Ticks as Vectors and African Tick Bite Fever Alex Heaney 3/9/12

Ticks as Vectors and African Tick Bite Fever Alex Heaney 3/9/12

Ticks as Disease Vectors African Tick Bite Fever
Lesson Summary Ticks as Disease Vectors African Tick Bite Fever After this talk, the audience should understand the mechanisms, global importance, and complexity of ticks as disease vectors. Also, they should understand African Tick Bite Fever and the obstacles we would face if an epidemic were to break out.

Ticks Arthropoda 2 types of ticks that are vectors for human disease
Hard ticks (Ixodidae class) soft ticks (Argasidae class) Ticks are members of the Arthropoda group (phyla) of animal parasites. This group also includes insects, spiders, and mites. There are two types of ticks that are vector for human disease: hard ticks and soft ticks. Significant differences exist between these two classes of ticks. Hard ticks have a hard scutum on their backs, which looks like a plate and they are generally very sexually dimorphic. Hard ticks tend to live in open environments and feed only when they need a blood meal to continue their life cycle. They can have 1,2, or 3 hosts and generally live from several months to three years. Hard ticks also take several days for one feeding, and can expand to 100 times their original size after a meal. Soft ticks do not have a hard scutum, and have no sexual dimorphism. They tend to live in sheltered environments, and continually take blood meals from different hosts during their lives. Amazingly, soft ticks can live up to 10 years. Their blood meals are much shorter than hard tick blood meals, on the order of minutes to hours, and they do not tend to increase in size a lot after a blood meal. Hard ticks are the vectors for diseases such as Lyme disease and Spotted Fever Rickettsiosis, while soft ticks are the vectors for Relapsing Fever Borreliosis and Q fever. The rest of this presentation is going to focus on hard ticks, because they are the vectors for the diseases that will be discussed. (Paddock, 2010) Picture Credit:

Life Cycle of a Hard Tick
Here is the life cycle of a hard tick. The steps in the life cycle are as follows: 6 legged larva – size of a period – hatch from eggs in the summer Blood Meal needed for growth in august Feed, fall off host, live in soil and vegetation for winter Spring larva molts into 8 legged nymph Nymph seeks blood meal Nymph lives in soil and molts to become adult in the fall 8-legged adult seeks blood meal Lay thousands of eggs and then die This life cycle includes three hosts, but a hard tick can have one or two hosts as well. With three hosts, the tick life cycle generally takes around three years from the nymph hatching to the death of the adult. At each of the points where the tick feeds, obtaining a blood meal is essential for the tick’s survival. If the tick failed to find a host at any of these important developmental times, it would not enter the next stage of development and would die as a result. This has interesting implications for vector control. If one of the host populations was wiped out theoretically, the ticks would not be able to obtain a blood meal and would therefore die. Another thing to note about the life cycle is that each tick feeds on different animals, but humans can be infected at any of the feeding stages of a tick. If ticks are questing on the low vegetation waiting for a horse to walk by, they will not reject a human if he or she walks by instead. So although ticks generally feed on domestic and wild animals, they are able to feed on humans and that facilitates disease spread. Also, ticks can carry diseases throughout their entire lives. There are three ways that a tick can become infected with a pathogen. First, they can feed on a host animal that is infected and inject the pathogen with the host blood. Second, ticks can perform transovarial transmission for most diseases, meaning mothers can pass on the pathogen to her offspring. Third, co-feeding, or multiple ticks feeding at once on the same host, can cause infection. Therefore, ticks can carry diseases at every point in their lives and so each time a tick needs a blood meal, humans are at risk for catching the disease. Image and Information found: Centers for Disease Control and Prevention; Ticks (2011) < >

Connecting to a Host Questing: ticks feed by perching in low vegetation and waiting for a mammal to walk by When it is time for the tick to have a blood meal, it has a couple methods for seeking out and attaching to a host animal. First, the tick can get to the top of low vegetation, like tall grass or weeds, and stick up its front legs. This is called questing, and when a mammal brushes by this questing tick, the tick will grab on to the fur and therefore attach to the animal. Information: Vredevoe, Larisa. Tick Biology, University of California Davis. < Photo Credit: Local Public Health Institute of Massachusetts

Connecting to a Host Questing Ticks use chemical stimuli, airborne vibrations, and body temperatures to locate mammals Simultaneously, the tick is using chemical stimuli such as CO2, NH3, phenols, humidity, and aromatic chemicals to determine the location of mammals. The ticks also use airborne vibration and body temperatures to seek out mammal hosts. Information: (Parola, 2001) Photo Credit: Local Public Health Institute of Massachusetts

Ticks as Disease Vectors
transmit a greater variety of pathogenic micro-organisms than any other arthropod vector group Bacteria/virus/protozoa in saliva of tick Injected during a blood meal Ticks transmit a great variety of pathogenic micro-organisms than any other arthropod vector group. Ticks can carry bacteria, viruses, and protozoa as pathogens for human disease and these pathogens are generally found in tick saliva. When a tick takes a blood meal it attaches to the skin using a mouthpiece called a hypostoma (discussed more later). Once attached, there are alternating periods of sucking blood and salivation, with regurgitation occurring frequently. The periods of salivation allow the pathogen to enter the body and infect the host. First bullet point (Sanson, 2011) Second bullet point (Parola, 2001) Photo Credit: Lyme Disease Action

Hypostoma attaches to the host’s skin using hooks Once the tick has connected with its host, it inserts a mouth piece into the skin called the hypostoma. As seen in these electron micrographs, the hyopstoma has hooks that, once inserted into the skin, serve to anchor it in place. This is the first of several mechanisms ticks use to remain on the host during their blood meals. (Sanson, 2011) Second Picture from (Parola, 2001) Photo by Larisa Vredevoe, UC. Davis Picture from (Parola, 2001)

Substances secreted into skin Cementing substance Glues the hypostoma in place Immunosuppressive, Anti-inflammatory chemicals Helps the tick go unnoticed by the host Anticoagulant Allows blood to go where it needs to go in the body Once the tick has inserted its hypostoma into the skin, it starts to secrete several different substances. First, it secretes a cementing substance that glues the hypostoma into place. At this point, there are hooks and cement keeping the tick’s mouthpiece lodged into the host skin. Second, the tick secretes immunosuppressive and anti-inflammatory chemicals that serve to help the tick go unnoticed by the host. If the host were to have an immune reaction or an inflammatory response, it is likely that the tick would be noticed and removed more quickly. Lastly, the tick is secreting an anticoagulant which prevents the blood from clotting. This allows blood to flow freely into the tick and throughout the body. All of these secretions help the pathogen establish a foothold in the host. The longer a tick is connected to the skin, the more pathogens will be transferred into the host. Also if the blood is clotting near the tick’s mouth the pathogen will not be able to readily enter or travel though the host. (Sanson, 2011) All help the pathogen to establish a foothold in the host

Epidemiology of Tick Borne Diseases
Ticks are second only to mosquitoes as vectors of human infectious disease throughout the world (Paddock, 2011)

Epidemiology of Tick Borne Diseases in US
Recent dramatic increase in prevalence Graph taken from GIDEON In the past 20 years there has been a dramatic increase in the reported occurrence of tick borne diseases in the US. The rates of the most prevalent tick borne diseases in the US (Lyme Disease, Rocky Mountain Spotted Fever, and Ehrlichiosis) have all shot up over the past twenty years. Because of this increase in disease cases, an overall shift to increased awareness and worry about tick borne disease has occurred. Lyme disease is now the most commonly reported vector borne disease in the US, with about 10 cases for every 10,000 people annually. In addition, RMSF now has a higher rate of prevalence and a steeper increase in cases than ever before in recorded history. Although these facts are striking, the trends are not solely a result of an increase in prevalence of these diseases. The dramatic increase in reported cases can also be explained by an increase in disease recognition. Before 20 years ago, scientists did not have the knowledge or the tools to diagnose these diseases. Scientists are now identifying more pathogen species carried by ticks. Since 1984, 10 new strains of the rickettsiae bacteria have been recognized. More diagnostic techniques have recently been developed that will be discussed later in the presentation, and vaccine research is currently being done. (Paddock, 2011)

Recent dramatic increase in prevalence Prevalence varies within differing populations Within the US, there has been shown to be increased prevalence of Rocky Mountain Spotted Fever within American Indian Populations when compared to the national prevalence. Not only is is much higher, but there has been a significant increase in reported cases of RMSF within American Indians starting in 2000, while there was only a slight national increase. The author of this paper attributed this increase to cultural, racial and socioeconomic homogeneity existing among the American Indian population, but realistically this could also have been caused by many other factors. For example, there could have been a change in climate or environment for these people that fostered the transmission of Rock Mountain Spotted fever, or the specific tick vector could have been introduced into their environment. Information and Image taken from: (Paddock, 2011)

Possible explanations of increase in prevalence: warming temperatures/increasing humidity residential development in preferred tick ecosystems Increased contact between ticks and humans more competent tick vectors international trade and travel distributing tick vectors and their preferred animal hosts From the data previously shown it can be seen that tick borne diseases are becoming more prevalent. Several hypotheses for why this is the case have been put forward although the exact mechanisms and effects have yet to be shown. Some of these ideas include warmer temperatures and higher humidity. In theory, this would increase tick fitness and therefore pathogen transmission. More people living in ideal tick ecosystems would lead to increased contact between ticks and humans and therefore increase the number of humans getting infected. Tick vectors could be more competent given competitive advantages by environmental and genetic changes. Lastly, globalization of the world allows people infected with diseases to travel and introduce them to new places. The tick vectors themselves could also be transported to non endemic areas and increase disease prevalence there. (Mandell, 2011)

Epidemiology of Tick Borne Diseases in Lithuania
This is an example of how the prevalence of tick borne disease can increase due many different factors. At the end of Soviet Rule, Lithuania saw increases in tick borne diseases and this graphic depicts some causative factors of this increase. The overall cause and effect here is going from socio-economic transition created by the war and to high Tick Borne Disease incidence in Lithuania. One effect of this socio-economic transition is a decline in agriculture. I will mention this again in the context of tick control, but the main idea is that ticks need vegetation to perch on or “quest” in order to attach to their hosts. Agriculture usually implied getting rid of the long grasses or shrubs that ticks normally would perch on. So, if we see a decline in agriculture there will be a regeneration of the shrubs and then more places for ticks to quest. Also, as depicted in this diagram, a regeneration of shrubs will help foster rodent populations, providing more hosts for the young ticks to feed on. Therefore, a decline in agriculture will lead to a higher TBD incidence. There is no time to go into detail of the other mechanisms, such as reduced industrial pollution, sudden temperature increases, more hosts, and increased human exposure to ticks. However, all of these mechanisms again emphasizes the complex regulatory influences on tick borne diseases and ticks as vectors. Information and Image taken from: (Paddock, 2010)

This is an example of how the prevalence of tick borne disease can increase due many different factors. At the end of Soviet Rule, Lithuania saw increases in tick borne diseases and this graphic depicts some causative factors of this increase. The overall cause and effect here is going from socio-economic transition created by the war and to high Tick Borne Disease incidence in Lithuania. One effect of this socio-economic transition is a decline in agriculture. I will mention this again in the context of tick control, but the main idea is that ticks need vegetation to perch on or “quest” in order to attach to their hosts. Agriculture usually implied getting rid of the long grasses or shrubs that ticks normally would perch on. So, if we see a decline in agriculture there will be a regeneration of the shrubs and then more places for ticks to quest. Also, as depicted in this diagram, a regeneration of shrubs will help foster rodent populations, providing more hosts for the young ticks to feed on. Therefore, a decline in agriculture will lead to a higher TBD incidence. There is no time to go into detail of the other mechanisms, such as reduced industrial pollution, sudden temperature increases, more hosts, and increased human exposure to ticks. However, all of these mechanisms again emphasizes the complex regulatory influences on tick borne diseases and ticks as vectors. Information and Image taken from (Paddock, 2010)

This is an example of how the prevalence of tick borne disease can increase due many different factors. At the end of Soviet Rule, Lithuania saw increases in tick borne diseases and this graphic depicts some causative factors of this increase. The overall cause and effect here is going from socio-economic transition created by the war and to high Tick Borne Disease incidence in Lithuania. One effect of this socio-economic transition is a decline in agriculture. I will mention this again in the context of tick control, but the main idea is that ticks need vegetation to perch on or “quest” in order to attach to their hosts. Agriculture usually implied getting rid of the long grasses or shrubs that ticks normally would perch on. So, if we see a decline in agriculture there will be a regeneration of the shrubs and then more places for ticks to quest. Also, as depicted in this diagram, a regeneration of shrubs will help foster rodent populations, providing more hosts for the young ticks to feed on. Therefore, a decline in agriculture will lead to a higher TBD incidence. There is no time to go into detail of the other mechanisms, such as reduced industrial pollution, sudden temperature increases, more hosts, and increased human exposure to ticks. However, all of these mechanisms again emphasizes the complex regulatory influences on tick borne diseases and ticks as vectors. Information and Image taken from: (Paddock, 2010)

Diseases Carried by Ticks
Anaplasmosis Ehrlichiosis Lyme Disease Rickettsiosis Rocky Mountain Spotted Fever Southern Tick-Associated Rash Illness Tickborne relapsing fever Tularemia African Tick Bite Fever 364D Rickettsiosis Meningoencephalitis Colorado tick fever Crimean Congo hemorrhagic fever Babesiosis Cytauxziinosis Bacteria Anaplasma phagocytophilum Ehrlichia Borrelia burgdorferi Rickettsiae Borellia spirochetes Francisella tularensis Virus TBEV virus CTF virus CCHF virus Protozoa Babesia microti C. Felis This slide illustrates the magnitude of diseases and pathogens that can be carried by ticks. The diseases listed on the left are considered by the CDC to be the most important tick borne diseases and all are caused by one of the pathogens listen on the right hand side. Pathogens carried by ticks, as states earlier, can be bacteria, viruses, or protozoa but this list shows that more bacterial pathogens exist. Diseases and names of Bacteria came from: Centers for Disease Control and Prevention; Ticks (2011) < 2011>

Diseases Carried by Ticks
Anaplasmosis Ehrlichiosis Lyme Disease Rickettsiosis Rocky Mountain Spotted Fever Southern Tick-Associated Rash Illness Tickborne relapsing fever Tularemia African Tick Bite Fever 364D Rickettsiosis Meningoencephalitis Colorado tick fever Crimean Congo hemorrhagic fever Babesiosis Cytauxziinosis Bacteria Anaplasma phagocytophilum Ehrlichia Borrelia burgdorferi Rickettsiae Borellia spirochetes Francisella tularensis Virus TBEV virus CTF virus CCHF virus Protozoa Babesia microti C. Felis Rickettsiae bacteria cause many of these diseases and different rickettsiae bacteria are found worldwide. In the left column, all of the diseases highlighted in red are caused by a rickettsiae bacteria and the second half of the presentation is going to focus on African Tick Bite Fever.

African Tick Bite Fever
Vector: Amblyomma hebraeum and A. variegatum ticks Bacteria: Rickettsia africae and Rickettsia parkeri Thrive in tick salivary glands Multiply in tick salivary glands and ovaries of tick Once injected in host, initially spread via lymphatics, then travels to vascular endothelial lining cells of CNS, lungs, and myocardium The vector of African Tick Bite Fever is the Ambylomma hebraeum and the Amblyomma variegatum tick species. The disease is caused by the Rickettsia africae and the Rickettsia parkeri bacteria strains. These bacteria, just like the pathogens discussed earlier reside in the salivary glands of the tick and are transmitted to the host (in this case a human) during the tick blood meal. Inside the tick, these bacteria multiply in the ovaries and the saliva. This is extremely important because it allows the tick to pass the infection on to its progeny and also infect a host. Once the bacteria has entered the host, it spread through the lymphatics in the body and travels to the vascular endothelial lining cells (cells directly in contact with blood) of the central nervous system, the lungs and the myocardium (muscle tissue of the heart). Once the bacteria reaches these destinations, it divides rapidly and causes trauma in the body. Information from (Mandell, 2010) and (Parola, 2001)

Epidemiology Amblyomma hebraeum
African Tick Bite Fever is mainly found in Sub-Saharan Africa, but sometimes found in the Americas and the Caribbean. The distribution of the diseases is proportional to the presence of the two tick vector species. Data shows that there is a % infection rate of these vectors with the Rickettsia africae bacteria. This image shows, on the left, countries in Africa that are endemic to African Tick Bite Fever and the corresponding map of tick vector distribution. Although it is not a perfect match, the relationship between the countries endemic to ATBF and the presence of the tick vectors is clear. Image and Information from (Perry, 2004) Endemic African Countries Prevalence of A. hebraeum Tick

Epidemiology Not many cases reported within endemic countries
People in endemic countries are infected at a younger age At this age, disease is not serious enough to warrant medical attention Misdiagnosed as malaria Something interesting about African Tick Bite Fever is that there are hardly any cases reported within Africa itself. Most of the reported cases are of travelers that have gone to endemic countries and then return home with the disease. Eldryd Perry, in Principles of Medicine, suggested two possible explanations for this phenomena. First, it could be that people living in endemic countries acquire the disease early in life and that the severity of the symptoms at that age are not very serious. This would result in few cases being reported, as not many people would seek medical care. Second, African Tick Bite Fever can easily be misdiagnosed as malaria as both diseases are febrile and there is co-endemicity in many countries. (Perry, 2004) Photo credit:

A Case Study (France) Patient: 69 year old white man
History: had just returned from a 6 day trip to Zimbabwe Had visited farms and other rural areas Admitted with a fever Signs/Symptoms: multiple eschars on the right leg headaches, dry cough, nausea, chills, back pain, dysphagia lymphangitis and edema of the right leg Imagine you are a doctor in a French Clinic. A 69 year old man is admitted with a fever, and the first thing you notice is that he has multiple eschars on his right leg. He complains of a headache, cough, nausea, chills and back pain. You also notice that he has extremely swollen lymph nodes on his right leg near the eschar. When you ask him about his medical history he reports that he has just returned from a trip to Zimbabwe where he was visiting farms and other rural areas. Case taken from (Brouqui et al, 1997)

Clinical Presentation
Symptoms start 1-2 weeks after infection rash and/or eschar at site of tick bite Rash starts on wrists/ankles and spreads to the limbs Enlarged lymph nodes near eschar African Tick Bite Fever has an incubation period of around 1-2 weeks. At this point, all patients will present with an eschar and possibly a rash. The eschar is where the tick actually inserted its hypostoma. It usually is inflamed and has a black scab in the center. An eschar is a very strong sign that the patient may have a tick transmitted disease. The rash consists of small red bumps, and they start around the wrists and ankles and then spread up the limbs. In some forms of Spotted Fever Rickettsiosis there is always a rash, but people with African Tick Bite Fever only present with this rash 50% of the time. Usually, the patient will have enlarged lymph nodes around the site of the eschar. This is due to the path of the bacteria. As stated previously, the bacteria initially travels through the body via the lymph nodes, which will cause swelling in the lymph nodes. (Mandell, 2011) Photo by Mark Wise, Travel Clinic

Clinical Presentation
fever, headache, nausea, malaise, vomiting, abdominal pain Severe problems Vascular epithelial cell damage by microbial replication Vascular inflammation Pulmonary edema Distal, digital skin necrosis People with African Tick Bite Fever almost always present with general symptoms such as a fever, headache, nausea, malaise, vomiting, and abdominal pain. Generally, the immune system can combat this disease and there are no severe consequences. The morbidity rate is extremely low, and data shows that up to 80% of Africans in endemic areas have antibodies against this disease. However, serious complication can occur rarely. Damage to the epithelial cells can occur due to the bacteria replicating within those cells. Vascular inflammation, Pulmonary edema, and skin necrosis (due to the eschars and rashes) can also occur. (Perry, 2004) and (Mandell, 2011)

Diagnostic Challenges
Clinical Presentation similar for many different rickettsiae infections tick bites, eschars, rash, painful regional lymphadenopathy Antibody-based laboratory techniques are not sufficient Rickettsiae bacteria all cause similar immune responses in humans Can be misdiagnosed as Malaria There are several problems with diagnosing African Tick Bite Fever. First, as mentioned earlier, there are many different diseases that are caused by Rickettsiae bacteria and all of these diseases present very similarly. Most of these “spotted fevers” present with a fever, a rash, eschars, and enlarged lymph nodes. Therefore, someone with these symptoms could have numerous diseases and a diagnosis can not be made based upon clinical signs and symptoms. Second, spotted fever rickettsiae pathogens cause an immune reaction in humans that can be difficult to distinguish using antibody-based laboratory techniques. In other words, the antibodies made in the bodies of people to combat two different rickettsiae bacteria look very similar and are hard to distinguish in a lab setting. Third, African Tick Bite Fever is a febrile disease and has overlapping endemicity with Malaria in many African countries. So, as stated earlier, ATBF can be misdiagnosed as malaria. These difficulties show that diagnosis of African Tick Bite Fever is very difficult if the diagnostician is lacking necessary laboratory tools. Therefore, if there were to be an outbreak of African Tick Bite Fever in rural Africa, diagnosis would be an significant challenge. (Perry, 2004)

Preferred Diagnostic Techniques
Sample: Swab or skin biopsy from rash or eschar PCR test Also possible with blood sample Immunohistochemical detection Culture isolation Although there are many challenges to diagnosis, the right equipment can provide easy identification of the R. africae or R. parkeri bacteria. The preferred diagnostic techniques for this disease utilize a swab or a skin biopsy from the patient’s rash or eschar. The easiest and most preferred method is the polymerase chain reaction (PCR) test. This test looks for the specific DNA sequence of the bacteria within the patient’s skin sample. Second, you can use immunohistochemical detection to identify the bacteria. This involves visualizing the presence of specific antibodies that can bind to antigens on the bacteria surface. If the antibodies bind then the bacteria is present in the sample. Lastly, bacterial culture can be used to try and isolate the bacteria from the skin sample. Clearly, all of these techniques require intensive lab procedures and expertise. We are therefore currently lacking an easy and inexpensive way to diagnose this disease. Luckily, as a doctor for your French patient, you have access to more advanced diagnostic technology. For your patient X, you use the PCR method to identify rickettsia africae bacteria in his body. (Brouqui et al, 1997) and (Mandell, 2011) Skin Biopsy

Treatment Doxycycline 200 mg/day 3-14 days
Once he was diagnosed, the patient was given doxycycline (200mg/day) for 10 days and he remained well at a follow up visit 3 weeks later. The most common antibiotic treatment used against African Tick Bite Fever is Doxycycline. It is given at a dosage of 200mg/day for 3-14 days or until the patient’s fever has been gone for 48 hours. (Mandell, 2011) and (Brouqui et al, 1997)

Personal Methods of Prevention
Body be checked every few hours for ticks diethyl-3-methylbenzamide (DEET) and KBR 3023 lotions As mentioned earlier, it appears as if African Tick Bite Fever is primarily a travelers disease at this time. Because this is the case, methods for preventing infection when traveling to an endemic country are emphasized in the literature. First, and most obviously, one should continuously check himself or herself for ticks throughout the day. The less time a tick is feeding, the lower the probability of infection. Second, specific lotions have been created that act as barriers on the skin to prevent ticks from inserting their hypostoma. These are called DEET and KBR lotions, and they have significant but short lasting effects against questing A. hebraeum ticks. According to one study, the lotions must be more than 20% DEET or KBR to be effective. They are 90% effective when first applied, but decrease to only 50% effective after two hours. Therefore, constant application is also necessary for full protection with these lotions. (Jensenius, 2005)

Large Scale Preventative Strategies
Deforestation or agricultural activities disrupt tick lifecycle Insecticides Negative impact on environment Ex. Amitraz, Decamethrin Tail tags The literature does not seem to contain any instances of widespread outbreaks of African Tick Bite Fever, so large scale public health interventions were also scarce. However, there are a few techniques that can be used to control the disease and they all work to disrupt the tick lifecycle. As already discussed in the previous example of Lithuania after war time, agricultural activities and and deforestation can interrupt the tick life cycle. Both deforestation and increased agriculture lead to cutting down vegetation on which ticks would quest. If the grass that used to aid ticks in connecting with hosts is cut down, they will not be able to get blood meals as easily and their lifecycle will halt. Further more, ticks live in the soil when they are not connected to a host and agriculture changes the composition of the soil. This can lead to a less hospitable environment for dwelling ticks. Insecticides are another possible method for controlling tick populations. One article cites that Amitraz and Decamethrin were successful in reducing tick populations, but the details are unclear about how much should be used and where these insecticides were tested. These chemicals are probably not the best option for vector control because they are known to have a negative effect on the environment. Some can be poisonous to other animals and plants. Another intervention that has proven effective is the use of tail tags on cattle. The Amblyomma ticks tend to feed on cattle, so the use of tail tags is directly preventing the infection of cattle with rickettsiae bacteria. However, ticks can become infected if they feed on an infected cow. This newly infected tick could then attach to a human and infecting the human. Therefore, this intervention indirectly protects humans from infection because the ticks are biting cattle less frequently and thus the proportion of infected ticks is decreasing. The tail tags work by mimicking a secondary mechanism that Amblyomma ticks use to connect to their host. This species of tick sends out specific chemicals when it attaches to a host. Those chemicals serve as summoning signals to other ticks nearby, and that results in multiple ticks feeding in the same place. Scientists isolated those chemicals and put them onto the tail tags, which are clasped around the cattle’s tail. So, if a tick is nearby it will pick up the chemical signals being emitted from the tag and migrate towards it. Once the tick crawls on the tail tag, a chemical called ascaricide kills it. Tests have shown that these tail tags have excellent (99%) efficacy in controlling A. hebraeum ticks on cattle in Zimbabwe Overall, there has not been a lot of research or interest in large scale interventions against African Tick Bite Fever, most likely because it has not proven to be a very dangerous disease. However, if an epidemic were to occur, pursuing these methods of vector control would become extremely important for controlling the outbreak. (Norval, 1996) and (Kazar, 1991) Photo of tail tag from Photo of ticks from UC Davis Veterinary School Picture credits: UC Davis Veterinary School (top) and (bottom)

Ticks as Disease Vectors Summary
Anthropoda phyla of animal parasites hard ticks and soft ticks transmit human diseases Hard tick life cycles can include 1-3 feeding hosts, and humans are at risk of becoming an "accidental host" during feeding periods in the lifecycle Ticks use methods such as questing, chemical stimuli, and summoning signals to find a hosts Ticks transmit Bacteria/virus/protozoa during blood meals by secreting saliva (containing the pathogen) into the host Increasing reports of occurrence in tick borne diseases are due to changing environmental factors and growing disease recognition

African Tick Bite Fever Summary (1 of 2)
Vector: Amblyomma hebraeum and A. variegatum ticks Bacteria: Rickettsia africae and Rickettsia parkeri Epidemiology Mainly endemic to Sub-Saharan Africa, but some endemicity in Caribbean and Americas Mainly a "traveler disease” - few reported cases in endemic countries Clinical Presentation rash, eschar, lymphangitis, fever, rare severe complications Diagnosis Challenges in distinguishing it from other Rickettsial and febrile diseases Use PCR, Immunohistochemical detection, culture isolation on skin biopsy

African Tick Bite Fever Summary (2 of 2)
Treatment Doxycycline Control Methods Mainly personal prevention like DEET/KBR lotions Some larger interventions like deforestation, insecticides, and tail tags If epidemic were to occur, obstacles for control would be lack of diagnostic tools and lack of large scale control methods

Questions??

Works Cited Centers for Disease Control and Prevention; Ticks (2011) Grouqui, Philippe (1997). African Tick-Bite Fever; An Imported Spotless Rickettsiosis. Arch Intern Med,157(1), Jensenius, Mogens (2005) Repellent efficacy of four commercial DEET lotions against Amblyomma hebraeum (Acari: Ixodidae), the principle vector of Rickettsia africae in southern Africa. Transactions of the Royal Society of Tropical Medicine, 99 (9), Kazar, J. (1991) Control of Rickettsial Diseases. European Journal of Epidemiology, 7(3), Ndip, Lucy (2004) Detection of Rickettsia Africae in patients and ticks along the coastal region of Cameroon. American Journal of Tropical Medicine and Hygiene, 71(3), Mandell, GL (2011). Principles and Practice of Infectious Disease. Churchill Livingstone Elsevier: Philadelphia, PA Norval, R.A.I. (1996) Efficacy of pheromone-acaricide impregnated tail-tag decoys for controlling the bont tick, Amblyomma hebraeum (Acari: Ixodidae), on cattle in Zimbabwe. Experimental and Applied Acarology, 20, 31-46 Paddock, Christopher (2010). Through a glass, darkly: The global incidence of tick-borne diseases. Draft background paper written to stimulate discussion for the Institute of Medicine Committee on Lyme Disease and OTher Tick-Borne Diseases: The State of the Science Parola, Philippe (2001).Ticks and Tickborne Bacterial Diseases in Humans: An emerging Infectious Threat. Clinical Infectious Diseases, 32 (6), Parry, Eldryd (2004) Principles of Medicine in Africa. New York, NY: Cambridge University Press Robinson, Jennilee (2009) New Approaches to Detection and Identification of Rickettsia africae and Ehrlichia ruminantium in Amblyomma variegatum, (Acari: Ixodidae) Ticks from the Caribbean. Journal of Medical Entomology, 46 (4), Sanson, Tracy (2011) Tick-Borne Diseases. <emedicine.medscape.com> Vredevoe, Larisa. Tick Biology, University of California Davis. <

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