Question 2

What is Rickettsia conorii and how is it transmitted?

Rickettsia conorii is a Gram-negative, obligate intracellular bacterium of the genus Rickettsia that causes human disease called Boutonneuse fève, Mediterranean spotted fever, Israeli tick typhus, Astrakhan spotted fever, Kenya tick typhus, Indian tick typhus, or other names that designate the locality of occurrence while having distinct clinical features.

This disease is a member of the spotted fever group and R. conorii is the most geographically dispersed species in the group, recognized in most of the regions bordering on the Mediterranean and Black Sea, Israel, Kenya, and other parts of North, Central, and South Africa, and India.

The vector is the brown dog tick, Rhipicephalus sanguineus.1

The tick serves as a vector for the bacterium and a host as it feeds on other hosts i.e. small animals including dogs – the main reservoir being dogs, rabbits and small rodents. Following a tick bite, the bacterium enters the bloodstream of the human host and, as it is an obligate intracellular organism, it multiplies in the nucleus of the cells as well as the cytoplasm, causing cellular death. It also multiplies in the nuclei of endothelial cells of the arterioles and venules resulting in vasculitis and increased vascular permeability causing blood leakage into adjacent tissues, a rash, and platelet breakdown resulting in thrombocytopenia.

Question 3 - What is the distribution of R. conorii?

Question 3:

What is the distribution of R. conorii?

It is found mainly in the Mediterranean, Israel and Africa. ³

Question 5

What are the broad differential diagnoses of fever in a returning traveller, with or without confusion?

Bacterial infections
    Meningococcaemia*
    Secondary syphilis*
    Disseminated gonococcal disease*
    Bacterial endocarditis*
    Scarlet fever
    Rat bite fever*
    Lyme disease
    Relapsing fever
    Leptospirosis
    Murine typhus
    Rickettsial pox
    Sylvatic and epidemic typhus
    Scrub typhus
    Capnocytophaga canimorsus infection
    Mycoplasma pneumoniae infection
    Typhoid and paratyphoid fever

Viral infections
    Hand, foot, and mouth disease*
    Roseola
    Measles
    Rubella
    Mononucleosis
    Acute (primary) HIV infection
    Cytomegalovirus infection
    Human parvovirus B19 infection
    Chickenpox
    Colorado tick fever
    West Nile virus disease
    Chikungunya virus disease
    Dengue fever
    Zika virus disease
    Viral hemorrhagic fever
    Japanese encephalitis (travel to Asia and Western Pacific)

Other conditions
    Drug eruptions*
    Kawasaki disease*
    Thrombotic thrombocytopenic purpura Immune thrombocytopenic purpura Immune complex vasculitis
    Toxic shock syndrome*
    Erythema multiforme* Stevens-Johnson syndrome* (4)

• might cause rash involving the palms of the hands and the soles of the feet.

Question 6 - What are the laboratory features of tick bite fever and associated encephalitis?

Question 7

What is the treatment of suspected tick-bite fever?

Doxycycline remains the first-line treatment in all suspected cases of tick-bite fever and should be started without delay. Ceftriaxone can be started simultaneously if there is a high index of suspicion of a bacterial meningoencephalitis and where the lab results are still unavailable.

For tick-bite fever in children under the age of 8 years, either proven or suspected, doxycycline remains the first-line treatment. Studies have shown that short-term treatment of 5-7 days in the correct dosage does not cause any damage to bone or enamel of teeth.4

CASE DISCUSSION

The above patient was admitted with a presumptive diagnosis of rickettsial encephalitis based on the travel history and clinical features. Doxycycline was administered, pending results, and the patient showed slight improvement but still had some psychotic features.

The patient had a lumbar puncture and the raised CSF protein was a red flag.

The patient had a negative blood IgM for rickettsiosis, but IgG remained positive with a titre of 128, suggesting resolved tick-bite fever. The lumbar puncture was repeated, and the CSF protein normalised. The patient’s psychotic features remained, and he was treated and transferred for management of a substance-induced psychosis secondary to his use of cannabis and for further psychiatric evaluation.

Tetrahydrocannabinol

Tetrahydrocannabinol, the psychoactive agent, can have perceptible effects within minutes, is extremely lipid soluble, can accumulate in fatty tissues reaching peak concentrations within 4 -5 days. It is then slowly released back into the neocortical, limbic, sensory and motor areas of the brain. The tissue elimination half-life is 7 days and absolute elimination is 30 days. Cannabis-induced psychosis can produce short term exacerbation of pre-existing psychotic diseases or lead to acute intoxication. Symptoms experienced during drug-free periods are seldom reported.

The most common symptoms with cannabis use remains auditory and visual hallucinations as well as persecutory delusions, anxiety, grandiosity and irritability. In this case, the patient did not present with any of the symptoms commonly found with cannabis use, but it still cannot be completely excluded.7

Lessons learned

The diagnosis of tick-bite fever-associated encephalitis cannot be excluded completely owing to clinical features of an overlapping psychosis and encephalitis. The only indicator of possible tick-bite fever is the observed decrease in CSF protein and negative blood IgM after treatment with doxycycline.

The other important thing to consider is the travel history. The patient may have had a tick bite in Egypt or South Africa.

If the patient had followed up after his initial consultation, neurological function and abnormalities could have been followed up and signs and symptoms might not have exacerbated, camouflaging other possible clues.

References:

1. Definition of Rickettsia available at: https://www.ncbi.nlm.nih.gov/books/NBK7624/ 


2. Companion Vector borne diseases: Rickettsioses available at: http://www.cvbd.org/en/tick-borne-diseases/rickettsioses/rocky-mountain-spotted-fever/pathogenesis-and-transmission/


3. Warmer weather linked to tick attack and emergence of severe rickettsioses available at: https://openi.nlm.nih.gov/detailedresult.php?img=PMC2581602_pntd.0000338.g006&req=4


4. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States. A Practical Guide for Health Care and Public Health Professionals available at: https://www.cdc.gov/mmwr/volumes/65/rr/pdfs/rr6502.pdf


5. Laboratory Diagnosis of Rickettsioses: Current Approaches to Diagnosis of Old and New Rickettsial Diseases available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC230049/pdf/352715.pdf


6. Guidelines for the diagnosis of tick-borne bacterial diseases in Europe available at: http://onlinelibrary.wiley.com/doi/10.1111/j.1469-0691.2004.01019.x/full


7. Cannabis-induced bipolar disorder with psychotic features can be found at : https://www.ncbi.nlm.nih.gov/pmc/articles/pm2811144/