Typhus clinical features and pathology
Typhus clinical features and pathology
Typhus clinical features and pathology
Louse-borne typhus (Rickettsia prowazekii) occurs in louse-infested populations. These are usually relatively poor people living where night-time temperatures are low even though it may be hot in the day; people wear as much clothing as they can to keep warm, and do not change or Epidemic typhus (R. prowazekii) Murine typhus (R. typhi) Rocky Mountain spotted fever (R. rickettsii) Mediterranean spotted fever (R. conori) Highland regions: South America, Africa and AsiaTexas (USA), Africa, Asia.Body lice are frequent biters andfeeders and are very sensitive to dehydration. If clothes are changed and washed then transmission of louse-bornetyphus is prevented. Mountainous areas of South America,the Himalayas and highland regions of Ethiopia areendemic areas. Louse-borne typhus had become lesscommon, but there was a large outbreak of 30000 cases in Burundi in relation to the civil war there, with largenumbers of displaced persons crowded together in unsanitary conditions. In louse-borne typhus humans are thereservoir of infection, with latent infections recrudescing under the stress of displacement and war (Brill-Zinsserdisease), infecting body lice which spread from person toperson carrying the infection. Murine typhus (R. typhi) iswidely distributed in warmer climates in Africa, Asia,Europe and southern parts of the USA. The rat fleaspreads the infection.
Spotted fever group Rocky Mountain spotted fever (R. rickettsii) occurs mostoften in the hills and mountains of the eastern seaboardand southern states of the USA. South American countriesare also affected.African tick typhus affects the countries of North Africa,and eastern, central and southern Africa. The incidence isunknown. African tick typhus, caused by either R. conori (Mediterranean spotted fever) or R. africae, is the common estimported rickettsial infection in the UK.Rickettsial pox (R. akari) infections occur in Asia, Asianregions of the CIS (former USSR) and Korea. With increased interest in rickettsiae, pathogens such as R. helvetica, firstdescribed from Switzerland, with a widespread distributionthrough Europe, R. sibirica in Siberia and China, and R.slovaca from the Balkan region, have been recognized.
Transmission and epidemiology Typhus groupLouse-borne typhus is transmitted by Pediculus humanus,the body louse. The head louse does not transmitthis infection. After taking a blood meal the louse defecates,and R. prowazekii in the faeces of an infected louseis scratched into the bite site or abrasions in the skin.Humans are the reservoir for R. prowazekii, and infectionpasses from one person to another as the lice pass betweenpeople. The louse dies by 14 days after infection. Epidemicdisease occurs when infection is introduced into a largegroup of people not previously exposed. Refugee campspresent an ideal situation for such epidemics.Spotted fever groupThis is transmitted by the bite of infected ticks, which arealso the reservoir of infection. Occupational and leisureactivities, such as walking, camping, farming, lumber workand hunting, take people into tick-infested areas in NorthAmerica. Tourism, tending animals and gathering woodtake people into similar areas in Africa.
Pathology and pathogenesis These organisms replicate within vascular endothelial cellsof small vessels in many tissues, and vasculitic responsesand blood vessel damage underlie the pathogenesis. R.rickettsii infection is more invasive than other organisms,and causes more severe illness owing to full-thicknessvessel wall damage. The effect of blood vessel damage is arash that may become purpuric and haemorrhagic, evenecchymotic in louse-borne typhus and R. rickettsii infection.Gangrene with loss of fingers and toes can occur inRocky Mountain spotted fever. Leakage of protein-richfluid from the vascular compartment into the interstitiumcauses hypovolaemia, hypotension and reduced tissue perfusion.Thrombotic lesions occur in a variety of organs,including the brain. Renal and liver damage from vasculitisoccurs in severe cases.Clinical featuresTyphus groupThe incubation period is usually about 12 days, with arange of 10-14 days. Headache and mild fever are the usualinitial symptoms, followed after 48 hours by a sharp rise intemperature to 40C, which is sustained. Conjunctival suffusion is seen. Meningism and photophobia also occur. Therash occurs on about the 6th day and begins as red macularlesions on the axillary folds and trunk, spreading on to thelimbs, with the palms, soles and face affected in the mostsevere cases. The rash may evolve through purpuric stagesto form ecchymoses. Initial bradycardia progresses totachycardia in hypotensive patients. Haemorrhagic manifestationsand hypotension lead to renal involvement, withrising blood urea and falling urine output. Mild cases getbetter in the second week of the disease, but untreatedsevere cases may go into the third week before recoverybegins. Death from shock, cerebral involvement or renalfailure occurs in the second or third week. Mortality ratesof 10-40% without treatment are recorded, and increasingage is associated with higher fatality rates. Brill-Zinsserdisease is a mild form of louse-borne typhus caused by therecrudescence of latent infection, and in this conditionrecovery is the rule.Spotted fever groupThe incubation period is about 7 days for Rocky Mountainspotted fever (RMSF) and African tick typhus, and ratherlonger (around 13 days) in rickettsial pox. Fever andheadache with generalized limb pains are usual early in thecourse. The clinical features are similar to those of typhus.There is early deterioration in those with severe RMSF.Death may occur between 3 and 6 days of onset, occurringin up to 25% of patients not receiving specific treatment inRMSF. African tick typhus is generally mild and selflimiting.Fever, systemic upset and headache are the usualpresenting features. Rash may occur, causing macularlesions which have a widespread distribution on the trunkand limbs. The palms and soles may be affected. A blackulcerated eschar is usually found marking the site of the tickbite.DiagnosisThe clinical features usually lead to suspicion of a rickettsialinfection. This can be confirmed by serological testsusing group-specific rickettsial antigens. The main differentialdiagnosis in RMSF is meningococcal septicaemia,which also requires urgent treatment.Laboratory featuresSeverely affected patients with all forms of rickettsialdisease will show generalized derangement of coagulationand evidence of liver and renal dysfunction. Platelet countsare low, in association with prolongation of the prothrombintime, reduced fibrmogen levels and elevated levels offibrin degradation products. Anaemia is usual. Plasmaalbumin levels fall. Declining urine output indicates renalfailure.ManagementDoxycycline (100 mg 12-hourly orally or i.v. for 7 days, orfor 2 days after defervescence) is effective against all formsof rickettsial infection. Doxycycline 200 mg as a single doseis effective in epidemic typhus. Pregnant women andchildren under 8 years should receive chloramphenicol(50mg/kg/day in divided doses for 7 days or for 2 days afterdefervescence; 25mg/kg/day in divided doses for infantsunder 1 month).Supportive measuresPrompt administration of antibiotics is essential in RMSFand louse-borne-typhus. Additional management is essentiallysupportive, depending on the facilities available, andcomprises restoring blood volume with infusions of plasmaand fluids, and restoring coagulation mechanisms by freshblood transfusions or fresh frozen plasma.Prevention and controlDelousing is the main way to control louse-borne typhus.Thorough and regular washing of clothes in hot water withdetergent kills lice and their eggs. DDT 10% or malathion1% can be applied to clothed people with good effect.Appropriate clothing should be worn to prevent ticks reachingthe skin. In tick-infested areas the skin should be carefullyinspected at the end of the day. Any ticks that are foundshould be removed by gentle pulling to keep them intact.The duration of tick attachment, which can last 5 days,is important in relation to development of disease andstrength of attachment, with 20 hours being the length oftime needed to give a greater chance of infection.
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