CD Alert Monthly Newsletter of National Centre for Disease Control, Directorate General of Health Services, Government of India
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CD Alert Monthly Newsletter of National Centre for Disease Control, Directorate General of Health Services, Government of India May - July 2009 Vol. 13 : No. 1 SCRUB TYPHUS & OTHER RICKETTSIOSES it lacks lipopolysaccharide and peptidoglycan RICKETTSIAL DISEASES and does not have an outer slime layer. It is These are the diseases caused by rickettsiae endowed with a major surface protein (56kDa) which are small, gram negative bacilli adapted and some minor surface protein (110, 80, 46, to obligate intracellular parasitism, and 43, 39, 35, 25 and 25kDa). There are transmitted by arthropod vectors. These considerable differences in virulence and organisms are primarily parasites of arthropods antigen composition among individual strains such as lice, fleas, ticks and mites, in which of O.tsutsugamushi. O.tsutsugamushi has they are found in the alimentary canal. In many serotypes (Karp, Gillian, Kato and vertebrates, including humans, they infect the Kawazaki). vascular endothelium and reticuloendothelial GLOBAL SCENARIO cells. Commonly known rickettsial disease is Scrub Typhus. Geographic distribution of the disease occurs within an area of about 13 million km2 including- The family Rickettsiaeceae currently comprises Afghanistan and Pakistan to the west; Russia of three genera – Rickettsia, Orientia and to the north; Korea and Japan to the northeast; Ehrlichia which appear to have descended Indonesia, Papua New Guinea, and northern from a common ancestor. Former members Australia to the south; and some smaller of the family, Coxiella burnetii, which causes islands in the western Pacific. It was Q fever and Rochalimaea quintana causing first observed in Japan where it was found to trench fever have been excluded because the be transmitted by mites. The disease was, former is not primarily arthropod borne and therefore, called tsutsugamushi (from tsutsuga the latter is not an obligate intracellular parasite, meaning dangerous and mushi meaning being capable of growing in cell-free media, insect or mite). This is found only in areas besides being different in genetic properties. with a suitable climate, plenty of moisture and Scrub typhus will be dealt in detail. scrub vegetation. Recently, rickettsioses has SCRUB TYPHUS been an emerging disease along the Thai Myanmar border. There are reports of CAUSATIVE AGENT emergence of scrub typhus in Maldive Islands and Micronesia. Scrub typhus (Chigger borne typhus, Tsutsugamushi fever) is caused by Orientia INDIAN SCENARIO tsutsugamushi. Orientia is a small (0.3 to 0.5 by 0.8 to 1.5 µm), gram negative bacterium of In India, scrub typhus has been reported from the family Rickettsiaceae. It differs from the Rajasthan, Jammu & Kashmir and Vellore. In other members in its genetic make up and in addition, few cases have been tested positive the composition of its cell wall structure since for IgM antibodies for scrub typus from Sikkim, 1 Darjeeling, Nagaland & Manipur (unpublished morning, chiggers can be collected from the data). In a study conducted from July through body of the sentinel animals. The mites can October 2004 in Himalayas, among several be preserved in 70% alcohol till they reach cases of acute febrile illness of unknown origin, laboratory for identification. Chigger index O.tsutsugamushi was identified as causative (average number of chiggers infesting a single agent by microimmunofluorescence and PCR. host) of > 0.69 (critical value) is an indicator In an entomolgic study in Himachal Pradesh, for implementation of vector control measures. vector species Leptotombidium deliense and Gahrliepia spp. were recorded. Habitats favorable for disease transmission Scrub typhus, originally found in scrub jungles, DISEASE TRANSMISSION has also been identified in a variety of Scrub typhus is transmitted by the mite other habitats, such as sandy beaches, Leptotrombidium deliense. The vector mites mountain deserts and equatorial rain forests. inhabit sharply demarcated areas in the soil Incubation Period where the microecosystem is favourable (mite islands). Human beings are infected when they Incubation Period: 1 – 3 weeks. trespass into these mite islands and are bitten by the mite larvae (chiggers). The mite feeds CLINICAL PICTURE on the serum of warm blooded animals only once during its cycle of development, and adult A Papule develops at the site of inoculation. mites do not feed on man. The microbes are The papule ulcerates and eventually heals transmitted transovarially in mites. Scrub with development of a black eschar. typhus normally occurs in a range of General symptoms are sudden fever mammals, particularly field mice and rodents. (>40ºC [104ºF]) with relative bradycardia, The L.deliense group of vector mites are widely severe headache, apathy, myalgia, distributed all over the country coexisting generalized lymphadenopathy, photophobia primarily with rodents and other small and a dry cough. mammals. On the body of small mammalian Approximately one week later, a spotted and hosts, the chiggers attach in clusters on the then maculopapular rash appears first on tragus of the ear, the belly and on the thighs. the trunk and then on the extremities and The Leptotrombidium mites, on the rat host, blenches within a few days. may appear orange or pink. The typical vector Complications are interstitial pneumonia L.deliense is generally found associated with (30 to 65% of cases), meningoencephalitis either established forest vegetation or and myocarditis. secondary vegetation after clearance of forest areas. This species is generally abundant on Symptoms generally disappear after two grasses and herbs where bushes are scarce. weeks even without treatment. Sentinel animals can also be used for collection In severe cases with pneumonia and of trombiculid mites from the field. These myocarditis, the mortality rate may reach animals are generally white laboratory mice or 30%. rats kept in small cages containing food and water and placed in the field overnight to attract DIAGNOSIS chiggers. Chiggers can also be collected from field directly on human beings, by walking in Routine laboratory tests are unlikely to be the field after wearing stockings. The following diagnostic for any rickettsial diseases. 2 Common clinical manifestations of the Rickettsial Diseases Scrub Typhus axillary eschar Maculopapular rash on back of a case of scub typhus However, investigation may reveal Laboratory diagnosis early lymphopenia with late lymphocytosis. Scrub typhus may be diagnosed in the laboratory Albuminuria is a common laboratory by: finding. Thrombocytopenia is observed in more (i) isolation of the organism than half of the patients with epidemic (ii) serology typhus. (iii) molecular diagnosis (PCR). 3 Collection, storage & transportation of Label all specimens accurately and send specimen all pertinent information to laboratory which will help in better interpretation of the The collection, transportation and storage of laboratory findings. specimens are extremely vital steps in laboratory diagnosis and hence, must be undertaken with Isolation of the organism utmost care. As rickettsiae are highly infectious and have Specimen caused several serious and fatal infections among laboratory workers, it comes under Risk Serum Group 3 organisms. Isolation should be done in Blood collected in tubes containing EDTA laboratories equipped with appropriate safety or Sodium citrate provisions preferably Biosafety level-3 labora- tory following strict biosafety precautions. Blood clot Rickettsia may be isolated in male guinea pigs Blood collection in tubes and vials or mice; yolk sac of chick embryos; vero cell line or MRC 5 cell lines from patients in early Aseptically collect 4-5 ml of venous blood. phase of the disease. Egg and animal inocula- Allow blood to clot at room temperature, tion methods have been replaced by faster and centrifuge at 2000 rpm to separate serum. more sensitive cell cultures. Rickettsiae grow well in 3-5 days on Vero cell and MRC 5 cell Collect the serum in sterile dry vial. coverslip cultures and can be identified by im- munofluorescence using group and strain spe- Fix the cap with adhesive tape, wax or other cific monoclonal antibodies. sealing material to prevent leakage during transport. Serological diagnosis Use adhesive tape marked with pencil, Diagnosis of the etiology of rickettsial diseases indelible ink, or a typewritten self adhesive can be accomplished most easily and rapidly label to identify the container. The name of by demonstrating a significant increase in anti- the patient, identification number and date of bodies in the serum of the patient during the collection must be indicated on the label. course of infection and convalescence. Several serological tests are currently available for the Do’s/Don’ts while collecting specimen: diagnosis of rickettsial diseases like Weil-Felix Collect sufficient quantity of specimen Test (WFT), Indirect Immunoflourescence (IIF), Enzyme linked Immunosorbent assay (ELISA) Avoid contamination by using sterile etc. Although many techniques have been used equipment and aseptic precautions. successfully for rickettsial sero diagnosis, rela- tively few are used regularly by most laborato- Despatch the specimen immediately to ries. BSL-3 Lab is not required for performing laboratory at 2-8ºC (ice box) as soon as serological tests. possible. Weil-Felix Test (commonly used test) Don’t freeze whole blood as haemolysis may interfere with serology test results. The Weil-Felix test is helpful in establishing presumptive diagnosis