Heartwater and other rickettsial disease of goats

09/06/2023

Where does pink eye come from? Though flies and other insects may serve as vectors, goat pink eye comes from other goats. It often shows up after shows, where goats may contract the disease then become more susceptible due to stress from transport. Or it may break out within a herd during kidding season. Crowded barn conditions exacerbate problems. Goats rub against each other at feed troughs and contact the same bedding, so separate affected animals to avoid further transmission.

Early goat pink eye signs include squinting due to increased light sensitivity, frequent blinking, swelling of tissue around the eyes, watery discharge from the eyes, and reddening of the sclera (white of the eye.) Later symptoms include cloudiness within the cornea which looks like a white or bluish milky film over the iris and pupil. Blood vessels may grow across it and the entire cornea may appear red. In severe cases, the pupil may develop a pit-like ulcer, which will cause blindness if it ruptures. This can then spread infection, and the blood may turn septic, which is quickly lethal.

09/06/2023

Goat pink eye, formerly called infectious keratoconjunctivitis, refers to inflammation of both the cornea and conjunctiva. It can be the scourge of an otherwise healthy herd during summer months when flies cluster around eye tissue but is a highly contagious and communicable eye infection in goats at any time of the year. Caused by several different bacteria, goat pink eye usually leaves no long-term damage.

18/04/2023

18/04/2023

Heartwater (cowdriosis) is an important, often fatal, tick-borne disease of domestic and wild ruminants in sub-Saharan Africa and some Indian Ocean and Caribbean islands. The causal agent, Cowdria ruminantium (Cowdry 1925), is a rickettsia closely related to members of the genus Ehrlichia, and is probably a part of a complex of genomic species. Imported breeds of sheep and goats (especially Angoras) are highly susceptible, but indigenous populations of endemic areas may be resistant to infection. Very young stock (less than 9 d old) possess a natural resistance that is unrelated to the immune status of the dams. Symptoms of heartwater vary, but usually begin with fever and may involve neurological signs and respiratory distress. Clinical diagnosis is based on symptoms, history of tick-exposure and post-mortem findings, and is confirmed by demonstration of characteristic rickettsial organisms in vascular endothelial cells. Laboratory diagnosis is retrospective and includes fluorescent antibody and enzyme-linked immunosorbent assays. Serological tests are compromised by non-specific reactions with certain Ehrlichia spp. DNA and oligonucleotide probes have been developed, but are thus far unavailable in many countries affected by heartwater. Treatment with tetracyclines is effective if begun in the early stages of infection. Control is based on a knowledge of the disease cycle in nature, and is achieved through judicious tick control, vaccination or both. A virulent, blood-based vaccine is available. Existence of a carrier state in recovered animals, including wild ruminants, complicates control efforts, and eradication is feasible only in circumscribed foci. Problem areas in fundamental and applied research on heartwater, as it affects sheep and goats, are discussed.

14/03/2023

Two main methods are currently being used by farmers in the heartwater regions to control this disease in cattle and other stock, namely strategic control of ticks and total control of ticks. Some farmers make successful use of the latter method, particularly in areas which are marginal for the disease. Total tick control requires top managerial skills, which includes continual expert supervision, a relatively rare asset. The majority of farmers, often unintentionally, apply strategic control of ticks to control heartwater, either without or with vaccination against the disease. In this case the objective of tick control is to minimize "tick worry" without interfering too drastically with natural transmission of the disease. This method would make provision for natural immunization of young animals (a more uncertain method than vaccination) and the maintenance of immunity. In practice these methods appear to diminish deaths from heartwater appreciably, but do not protect all animals from the disease. Furthermore, they appear to be more effective in cattle than other stock. Although strategic control has an evolutionary background and considerable merit under African conditions, it is being applied in an empirical way because of paucity of information on the epidemiology of heartwater. More information on the infection rate in and infectivity of ticks (percentage of infected ticks) offer challenging research possibilities.

Cowdriosis an infectious, noncontagious, tickborne rickettsial disease of ruminants. The disease is

04/09/2022

Rickettsial infections and related infections (such as anaplasmosis, ehrlichiosis, and Q fever) are caused by an unusual type of bacteria that can live only inside the cells of another organism.
Most of these infections are spread through ticks, mites, fleas, or lice.
A fever, a severe headache, and usually a rash develop, and people feel generally ill.
Symptoms suggest the diagnosis, and to confirm it, doctors do special tests that use a sample from the rash or blood.
Antibiotics are given as soon as doctors suspect one of these infections.
Rickettsiae and related (rickettsia-like) bacteria (such as Ehrlichia, Anaplasma, and Coxiella burnetii bacteria) are an unusual type of bacteria that cause several similar diseases, including the following:
Rocky Mountain spotted fever
Epidemic typhus
Ehrlichiosis
Anaplasmosis
Q fever
These bacteria differ from most other bacteria in that they can live and multiply only inside the cells of another organism (host) and cannot survive on their own in the environment.
Many species of these bacteria live in small animals (such as rats and mice), which are called the host. Cattle, sheep, or goats are the hosts for Coxiella burnetii, which causes Q fever. Humans are the usual host for Rickettsia prowazekii, which causes epidemic typhus. Host animals may or may not be ill from the infection.
Rickettsiae and rickettsia-like bacteria are usually spread to people through the bites of ticks, mites, fleas, or lice that previously fed on an infected animal. Ticks, mites, fleas, and lice are called vectors because they spread (transmit) organisms that cause disease from one host to another. Q fever, caused by Coxiella burnetii, can be spread through the air or in contaminated food and water and do not require a vector.
Each species of rickettsiae and rickettsia-like bacteria has its own hosts and usually vectors.
Some of these bacteria (and the diseases they cause) occur worldwide. Others occur only in certain geographic regions.
Some of these bacteria infect the cells lining small blood vessels, causing the blood vessels to become inflamed or blocked or to bleed into the surrounding tissue. Other bacteria (Ehrlichia and Anaplasma) enter white blood cells.
Where damage occurs and how the body responds determine which symptoms develop
Some Rickettsial and Related Infections
Symptoms of Rickettsial Infections
Different rickettsial infections tend to cause similar symptoms:
Fever
Severe headache
A characteristic rash
A general feeling of illness (malaise)
A sore covered by a black scab (eschar) may form at the site of the bite. Because the rash often does not appear for several days, early rickettsial infection is often mistaken for a common viral infection, such as influenza. People may have swollen lymph nodes.
As the infection progresses, people typically experience confusion and severe weakness—often with cough, difficulty breathing, and sometimes vomiting.
Scrub Typhus
Scrub Typhus
IMAGES COURTESY OF YOSHIKI TANIGUCHI, MD, AND THE DERMATOLOGY ONLINE JOURNAL.
When the infection is advanced, gangrene may develop, the liver or spleen may enlarge, the kidneys may malfunction, and blood pressure may fall dangerously low (causing shock). Death can result.
Diagnosis of Rickettsial Infections
A doctor's evaluation
Blood tests and biopsy of the rash
Because rickettsiae and rickettsia-like bacteria are transmitted by ticks, mites, fleas, and lice, doctors ask people
Whether they have been bitten by a tick or another vector
Whether they have traveled to an area where these infections are common
Being bitten is a helpful clue—particularly in geographic areas where rickettsial or a related infection is common. However, many people do not recall such a bite.
If doctors suspect Q fever, they may also ask whether people were at or near a farm (because cattle, sheep, and goats are the host for the bacteria that cause this infection).
Symptoms also help doctors diagnose these infections. Doctors ask people
How long it took for the rash to appear after they were bitten (if known)
Whether they have other symptoms
A physical examination is done to determine which parts of the body are affected and what the rash looks like. Doctors also look for an eschar that people may not have noticed and for swollen lymph nodes.
Testing
Testing is usually needed to confirm the diagnosis. Often, doctors cannot confirm an infection with rickettsiae or rickettsia-like bacteria quickly because these bacteria cannot be identified using commonly available laboratory tests. Special blood tests for these bacteria are not routinely available and take so long to process that people usually need to be treated before test results are available. Doctors base their decision to treat on the person's symptoms and the likelihood of possible exposure.
Useful tests include
Blood tests that detect antibodies to rickettsiae or rickettsia-like bacteria
If people have a rash, removal of a small sample of affected skin for testing (biopsy)
Doctors use two techniques to make the bacteria easier to detect and identify:
In immunofluorescence assays, foreign substances produced by the bacteria (antigens) are labeled with a fluorescent dye.
The polymerase chain reaction (PCR) technique is used to increase the amount of the bacteria's DNA, so that the bacteria can be detected more rapidly.
Treatment of Rickettsial Infections
Antibiotics
Antibiotics are usually started without waiting to get the results of tests. Early treatment of rickettsial infections can prevent complications from developing, reduce the risk of dying, and shorten the recovery time.
Rickettsial infections respond promptly to early treatment with the antibiotics (doxycycline preferred). These antibiotics are given by mouth unless people are very sick. In such cases, antibiotics are given intravenously.
After treatment, most people with a mild infection noticeably improve in 1 or 2 days, and fever usually disappears in 2 to 3 days. People take the antibiotic for a minimum of 1 week—longer if the fever persists. When treatment begins late, improvement is slower and the fever lasts longer. If the infection is untreated or if treatment is begun too late, people may die, especially if they have epidemic typhus, scrub typhus, or Rocky Mountain spotted fever.
Ciprofloxacin and other similar antibiotics may be used to treat Mediterranean spotted fever but are usually not used to treat other rickettsial or related infections.

04/09/2022

A study was undertaken to assess the prevalence of anaplasmosis infection in goats of Ramanathapuram district of Tamil Nadu for the period from September 2015 to February 2016. Total of 130 blood smears were collected from goats flocks reared in and around Melakidaram village of Ramanathapuram district with the history of dullness, severe dehydration, tick infestation, and anorexia. Clinical examination revealed that all animals were anaemic with pale mucous membrane and watery blood and all animals were highly infested with Rhipicephalus species. Blood smears were subjected on Giemsa stained and examined under light microscope. Out of 130 smears, 34 were found to be positive for anaplasmosis with the per cent positivity of 26.15. Age wise prevalence indicated that 8 (19.04%), 21 (28.37%) and 5 (35.71%) goats were found to be positive under less than six months, 6 months to one year and above one year, respectively. All the suspected goats were responded to the treatment with tetracycline @ 20 mg/kg body weight and haematinics. The present study emphasis the stake holders should take appropriate measures to control the tick population and also institute the chemoprophylaxis before onset of monsoon season.

04/09/2022

Prevention
Tick control in pastures is the mainstay of cowdriosis prevention. Control is difficult to achieve, because Amblyomma ticks have developed acaricide resistance and because ticks feed off many hosts and have a high rate of reproduction. Complete elimination of tick infestation may not be possible in some localities and in any case is not desirable, because exposure to low levels of the organism is effective in developing immunity. In some parts of South Africa, goat herds are given oxytetracycline every 14 days during the summer months. Controlled infection followed by antibiotic administration has been tried as a means of immunizing small ruminants. Such a method is effective in preventing disease caused by a homologous strain of E. ruminantium but has no effect against a heterologous strain.
An attenuated live strain of E. ruminantium is available as a vaccine, but it has not been tested in field conditions. Immunity after disease is not lifelong; time to emergence of susceptibility to reinfection varies, ranging between 6 and 58 months. Mortality rates in sheep range between 6% and 80%, depending on the breed (Persian or Africander sheep versus Merino sheep). Mortality rates for Angora goats can exceed 90%.4-6

31/08/2022

Lifecycle
The bont tick is a three-host tick, where every stage (larvae, nymph, adult) of the tick feeds on a different animal. The bont tick get infected when it feeds on infected or carrier animals and then transmits the disease to a susceptible animals with their next feeding on second- or third host.

31/08/2022

Heartwater is a tick-borne disease, which negatively affects the South African livestock industry and is transmitted by the Bont tick (Amblyomma herbraeum)
Symptoms
Symptoms become noticeable in sheep 7-35 days, and in cattle, 9-29 days, after infection. Symptoms include foaming at the mouth, listlessness, high fever and loss of appetite. Animals start to make constant chewing movements, have difficulty breathing, and exhibit a high-stepping gait. Other symptoms include head pressing, lying down with the head pulled backwards and legs stretched out, and padding movements. Fluid builds up around the chest, belly, sac around the heart, lungs, and windpipe of the infected animal.

04/05/2022

Clinical Diagnosis
Infected domestic ruminants exhibit a wide range of clinical signs varying from a peracute to mild (clinically inapparent) form. The incubation period in naturally infected cattle ranges from 9 to 29 days (average 18 days) and that of sheep and goats 7-35 days (average 14 days). Peracutely affected animals die within a few hours after the initial fever, either with or without any clinical signs
Acute heartwater is the most common form of the disease in endemic areas. Fever of 40°C in bovine or higher for sheep and goats (40.5°C), which usually persists for 3-6 days and is followed by a drop of 1°C or more shortly before death. Animals gradually show inappetence and eventually stop feeding. Cessation of rumination and difficult breathing follows. Petechiae are visible on the mucous membranes of the conjunctiva (mainly cattle). During the latter stage of acute heartwater, the majority of animals manifest nervous symptoms ranging from a mild incoordination to pronounced convulsions. They are hypersensitive when handled or startled. The gait of affected animals becomes progressively more unsteady, whereas some animals show hypermetria, especially of the forelegs (mainly cattle). They eventually become prostrate, assume a position of lateral recumbency and show intermittent leg-paddling, chewing movements, opisthotonus, licking of the lips and nystagmus. A large amount of froth is usually present at the mouth and nostrils. Diarrhoea is occasionally seen in cattle, sheep and goats.
Less severe cases (subacute and mild) occur with clinical signs ranging from slightly less intense than the acute form to little or no signs at all.

04/05/2022

Macroscopic pathology
Lesions in cattle, sheep and goats are similar, although quite variable in extent and some changes are more common in certain species than in others. Effusion of body cavities, (hydropericardium, hydrothorax, and, in some cases a degree of ascites) is a very common change in most fatal cases of heartwater. The transudate is usually transparent or slightly turbid, light yellow fluid that often coagulates on exposure to air. The volume of fluid ranges from 20 ml in goats, about 0.5 L in sheep to several litres in cattle (Steck, 1928). A hydropericardium, as indicated by the name ‘heartwater’, is a striking change in most animals that die of the disease and is usually more pronounced in sheep and goats than in cattle (Henning, 1956).
Oedema of the lungs is a regular finding and appears to be more severe in most animals that die peracutely from the disease (Pypekamp and Prozesky, 1987). The interlobular septa of the lungs, mediastinum and associated lymph nodes are oedematous and serous frothy fluid oozes from the cut surface of the lung. The trachea and bronchi often contain serofibrinous exudates, and their mucosae are congested, with petechiae and ecchymoses.
Splenomegaly is present although less strikingly in sheep and goats. The cut surface is dark red in colour and has a pulpy consistency. In animals that die peracutely, it is often impossible to make a diagnosis on macroscopical lesions alone; splenomegaly, epi- and endocardial haemorrhages are sometimes the only significant changes (Alexander, 1931). Hepatic lesions are less striking with only a mild hepatomegaly present and the gallbladder slightly distended.
Congestion and/or oedema of the mucosa of the abomasum are regularly seen in cattle, but are less common in sheep and goats. Enterorrhagia (small and large intestine) is present in a small percentage of domestic ruminants, particularly Jersey cattle.
The lymph nodes are moderately swollen in most animals. The cut surface is moist and petechiae are often present, especially in the retropharyngeal, submaxillary, cervical, bronchial and mediastinal lymph nodes (Alexander, 1931). Petechiae are frequently visible on mucous membranes of tissues including those of the urinary bladder, va**na, epi- and endocardium and conjunctiva.
The nervous symptoms observed in affected animals are usually attributed to oedema of the brain, although it is often difficult and sometimes impossible to detect swelling of the brain macroscopically. Occasionally, the entire brain, but particularly the gyri of the cerebellum may be strikingly swollen and severe oedema of the brain may even result in a partial prolapse (herniation) of the cerebellum through the foramen magnum. Most animals that die of heartwater show congestion and oedema of the meninges. There is an accumulation of excessive fluid in the subarachnoid space and thickening of the choroid plexus, which has a dull greyish appearance. In some animals, petechiae and ecchymoses and sometimes sugillations are evident in the midbrain, brain stem and cerebellum (Pienaar et al., 1966).
Histopathology
Comprehensive studies on the histopathological changes of heartwater were made by Steck (1928), Alexander (1931) and Pienaar et al. (1966).
Lungs: An alveolar and interstitial oedema occurs in most animals but is not always discernible histopathologically.
Kidneys: Nephrosis of varying degree is a common change in domestic ruminants that die of heartwater. The observations of Steck (1928) of a multifocal lymphocytic interstitial nephritis occurring in cattle, sheep and goats could not be confirmed in subsequent studies (Uilenberg, 1983).
Brain: Lesions in the brain of cattle, sheep and goats were described by Pienaar et al. (1966) and are characterized by changes compatible with oedema, such as widened perivascular spaces which sometimes contain oedematous fluid or protein droplets; swollen, often necrotic, astrocytes; swollen axons, and multifocal microcavitations and haemorrhages affecting mainly the midbrain, brain stem, cerebral white matter and cerebral peduncles. A perivascular accumulation of cells, mainly macrophages and a few neutrophils, and occasionally a vasculitis, were observed in all the bovines and in only about 50% of the sheep. A diffuse meningitis, mainly macrophages, was present in a few bovines only. In the majority of animals, a fibrinous choroiditis occurred and occasionally mutifocal glial nodules, mainly confined to the neutrophil around small blood vessels, were apparent in sheep and cattle. Brain lesions in recumbent animals often comprise different degrees of status spongiosus and in severe cases, the white matter of the entire brain may be affected.
Other organs: in most animals that die of heartwater the hepatic changes are inconspicuous; the lymph nodes are congested and oedematous; and congestion is the only splenic change.
Variable numbers of E. ruminantium colonies are discernable in the cytoplasm of endothelial cells, particularly those of the brain and lungs. Cowdry (1926) and Steck (1928) frequently also observed colonies in the endothelial cells of glomerular capillaries. As a general rule, however, these colonies are difficult to find in haematoxylin- and eosin-stained sections.
Several species of game are susceptible to heartwater but reports on the pathological changes in game that died of heartwater are limited and in most cases, lesions are very similar to that described in domestic animals (Young and Basson, 1973; Prozesky, 1987).
Transmission electron microscopy studies of the lung lesions in sheep and goats reveal the presence of minor cytopathic changes in endothelial cells. Apart from mild swelling of mitochondria and endoplasmic reticulum, no other changes occur in most parasitized alveolar endothelial cells. Non-parasitized endothelial cells are sometimes swollen, or even necrotic, and are separated from their basement membranes. Oedema of blood vessel walls is infrequently seen (Prozesky and Plessis, 1985a, b).
In all suspected cases, a diagnosis of heartwater must be confirmed by the demonstration of Ehrlichia organisms in Giemsa-stained preparations made from the hippocampus.

04/05/2022

Heartwater only occurs where its tick vectors, Amblyomma, are present. Countries where heartwater has been conclusively diagnosed are listed in the table. The improvement of molecular diagnosis allows confirmation of the presence of E. ruminantium in different countries. In South Africa, Plessis and Kümm (1971) isolated E. ruminantium, named the Kümm strain, from a Hyalomma tick removed from an eland in a non-heartwater endemic area where A. hebraeum ticks are not present.
According to Camus et al. (1996), after examining various reports and veterinary literature since 1930, heartwater does not occur in Guinea, Sierra Leone, Togo, Saudi Arabia and Yemen, even though there is at least one efficient vector present in these countries and it occurs in the neighbouring countries. However, three cases were reported in Oman in 2018 (El-Neweshy et al., 2019). A nervous condition and lesions very reminiscent to those of heartwater have been described in cattle in Cuba (Figueroa and Sutherland, 1968; Figueroa et al., 1970; Figueroa and Sutherland, 1972) and in French Guiana (Sapin, 1981). However, until now, no report or confirmation of a heartwater clinical case has been made in both countries. Although no African vectors have been found in these countries, a potential vector, Amblyomma cajennense, does occur there (Camus et al., 1996). In the Caribbean regions, only Guadeloupe and Antigua are infected with heartwater whereas Amblyomma variegatum is present in several islands of the lesser Antilles at lower level of infestation.
Therefore, all countries where known Amblyomma vectors are parasites of livestock, or where neighbouring countries are infected, are at risk from the disease. These include the countries listed above, most of the Caribbean islands and the American continent. Quite surprisingly, heartwater has never been observed in Asia from where most ruminants originated, and despite the fact that many Amblyomma spp. ticks occur there.
According to African Union-Interafrican Bureau for Animal Resources (2011), heartwater is present in Africa south of the Sahara and the islands of the Comoros, Zanzibar, Madagascar, Sao Tomé, Réunion and Mauritius. Many ruminants, including some antelope species, are susceptible.

04/05/2022

Heartwater is an infectious, noncontagious, tickborne rickettsial disease of ruminants. The disease is seen only in areas infested by ticks of the genus Amblyomma. These include regions of Africa south of the Sahara and the islands of the Comores, Zanzibar, Madagascar, Sao Tomé, Réunion, and Mauritius. Heartwater was introduced to the Caribbean, and it and its vector (A variegatum) are endemic on the islands of Guadeloupe and Antigua. A variegatum, but not the rickettsia, has since spread to several other islands despite attempts at eradication. Possible spread to the mainland threatens the livestock industry of regions from northern South America to Central America and the southern USA. In heartwater endemic areas in southern Africa, it is estimated that mortalities due to the disease are more than double those due to bacillary hemoglobinuria (red water, see Bacillary Hemoglobinuria in Animals) and anaplasmosis (see Anaplasmosis in Ruminants) combined. Cattle, sheep, goats, and some antelope species are susceptible to heartwater. In endemic areas, some animals and tortoises may become subclinically infected and act as reservoirs. Indigenous African cattle breeds (Bos indicus), especially those with years of natural selection, appear more resistant to clinical heartwater than B ta**us breeds.
Etiology and Transmission:
The causative organism is an obligate intracellular parasite, previously known as Cowdria ruminantium. Molecular evidence led to reclassification of several organisms in the order Rickettsiales, and it is now classified as Ehrlichia ruminantium. Under natural conditions, E ruminantium is transmitted by Amblyomma ticks. These three-host ticks become infected during either the larval or nymphal stages and transmit the infection during one of the subsequent stages (transstadial transmission). The progeny of an infected female tick are most probably not infective (ie, there is no epidemiologically significant transovarial transmission). This and the fact that ticks are indiscriminate feeders probably play a role in the low infection rate in tick populations.
E ruminantium can be propagated experimentally by serial passage, either by inoculating infective blood into, or by feeding infected nymphal or adult stages of a vector tick on, susceptible animals. The organism can also be propagated in tissue culture, most reliably in endothelial cells, but also in primary neutrophil cultures and macrophage cell lines. At room temperature, infective material loses its infectivity within a few hours, but the organism, together with suitable cryoprotectants, may be viably preserved in liquid nitrogen for years.
Immunity to heartwater appears to be chiefly, if not exclusively, cell mediated, because spleen cells from an immune donor inoculated into susceptible recipients protects, whereas serum from an immune donor fails to protect recipients when challenged. There is no, or only partial, cross-protection between different stocks (strains) of E ruminantium. Most of these stocks are infective for, but cannot be serially passaged in, mice; however, a few are pathogenic to mice infected by the IV route.
Pathogenesis:
The pathogenesis of heartwater has not been elucidated; however, the tick probably infects the host via organisms in the saliva or regurgitated gut content while feeding. Replication of the E ruminantium organisms in the tick probably occurs in the intestinal epithelium and is significantly amplified. Once in the host, the organisms may replicate first within the regional lymph nodes with subsequent dissemination via the bloodstream to invade endothelial cells of blood vessels elsewhere in the body. In domestic ruminants, there does seem to be a predilection for endothelial cells of the brain. Organisms can often be found in colonies (commonly but mistakenly referred to as morulas) within the cytoplasm of endothelial cells. Colonies can vary in size, as can the organisms that reside in them. Generally, small-sized organisms are found in larger colonies and vice versa. The smaller organisms are usually referred to as elementary bodies and represent the infective stage, the larger organisms as reticulated bodies and the proliferative stage, and those in between as intermediate bodies.
During the febrile stage, and for a short while thereafter, the blood of infected animals is infective to susceptible animals if subinoculated. Signs and lesions are associated with functional injury to the vascular endothelium, resulting in increased vascular permeability without recognizable histopathologic or even ultrastructural pathology. The concomitant fluid effusion into tissues and body cavities precipitates a fall in arterial pressure and general circulatory failure. The lesions in peracute and acute cases are hydrothorax, hydropericardium, edema and congestion of the lungs and brain, splenomegaly, petechiae and ecchymoses on mucosal and serosal surfaces, and occasionally hemorrhage into the GI tract, particularly the abomasum. The typically straw-colored effusions are high in large-molecular-weight proteins, including fibrinogen; hence, this fluid readily clots on exposure to air. The amount of effusion seen, particularly in body cavities, is not necessarily proportionate to the concentration of parasitic colonies detected in endothelial cells.
Clinical Findings:
Typical opisthotonus and “pedaling” of the limbs in heartwater, young bullock
heartwater_opisthotonus_and_pedaling_of_limbs_young_bullock_high
Heartwater case, typical nervous signs and pedaling, calf
Heartwater case, exaggerated blinking and hyperesthesia,
Heartwater case, goose stepping and wide stance, cow
Heartwater case, pedaling, goat
Heartwater case, respiratory distress, goat
Heartwater case, signs and treatment, goat
The clinical signs are dramatic in the peracute and acute forms. In peracute cases, animals may drop dead within a few hours of developing a fever, sometimes without any apparent clinical signs; others display an exaggerated respiratory distress and/or paroxysmal convulsions. In the acute form, animals often show anorexia and depression along with congested and friable mucous membranes. Respiratory distress slowly develops along with nervous signs such as a hyperaesthesia, a high-stepping stiff gait, exaggerated blinking, and chewing movements. Terminally, prostration with bouts of opisthotonus; “pedaling,” “thrashing,” or stiffening of the limbs; and convulsions are seen. Diarrhea is seen occasionally. In subacute cases, the signs are less marked and CNS involvement is inconsistent.
Diagnosis:
In clinical cases, heartwater must be differentiated from a wide range of infectious and noninfectious diseases, especially plant poisonings, that manifest with CNS signs. In acute clinical cases in endemic areas, clinical signs alone may suggest the etiology, but demonstration of colonies of organisms in the cytoplasm of capillary endothelial cells is necessary for a definitive diagnosis. Traditionally, this is done with “squash” smears of cerebral or cerebellar gray matter stained with Romanowsky-type stains. Low concentration Giemsa stain developed for 30 min gives the best color differentiation and batch-to-batch consistency. Organisms in autolyzed material lose their stainability, and diagnosis then becomes difficult.
For the “brain squash smear,” a piece of gray matter (~3 × 3 mm) is macerated between two microscope slides; the softened material is then spread like a blood smear with the material pushed rather than pulled along. A slight lifting of the spreader slide about every 5–10 mm creates several thick ridges across the slide, from which capillaries are arranged straight and parallel in the thin sections of the smear for easier examination. The endothelial cells of all the capillaries on a smear should be carefully scrutinized for presence of the dark purple colonies made up of clusters of individual organisms (granules) of E ruminantium. The size of the granules can vary between animals, or smears from the same animal, or even between colonies on the same smear, but is usually uniform within a particular colony.
E ruminantium near the endothelial cell nucleus
e_ruminantium_high
COURTESY OF DR. A.S. SHAKESPEARE.
Using immunoperoxidase staining methods, a definitive diagnosis can be made on any formalin-fixed tissue samples, even from autolyzed carcasses. The contrasting color makes the search for and identification of the rickettsial colonies much quicker, although the substructure of the colonies should be identified before the diagnosis is confirmed. Because of the nature of the test, false-positive reactions may arise with some closely related organisms. On brain squash smears, Chlamydia pecorum can be confused with E ruminantium, but histopathology or the immunoperoxidase technique allow differentiation. Serodiagnosis of animals previously exposed to the disease, ie, recovered from subclinical or clinical infection, still poses problems. Several tests are in use, including several indirect fluorescent antibody and ELISA tests. All serologic tests, including an ELISA that uses recombinant antigen, are plagued by cross-reactions with sera from animals infected with one of several Ehrlichia or Anaplasma organisms (false positive) and the fact that immune cattle on repeated exposure may become seronegative (false negative). DNA probes, available at research institutions, can be used together with PCR technology. A combination of a pCS20 probe and probes to 16S ribosomal RNA of several of the stocks are used routinely to examine samples from animals when permits for movement of animals from endemic to nonendemic areas are required. Real-time PCR has also come into use.
Treatment, Control, and Prevention:
Oxytetracycline at 10 mg/kg/day, IM, or doxycycline at 2 mg/kg/day will usually effect a cure if administered early in the course of heartwater infection. A higher dosage of oxytetracycline (20 mg/kg) is usually required if treatment begins late during the febrile reaction or when clinical signs are evident. In such cases, the first treatment should preferably be given slowly IV. A minimum of three daily doses should be given regardless of temperature; if fever persists, oxytetracycline treatment should continue for a fourth and fifth day. If the fever still does not abate, a potentiated sulfonamide at 15 mg/kg/day, IM, has been successful. The withdrawal times for milk and meat after treatment with doxycycline, short- or long-acting oxytetracycline, and sulfonamides must be observed based on local regulations.
Corticosteroids have been used as supportive therapy (prednisolone 1 mg/kg, IM), although there is debate as to the effectiveness and rationale for their use.
Diazepam may be required to control convulsions.
Affected animals must be kept quiet in a cool area with soft bedding and be totally undisturbed; any stimulation can preempt a convulsive episode and subsequent death.
Vaccination can help with the control of heartwater; however, it is neither easily administered nor monitored and gives variable to no cross-protection to the various E ruminantium stocks. The “infection and treatment method” for immunization is in use in southern Africa, where infected sheep blood containing fully virulent organisms of the Ball 3 stock is used for infection, followed by monitoring of re**al temperature and antibiotic therapy after a fever develops. In certain circumstances, the “controlled” infection is followed by preventive “block treatment” without temperature recording (cattle on day 14 [susceptible B ta**us breeds] or day 16 [for the more resistant B indicus breeds], sheep and Angora goats on day 11, and Boer and crossbreed goats on day 12). Young calves (