4 Tick Borne Cattle Disease
Tick Borne Cattle Disease: Livestock is an integral part of the livelihood of smallholder farmers in Kenya ranging from the high potential areas where mixed crop and rearing of various types of livestock is the main agricultural activity to the arid and semi-arid rangelands where pastoralism and extensive livestock rearing are the main methods of keeping cattle.
Agriculture directly influences rural livelihoods by providing incomes, employment and products for home consumption. It also directly influences prices of commodities and labour markets, amongst other farm-non-farm linkages. In Kenya, this sector accounts for over 27% of Kenya’s gross domestic product (GDP) and 70% of foreign exchange earnings.
The main constraints to livestock production in Kenya includes livestock diseases (mostly tick-borne diseases), poor access to livestock and livestock product markets, poor veterinary infrastructure and inadequate feeds.
1. Theileriosis/ East Coast fever (ECF)
Aetiology of East Coast Fever Cattle Disease
Theileriosis refers to a complex of infections caused by several species of protozoan parasites of the genus Theileria. In Kenya, Theileria parva which causes the classical syndrome referred to as East Coast fever (ECF), is the most economically important tickborne disease. It is widely believed that theileriosis in cattle originated from buffalo populations in Eastern and Central Africa. The main species of Theileria which infect cattle include: Theileria annulata, Theileria mutans, Theileria buffeli, Theileria parva, Theileria taurotragi and Theileria velifera.
East Coast fever was first reported in Kenya in 1904 and spread fast from the two main foci; the Lake Victoria basin and the Coastal strip, as ox transport increased. The economic impact of the disease escalated as the more susceptible Bos Taurus cattle continued to be kept in endemic areas by the European settlers. Theileria parva until recently was thought to exist in three sub-species, namely, T. parva parva, T. parva lawrencei and T. parva bovis causing ECF, Corridor disease and January disease, respectively.
However, new methods of studying the parasites using monoclonal antibodies and deoxyribonucleic acid (DNA) characterization have shown that the three subspecies are not genetically different. Therefore, the parasite is characterised as either cattle or buffalo derived T. parva.
Transmission and life cycle of East Coast Fever Cattle Disease
The main vector of ECF is Rhipicephalus appendiculatus, a three-host tick, commonly known as the brown ear tick. Although the vector for T. parva was identified as early as 1904 details of the life cycle of the parasite in both the tick and in the host animals, has been elucidated only recently . Transmission of T. parva in the tick vector is transstadial whereby it is passaged through the larval or nymphal stages to the adult stage as the tick molts.
After ingestion of infected blood by the vector tick, the infected erythrocytes are lysed leading to the release of piroplasms. In the mid gut of the tick, the piroplasms undergo sexual stages of development leading to formation of macro-gametes, which then undergo syngamy to form kinetes. The kinetes develop further into motile forms which then infect salivary glands epithelium. Tick feeding triggers the process of sporogony where kinetes develop into the infective sporozoites within 3-4 days of feeding.
Following a bite by an infected tick, T. parva sporozoites are injected with the tick’s saliva, enter the host’s lymphoid cells and initiate a reversible transformation of infected cells. This leads to a rapid and exponential increase of infected cells which infiltrate all lymphoid and other tissues. The T. parva sporozoites develop into spherical schizonts then into merozoites leading to the destruction of lymphoid cells 12-14 days after infection. The merozoites are then released and may infect the erythrocytes. In the erythrocytes, merozoites develop into comma or bar-shaped piroplasms.
The clinical syndrome of East Coast Fever Cattle Disease
The predominant clinical signs of ECF include pyrexia, lymphadenopathy, pulmonary and subcutaneous oedema, petechiation and corneal opacity. Acute cases are characterized by sudden weight loss while complete blindness is common in chronic cases. In terminal cases, recumbency, cachexia, hypothermia and nervous signs are common.
Diagnosis of East Coast Fever Cattle Disease
Diagnosis of ECF in the field continues to be predominantly based on clinical signs as a result of inadequate laboratory facilities.
The presence of vector ticks feeding on cattle and knowledge of the distribution and occurrence of the disease contributes towards the diagnosis. In some rare instances, confirmation of diagnosis is achieved through examination of stained blood for piroplasms and lymph node biopsy smears for macroschizonts. Confirmation of Theileria species on microscopic morphology is highly dependent on quality of the smears and skill of the operator.
Aetiology, biology and clinical syndrome of anaplasmosis cattle disease
Anaplasma marginale and A. centrale are the most important anaplasma parasites of cattle in Africa and are rickettsial organisms which infect erythrocytes of cattle. Anaplasma marginale are found near the margins of the erythrocytes while Anaplasma centrale parasites occupy a more central position.
Susceptibility of cattle to anaplasmosis increases with age and adult cattle of any breed are susceptible. Young animals often do not exhibit clinical signs of the disease.
Anaplasmosis presents as an acute, sub-acute or chronic clinical syndrome characterized by high fever and progressive anaemia manifested as pale mucuos membrane and jaundice. In chronic cases, debility and emaciation are common.
In addition to direct effects, pathogenicity due to anaplasma infections is mainly related to destruction of erythrocytes that predisposes the animals to other conditions. Although Boophilus decoloratus ticks are incriminated as the main vectors for anaplasmosis, mechanical transmission and biting flies are also important modes of transmission. Mechanical transmission through repeated use of hypodermic needles as in vaccination campaigns is common.
Diagnosis of anaplasmosis cattle disease
Diagnosis of anaplasmosis is dependent on clinical signs, case history and microscopic detection of initial bodies in stained thin blood films. Knowledge of the microdistribution of the disease is important in the diagnosis as the clinical signs are not pathognomonic.
Antibody-detection serological tests have been developed and validated in laboratory and field studies. The main serological tests include card agglutination test, indirect haemaglutination assay.
Treatment of of anaplasmosis cattle disease
Anaplasmosis is routinely treated with oxytetracylines based formulations and Imidocarb. The success of the treatment is, however, variable depending on the stage and severity of the disease.
Aetiology, biology and clinical syndrome of bovine babesiosis cattle disease
Babesiosis is caused by babesia parasites that are intra-erythrocyte protozoa with worldwide distribution. The main species of babesia that infect cattle in Africa are Babesia bovis and Babesia bigemina. The main tick vector for B. bigemina is Boophilus decoloratus. Boophilus microplus transmits both B. bovis and B. bigemina. The mode of transmission between the ticks and hosts is transovarial where either the nymphs or adult ticks can transmit the disease.
Clinical manifestations of bovine babesiosis varies from a very mild and often symptom less infection to acute and often fatal episodes depending on the species of babesia and the susceptibility of the host animal.
The clinical signs of the acute form are pyrexia, anorexia, depression, weakness and a fall in milk yield. Pale mucuos membrane is the main clinical manifestation. As a result of the destruction of erythrocytes (which is mediated by the release of pharmacologically active sustances), haemoglobinuria and jaundice are the common signs especially in the terminal stages. In the chronic cases, colic, tenesmus and diarrhea are other common signs. Nervous signs may be observed in chronic cases of B. bovis infections.
Diagnosis of bovine babesiosis cattle disease
Babesiosis cattle disease is diagnosed by clinical signs especially haemoglobinuria, pale mucuos and jaundice. Examination of Giemsa-stained blood smears from affected animals is essential for confirmation.
Treatment of bovine babesiosis cattle disease
Various drugs are available for the management of babesia infections but the response depends on the parasite species and clinical stage of the disease. Some of the most commonly used chemotherapeutic compounds include trypan blue, quinoronium sulphate, phenamidine isothionate, diminazene aceturate and amicarbalide isethionate.
4. Heartwater Cattle Disease
Aetiology, biology and clinical signs of Heartwater Cattle Disease
Heartwater is the second most important tick-borne disease of ruminants in Eastern Africa, causing substantial economic losses due to mortality and indirectly, through losses associated with its control (Pegram et al., 1993). It is the most important tickborne disease of small ruminants.
Heartwater affects cattle, sheep, goats and Asian buffaloes. Ticks of the genus Amblyomma are the only known vectors of Ehrlichia ruminantium. Of these A. variegatum is the main vector species throughout most of sub-Sahara Africa.
The distribution of heartwater in Kenya is not well mapped out as is the case with East Coast fever. Though the vector is widely distributed in Western, Eastern and parts of the Rift Valley, the disease is more prevalent in more arid areas of the country such Machakos, Narok, Baringo and Galana.
Clinical signs of which fever and nervous signs are the main ones, range from peracute to innaparent. Invasion of brain tissues leads to the characteristic nervous symptoms including a high-stepping unsteady gait, walking in circles, exaggerated blinking of eyes and chewing movements. Diarrhea and gastro-enteritis may also be observed. Prostration and death are often preceded by convulsions.
Diagnosis of Heartwater Cattle Disease
Since the cattle disease is characterized by sudden death, provisional diagnosis is based on case history, clinical signs and postmortem lesions. Confirmation of diagnosis is by examination of Giemsa-stained brain crush smears where colonies of the organism are detectable in the cytoplasm of vascular endothelial cells. Van Vliet et al. (1995) developed the indirect MAP1-B ELISA which detects antibodies to E. ruminantium. The test has proved to be highly specific and sensitive for use with experimental and field ovine and caprine sera.
Treatment of Heartwater Cattle Disease
The sudden death syndrome makes it impossible to treat the majority of cases of heartwater . If diagnosed early, tetracylines formulations are effective
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