Diarrhea in Neonatal Ruminants - The Merck Veterinary Manual

Diarrhea in Neonatal Ruminants
(Scours)

Etiology

Bacteria

Viruses

Protozoa

Other Causes

Epidemiology and Transmission

Prevention and Control

Zoonotic Risk

Diarrhea is common in newborn calves, lambs, and kids. The acute disease is characterized by progressive dehydration and death, sometimes in as few as 12 hr. In the subacute form, diarrhea may persist for several days and result in malnutrition and emaciation. This discussion emphasizes the disease in calves, but the principles of pathophysiology and treatment apply to lambs and kids as well.

Etiology:

Several enteropathogens are associated with neonatal diarrhea. Their relative prevalence varies geographically, but the most prevalent infections in most areas are Escherichia coli , rotavirus, coronavirus, and Cryptosporidium parvum . Cases of neonatal diarrhea are commonly associated with more than one of these agents, and the cause of most outbreaks is multifactorial. Determining the particular agents associated with an outbreak of diarrhea can be important because specific therapy is available for some. Also, some agents have zoonotic risk. Diarrhea is also present in septicemic colibacillosis.

Bacteria:

E coli is the most important bacterial cause of diarrhea in calves; at least 2 distinct types of diarrheal disease are produced by different strains of this organism. One type is associated with enterotoxigenic E coli , which has 2 virulence factors associated with the production of diarrhea. Fimbrial antigens enable them to attach to and colonize the villi of the small intestine. Strains in calves most commonly possess K99 (F5) or F41 fimbrial antigens, or both. These antigens are the focus of immunologic protection. Enterotoxigenic E coli also elaborate a thermostable, nonantigenic enterotoxin (Sta) that influences intestinal ion and fluid secretion to produce a noninflammatory secretory diarrhea. Diarrhea in calves and lambs also has been associated with enteropathogenic E coli that adhere to the intestine to produce an attaching and effacing lesion, with dissolution of the brush border and loss of microvillous structure at the site of attachment, a decrease in enzyme activity, and changes in ion transport in the intestine. These enteropathogens are also called “attaching and effacing E coli .” Some produce verotoxin, which may be associated with a more severe hemorrhagic diarrhea. The infection most frequently is in the cecum and colon, but the distal small intestine can also be affected. The damage in severe infections can result in edema and mucosal erosions and ulceration, leading to hemorrhage into the intestinal lumen.

Salmonella spp , especially S typhimurium and S Dublin, but occasionally other serovars, cause diarrhea in calves 2-12 wk old. Salmonellae produce enterotoxins but are also invasive and produce inflammatory change within the intestine. In calves, infection commonly progresses to a bacteremia. See also salmonellosis, Salmonellosis: Introduction .

Clostridium perfringens types A, B, C, and E produce a variety of necrotizing toxins and cause a rapidly fatal hemorrhagic enteritis in calves. The disease in calves is rare and usually sporadic. Infection with type B or C is a common cause of enteritis and dysentery in lambs (see also Enterotoxemias: Overview). Campylobacter jejuni and Yersinia enterocolitica may be present in the feces of calves and lambs with diarrhea but also may be found in the feces of healthy animals.

Viruses:

Rotavirus is the most common viral cause of diarrhea in calves and lambs. Groups A and B rotavirus are involved, but group A is most prevalent and clinically important and contains several serotypes of differing virulence. Rotavirus replicates in the mature absorptive and enzyme-producing enterocytes on the villi of the small intestine, leading to rupture and sloughing of the enterocytes with release of virus to infect adjacent cells. Rotavirus does not infect the immature cells of the crypts. With virulent strains of rotavirus, the loss of enterocytes exceeds the ability of the intestinal crypts to replace them; hence, villous height is reduced, with a consequent decrease in intestinal absorptive surface area and intestinal digestive enzyme activity.

Coronavirus is also commonly associated with diarrhea in calves. It replicates in the epithelium of the upper respiratory tract and in the enterocytes of the intestine, where it produces similar lesions to rotavirus but also infects the epithelial cells of the large intestine to produce atrophy of the colonic ridges.

Other viruses, including Breda virus, a calicilike virus, astrovirus, and parvovirus, have been demonstrated in the feces of calves with diarrhea and can produce diarrhea in calves experimentally. However, these agents can also be demonstrated in the feces of healthy calves. The importance of these agents in the syndrome of neonatal diarrhea has yet to be determined. The viruses of bovine virus diarrhea and infectious bovine rhinotracheitis are reported to cause calf diarrhea, but this is not a common manifestation of these infections.

Protozoa:

C parvum ( Cryptosporidiosis) is a common cause of diarrhea in calves and lambs. The parasite does not invade but adheres to the apical surface of enterocytes in the distal small intestine and the colon. This results in loss of microvilli, decreased mucosal enzyme activity with villous blunting and fusion (leading to a reduced villous surface absorptive area), and inflammatory changes in the submucosa. Mammalian cryptosporidia lack host specificity. Giardia duodenalis is a common asymptomatic infection in the intestine of young calves and lambs. It has been demonstrated in the feces of poorly growing calves that have a chronic mucoid diarrhea, but there is little evidence for a causative association of this organism with diarrhea in calves or lambs.

Other Causes:

Calves that are fed large amounts of milk or inappropriately formulated milk replacers produce a large volume of feces with a greater than normal fluid content but do not have a fluid diarrhea with weight loss. Similarly, calves sucking high-producing beef cows grazing lush pasture may have loose feces. Milk replacers with poor quality, heat-denatured proteins or with excessive amounts of soybean or fish protein or carbohydrates of nonmilk origin have a higher risk of producing diarrhea.

There is some evidence that the oral administration of chloramphenicol, neomycin, or tetracycline to young calves for 3-5 days can result in villous change with resultant malabsorption and mild diarrhea. Prolonged and high-dose antibiotic treatment of calves can lead to diarrhea associated with bacterial superinfection of the intestine. Colisepticemia ( Colisepticemia: Introduction) and ruminal drinking ( Ruminal Drinkers) can also be accompanied by diarrhea.

Epidemiology and Transmission:

Enteropathogens associated with diarrhea are commonly found in the feces of healthy calves; whether intestinal infection leads to diarrhea depends on a number of determinants, including differences in virulence of different strains of a pathogen and the presence of more than one pathogen. The resistance of the calf is of major importance and is largely determined by successful passive transfer of colostral immunoglobulins. Colostrum-deprived calves are highly susceptible to infection with enteropathogens and develop severe and often fatal disease. The progression of infection, the severity of lesions produced, and the severity of the diarrhea can be modulated by immunoglobulins received via colostrum. Immunoglobulins act directly on pathogens in the intestinal lumen during the period of colostrum ingestion as well as after, because significant amounts of circulating immunoglobulins are re-secreted into the intestine, especially when the concentration of circulating immunoglobulin is high. The lack of specific antibodies in dams that have not been exposed to specific pathogens, and the use of specific vaccines, further modulate this influence. Stress caused by a poor environment, inadequate protection from the weather, or an insufficient or inappropriate diet also increases the risk for disease. With all of the enteropathogens, healthy adult cattle may be carriers and periodically excrete the organism in feces. Excretion may increase with the stress of parturition and be more frequent in primiparous cows. This can lead to contaminated calving areas and infection of the udder and perineum of the dam. Other sources of infection include the feces of healthy calves and the feces of diarrheic calves, which contain large numbers of organisms early in the course of infection. A few scouring calves can result in severe contamination of the calf-rearing area. Transmission is by fecal-oral contact, fecal aerosol, and, in the case of coronavirus, also by respiratory aerosol.

Pathogenesis:

Diarrhea in neonatal ruminants is usually associated with disease of the small intestine and can be caused by either hypersecretion or malabsorption. Hypersecretory diarrhea develops when an abnormal amount of fluid is secreted into the gut, exceeding the resorptive capacity of the mucosa. In malabsorptive diarrhea, the capacity of the mucosa to absorb fluid and nutrients is impaired to the extent that it cannot keep up with the normal influx of ingested and secreted fluids. This is usually the result of villous atrophy, in which the loss of mature enterocytes at the tips of the villi results both in a decrease in villous height (with a consequent decrease in the surface area for absorption) and in loss of the brush border digestive enzymes. The extent and distribution of villous atrophy varies with different pathogens and can explain variation in the severity of clinical disease. Malabsorptive diarrhea may be aggravated by the colonic fermentation of nutrients that normally would have been absorbed in the small intestine. Fermentation products, especially lactic acid, appear to draw water into the colon osmotically, which contributes to the severity of diarrhea. Inflammation contributes to the pathophysiology of diarrhea in most intestinal infections, and mediators of inflammation can affect ion flux within the intestine. Inflammation also leads to vascular and lymphatic damage and to structural damage of the crypt-villus unit. Most infectious forms of diarrhea have hypersecretory, inflammatory, and malabsorptive components, although one usually predominates. These lead to a net loss of water, sodium, potassium, and bicarbonate; if severe, the calf develops hypovolemia, hyponatremia, acidosis, and prerenal azotemia.

Enterotoxigenic E coli produce the enterotoxin Sta, which stimulates marked hypersecretion by activating guanylate cyclase and by inducing a net secretion of sodium and chlorine. The membrane-bound sodium-glucose cotransport system remains functional. Salmonellae also elaborate enterotoxins. Inflammation, leading to necrosis of the enterocyte, submucosal inflammatory infiltration, and villous atrophy, is also a major component of the pathophysiology of diarrhea produced by salmonellae, as well as of diarrhea produced by enteropathogenic E coli and by toxigenic Clostridium perfringens . Infections with verotoxin-producing enteropathogenic E coli result in accumulation of fluid within the large intestine and extensive damage to the large intestinal mucosa, with edema, hemorrhage, and erosion and ulceration of the mucosa, which results in blood and mucus in the lumen.

Viruses usually produce a malabsorptive diarrhea by destroying the absorptive cells of the mucosa, thus shortening the intestinal villi. The mechanism by which cryptosporidia produce diarrhea is not completely understood, but it appears to have both malabsorptive and inflammatory components.

Inappropriately formulated milk replacers produce diarrhea by 2 mechanisms, both associated with malabsorption. Vegetable (especially soybean) products are commonly used as protein sources in the manufacture of milk replacers. Depending on the degree of refinement, these products may contain carbohydrates that are indigestible in young calves. Such carbohydrates are not absorbed in the small intestine and may contribute to diarrhea via colonic fermentation. In addition, most calves <3 wk old appear to have an allergic reaction to soy proteins that results in villous atrophy, leading to diarrhea that is probably malabsorptive.

Clinical Findings:

The major signs are diarrhea, dehydration, profound weakness, and death within one to several days of onset.

Diarrhea due to enterotoxigenic (K99-bearing) E coli is seen in calves <3-5 days old, rarely later. However, the age of susceptibility may be extended in the presence of other pathogens. Onset is sudden. Profuse amounts of liquid feces are passed, and the calves rapidly become depressed and recumbent. Calves may lose over 12% of body weight in fluid, and hypovolemic shock and death may occur in 12-24 hr. Body temperature may be increased but is commonly normal or subnormal. If fluid and electrolyte therapy is administered early, response is usually good. Disease produced by attaching and effacing E coli is seen predominantly in calves from 4 days to 2 mo old and may manifest with diarrhea or primarily as dysentery with blood and mucus in the feces. The clinical course is short. Diarrhea due to Salmonella spp usually is not seen in calves <14 days old. It is characterized by feces that are foul smelling and contain blood, fibrin, and copious amounts of mucus. Septicemia, with high fever and depression progressing to prostration and coma, is the salient manifestation of salmonellosis in calves and, although diarrhea is present, death is usually from septicemic rather than from hypovolemic shock. Calves with salmonellosis usually lose weight rapidly and often die in spite of vigorous therapy. Hemorrhagic enterotoxemia due to C perfringens type B or C is characterized by acute onset of depression, weakness, bloody diarrhea, abdominal pain, and death within a few hours. It usually develops in vigorous calves that are just a few days old that have large appetites and a ready source of milk. Calves affected with C perfringens usually die before treatment can be instituted.

Diarrhea due to rotavirus, coronavirus, and other viruses usually is seen in calves 5-15 days old but can affect calves to several months of age. Affected calves are only moderately depressed and often continue to suck or drink milk. The feces are voluminous, soft to liquid, and often contain large amounts of mucus. Diarrhea commonly persists for three to several days, with some cases of coronaviral diarrhea becoming chronic. Cases of viral diarrhea that are uncomplicated by other pathogens commonly respond within a few days to fluid and electrolyte therapy and adequate nutritional support.

Cryptosporidiosis ( Cryptosporidiosis) is seen in calves 5-35 days old but most commonly in the second week of life. It is characterized by persistent diarrhea that does not respond to therapy. Diarrhea due solely to Cryptosporidium spp is often mild and self-limiting, although the severity may be related to the general strength of the calf and to the intensity of challenge with the organism. Combination infections with cryptosporidia, rotavirus, and coronavirus are common and result in persistent diarrhea often characterized by emaciation and death. Death from hypoglycemia also occurs as a sequela of cryptosporidiosis in calves 3-4 wk of age that have recovered from diarrhea but are still emaciated. Death often occurs during a bout of cold weather and is more likely to occur on farms where there is a policy of reducing the amount of milk fed to calves during periods of diarrhea.

Dietary diarrheas are seen in calves <3 wk old and are characterized by voluminous feces of pasty to gelatinous consistency. Initially, the calves are bright and alert and have good appetites. Eventually, however, they become weak and emaciated if the diet is not corrected. Infectious forms of diarrhea are often complicated by poor-quality diets or insufficient nutritional intake.

Diagnosis:

Usually, it is difficult to make a definite etiologic diagnosis based solely on clinical findings. However, the history, age of the animal(s) affected, and clinical signs may permit a presumptive diagnosis. Fecal samples can be submitted for isolation and characterization of the common enteropathogens. Samples should be taken from several untreated calves in the early stages of diarrhea. Special techniques are necessary for the demonstration of viruses, cryptosporidia, and K99-bearing E coli . The interpretation of fecal microbiology can be difficult because of mixed infections and because enteropathogens are commonly present in the feces of healthy calves. The best diagnostic information is usually obtained by submitting untreated, acutely affected animals for necropsy. This allows examination of intestinal mucosa for evidence of diagnostic lesions and for the presence of enteropathogens such as cryptosporidia. It may be the only way that disease such as that associated with attaching and effacing strains of E coli can be diagnosed. The diagnostic value of a necropsy diminishes quickly with time after death; important lesions can disappear within minutes due to autolysis. Complete laboratory examination can be expensive, and it has also been argued that there is little value in expending large amounts of money on diagnosis unless there are specific control procedures that can be implemented based on the information gained. In all cases, information on total milk or milk replacer consumption should be obtained. When milk replacer is being fed, the composition of the diet should be evaluated. Nonspecific immunity should be assessed by determining immunoglobulin and vitamin A concentrations in serum.

Treatment:

Many of the factors involved in disease resistance are nonspecific; thus, important preventive measures can be taken and therapy can be initiated before an etiologic diagnosis has been established. Treatment includes fluid and electrolyte replacement, alterations of the diet, antimicrobial and immunoglobulin therapy, and use of antidiarrheal drugs and adsorbents. Fluid and electrolyte therapy is most important and should be instituted as soon as possible regardless of whether clinical evidence of dehydration has developed (clinical signs of dehydration are not apparent until the calf has lost at least 6% of its body weight in fluid). Calves that are still able to stand and that are willing and able to suck can often be treated with oral electrolytes alone. Fluids for oral rehydration should promote the cotransport of sodium with glucose and amino acids and should contain sodium, glucose, glycine or alanine, potassium, and either bicarbonate or citrate or acetate as a bicarbonate precursor. Several commercial preparations are available. These can be administered by nipple bottle or, if necessary, by stomach tube. The solutions should be used liberally until the animal is rehydrated.

Whether or not milk should be fed during the rehydration period is controversial. Feeding milk may increase fecal volume, but it provides energy to the calf and may promote gut healing. Calves have large energy requirements and little reserve. Electrolyte solutions do not meet calf energy requirements, and milk should not be withheld for >24-36 hr.

Calves that are recumbent and weak and show evidence of water loss ≥8% of their body weight require IV fluid and electrolyte therapy. These calves are usually acidotic, and the fluid and base deficits can be corrected initially by administering an isotonic (13 g/L) solution of sodium bicarbonate, ideally at 100 mL/kg over 4-6 hr. Because the calves are frequently hypoglycemic, addition of 25-50 g of dextrose to the bicarbonate solution is often beneficial. The bicarbonate solution should be followed by continuous IV fluid therapy with a physiologically balanced electrolyte solution administered at 5-8 mL/kg/hr for the next 20 hr; higher rates may be necessary depending on the severity of diarrhea. Oral electrolyte solutions should probably be used concurrently with IV therapy.

The use of antimicrobials is not supported by most clinical trials and not indicated in diarrhea induced by viruses or protozoa. Antibiotics may be of value in treating diarrhea associated with enterotoxigenic or attaching and effacing E coli . The route of administration should be oral, and the choice based on sensitivity testing. When septicemic disease, due to inadequate transfer of colostral immunoglobulins, is suspected as a complication, parenterally administered antibiotics are also indicated. Salmonellosis should be treated with parenteral antimicrobials. Several drugs, such as flunixin meglumine, indomethacin, loperamide, diphenoxate, and bismuth subsalicylate, have antisecretory and anti-inflammatory activity and are used in treatment, but there are no clinical trials of their efficacy in calves. Intestinal gels and adsorbents, such as kaolin and pectin, are in general use, but their only established effect is to increase fecal consistency; they do not reduce the loss of water and ions.

Prevention and Control:

Because of the complex nature of diarrhea in neonates, it is unrealistic to expect total prevention—economical control is the major objective. The incidence of clinical disease and the case fatality rate depend on the balance between the levels of exposure to infectious agents and the resistance in the calf. Differences in herd size; availability of facilities, land, and labor; and general management objectives make it impossible to recommend specific management procedures that are applicable to all situations. However, 3 broad principles apply in all herds: 1) the degree of exposure of neonates should be reduced by isolating diseased animals or by moving calving and calf rearing to a separate area, and by practicing good general hygiene; 2) nonspecific resistance should be maximized by providing good nutrition to the dam and neonate and assuring that newborn calves consume ≥5% of their body wt of high-quality colostrum, preferably within 2 hr and certainly within 6 hr of birth, followed by equivalent amounts at 12-hr intervals for the next 48 hr; and 3) the specific resistance of the newborn should be increased by vaccinating the dam or the newborn. A significant portion of both naturally sucking dairy calves and calves handfed colostrum do not acquire adequate amounts of immunoglobulin because of delayed sucking or feeding, ingestion of an inadequate volume of colostrum, or ingestion of colostrum of inferior immunoglobulin concentration. When time constraints on labor preclude an ensured intake of colostrum by nipple-bottle feeding, administration of 3.8 L of colostrum by esophageal feeder within the first 2 hr of life can be the best colostrum feeding policy. (See also disease-management interaction: cattle, Health-management Interaction: Cattle, and management of reproduction: cattle,.)

Immunization of calves against colibacillosis by vaccination of pregnant dams can control enterotoxigenic colibacillosis. The pregnant dam is vaccinated 6 and 2 wk before parturition to stimulate antibodies to strains of enterotoxigenic E coli ; these antibodies are then passed on to the newborn through the colostrum (provided the calf ingests it). A single booster is given in subsequent years. Monoclonal K99 E coli antibody is commercially available for oral administration to calves immediately after birth. It is an effective substitute for the K99-specific antibody in the colostrum of vaccinated cows, although calves that receive this product should also receive colostrum for its nonspecific protection.

Vaccination of pregnant cows with rotavirus and coronavirus vaccines increase the amount of specific antibody in colostrum and milk, but the concentration of antibodies in milk may be insufficient to provide local antibody in the intestinal lumen during the period of peak prevalence of infection which, in calves, is 5-15 days of age. Controlled trials of commercial vaccines have shown variable results. The addition of small amounts of immune colostrum to milk fed during the period of susceptibility can provide some protection against disease.

Zoonotic Risk:

Several of the agents that produce diarrhea in calves can also produce diarrheal disease in humans. Cryptosporidium parvum and Salmonella serovar typhimurium can produce serious disease, particularly in immunocompromised individuals. These organisms are commonly present as subclinical infections in the gut of calves and lambs; immunocompromised people should avoid contact with young ruminants and possibly all farm animals. Cattle, including calves, are one of the reservoirs for the verotoxic E coli serotype O157:H7 that is associated with human hemorrhagic colitis and the hemolytic uremic syndrome. Infection in humans is usually acquired by consumption of contaminated food, but the infective dose is low, and the possibility of infection by direct contact exists. Other verotoxic E coli associated with human disease can also be isolated from the feces of healthy cattle.