Hermsi Ticks Case Study
BHS432 Module 2 – Case Assignment:
Vectors and Pathogens
Spring 2013
Question 1a:
Describe differentiating characteristics between Dermacentor variabilis, Ixodes pacificus, and Ornithodoros hermsi ticks.
Question 1b:
Identify vectorborne diseases associated with these ticks, and describe the pathogens associated with these diseases.
Question 1c:
Describe preferred feeding locations of ticks.
Question 2:
Describe the effect of climate on vectors and vectorborne diseases.
The western-blacklegged tick (Ixodes pacificus) can transmit the organisms responsible for causing anaplasmosis and Lyme disease in humans. Wild rodents and other mammals are likely reservoirs of these pathogens. This tick is distributed along the Pacific coast of the United States. ” Larvae and nymphs feed on birds and small rodents, while adult ticks feed on deer and other mammals” (J. BURRASCANO, 1988). Adult ticks are primarily associated with pathogen transmission to humans.
Ornithodoros hermsi are called “soft” ticks because they have a soft outer covering Argasid ticks have multiple life stages. Each life stage may feed several times, for only minutes at a time. Most patients rarely every see or know they have been bitten by a soft tick.
Primary vector of Rocky Mountain Spotted Fever (RMSF) in southeastern states. Adult tick preferred …show more content…
host: large and medium-sized mammals including domestic dog. “Often bites humans. Immature stages preferred host: small rodents” (K. Clark, 2004). Dermacentor variabilis, also known as the American dog tick or wood tick, is found predominantly in the United States, east of the Rocky Mountains and as its name suggests, and is most commonly found on dogs as an adult. The tick also occurs in certain areas of Canada, Mexico and the Pacific Northwest of the U.S.. Dermacentor variabilis is a 3-host tick, targeting smaller mammals as a larva and nymph and larger mammals as an adult. “Although it is normally found on dogs, this tick will readily attack larger animals, such as cattle, horses, and even humans” (http://www.stlmosquitocontrol.com/ticks/type-of-ticks/). The 8-legged adult is a vector of the pathogens causing Rocky Mountain spotted fever (RMSF) and tularemia, and can cause canine tick paralysis. While the American dog tick can be managed without pesticides, when necessary a recommended acaricide is an effective way of eliminating an existing tick infestation near residences. The Argasidae (argasids, “leathery” or “soft ticks”) and the Ixodidae (ixodids, “hard ticks”). Although they share certain basic properties, argasids and ixodids differ in many structural, behavioral, physiologic, ecologic, feeding, and reproductive patterns. Tropical and subtropical species may undergo 1, 2, or rarely 3 complete life cycles annually. In temperate zones, there is often 1 annual cycle; in northern regions and at higher elevations in temperate regions, 2-4 yr. is required by most species. There are 4 developmental stages: egg, larva, nymph, and adult. All larvae have 3 pairs of legs; all nymphs and adults, 4. Adults have a distinctive genital and anal area on the ventral body surface. The foreleg tarsi of all ticks bear a unique sensory apparatus—Haller’s organ—for sensing carbon dioxide, chemical stimuli (odor), temperature, humidity, etc. Pheromones stimulate group assembly, species recognition, mating, and host selection.
“Certain tick species that parasitize livestock can survive several months and occasionally a few years, without food if environmental conditions permit”(VCA Animal Hospitals, 2011). Tick host preferences are usually limited to a certain genus, family, or order of vertebrates; however, certain ticks are exceptionally adaptable to a variety of hosts, so each species must be evaluated separately. The larvae and nymphs of most ixodids that parasitize livestock feed on small wildlife such as birds, rodents, small carnivores, or even lizards.
In the Argasidae, the leathery dorsal surface lacks a hard plate (scutum). Male and female argasids appear to be much alike, except for the larger size of the female and differences in external genitalia. The argasid capitulum (mouthparts) arises from the anterior of the body in larvae but from the ventral body surface in nymphs and adults.
In the Ixodidae, the male dorsal surface is covered by a scutum. The scutum of the ixodid female, nymph, and larva covers only the anterior half of the dorsal surface. The ixodid capitulum arises from the anterior end of the body in each developmental stage. Each species has one or more favored feeding sites on the host, although in dense infestations, other areas of the host may be used. Some feed chiefly on the head, neck, shoulders, and escutcheon; others in the ears; others around the anus and under the tail; and some in the nasal passages. Other common feeding sites are the axillae, udder, male genitalia, and tail brush. Immatures and adults often have different preferred feeding sites. Attachment of the large, irritating Amblyomma spp is regulated by a male-produced aggregation-attachment pheromone, which ensures that the ticks attach at sites least vulnerable to grooming. Climate is one of many important interacting variables that affect people’s risk for vector-borne diseases.
Climate can have a direct effect on physical conditions (temperature, rainfall, etc.) and an indirect effect on biologic conditions (plants, animals). These physical and biologic conditions can, in turn, influence vector-borne disease risk by impacting the abundance and distribution of tick vectors, the percent of vectors infected with disease agents, the abundance and distribution of animal reservoirs, the presence of suitable habitat for these vectors, and people’s behaviors that bring them into contact with infected
vectors.
Climate directly affects short-term and long-term weather conditions at the local and regional levels. Most arthropod vectors of disease are sensitive to physical conditions, such as levels of humidity, daily high and low temperatures, rainfall patterns, severity and snowpack of winter, and so on. For instance, blacklegged ticks (a.k.a. “deer ticks”), which carry Lyme disease, are most active on warm, humid days.
References
J. BURRASCANO, 1988 http://www.lymenet.org/BurrGuide200810.pdf Retrieved on
24 January 2013
K. Clark, 2004 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC525154/ Retrieved on
24 January 2013
http://www.stlmosquitocontrol.com/ticks/type-of-ticks/ Retrieved on 24 January 2013
VCA Animal Hospitals, 2011 http://www.vcahospitals.com/main/pet-health-
information/article/animal-health/ticks-in-dogs/725 Retrieved on 24 January 2013
Vectors and Pathogens
Spring 2013
Question 1a:
Describe differentiating characteristics between Dermacentor variabilis, Ixodes pacificus, and Ornithodoros hermsi ticks.
Question 1b:
Identify vectorborne diseases associated with these ticks, and describe the pathogens associated with these diseases.
Question 1c:
Describe preferred feeding locations of ticks.
Question 2:
Describe the effect of climate on vectors and vectorborne diseases.
The western-blacklegged tick (Ixodes pacificus) can transmit the organisms responsible for causing anaplasmosis and Lyme disease in humans. Wild rodents and other mammals are likely reservoirs of these pathogens. This tick is distributed along the Pacific coast of the United States. ” Larvae and nymphs feed on birds and small rodents, while adult ticks feed on deer and other mammals” (J. BURRASCANO, 1988). Adult ticks are primarily associated with pathogen transmission to humans.
Ornithodoros hermsi are called “soft” ticks because they have a soft outer covering Argasid ticks have multiple life stages. Each life stage may feed several times, for only minutes at a time. Most patients rarely every see or know they have been bitten by a soft tick.
Primary vector of Rocky Mountain Spotted Fever (RMSF) in southeastern states. Adult tick preferred …show more content…
host: large and medium-sized mammals including domestic dog. “Often bites humans. Immature stages preferred host: small rodents” (K. Clark, 2004). Dermacentor variabilis, also known as the American dog tick or wood tick, is found predominantly in the United States, east of the Rocky Mountains and as its name suggests, and is most commonly found on dogs as an adult. The tick also occurs in certain areas of Canada, Mexico and the Pacific Northwest of the U.S.. Dermacentor variabilis is a 3-host tick, targeting smaller mammals as a larva and nymph and larger mammals as an adult. “Although it is normally found on dogs, this tick will readily attack larger animals, such as cattle, horses, and even humans” (http://www.stlmosquitocontrol.com/ticks/type-of-ticks/). The 8-legged adult is a vector of the pathogens causing Rocky Mountain spotted fever (RMSF) and tularemia, and can cause canine tick paralysis. While the American dog tick can be managed without pesticides, when necessary a recommended acaricide is an effective way of eliminating an existing tick infestation near residences. The Argasidae (argasids, “leathery” or “soft ticks”) and the Ixodidae (ixodids, “hard ticks”). Although they share certain basic properties, argasids and ixodids differ in many structural, behavioral, physiologic, ecologic, feeding, and reproductive patterns. Tropical and subtropical species may undergo 1, 2, or rarely 3 complete life cycles annually. In temperate zones, there is often 1 annual cycle; in northern regions and at higher elevations in temperate regions, 2-4 yr. is required by most species. There are 4 developmental stages: egg, larva, nymph, and adult. All larvae have 3 pairs of legs; all nymphs and adults, 4. Adults have a distinctive genital and anal area on the ventral body surface. The foreleg tarsi of all ticks bear a unique sensory apparatus—Haller’s organ—for sensing carbon dioxide, chemical stimuli (odor), temperature, humidity, etc. Pheromones stimulate group assembly, species recognition, mating, and host selection.
“Certain tick species that parasitize livestock can survive several months and occasionally a few years, without food if environmental conditions permit”(VCA Animal Hospitals, 2011). Tick host preferences are usually limited to a certain genus, family, or order of vertebrates; however, certain ticks are exceptionally adaptable to a variety of hosts, so each species must be evaluated separately. The larvae and nymphs of most ixodids that parasitize livestock feed on small wildlife such as birds, rodents, small carnivores, or even lizards.
In the Argasidae, the leathery dorsal surface lacks a hard plate (scutum). Male and female argasids appear to be much alike, except for the larger size of the female and differences in external genitalia. The argasid capitulum (mouthparts) arises from the anterior of the body in larvae but from the ventral body surface in nymphs and adults.
In the Ixodidae, the male dorsal surface is covered by a scutum. The scutum of the ixodid female, nymph, and larva covers only the anterior half of the dorsal surface. The ixodid capitulum arises from the anterior end of the body in each developmental stage. Each species has one or more favored feeding sites on the host, although in dense infestations, other areas of the host may be used. Some feed chiefly on the head, neck, shoulders, and escutcheon; others in the ears; others around the anus and under the tail; and some in the nasal passages. Other common feeding sites are the axillae, udder, male genitalia, and tail brush. Immatures and adults often have different preferred feeding sites. Attachment of the large, irritating Amblyomma spp is regulated by a male-produced aggregation-attachment pheromone, which ensures that the ticks attach at sites least vulnerable to grooming. Climate is one of many important interacting variables that affect people’s risk for vector-borne diseases.
Climate can have a direct effect on physical conditions (temperature, rainfall, etc.) and an indirect effect on biologic conditions (plants, animals). These physical and biologic conditions can, in turn, influence vector-borne disease risk by impacting the abundance and distribution of tick vectors, the percent of vectors infected with disease agents, the abundance and distribution of animal reservoirs, the presence of suitable habitat for these vectors, and people’s behaviors that bring them into contact with infected
vectors.
Climate directly affects short-term and long-term weather conditions at the local and regional levels. Most arthropod vectors of disease are sensitive to physical conditions, such as levels of humidity, daily high and low temperatures, rainfall patterns, severity and snowpack of winter, and so on. For instance, blacklegged ticks (a.k.a. “deer ticks”), which carry Lyme disease, are most active on warm, humid days.
References
J. BURRASCANO, 1988 http://www.lymenet.org/BurrGuide200810.pdf Retrieved on
24 January 2013
K. Clark, 2004 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC525154/ Retrieved on
24 January 2013
http://www.stlmosquitocontrol.com/ticks/type-of-ticks/ Retrieved on 24 January 2013
VCA Animal Hospitals, 2011 http://www.vcahospitals.com/main/pet-health-
information/article/animal-health/ticks-in-dogs/725 Retrieved on 24 January 2013