62 Chapter 3
cycle with two size variants which exhibit
different antigens. This may explain the high
resistance of C. burnetii to chemical agents.
Clinical presentation is usually pneumonia
and/or hepatitis. It can be isolated from
vaginal mucus, milk, feces, urine, and semen
of infected animals; however, infection is
usually via the aerosol route. It is highly
infectious. Interleukin 10 seems to play a key
role in chronic infection. The organism can
be detected using a PCR assay based on the
IS1111 transposon - like region. Bearing in
mind the volume of raw milk consumed
worldwide, the reports of milkborne Q fever
are much fewer than expected (Ryser, 2001 ).
For a review, see Raoult et al. (2005).
Pathogenic Escherichia coli. Shiga/
verotoxin producing E. coli strains have been
associated with disease ranging from diar-
rhea to hemolytic uremic syndrome (HUS).
This is mostly associated in the European
continent with O157 : H7, but other sero-
types can be involved e.g., 26, O111. Contam-
ination of raw milk is mainly via feces,
though pathogenic E. coli strains can cause
mastitis in which case it is directly excreted
in the milk. Dairy isolates tend to harbor
Shiga toxin 1 with a minority possessing
intimin ( eae ), serine protease, and/or catalase
virulence factors. Because of the promiscu-
ous nature of the species, a wide and varied
range of virulence factors can be harbored
including the putative factors, cytotoxic nec-
rotizing factors, and cytolethal distending
toxins. Therefore, pathogenicity is best deter-
mined by multiplex PCR assays directed at
individual virulence factors. The serotype
O157 : H7 is clearly of concern to the dairy
industry since it has been detected in 2% to
5% of the raw milk supply (D ’ Aoust, 1989 ;
Wells et al., 1991 ), and more than 60 attrib-
uted cases are associated with the consump-
tion of raw milk (Ryser, 2001 ). For a review
of the organism, see Bell and Kyriakides
(2002).
Campylobacter jejuni. Campylobacter
jejuni is considered one of the main causesreference and hence the microorganisms are
largely organized in alphabetical order. A
more detailed discussion of the major patho-
gens follows.
Coliform organisms such as Escherichia
coli are used in many foods and water as
indicators of fecal contamination and hence
hygiene, but it is well recognized that they
cannot be used for this purpose for raw milk.
Coliforms can rapidly grow in moist, milky
residues in milking equipment, which can
then represent major foci of contamination
(Singh and Bennett, 2002 ).
The following section is a more detailed
description of selected pathogenic microor-
ganisms potentially found in raw milk.
Pathogens found in raw milk but which have
particular relevance to other dairy products
have been excluded and dealt with elsewhere
in this chapter.
Brucella abortus and Br. melitensis.
Brucella abortus primarily affects cattle and
Br. melitensis affects goats and sheep, though
both are pathogenic to humans. The disease
presents in various forms and should be
included in the differential diagnosis of
arthritis, particularly in children. Human
infections arise through contact with infected
animals or their discharges, including milk
and milk products.
Infected animals can be detected through
serum antibody tests (e.g., compliment fi xa-
tion and ELISA or the blue ring test for milk).
A PCR assay based on the omp25 sequence is
also available. A useful reference is PHLS
Surveillance Centre (1995). Consumption of
unpasteurized milk (Foley et al., 1970), cream
(Barrow et al., 1968 ), and cheese (Young and
Suvannoparrat, 1975 ) has accounted for
approximately 10% of all reported brucel-
losis cases, with the remainder occurring
primarily among veterinarians, farmers, and
meat processors (Wallach et al., 1997 ).
Coxiella burnetii. Coxiella burnetii is a
small obligate intracellular Gram - negative
bacterium. Antigenic phase I is the virulent
form. The organism exhibits a developmental