|African tick bite fever|
|Leg lesion from a Rickettsia africae infection|
|Symptoms||Fever, headache, muscles pains, rash|
|Complications||Rare (joint inflammation)|
|Usual onset||4 to 10 days after the bite|
|Causes||Rickettsia africae spread by ticks|
|Diagnostic method||Based on symptoms, confirmed by culture, PCR, or immunofluorescence|
|Prevention||Avoiding tick bites|
|Medication||Doxycycline, chloramphenicol, azithromycin|
|Frequency||Relatively common among travelers to sub-Saharan Africa|
African tick bite fever (ATBF) is a bacterial infection spread by the bite of a tick.Symptoms may include fever, headache, muscles pains, and a rash. At the site of the bite there is typically a red skin sore with a dark center. Onset usually occur 4–10 days after the bite. Complications are rare, however may include joint inflammation. Some people do not develop symptoms.
Ticks are small arachnids, typically 3 to 5 mm long, part of the order Parasitiformes. Along with mites, they constitute the subclass Acari. Ticks are ectoparasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks had evolved by the Cretaceous period, the most common form of fossilisation being immersed in amber. Ticks are widely distributed around the world, especially in warm, humid climates.
Reactive arthritis, formerly known as Reiter's syndrome, is a form of inflammatory arthritis that develops in response to an infection in another part of the body (cross-reactivity). Coming into contact with bacteria and developing an infection can trigger the disease. By the time the patient presents with symptoms, often the "trigger" infection has been cured or is in remission in chronic cases, thus making determination of the initial cause difficult.
The disease is caused by the bacterium Rickettsia africae .The bacterium is spread by ticks of the Amblyomma type. These generally live in tall grass or bush rather than in cities. The diagnosis is typically based on symptoms. It can be confirmed by culture, PCR, or immunofluorescence.
Rickettsia africae is a species of Rickettsia.
Polymerase chain reaction (PCR) is a method widely used in molecular biology to make many copies of a specific DNA segment. Using PCR, a single copy of a DNA sequence is exponentially amplified to generate thousands to millions of more copies of that particular DNA segment. PCR is now a common and often indispensable technique used in medical laboratory and clinical laboratory research for a broad variety of applications including biomedical research and criminal forensics. PCR was developed by Kary Mullis in 1983 while he was an employee of the Cetus Corporation. He was awarded the Nobel Prize in Chemistry in 1993 for his work in developing the method.
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on microbiological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows visualization of the distribution of the target molecule through the sample. The specific region an antibody recognizes on an antigen is called an epitope. There have been efforts in epitope mapping since many antibodies can bind the same epitope and levels of binding between antibodies that recognize the same epitope can vary. Additionally, the binding of the fluorophore to the antibody itself cannot interfere with the immunological specificity of the antibody or the binding capacity of its antigen. Immunofluorescence is a widely used example of immunostaining and is a specific example of immunohistochemistry. This technique primarily makes use of fluorophores to visualise the location of the antibodies.
There is no vaccine.Prevention is by avoiding tick bites by covering the skin, using DEET, or using permethrin treated clothing. Evidence regarding treatment, however, is limited. The antibiotic doxycycline appears useful. Chloramphenicol or azithromycin may also be used. The disease will also tend to resolve without treatment.
A vaccine is a biological preparation that provides active acquired immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future. Vaccines can be prophylactic, or therapeutic.
N,N-Diethyl-meta-toluamide, also called DEET or diethyltoluamide, is the most common active ingredient in insect repellents. It is a slightly yellow oil intended to be applied to the skin or to clothing and provides protection against mosquitoes, ticks, fleas, chiggers, leeches and many biting insects.
Permethrin, sold under the brand name Nix among others, is a medication and insecticide. As a medication, it is used to treat scabies and lice. It is applied to the skin as a cream or lotion. As an insecticide, it can be sprayed on clothing or mosquito nets to kill the insects that touch them.
The disease occurs in sub-Saharan Africa, the West Indies, and Oceania.It is relatively common among travelers to sub-Saharan Africa. Most infections occur between November and April. Outbreaks of the disease may occur. The earliest descriptions of the condition are believed to be from 1911. African tick bite fever is a type of spotted fever. It has previously been confused with Mediterranean spotted fever.
The sub-Saharan Africa is, geographically, the area of the continent of Africa that lies south of the Sahara. According to the United Nations, it consists of all African countries that are fully or partially located south of the Sahara. It contrasts with North Africa, whose territories are part of the League of Arab states within the Arab world. The states of Somalia, Djibouti, Comoros and the Arabic speaking Mauritania are however geographically in sub-Saharan Africa, although they are members of the Arab League as well. The UN Development Program lists 46 of Africa’s 54 countries as “sub-Saharan,” excluding Algeria, Djibouti, Egypt, Libya, Morocco, Somalia, Sudan and Tunisia.
The West Indies is a region of the North Atlantic Ocean in the Caribbean that includes the island countries and surrounding waters of three major archipelagos: the Greater Antilles, the Lesser Antilles and the Lucayan Archipelago.
Oceania is a geographic region comprising Australasia, Melanesia, Micronesia and Polynesia. Spanning the eastern and western hemispheres, Oceania covers an area of 8,525,989 square kilometres (3,291,903 sq mi) and has a population of 40 million. Situated in the southeast of the Asia-Pacific region, Oceania, when compared to continental regions, is the smallest in land area and the second smallest in population after Antarctica.
African tick bite fever is often asymptomatic or mild in clinical presentation and complications are rare.The onset of illness is typically 5–7 days after the tick bite, although in some cases it may take up to 10 days for symptoms to occur. Symptoms can persist for several days to up to three weeks. Common presenting symptoms include:
An eschar is a slough or piece of dead tissue that is cast off from the surface of the skin, particularly after a burn injury, but also seen in gangrene, ulcer, fungal infections, necrotizing spider bite wounds, spotted fevers and exposure to cutaneous anthrax. The term "eschar" is not interchangeable with "scab". An eschar contains necrotic tissue, whereas a scab is composed of dried blood and exudate.
Lymphadenopathy or adenopathy is disease of the lymph nodes, in which they are abnormal in size, number, or consistency. Lymphadenopathy of an inflammatory type is lymphadenitis, producing swollen or enlarged lymph nodes. In clinical practice, the distinction between lymphadenopathy and lymphadenitis is rarely made and the words are usually treated as synonymous. Inflammation of the lymphatic vessels is known as lymphangitis. Infectious lymphadenitis affecting lymph nodes in the neck is often called scrofula.
A maculopapular rash is a type of rash characterized by a flat, red area on the skin that is covered with small confluent bumps. It may only appear red in lighter-skinned people. The term "maculopapular" is a compound: macules are small, flat discolored spots on the surface of the skin; and papules are small, raised bumps. It is also described as erythematous, or red.
Complications are rare and are not life-threatening.No deaths due to African tick bite fever have been reported. Reported complications include:
Rickettsia africae is a gram-negative, obligate intracellular, pleomorphic bacterium.It belongs to the genus Rickettsia , which includes many bacterial species that are transmitted to humans by arthropods.
Two species of hard ticks, Amblyoma variegatum and Amblyomma hebraeum are the most common vectors of R. africae. Typically, Amblyomma hebraeum transmits the bacteria in South Africa while Amblyoma variegatum carries R. africae throughout West, Central and East Africa and through the French West Indies. Other species of Amblyomma in sub-Saharan Africa can also transmit R. africae and it may be that up to 100% of Amblyomma ticks in sub-Saharan Africa carry R. africae. Amblyomma ticks are most active from November to April. These tick species frequently feed on cattle and other livestock, but can also be found feeding on wild animals in areas where farm animals are not found. Unlike other hard tick species, which passively seek hosts by clinging to plants and waiting for a potential host to brush by in passing, the Amblyomma hard ticks actively seek out hosts.
Groups of tourists visiting Africa have returned to their own countries and were diagnosed there as having been infected.
Up until 1998, it was thought that only ticks in sub-Saharan Africa carried R. africae. However, a case of locally transmitted African tick bite fever in the French West Indies led to the discovery of R. africae carried by Amblyomma varigatum ticks introduced through cattle shipped from Senegal to Gaudeluope more than a century ago.R. africae has been isolated from ticks on several Caribbean islands, though the only cases in humans in the Caribbean have occurred in the French West Indies. R. africae has also been found in Amblyomma loculosum ticks in Oceania.
After the rickettsia bacteria infects humans through a tick bite, it invades endothelial cells in the circulatory system (veins, arteries, capillaries).The body then releases chemicals that cause inflammation, resulting in the characteristic symptoms like headache and fever. The hallmark of all rickettsial diseases is a histology (cellular) finding called lymphohistiocytic vasculitis that involves immune cell deposition into the endothelial cells that make up vessels. This occurs secondary to the chemicals mentioned above, as well as damage from the infection, and involves signals to immune cells (T cells and macrophages) to come to the site of the infection.
Rickettsia bacteria species like R. africae replicate around the area of the initial tick bite, causing necrosis (cell death) and lymph node inflammation.This is the cause of the characteristic eschar.
Many patients with ATBF who live in areas with a high number of infections (Africa and the West Indies) do not visit a doctor, as most patients only have mild symptoms.This disease can, however, cause more serious symptoms in travelers who have never been exposed to the Rickettsia africae bacterium before and are not immune. Travelers who present to a doctor after a trip to affected areas can be hard to diagnose, as many tropical diseases cause a fever similar to that of ATBF. Other diseases that may look similar are malaria, dengue fever, tuberculosis, acute HIV and respiratory infections. In addition to questions about symptoms, doctors will ask patients for an accurate travel history and whether he/she was near animals or ticks. Microbiological tests are available for doctors, but are expensive and often must be done by special laboratories.
The antibiotic treatment available for rickettsiae infections has very few side effects, so if a doctor has a high suspicion of the disease, he or she may simply treat without doing more laboratory tests.
Diagnosis of ATBF is mostly based on symptoms, as many laboratory tests are not specific for ATBF. Common laboratory test signs of ATBF are a low white blood cell count (lymphopenia) and low platelet count (thrombocytopenia), a high C-reactive protein, and mildly high liver function tests.
Biopsies or cultures of a person's tick wound (eschar) are used to diagnose ATBF. However, this requires special culture media and can only be done by a laboratory with biohazard protection.There are more specialized laboratory tests available that use quantitative polymerase chain reactions (qPCR), but can only be done by laboratories with special equipment. Immunofluorescence assays can also be used, but are hard to interpret because of cross-reactions with other rickettsiae bacteria.
Prevention of ATBF centers around protecting oneself from tick bites by wearing long pants and shirt, and using insecticides like DEET on the skin.Travelers to rural areas in Africa and the West Indies should be aware that they may come in contact with ATBF tick vectors. Infection is more likely to occur in people who are traveling to rural areas or plan to spend time participating in outdoor activities. Extra caution should be taken in November - April, when Amblyomma ticks are more active. Inspection of the body, clothing, gear, and any pets after time outdoors can help to identify and remove ticks early.
African tick bite fever is usually mild, and most patients do not need more than at-home treatment with antibiotics for their illness.However, because so few patients with this infection visit a doctor, the best antibiotic choice, dose and length of treatment are not well known. Typically doctors treat this disease with antibiotics that have been used effectively for the treatment of other diseases caused by bacteria of similar species, such as Rocky Mountain Spotted Fever. For mild cases, people are usually treated with one of the following:
If a person has more severe symptoms, like a high fever or serious headache, the infection can be treated with doxycycline for a longer amount of time.Pregnant women should not use doxycycline or ciprofloxacin as both antibiotics can cause problems in fetuses. Josamycin has been used effectively for treatment of pregnant women with other rickettsial diseases, but it is unclear if it has a role in the treatment of ATBF.
Cases of African tick bite fever have been more frequently reported in the literature among international travelers.Data examining rates in local populations are limited. Among locals who live in endemic areas, exposure at a young age and mild symptoms or lack of symptoms, as well as decreased access to diagnostic tools, may lead to decreased diagnosis. In Zimbabwe, where R. africae is endemic, one study reported an estimated yearly incidence of 60-80 cases per 10,000 patients.
Looking at published data over the past 35 years, close to 200 confirmed cases of African tick bite fever in international travelers have been reported. The majority (~80%) of these cases occurred in travelers returning from South Africa.
Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period is 9–40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.
Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. It typically begins with a fever and headache, which is followed a few days later with the development of a rash. The rash is generally made up of small spots of bleeding and starts on the wrists and ankles. Other symptoms may include muscle pains and vomiting. Long-term complications following recovery may include hearing loss or loss of part of an arm or leg.
Boutonneuse fever is a fever as a result of a rickettsial infection caused by the bacterium Rickettsia conorii and transmitted by the dog tick Rhipicephalus sanguineus. Boutonneuse fever can be seen in many places around the world, although it is endemic in countries surrounding the Mediterranean Sea. This disease was first described in Tunisia in 1910 by Conor and Bruch and was named boutonneuse due to its papular skin rash characteristics.
Doxycycline is an antibiotic that is used in the treatment of infections caused by bacteria and certain other parasites. It is useful for bacterial pneumonia, acne, chlamydia infections, early Lyme disease, cholera and syphilis. It is also useful for the treatment of malaria when used with quinine and for the prevention of malaria. Doxycycline can be used either by mouth or intravenously.
Scrub typhus or bush typhus is a form of typhus caused by the intracellular parasite Orientia tsutsugamushi, a Gram-negative α-proteobacterium of family Rickettsiaceae first isolated and identified in 1930 in Japan.
Rickettsia rickettsii is a gram-negative, intracellular, coccobacillus bacterium that is around 0.8 to 2.0 micrometers long. R. rickettsi is the causative agent of Rocky Mountain spotted fever. R. rickettsii is one of the most pathogenic Rickettsia strains. It affects a large majority of the Western Hemisphere and small portions of the Eastern Hemisphere.
Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. Tick-borne illnesses are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. Because individual ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. As of 2016, 16 tick-borne diseases of humans are known.
Meningoencephalitis, also known as herpes meningoencephalitis, is a medical condition that simultaneously resembles both meningitis, which is an infection or inflammation of the meninges, and encephalitis, which is an infection or inflammation of the brain.
Anaplasma phagocytophilum is a Gram-negative bacterium that is unusual in its tropism to neutrophils. It causes anaplasmosis in sheep and cattle, also known as tick-borne fever and pasture fever, and also causes the zoonotic disease human granulocytic anaplasmosis.
A rickettsiosis is a disease caused by intracellular bacteria.
Orientia tsutsugamushi is a mite-borne bacterium belonging to the family Rickettsiaceae and is responsible for a disease called scrub typhus in humans. It is a natural and an obligate intracellular parasite of mites belonging to the family Trombiculidae. With a genome of only 2.4–2.7 Mb, it has the most repeated DNA sequences among bacterial genomes sequenced so far. The disease, scrub typhus, occurs when infected mite larvae accidentally bite humans. Primarily indicated by undifferentiated febrile illnesses, the infection can be complicated and often fatal.
Heartwater is a tick-borne rickettsial disease of domestic and wild ruminants. It is caused by Ehrlichia ruminantium - an intracellular gram-negative coccal bacterium. The disease is spread by bont ticks, which are members of the genus Amblyomma. Affected mammals include cattle, sheep, goats, antelope, and buffalo, but the disease has the biggest economic impact on cattle production in affected areas. The disease’s name is derived from the fact that fluid can collect around the heart or in the lungs of infected animals.
Southern tick-associated rash illness (STARI) or Masters' disease is an emerging infectious disease related to Lyme disease that occurs in southeastern and south-central United States. It is spread by tick bites, but the organism that causes the infection is unknown.
Ehrlichia chaffeensis is an obligate intracellular gram-negative species of rickettsiales bacteria. It is a zoonotic pathogen transmitted to humans by the lone star tick. It is the causative agent of human monocytic ehrlichiosis.
Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by ticks of the Ixodes ricinus species complex, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.
Ehrlichiosis ewingii infection is an infectious disease caused by an intracellular bacteria, Ehrlichia ewingii. The infection is transmitted to humans by the tick, Amblyomma americanum. This tick can also transmit Ehrlichia chaffeensis, the bacteria that causes human monocytic ehrlichiosis (HME).
Rickettsia helvetica, previously known as the Swiss Agent, is a bacterium found in Dermacentor reticulatus and other ticks which has been implicated as a suspected but unconfirmed human pathogen. First recognized in 1979 in Ixodes ricinus ticks in Switzerland as a new member of the spotted fever group of Rickettsia, the Rickettsia helvetica bacterium was eventually isolated in 1993. Although R. helvetica was initially thought to be harmless in humans and many animal species, some individual case reports suggest that it may be capable of causing a non-specific fever in humans. In 1997 a man living in eastern France seroconverted to Rickettsia 4 weeks after onset of an unexplained febrile illness. In 2010, a case report indicated that tick-borne R. helvetica can also cause meningitis in humans.
Rickettsia felis is a species of bacterium, the pathogen that causes cat-flea typhus in humans. In cats the disease is known as flea-borne spotted fever. Rickettsia felis also is regarded as the causative organism of many cases of illnesses generally classed as fevers of unknown origin in humans in Africa.