Foodborne Listeriosis
609
In spite of the high fatality rate associated with foodborne listeriosis, overall the disease is relatively
rare. Not all L. monocytogenes isolates are equally pathogenic, and just what makes a foodborne isolate
infectious or noninfectious is poorly understood as are the reasons for the predominance in foods of
serotypes 1/2a, 1/2b, and 4b.
69
Syndromes
Listeriosis in humans is not characterized by a unique set of symptoms because the course of the disease depends on the state of the host. Non-pregnant healthy individuals who are not immunosuppressed
are highly resistant to infection by L. monocytogenes, and there is little evidence that such individuals
ever contract clinical listeriosis. However, the following conditions are known to predispose to adult
listeriosis and to be significant in mortality rate: neoplasm, AIDS, alcoholism, diabetes (type 1, in particular), cardiovascular disease, renal transplant, and corticosteroid therapy. When susceptible adults
contract the disease, meningitis and sepsis are the most commonly recognized symptoms. Of 641
human cases, 73% of victims had meningitis, meningoencephalitis, or encephalitis. Cervical and generalized lymphadenopathy are associated with the adult syndrome, and thus the disease may resemble
infectious mononucleosis. Cerebrospinal fluid initially contains granulocytes, but in later states, monocytes predominate. Pregnant females who contract the disease (and their fetuses are often congenitally
infected) may not present any symptoms, but when they do, they are typically mild and influenzalike.
Abortion, premature birth, or stillbirth is often the consequence of listeriosis in pregnant females.
When a newborn is infected at the time of delivery, listeriosis symptoms typically are those of meningitis, and they typically begin 1–4 weeks after birth, although a 4-day incubation has been recorded.
The usual incubation time in adults ranges from 1 to several weeks. Among the 20 case patients studied
from the cluster of cases in the Boston episode, 18 had bacteremia, 8 developed meningitis, and 13
complained of vomiting, abdominal pain, and diarrhea 72 hours before onset of symptoms.
The control of L. monocytogenes in the body is affected by T lymphocytes and activated
macrophages, and thus any condition that adversely affects these cells will exacerbate the course
of listeriosis. The most effective drugs for treatment are coumermycin, rifampicin, and ampicillin,
with the last plus an aminoglycoside antibiotic being the best combination.
33 Even with that regimen,
antimicrobial therapy for listeriosis is not entirely satisfactory because ill patients and compromised
hosts are more difficult than competent hosts.
RESISTANCE TO LISTERIOSIS
Resistance or immunity to intracellular pathogens such as viruses, animal parasites, and L. monocytogenes is mediated by T cells, lymphocytes that arise from bone marrow and undergo maturation
in the thymus (hence, T for thymus derived). Unlike B cells, which give rise to humoral immunity
(circulating antibodies), activated T cells react directly against foreign cells. Once a pathogen is inside
a host cell, it cannot be reached by circulating antibody, but the presence of the pathogen is signaled
by structural changes in the parasitized cell, and T cells are involved in the destruction of this invaded
host cell, which is no longer recognized as “self.”
Macrophages are important to the actions of T cells, and their need for the destruction of L. monocytogenes and certain other intracellular pathogens was shown by Mackeness.
87 First, macrophages
bind and “present” L. monocytogenes cells to T cells in such a way that they are recognized as being
foreign. When T cells react with the organism, they increase in size and form clones specific for the
same organism or antigen. These T cells, said to be activated, secrete interleukin-1 (IL-1). As the
activated T cells multiply, they differentiate to form various subsets.
609
In spite of the high fatality rate associated with foodborne listeriosis, overall the disease is relatively
rare. Not all L. monocytogenes isolates are equally pathogenic, and just what makes a foodborne isolate
infectious or noninfectious is poorly understood as are the reasons for the predominance in foods of
serotypes 1/2a, 1/2b, and 4b.
69
Syndromes
Listeriosis in humans is not characterized by a unique set of symptoms because the course of the disease depends on the state of the host. Non-pregnant healthy individuals who are not immunosuppressed
are highly resistant to infection by L. monocytogenes, and there is little evidence that such individuals
ever contract clinical listeriosis. However, the following conditions are known to predispose to adult
listeriosis and to be significant in mortality rate: neoplasm, AIDS, alcoholism, diabetes (type 1, in particular), cardiovascular disease, renal transplant, and corticosteroid therapy. When susceptible adults
contract the disease, meningitis and sepsis are the most commonly recognized symptoms. Of 641
human cases, 73% of victims had meningitis, meningoencephalitis, or encephalitis. Cervical and generalized lymphadenopathy are associated with the adult syndrome, and thus the disease may resemble
infectious mononucleosis. Cerebrospinal fluid initially contains granulocytes, but in later states, monocytes predominate. Pregnant females who contract the disease (and their fetuses are often congenitally
infected) may not present any symptoms, but when they do, they are typically mild and influenzalike.
Abortion, premature birth, or stillbirth is often the consequence of listeriosis in pregnant females.
When a newborn is infected at the time of delivery, listeriosis symptoms typically are those of meningitis, and they typically begin 1–4 weeks after birth, although a 4-day incubation has been recorded.
The usual incubation time in adults ranges from 1 to several weeks. Among the 20 case patients studied
from the cluster of cases in the Boston episode, 18 had bacteremia, 8 developed meningitis, and 13
complained of vomiting, abdominal pain, and diarrhea 72 hours before onset of symptoms.
The control of L. monocytogenes in the body is affected by T lymphocytes and activated
macrophages, and thus any condition that adversely affects these cells will exacerbate the course
of listeriosis. The most effective drugs for treatment are coumermycin, rifampicin, and ampicillin,
with the last plus an aminoglycoside antibiotic being the best combination.
33 Even with that regimen,
antimicrobial therapy for listeriosis is not entirely satisfactory because ill patients and compromised
hosts are more difficult than competent hosts.
RESISTANCE TO LISTERIOSIS
Resistance or immunity to intracellular pathogens such as viruses, animal parasites, and L. monocytogenes is mediated by T cells, lymphocytes that arise from bone marrow and undergo maturation
in the thymus (hence, T for thymus derived). Unlike B cells, which give rise to humoral immunity
(circulating antibodies), activated T cells react directly against foreign cells. Once a pathogen is inside
a host cell, it cannot be reached by circulating antibody, but the presence of the pathogen is signaled
by structural changes in the parasitized cell, and T cells are involved in the destruction of this invaded
host cell, which is no longer recognized as “self.”
Macrophages are important to the actions of T cells, and their need for the destruction of L. monocytogenes and certain other intracellular pathogens was shown by Mackeness.
87 First, macrophages
bind and “present” L. monocytogenes cells to T cells in such a way that they are recognized as being
foreign. When T cells react with the organism, they increase in size and form clones specific for the
same organism or antigen. These T cells, said to be activated, secrete interleukin-1 (IL-1). As the
activated T cells multiply, they differentiate to form various subsets.