Other Streptococcus spp. infections

M M HENTON

GENERAL INTRODUCTION: GRAM-POSITIVE COCCI Streptococcus spp. infections

Introduction

Many of the primary and secondary purulent infections are caused by Streptococcus spp. (see the introduction, Streptococcus spp. infections: Table 1). Streptococcal infections, particularly those associated with genital tract disease and neonatal septicaemia and its consequences, are dealt with in this chapter. The introductory section should be consulted for information on the microbiological and epidemiological characteristics of the various Streptococcus spp.

Genital tract infections and neonatal disease

Streptococcus zooepidemicus is a common cause of genital tract disease in mares.⁷ Mares suffering from genital tract disease show a slight to copious, purulent vulval discharge which varies in nature from a cloudy, thin fluid to a thick, yellowish exudate which may be frothy; it is more prominent at oestrus than during dioestrus. The vulva of affected mares may gape and the vaginal mucous membrane is congested and inflamed. In severe cases the cervix and uterus are enlarged on rectal palpation. Streptococcal infections in mares usually cause reduced conception rates as a result of early embryonic death (usually before 35 days of gestation), but abortions or the birth of infected foals may also occur.⁹ Stallions usually act only as carriers; they harbour S. zooepidemicus as a commensal in the prepuce.

Streptococcus dysgalactiae subsp. equisimilis is the most common bacterium associated with vaginal discharges, lowered conception rates, metritis and abortion in sows in South Africa.⁵ Infection with beta-haemolytic streptococci of several serotypes is also associated with infertility and abortion in sows.¹² The effects of, and clinical signs caused by, S. dysgalactiae subsp. equisimilis infections in sows are similar to those of S. zooepidemicus infection in mares. Dual infection by S. dysgalactiae subsp. equisimilis and parvovirus in sows may cause abortions at any stage of pregnancy,^{3, 12} a high percentage of stillbirths, and the birth of weak piglets.¹⁰

Streptococcus spp. are not known to cause disease in the reproductive tract of boars.

On rare occasions, streptococcal infections are associated with abortions and genital infections in sheep, goats and cattle. In the Streptococcus spp. infections of the genital tract in ruminants, S. dysgalactiae subsp. dysgalactiae is the most common of the streptococci causing infertility, and may be isolated from normal semen and the sheath (where it rarely causes inflammation) of bulls and rams. These bacteria may be isolated together with Mycoplasma spp. from cases of ulcerative balanoposthitis and vulvovaginitis in sheep and goats (see Ulcerative balanoposthitis and vulvovaginitis of sheep).

In neonates of all livestock species, septicaemia, arthritis and meningitis or meningoencephalitis may be caused by Streptococcus spp. (in addition to a variety of other bacteria, such as Escherichia coli, Salmonella serovars, Klebsiella spp. and Actinobacillus equuli). Streptococcal septicaemia is, however, encountered particularly in foals and piglets.

Neonatal streptococcal septicaemia is often a sequel to purulent omphalophlebitis, but it may also follow infection via the oral or cutaneous routes. In South Africa, streptococcal septicaemia in foals is rare, but when it does occur, it is usually caused by S. zooepidemicus and only infrequently by S. dysgalactiae subsp. equisimilis. Neonatal septicaemia in South African piglets is predominantly caused by S. dysgalactiae subsp. equisimilis infection, although such infections by S. suis and S. porcinus are reasonably common.⁵

Streptococcus zooepidemicus¹¹ and S. dysgalactiae subsp. dysgalactiae are the most common types causing septicaemia and other infections in lambs and adult sheep. Streptococcus zooepidemicus septicaemia in adult sheep is often associated with Trueperella pyogenes infections.⁵

The initial clinical signs in neonates suffering from septicaemia are subtle, and include fever, listlessness, increased respiratory and heart rates and a disinclination to suckle. These are often followed by signs which indicate localization of infection in one or more tissues or organs, such as the meninges, joints, lungs and endocardium. If the route of entry to the body was via the umbilical cord, the umbilicus may show signs of slight or marked omphalophlebitis.

When the infection is severe, the umbilicus is markedly swollen and may discharge pus.¹⁰ Omphalophlebitis and subsequent septicaemia are also caused by infections with bacteria belonging to the Enterobacteriaceae (such as Escherichia coli and Salmonella serovars) or Actinobacillus spp., but these are usually more acute and rapidly fatal than are those caused by Streptococcus spp. Erysipelothrix rhusiopathiae infection in pigs may be difficult to distinguish clinically from streptococcal infections, as it also causes septicaemia, arthritis and valvular endocarditis.⁶

Streptococcal arthritis occurs in the young of all livestock species.² Streptococcus dysgalactiae subsp. equisimilis is the most common cause of a suppurative, proliferative arthritis of piglets from birth to six weeks of age, following infection in the birth canal or of skin wounds, tonsils or the umbilicus, but it also occurs in older animals.^{1, 4, 8} Affected animals are disinclined to move and their joints are swollen and...