthermore, parasites such as Theileria and Babesia are transmitted by tick vectors. In India, the annual financial losses due to tick-borne diseases and tick infestations are estimated at USD 191.15 million. Consequently, it can be inferred that the global annual losses from haemoprotozoan infections likely surpass those associated with tick-borne diseases and the losses from T. parva alone. The primary objective of the book "Haemoprotozoan Infections in Dairy Animals" is to provide a comprehensive discussion of blood parasites affecting dairy cattle. This book addresses important blood parasites, including Babesia, Theileria, and Trypanosoma. Additionally, it covers significant Rickettsial parasites that may complicate accurate diagnosis by mimicking haemoprotozoa infections. The book also explores crucial topics such as the diagnosis of haemoprotozoa infections, resistance to anti-protozoal drugs, role of nutrition in parasite control, and effective dairy farm management strategies to control these infections. The author hopes that this book will serve as a valuable resource for veterinary undergraduates and postgraduate students, educators, and veterinary professionals.

Protozoa are considered as unicellular eukaryotic organisms and evolved after bacteria and thousands years early to multi-cellular organisms as well as animals. This unicellular eukaryotic organism contains all the organelles or structures like multi-cellular organisms but in single cells. Similar to multicellular, the genetic information of protozoa is also stored in chromosomes. The protozoa differ from bacteria in different manners. The differentiating features of bacteria and protozoa are given in Table 1. 1. General Structures of Protozoa Protozoa, like other eukaryotic cells, contain a nucleus, endoplasmic reticulum, mitochondria, Golgi apparatus, and lysosomes. Beyond these common organelles, protozoa feature a range of unique structures with specific functions that enable them to operate independently. Protozoan cells can be categorized into two primary components: the cytoplasm and the nucleus.

Kingdom: Protozoa Phylum: Euglenozoa Class: Kinetoplasta Order: Trypanosomatida Family: Trypanosomatidae Genus: Trypanosoma Members of the genus Trypanosoma are responsible for trypanosomosis in animals and human beings and are found in the blood vascular system and tissues all over the world. All the species of trypanosomes are transmitted biologically or mechanically through an arthropod vector except T. equiperdum, which is transmitted through coitus in equines.

Theileriosis is a tick-borne protozoan disease that affects a wide range of domestic and wild animals, particularly cattle. While multiple species of Theileria exist, Theileria parva and Theileria annulata are the most important pathogens in terms of their impact on domestic cattle. This disease is transmitted by ixodid ticks and has a significant impact on cattle populations in tropical and subtropical regions. Theileriosis poses a substantial threat to livestock productivity, affecting economic stability in many countries, especially those that rely heavily on agriculture and cattle farming. The disease has two primary forms: East Coast fever (ECF), caused by T. parva, which predominantly affects cattle in eastern, central, and southern Africa; and tropical theileriosis, caused by T. annulata, which affects cattle across northern Africa, the Middle East, and parts of Asia. Both diseases are highly pathogenic and, if left untreated, can lead to high morbidity and mortality rates, significantly impacting livestock production.

Bovine babesiosis is a significant febrile disease, primarily affecting cattle and buffalo, transmitted by ticks. The disease is marked by the rapid proliferation of parasites within the bloodstream, leading to the extensive destruction of red blood cells. This results in a cascade of clinical symptoms, including anemia, jaundice, hemoglobinuria, and splenomegaly, with the potential for severe cases to culminate in death. The acute form of bovine babesiosis is particularly severe, often characterized by these pronounced symptoms, which can lead to rapid deterioration in the affected animals. Babesiosis is not merely an acute illness but can also persist as a chronic infection. Chronic bovine babesiosis is typified by ongoing anemia and varying degrees of weight loss, reflecting the enduring impact of the parasite within the host. Economically, this disease poses a formidable challenge, especially in regions where cattle are most susceptible. Since the first description of Babesia bovis by Victor Babes in Romania in 1888, numerous distinct species have been identified, each contributing to the global burden of this disease (Hunfeld et al., 2008). The impact of bovine babesiosis on livestock improvement efforts in endemic regions is profound. The introduction of susceptible, naive animals into these areas often leads to significant losses, as these animals are highly vulnerable to the disease.

The reclassification of the order Rickettsiales was predicated upon comprehensive genetic analyses of 16S rRNA, groESL, and surface protein genes. Consequently, organisms within this order were systematically assigned to one of two families: Anaplasmataceae and Rickettsiaceae. Within the Anaplasmataceae family, phylogenetic analyses consistently delineated four genetically distinct clades: (1) Anaplasma, (2) Ehrlichia, (3) Wolbachia, and (4) Neorickettsia. Despite the obligate intracellular nature of rickettsial organisms in both families, those classified under Rickettsiaceae proliferate freely within the host cell cytoplasm, whereas members of the Anaplasmataceae family are confined exclusively to membrane-bound vacuoles within the cytoplasm of host cells. The first documented cases of anaplasmosis trace back to the late 19th century in South Africa. However, it wasn’t until 1910 that the causative agent of the disease was conclusively identified morphologically as “marginal points” within red blood cells by Max Theiler, later named it Anaplasma marginale. A year later, he identified another species, A. centrale, which caused a milder form of the disease in cattle. During the 1930s, Sanborn, Stiles, and Moc demonstrated the mechanical transmission of A. marginale by horse flies and stable flies. In the late 1980s, the life cycle of A. marginale was fully elucidated in ticks belonging to the genus Dermacentor.

Haemoprotozoan parasites are responsible for causing severe infections in humans as well as animals across the world. The important hemoprotozoan diseases of livestock are trypanosomosis, theileriosis, babesiosis, and anaplasmosis, which are caused by several species of Trypanosoma, Theileria, Babesia, and Anaplasma, respectively, in several species of livestock. These diseases caused huge impact on health and productivity of livestock as well as human beings and causes great economic losses to the livestock production n terms of morbidity and mortality worldwide. In India, the annual economic loss has been esteemed in the livestock due to theileriosis, babesiosis and trypanosomosis of Rs 8426 crore, Rs 4000 crore and Rs 4474 core, respectively. The major clinical signs of the haemoprotozoan disease varies from fever, anorexia, anaemia, abortion, and even death in the acute form of infections. The symptomatological treatment is a quite common practice in the field condition to treat the animals suspected with haemoprotozon infection leading to the development of resistance in animals to currently available drugs against haemoprotozoans. The accurate and prompt diagnosis of haemoprotozoan infection is a key to control these diseases. Routine diagnosis of haemoprotozoan infection has been rely on clinical findings and microscopical demonstration of the infective parasitic stages in the blood or tissue fluid smear. Conventional diagnostic techniques such as Microscopical examination techniques and Immunological assay provide the definite clues about parasitic infections in general, but these tests have some limitations.

Livestock has been essential for Indian agriculture since prehistoric times. Livestock is crucial for tripling farmers’ revenue, for bovines—particularly cattle and buffaloes—play a crucial role in the economy. India has the largest number of livestock owners, with a wide variety of livestock and poultry breeds that are essential to the socioeconomic advancement of rural communities. The production of consumables and maintaining the country’s food security are inextricably related to the livestock and agricultural sectors. Numerous illnesses have a detrimental effect on the health and productivity of livestock and are highly significant economically. Livestock illnesses have negative effects on producers, costing them money in upkeep, resources, and production. Protozoal infections are a major contributor to the global burden of infectious diseases and have a profound effect on health, society, and the economy. Nearly one-sixth of the world’s population is at risk of dying from serious diseases like malaria (Plasmodium spp.), African sleeping sickness (Trypanosoma brucei), Chagas’ disease (Trypanosoma cruzi) and various forms of cutaneous and visceral leishmaniasis (Leishmania spp.). Although the burden of protozoal diseases primarily affects tropical and subtropical regions, environmental changes and ecological modifications brought about by both natural and manmade factors have had and are likely to continue to have a significant impact on the emergence and spread of these infections in high-income nations.

There are number of internal and external factors that affect the production performance of animals, among which parasites and parasitism are major of concern constraints to animal’s productivity especially in tropical countries. Feed intake and nutrient requirements have been recognized for long time as an important parameter for determining the efficiency of animal production. Most of the parasitic infection in domestic animals is caused by gastrointestinal nematode, which may result in depression in appetite, impairment in GI functions, alteration in protein, energy and mineral metabolism and changes in water balance. Nutrition can affect the ability of the host to cope with the consequences of parasitism and to contain and eventually to overcome parasitism. Since it is proposed that the host gives priority to the reversal of the pathophysiological consequences of parasitism over other body functions, it is to be expected that improved nutrition will always lead to improved resilience. On the other hand, it is proposed that the function of growth, pregnancy and lactation are prioritized over the expression of immunity. Improved nutrition may affect the degree of expression of immunity during these phases and can thus influence the resilience and resistance of host to parasite infection.

Dairy animals are the backbone of animal husbandry. India is the largest milk producer and ranks first in the world with a share of 25% of global milk production. Haemoprotozoan diseases pose significant limitations to the health and production of cattle. It leads to significant losses in the livestock industry worldwide. However, most protozoan parasites in the blood are known tocause anaemia by inducing erythro-phagocytosis. In terms of  mortality, reduced milk production and reduced immunity power, hemoprotozoan parasites pose a major threat to the livestock population. Theileria, Babesia, Anaplasma and Trypanosoma are the most important hemoprotozoan diseases of veterinary importance. These diseases affect different livestock species, caused by different species of Trypanosoma, Theileria, Babesia and Anaplasma. Tick-borne hemoprotozoan infections have a significant negative impact on the health and productivity of cattle and result in major losses to the global livestock industry. In tropical and subtropical regions, tick-borne hemoprotozoan infections have a significant impact on animal production. In India, these hemoprotozoan parasites have long posed a serious threat to the survival of exotic and crossbred cattle (Ananda et al., 2009). Haemoprotozoan diseases have deleterious impact on health and production of animals causing death in acute cases, production losses in chronically affected animals which decrease economic share of livestock sector (Bharti et al., 2022)