Clinical Manifestations and Pathology
Undulant fever due to B. melitensis is essentially a septicemia or blood poisoning characterized by an irregular temperature curve with intermittent waves of fever, usually lasting for 10 to 30 days.
Although case fatality rates are low, the protracted character of many cases makes it a serious and debilitating illness. Its duration varies; it may be only a few days, or it may last as long as a year. Subsequent relapses may occur over a period of several years, accompanied by general ill health alternating with periods of apparent recovery. Symptoms included weakness, muscular pain, nocturnal sweats, anorexia, chills, and nervous irritability. Recorded postmortem appearances include congestion and enlargement of the liver and hypertrophy of the spleen; cultures taken from both these organs have been found to be positive for B. melitensis in 100 percent of cases.B. abortus appears to be less capable than B. melitensis of producing clinical cases in humans, but more likely to give rise to latent infection, especially in veterinarians. Once established, however, the clinical disease seems to develop in similar fashion. It lasts an average of 13 weeks and may become chronic. B. abortus can also cause a short influenzalike illness, and sometimes a persistent low intermittent fever. In rare cases, infection in pregnant women has been followed by abortion.
Undulant fever caused by B. suis is clinically similar to the above types.