Causative agent

Rickettsial diseases can be categorised into scrub typhus, urban typhus, epidemic typhus and other rickettsial diseases, which include spotted fever. Different types of rickettsial diseases are caused by different types of 'rickettsiae'. Scrub typhus and spotted fever are more commonly seen in Hong Kong . Urban typhus is occasionally reported, while epidemic typhus has not been reported locally in the past few decades.

Clinical features

Rickettsial diseases in general present with features similar to a bad cold with fever, chills, headache and muscle pains, as well as rash. Scrub typhus and spotted fever are characterised by a punch-out skin ulcer at the site of bite of an infected arthropod. Nearby lymph nodes are also swollen and painful. Rickettsial diseases can cause severe complications and can cause death in severe cases.

Mode of transmission

Rickettsial diseases are transmitted mainly via vectors. Different types of rickettsial diseases are transmitted by different types of vectors, such as mite, flea, louse and tick.

Mite-borne typhus (Scrub typhus)

• Humans are infected through the bites of infected mites. The mites mainly feed on the blood of animals such as rats in scrubby areas.

Flea-borne typhus (Urban typhus)

• Humans are infected when the faeces of infected fleas get into the breaks in the skin or mucous membranes. The fleas mainly live on rats and cats. Infection can also occur when dried infective fleas faeces are inhaled.

Louse-borne typhus (Epidemic typhus)

• Humans are infected when the crushed tissues or faeces of infected lice get into the breaks in the skin or mucous membranes. The lice can live on human body. Infection can also occur when dried infective lice faeces are inhaled.

Tick-borne spotted fever

• Spotted fever is mainly transmitted through the bites of infected ticks that are found in habitats where there are dense vegetation and suitable host animals . Dogs and rats may carry ticks on their bodies. Infection can also occur when crushed tissues or faeces of the infected ticks get into the breaks in the skin or mucous membranes.

Incubation period

The incubation period for scrub, urban, and epidemic typhus is commonly 10 to 12 days, while that of spotted fever is 6 to 10 days.

Management

Treatments for most rickettsial illnesses are similar. The diseases should be treated by appropriate antibiotics with supportive care.

Prevention

The vectors transmitting scrub typhus and spotted fever are mainly found in the vegetated areas. Therefore, preventive measures should be taken when visiting rural areas to avoid bitten by these vectors.

Prepare for the visit:

• Wear light-coloured long-sleeved clothing and trousers
• Wear shoes that cover entire foot, avoid wearing sandal or open shoes
• Tuck trousers legs into socks or boot to prevent arthropods from reaching the skin.
• Apply insect repellent containing DEET (N, N-diethyl-m-toluamide) on body as well as clothing
• Avoid using fragrant cosmetics or skin care products

During the visit:

• Stay on footpaths and avoid walking through vegetation. Do not brush along the vegetation at the sides of footpaths
• Avoid resting on vegetation, or at humid and dark places
• Do not hang clothing on vegetation
• Do not feed wild or stray animals

After the visit:

• Inspect body parts and clothing. Clear any attached arthropods carefully
• Take a soapy shower and wash the clothes
• Inspect and clean the bodies of accompanying pets

If an attached tick is found:

• Remove the tick by grasping with tweezers or fine-tipped forceps the head of the tick close to the skin and gently pulling with constant pressure
• Do not crush or twist the tick during removal
• After removing the tick, disinfect the bite area and wash hands with soap and water

Control of vectors and the reservoir of the diseases are also useful preventive measures:

• Disinfest your pets regularly
• Inspect and disinfest pet beddings regularly
• Trim vegetation particularly the grass in your premises
• To prevent rat infestation, the best method is to deprive their food and shelter. Food and garbage should be properly stored and disposed. Holes at wall and ceiling should be repaired and filled

Besides, since lice can live on human body, maintaining good personal hygiene is effective to prevent the spread of louse-borne typhus.