Specimen Collection

Paired sera should be obtained wherever possible:

(a) acute sample - as early as possible in the illness, and
(b) convalescent sample 2 - 3 weeks after onset.

3.5 mL SST Serum (Preferred)

4 mL Plain Serum
Turnaround Time:

Testing is performed immediately.Results available within 3 working days.

Diagnostic Use and Interpretation

All patients will be tested for IgG and IgM antibodies to R.typhi, R.conorii and Orientia tsutsugamushi

Culture of Rickettsial organisms is not straight-forward and is potentially dangerous therefore the diagnosis is a serological one in the appropriate clinical context.

The common clinical features include fever and rash ( except Q fever ) +/- headache, myalgias and respiratory symptoms. In addition there is often generalised small vessel endothelial damage, thrombosis and tissue necrosis (again not with Q fever )

Species specific antibodies are usually detectable 5-10 days following the onset of illness with IgM initially rising with IgG following some days later. It should be noted that effective treatment given early in the course of the illness will significantly reduce the antibody responses.

In R.typhi testing, cross-reactivity can occur with other rickettsial members of the typhus group, although higher titres are seen with R.typhi infections than in infections caused by other members of the rickettsial typhus group.

In R.conorii testing, partial cross reactivity occurs with the different mite and tick borne rickettsial agents, although higher titres are seen in Boutonneuse fever as compared with infections due to the other rickettsial agents.

Serologic results must be interpreted with respect to patient history and clinical findings.

Members of the genus Rickettsia are morphologically and biochemically similar to other gram-negative bacteria, being short rod-shaped coccobacilliary organisms. Rickettsia species are carried as parasites by many ticks, fleas, and lice. Species in the genus have been subdivided into three groups of antigenically related micro-organisms: spotted fever, typhus and scrub typhus as presented in the following Table:

Biogroup	Species	Disease	Transmission	Distribution
Spotted Fever	R.rickettsii	RMSF	Tick bite	Western Hemisphere
	R.conori	MSF / Boutonneuse Fever	Tick bite	Mediterranean, Africa, India, SW Asia
	R.sibirica	Siberian tick typhus	Tick bite	Siberia, Mongolia, Northern China
	R.australis	Australian tick typhus	Tick bite	Australia
	R.akari	Rickettsialpox	Mite bite	USA, Russia
	R.japonica	Oriental Spotted Fever	Tick bite	Japan
Typhus	R.prowazekii	Epidemic typhus	Infected louse faeces	South American and African Highlands
		Recrudescent typhus	Latent infection reactivation	Worldwide
		Sporadic typhus	Flying squirrels	USA
	R.typhi / R.mooseri	Murine typhus	Infected flea faeces	Worldwide
Scrub typhus	O.tsutsugamushi	Scrub typhus	Chigger bite	Asia, Northern Australia, Pacific Islands

From a clinical perspective, rickettsial diseases have many features in common. For most, the incubation period ranges from 3-14 days. Most patients develop non-specific symptoms and signs. Onset of disease is sudden in about half the cases. Fever and headache are the most commonly reported symptoms, but chills, myalgias, arthralgias, malaise and anorexia are also noted. Fever increases in the first week of illness often reaching 40°C or higher. Rash is a hallmark of rickettsial infection, but it usually follows systemic symptoms. Its absence should not rule out a possible rickettsial aetiology, especially during the first week of illness. Conjunctivitis and pharyngitis are common. Photophobia is also observed, but evidence of more serious CNS involvement is found in only about 25% of patients with RMSF or typhus and is virtually never seen in other rickettsial diseases.

The courses and outcomes of rickettsial diseases vary. The primary determinants are the with RMSF, epidemic typhus and scrub typhus, but rare with murine typhus. Clinical studies have demonstrated that tetracyclines and chloramphenicol are the antibiotics of choice, however, ciprofloxacin therapy is an alternative.

There are many serologic methods (IFA, ELISA, CFT, LA, IHA, RIA and Weil-Felix) for establishing rickettsial infection. With IFA, antibodies can usually be detected 7-10 days after symptom onset. Patients with either murine typhus (R.typhi) or MSF (R.conorii) have much higher titres than infections caused by other rickettsial agents of their biogroups. It should be noted that early administration of antibiotic therapy may attenuate the immune response. Although laboratory testing plays an important role, patient history and clinical findings are essential for a diagnosis of rickettsial infection.

Reference

Manual of Clinical Microbiology 6^th Edition (1995)

Olson, J.G. and McDade, J.E. p 678 [There was an error loading this resource. Not an ISO 8859-1 character: