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are fastidious Gram-negative coccobacilli that
colonize mucosal surfaces. H. influenzae
and H. ducreyi
main pathogenic species.
Haemophilus influenzae expresses an antiphagocytic polysaccharide
capsule of which there are six types (a-f). It also expresses a
lipopolysaccharide (LPS) and an IgA1 protease. Septicaemia,
meningitis and osteomyelitis are usually associated with type b
infection in individuals who have not been vaccinated.
Infection occurs in preschool children, causing pyogenic meningitis,
acute epiglottitis, septicaemia, facial cellulitis or osteomyelitis.
Non-capsulate strains are usually commensal in the nasopharynx,
but may cause adult otitis media, sinusitis, and chest infection in
patients with obstructive airways disease.
Antigen detection provides rapid diagnosis in meningitis. Culture of
CSF, sputum, blood or pus is used. Increasingly, H. influenzae
as part of multiplex nucleic acid amplification tests (NAATs).
Treatment and Prevention
Many H. influenzae
express a β-lactamase and are ampicillin resistant.
Co-amoxiclav, clarithromycin, tetracycline or trimethoprim
can be used. Severe infections are treated with a β-lactam-stable
A protein-conjugated polysaccharide vaccine against type b has
almost eradicated childhood infection. Non-capsulate Haemophilus
is ubiquitous and predisposed patients cannot avoid infection.
is transmitted sexually and causes painful,
irregular, soft genital ulcers (chancroid). There is associated lymphadenopathy,
and suppurating inguinal lymph nodes may lead
to sinus formation. Infection is more common in developing countries
and facilitates the transmission of HIV.
Transmission is controlled by treatment with azithromycin,
ceftriaxone or a fluoroquinolone coupled with efficient contact
tracing (see Sources and transmission of infection
, B. abortus
and B. suis
have goats, cattle and
pigs, respectively, as their main hosts. They are aerobic or capnophilic
and require serum-containing medium to grow.
Brucella infection spreads to humans through direct contact
with domesticated animals or their products (e.g. unpasteurized
milk). Vets, farmers and abattoir workers are at increased risk of
Brucellae are able to survive inside the cells of the reticuloendothelial
system using superoxide dismutase and nucleotide-like substances
to inhibit the intracellular killing mechanisms of their host.
- Intermittent, high fever in the early stages of infection, giving
rise to its old name 'undulant fever'.
- Myalgia, arthralgia and lumbosacral tenderness.
- Complications of acute infection that include septic arthritis,
osteomyelitis and epididymo-orchitis.
- A chronic infection that may develop without treatment, which
may resolve or continue to give symptoms, often accompanied by
psychiatric complaints, for many years.
Culture of blood and bone marrow is diagnostic, although culture
is less likely to be positive in chronic disease. Incubation, in a high
containment facility, must be continued for up to 3 weeks. Serodiagnosis
is by enzyme immunoassay (EIA) to detect both IgG
Treatment and Prevention
Optimal treatment is with tetracycline for 1 month. Streptomycin
should be added for patients with complications. Transmission by
food can be prevented by pasteurization. Appropriate animal husbandry
techniques can reduce the risk of occupational infection.
An animal vaccine is available but is not sufficiently safe for
human use. Animal control measures have eradicated brucellosis
from farms in many countries.
This pathogen of rodents and deer can be found in North America
and northern Europe. Infection, which is spread by the aerial
route, direct contact with wild animals or by tick bite, is rare, being
found mainly in campers and hunters.
Infection may be ocular or localized to the skin, with regional
lymphadenopathy. Systemic infection gives a syndrome that
resembles typhoid, with 5-10% mortality. Diagnosis is by serology
or by culture. Treatment is with tetracycline.
infection is described in Zoonoses
This organism, morphologically and biochemically similar to Y.
, causes acute enteritis, mesenteric adenitis and, rarely, septicaemia.
It is transmitted to humans in food and water. Infection
may be complicated by polyarthritis and erythema nodosum.
Patients with iron-overload syndromes are especially susceptible.
Diagnosis is by isolation from faeces, blood or lymph node, or
detection of antibodies. Treatment with ciprofloxacin or co-trimoxazole
is indicated in serious infection; tetracycline is an alternative
This organism can cause mesenteric adenitis that mimics
are small Gram-negative bacteria that can invade host
red blood cells, epithelial and bone marrow cells. B. henselae
responsible for cat-scratch disease (see Zoonoses
and bacilliary angiomatosis, a febrile illness associated with a red,
papular rash that is commonly found in patients with AIDS. B.
, which is transmitted by lice, causes a relapsing febrile
illness found in severely disadvantaged individuals. B. bacilliformis
infection can cause Oroya fever, an acute febrile haemolytic
anaemia or mild fever with body pain, nausea and headache. It is
transmitted by sandflies and found only in Peru and neighbouring
countries. Diagnosis is by culture, but NAATs and sequencing are