Rickettsia spp .: typhus group (R. prowazekii, R. typhi), spotted fever group (R. conorii, R. africae, R. slovaca, R. rickettsii, R. sibirica, R. japonica, R. australis, ...), pustular typhus (R. akari) - Culture; IgG and IgM antibodies; Molecular diagnosis (PCR)
Information 11/26/15.
Rickettsial diseases are emerging arthropod - borne diseases, and produced by small obligate intracellular gram - negative bacilli (Family Rickettsiaceae, Order Rickettsial).
The differences in the clinical features differentiate three groups of rickettsial diseases: typhus group (TG: Typhus group), Rickettsia prowazeki produced by (epidemic typhus agent) and R. typhi (typhus endemic agent); group spotted fever (SFG: Spotted Fever Group) produced by several species of Rickettsia (R. conorii, R. africae, R. slovaca, R. rickettsii, R. sibirica, R. japonica, R. australis. .....), and pustular typhus caused by R. akari.
Clinical manifestations are different according to the group. In all rickettsial diseases fever is a common manifestation. Beside fever can other manifestations such as rash (rash), which may be present in all diseases rickettsial, but may also be absent, and nervous system involvement manifested by clouding (predominant in rickettsiois produced typhus group).
Of the three groups of rickettsiosis, the group spotted fever (SFG) is considered as a set of emerging human infections transmitted by ticks. In our environment, the three most prevalent rickettsial diseases are: Rickettsia conorii, producer of Mediterranean spotted fever, which is mainly found in countries bordering the Mediterranean in Southern Europe, Africa and the Middle East; R. africae, producer of African fever tick bites (ATBF: African Tick Bite Fever) found in several African countries, and R. slovaca. African tick - borne fever is the most common rickettsial diseases in sub - Saharan Africa, and should be considered in the differential diagnosis of patients with fever and / or rash returning from some African countries (South Africa, Zimbabwe, Mozambique, Tanzania, Kenya, Bostwana, Lesotho, Djibouti, Ethiopia, ...). African tick bite fever usually occurs as a frequent cause of acute febrile disease in international travelers, who travel to rural areas and sub - Saharan French Indies like Guadeloupe (Caribbean). In addition, it is the second most frequent cause of systemic febrile illness, behind malaria.
Transmission and reservoir
All species of Rickettsia are arthropod vectors (ticks -rickettsias producing manchadas- fevers or -tifus pustuloso- mites;; - - R. typhi lice fleas -tifus exantemático epidémico-) transmitted. The reservoir of typhus group rickettsiae (R. prowazekii and R. typhi) are the sickest patients. The reservoir of producing rickettsial spotted fever (R. conorii, R. africae, R. slovaca, R. rickettsii, R. sibirica, R. japonica, R. australis, ...) are the ticks that transmit their own infection to their offspring transovarially: R. conorii the dog tick (Rhipicephalus sanguineus); R. africae are Amblyomma species (A. variegatum and A. hebraeum) to R. rickettsii, production in Brazil of Brazilian spotted fever (BSF: Brazilian Spotted Fever) are Amblyomma cajennense and A. aureolatum. The peculiarity of transmission Amblyomma ticks is that they are not specific host, and different hosts bite vertebrates, including humans. This makes cases may arise in groups, resulting in single or multiple sores on the bite site. The disease is seasonal, and months of increased risk from November to April in the rural areas of sub - Saharan Africa.
Pathogeny
After inoculation by the tick, rickettsiae invade endothelial cells of capillaries, arterioles and venules, causing a phenomenon of vasculitis with thrombosis and development of perivascular nodules, perivascular lymphohistiocytic by infiltrate. This vasculitis results in increased vascular permeability and the appearance of focal hemorrhages. Therefore, rickettsial infections are considered systemic diseases and in general manifestations (fever). In some rickettsial general symptoms by causing the injury of vascular endothelium of internal organs (eg. Ex. Typhus) predominate. Rickettsiae, by contact with endothelial cells induce their own phagocytosis, and once within the cytoplasm of the host cell, leave the phagosome and multiply by binary fission in the cell cytoplasm. The infection starts in the inoculation (bite) and subsequently extends from one cell to another, and distance through the bloodstream.
The incubation period ranges from 3 to 15 days. The first to appear is fever (39-40 ° C) with chills, conjunctivitis, myalgia and arthralgia. The rash usually appears between the second and fifth day after the fever, and appears in the form of lenticular maculopapular lesions, which begins at the ankles or wrists, and then it spreads rapidly throughout the body (trunk, skull, face, palms and plants). Furthermore, it may be a blackish lesion at the site of the tick bite (s blackspot - tâche noir, French authors). Black spot can be as small as a pinhead or the size of a lentil. This ulcerated lesion and forms a black eschar, frequently accompanied by regional lindadenopatía. Fever is usually sender and persists for about 10 to 20 days, and the rash for about 5 to 10 days. The evolution is usually favorable, even without treatment. R. africae disease clinically manifests as influenza, acute, febrile, often accompanied by rash (46%), regional lymphadenopathy (51%), and pustular skin lesion at the site of inoculation (95%) type process . Other manifestations include myalgia (71%), arthralgia (43%), lung involvement (29%) or hepatomegaly (83%). In 54% of cases multiple scabs appear. ATBM symptoms are usually mild, but can be more severe in the elderly.
Treatment
The treatment of choice are tetracyclines (doxycycline) in a total dose of 1 or 2 g per day. Other authors have recommended chloramphenicol in the same doses. Treatment should be continued for 4 to 7 days after the fever disappeared. There in vitro experiments showing that fluoroquinolones are active, as well as the -macrólido- josamycin, which is of interest to those cases where the therapy of choice can not be used). There are no vaccines to prevent this infection and the only prophylactic measure is to prevent tick bites.
Diagnostic tests
Diagnosis can be performed by isolation of the bacterium by inoculating into cell cultures or experimental animals; by detecting antibodies or by molecular methods (PCR), of which the most widely used method is the detection of antibodies (serology), being the cheapest method to many laboratories, but has the drawbacks discussed below.
Culture isolation was only occasionally performed at specialized centers for risk to laboratory personnel, and the time required to be reached within 60 days, or somewhat less (7 to 14 days) when used in inoculation method-centrifugation (shell-vial), which limits its clinical utility. Various types of cell cultures (Vero, L-929, HEL, MRC5, etc.) can be used. In our center it can be performed if required.
Detection of antibodies encounters drawbacks that IgM antibodies require 15 to 25 days to be detected, so it is always a retrospective diagnosis, and is of little use to corroborate the clinical suspicion. On the other hand there are cross - reactive antigens between different species of Rickettsia, which prevents the identification of the causal species. When the diagnosis is made by detection of antibodies, it is recommended to take an initial sample as soon as possible at the beginning of the disease, and other subsequent sample elapsed 1 to 2 weeks to detect seroconversion (ie the increase in four times for amounts). If seroconversion is not detected, you should take another blood sample After a further 3 or 4 weeks. The most commonly used serological test is the indirect immunofluorescence test (IFAT) using as substrate antigenic cells infected with R. conorii. In these cells are both specific protein antigens of each species of Rickettsia, as lipopolisacarídicos antigens that are common to the different species, which can be found crossed by the presence of antibodies in patients who had experienced infections other reactions rickettsial species. In immunofluorescence tests with antigen R. conorii considered significant antibody titers equal or greater than 1:40 indirect immunofluorescence. These titles are usually found in 45% of patients between 5 and 9 disease progression; in 90% of patients between 20 and 29 evolution and in 100% of patients when it has been more days.
For the foregoing reasons, the current molecular diagnostic methods (PCR), are the most recommended because they allow the diagnosis more quickly in the early stages of disease and establish appropriate antimicrobial therapy. At the same time allowing the detection of genes in peripheral blood samples available as. They also allow causal know the species of Rickettsia. Several molecular diagnostic procedures aimed at detecting genes or conserved between species semiconserved rickettsial, allowing diagnose any of rickettsial, and subsequent sequencing allows differentiating the causal species. Other molecular targets are specific to a group of rickettsial, and others are species specific.
Tests in IVAMI:
- Isolation inoculation of cell culture.
- Detection of antibodies by ELISA or indirect immunofluorescence.
- Molecular diagnosis (PCR), to detect DNA of any species of Rickettsia.
Recommended sample:
- Whole blood collected with EDTA (2 to 5 mL). When the desired culture isolation sample should be taken before starting antibiotic treatment.
- Serum (1 to 2 mL), for antibody detection.
- Biopsy exanthematous pustulosis skin lesion or injury inoculation.
Preservation and shipment of sample:
- Refrigerated (preferred) for less than 2 days.
- Frozen: over 2 days.
Delivery term:
- Culture isolation (shell-vial): 14 days.
- Immunosorbent assay (ELISA or indirect immunofluorescence): 48 to 72 hours.
- Molecular diagnosis (PCR) for common target Rickettsia spp .: 24 to 48 hours.
Cost of the test:
Consult ivami@ivami.com