Bacterial Scours Vaccines

Gerald E. Duhamel • Victor S. Cortese

Enterotoxigenic Escherichia coli

(Calf Scours) Bacterins

Neonatal calf diarrhea associated with enterotoxigenic E. coli (ETEC) usually occurs within the first 72 hours of life.

Because calf scours associated with ETEC strains occurs so early in life, there is not enough time for a newborn calf to mount a protective immune response through vaccination. Therefore control of ETEC-induced calf scours is aimed at (1) limiting calf exposure to bacterial pathogens, (2) vaccinat­ing dams to provide high levels of fimbriae-specific colostral antibodies (i.e., usually against the F5 antigen), and (3) providing adequate volume of colostrum as soon as possible after birth to prevent bacterial colonization of the calf intestinal tract.³ Pregnant cows are vaccinated in late gestation to ensure high concentrations of anti-F5 colostral antibodies.

Nearly all strains of ETEC that have been isolated from neonatal calves have F5 fimbriae. Currently there is no evidence that a bacterin with multiple types of fimbrial antigens is more effective than products with only F5, so long as the vaccine and challenge strains share a common fimbrial antigen.¹ However, vaccines with multiple fimbrial antigens are more likely to have at least one of the antigens expressed by the challenge ETEC strain. Besides non-F5 ETEC strains poten­tially causing calf scours, a lack of efficacy of fimbriae-based ETEC vaccines may be due to E. coli belonging to a pathotype other than ETEC, including attaching and effacing E. coli (AEEC) and Shiga toxin-producing E. coli (STEC), which cause hemorrhagic enterocolitis in 1- to 6-week-old calves. Given that AEEC and STEC strains do not produce fimbrial adhesins, fimbriae-based ETEC bacterins will not protect against these strains.^6,7 Unfortunately, commercially available vaccines for prevention of calf scours associated with AEEC and STEC are not currently available.

Escherichia coli Vaccination Programs

The general recommendations for use of fimbriae-based ETEC vaccines (bacterins) are summarized in Table 48.10. ETEC bacterins are offered as single-antigen vaccines and in combination with other antigens designed to protect against other diseases in addition to ETEC infection. Oil-adjuvanted ETEC bacterins are administered by IM injection in a single dose 2 weeks to 6 months before calving, and administration is repeated annually.¹⁰ Non-oil-adjuvanted ETEC bacterins are recommended for IM or SC injection in two doses administered at a 2- to 4-week interval, with the second dose given 3 to 6 weeks before calving. In subsequent years a single booster dose should be administered 3 to 6 weeks before calving. ETEC bacterins do not protect calves that do not ingest adequate amounts of colostrum soon after birth. Also, because this protection is based on passive immunity, high environmental challenge levels may overwhelm the limited amount of antibod­ies present in the lumen of the calf's small intestine. This is consistent with the higher prevalence and severity of clinical ETEC infections in the offspring of replacement dairy heifers kept in overcrowded closed confinement than in less intensive cow-calf beef operations. Environmental control of bacterial contamination is paramount to effective NCED management.

■ TABLE 48.10

Currently Licensed^a Escherichia coli Bacterin Toxoids, Salmonella Bacterins, and Core Endotoxoid Vaccines

^aLicensed by the Animal and Plant Health Inspection Service, U.S. Department of Agriculture, as of 2018.

Salmonella Vaccines

Salmonellosis is due to infection by various pathogenic Salmo­nella enterica serotypes (see Chapter 32). Disease severity varies according to serotypes and strain-specific virulence determinants, but also according to the number of infective organisms, route of entry, and host natural and acquired resistance mechanisms. Bovine salmonellosis is caused predominantly by S.

A modified live and genetically altered (via deletion of aroA) S. Dublin vaccine marketed for parenteral use is effective in 2-week-old calves against challenge with S. Dublin, but it also provides cross-protection to challenge with S. Typhimurium.^12,13 As with many gram-negative bacterial vaccines, adverse reactions to this vaccine have been reported. Anecdotal reports of effective oral use in calves younger than 2 weeks old indicate that this route may help avoid some adverse reactions associated with injection of an endotoxin-containing product. Killed Salmonella bacterins can produce measurable serum antibody responses to bacterial proteins in calves and adult cattle.

Vaccination of adult cows, with passive transfer of antibody to calves through colostrum, is frequently used in dairies to control salmonellosis in neonates. Controlled trials evaluating passive protection have produced mixed results, with some indicating a lack of protection^18,21 and others demonstrating some protection in 5-day-old calves. Vaccination of dry cows may be useful for control of salmonellosis in calves younger than 3 weeks of age but is minimally effective for controlling salmonellosis in calves older than 3 weeks. There are anecdotal reports of protection against salmonellosis by repeated vaccina­tion of calves with an S. Typhimurium mutant LPS core antigen vaccine (ENDOVAC [IMMVAC Inc., Columbia, Mo.]). A J-5 E. coli Rc-mutant LPS core antigen-based bacterin (J-VAC [Merial Ltd., Athens, Ga.], ENVIRACOR J-5 [Zoetis], and Hygieia [Biological Laboratories, Woodland, Calif.]) improve survival and reduce morbidity rate from naturally occurring bacterial infections in dairy calves vaccinated at 3 and 17 days of age.

Gram-Negative Mutant Lipopolysaccharide Core Antigen Bacterins

■ TABLE 48.11

Currently Licensed Vaccines for Prevention of Calf Scour Associated With F5 (K99) Enterotoxigenic Escherichia coli Infection and Disease Associated With Salmonella enterica

are exposed to and infected with Salmonella in the first week or two after birth. Salmonellosis in dairy calves often occurs after 2 weeks of age. However, when vaccinated at age 3 and 10 days with an oil-adjuvant J-5 E. coli bacterin, calves do develop strong antibody responses by 17 days of age; this strong antibody response occurs even in the presence of passively acquired antibodies to LPS core antigens.³⁰ Consequently, a combined program in which both dry cows and neonatal calves are immunized against LPS core antigens might be a useful approach for reducing the severity of salmonellosis in neonatal dairy calves.