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RELAPSING FEVER DISEASE

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This is a disease caused by Spirochaeta spp., which is vectored by both ticks and lice (Phthiraptera), although other species have been suspected. Spirochaeta recurrentis (Lebert) may be the main incitant of the louse borne form (Matheson 1950), while in ticks Spirochaeta duttoni has been found to be the main incitant. The tick-borne typhus form and louse borne relapsing fever usually occur around the same time and in the same areas. However, sometimes their occurrences are staggered by several years. It has been noted that Tick-borne Relapsing Fever is the only important disease transmitted to humans by soft ticks (Table 1) (Service 2008). The body louse, Pediculus humanus corporis, has been found as the main vector in India where typhus does not occur (Mackie 1907) and subsequently at other world sites.

Symptoms include repeated bouts of fever, which last from 3-5 days. Apyrexia varies from 5-10 days.

The tick form of the disease, Spirochaeta duttoni, has been found to be vectored by Ornithodoros moubata (Murray) (Matheson 1950) or O. turcata (Weller & Graham 1930). Additional vector species have since been discovered (Table 2). Very young ticks are capable of transmission. Also, infection in the tick passes through the eggs even to the third generation. The ticks are believed to be main reservoirs of the disease, but other animals such as rodents may also be reservoirs.

Table 1. Distinction Between Hard & Soft Ticks (Derived from Service 2008)

Soft Ticks (Argasidae)	Hard Ticks (Ixodidae)
A shield or scutum is absent	A shield occurs on adults, larvae and nymphs, with males bearing larger ones.
Mouthparts (capitulum) are not visible dorsally in nymphs and adults but can be discerned in larvae.	Mouthparts are visible dorsally in adults, larvae and nymphs.
Palps appear as legs, while chelicerae with smooth sheaths.	Palps are club-shaped and chilicerae hve toothed sheathes.
Organs appear on the coxae.	Organs on coxae are not present.
Eggs laid in small batches of 15-100.	Eggs laid in one large batch of 1,000 or more.
Nymphs go through 4 or 5 stages.	Nymphs have only one stage.
Adults feed quickly on hosts, but at separate times.	Adults feed slowly on hosts for 1-4 weeks and females feed only once
Ticks usually feed on about 6 hosts.	Ticks usually feed on 2 or 3 hosts.
Ticks disperse little & remain around the homes of hosts.	Ticks attach to hosts for long durations, & thus can be dispersed
Ticks are vectors of Relapsing Fever.	Ticks vector typhuses, Lyme Disease and other viruses, and they can cause Tick Paralysis.

Chung & Feng (1936) studying the disease life cycle in both body and head lice found that the vector obtains the spirochetes while drawing blood from a host. Most of the spirochetes are then digested and vanish after 6-8 hours. However, several manage to penetrate the intestinal wall and reach the coelomic fluid in about two hours. The spirochetes then multiply in the body cavity by transverse division and distribute to all parts of the body. They do not invade the tissues nor are they transmitted through the egg or feces. They will remain in the louse for its entire life of about 20 days. Humans are infected when the lice are crushed on the skin near abrasions.

There have been epidemics of relapsing fever worldwide, and it is always associated with either lice or ticks. Matheson (1950) details the areas and severity where epidemics have occurred over many years. Mortality rates have sometimes killed large numbers of people as s in West Africa where 80,000 died during a two-year epidemic.

Table 2. Occurrence of Relasping Fever

(Derived from Matheson 1950)

VECTOR	TICK DISTRIBUTION	RELASPING FEVER OCCURRENCE
Ornithodoros turicata	Southwest USA, Florida & Mexico	New Mexico, Kansas, Oklahoma, Texas, Mexico
Ornithodoros hermsi	California, Colorado, Oregon, Washington, Nevada, Idaho above 3,000 feet	California, Colorado, Idaho, Nevada, Washington, British Columbia
Ornithodoros parkeri	Nine USA States from Washington to California and east to Montana and Colorado	California primarily
Ornithodoros talaje	California to Kansas & south to Argentina	Panama, Colombia, Guatemala
Ornithodoros rudis	Panama, Colombia, Venezuela, Paraguay	Panama, Colombia, Venezuela
Ornithodoros moubata	Africa from lake Chad east to the Red Sea & south to South African Cape	Throughout the tick's range
Ornithodoros savignyi	Same aea as O. moubata & also North Africa, Arabia & India	Throughout most of the vector's range
Ornithodoros erraticus	Coastal Western Mediterranean, Spain & south to Senegal	Southern Spain & portions of Africa
Ornithodoros tholozani	Caucasus, Iran, Syria	Cyprus, some parts of Russia
Ornithodoros nereensis	Turkmenia (Russia)	Turkmenia (Russia)

CONTROL

Control of louse populations is effective in eliminating the disease. Avoiding tick habitats and the diseases they carry is about the best way to avoid bites and infection. Traditionally various dips and sprays have been used for domestic animals. There are also vaccinations available for some diseases, and consulting a physician is advised for the latest treatments.

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Key References: <medvet.ref.htm> <Hexapoda>

Bates, L. B., L. H. Dunn & J. H. St. John. 1921. Relapsing fever in Panama. Amer. J. Trop. Med. 1: 183-210.

Bowman, A. S. & P. A. Nuttall (eds.). 2004. Ticks: biology, disease and control. Parasitology 129 (Suppl.): S1--S450.

Chung, H. & L. C. Feng. 1936. Studies on the development of Spirochaeta recurrentis in body louse. China Med. J.. 50: 1181-84.

Cunha, B. A. (ed.). 2001. Tickborne Infectious Diseases: Diagnosis & Management. Marcel Dekker, NY & Basel.

Davis, G. E. 1939. Ornithodoros parkeri; distribution and host data; spontaneous infection with relapsing fever spirochetes. U. S. Publ

Hlth. Repts. 54: 1345-1349.

Davis, G. E. 1943. Relapsing fever: the tick, Ornithodoros turicata as a spirochaetal reservoir. U. S. Pub. Hlth. Repts. 58: 839-842.

Francis, E. 1942. The longevity of fasting and non-fasting Ornithodoros turicata and the survival of Spirochaeta obermeieri within them.

IN: Symposium on relapsing fever in the Americas. Amer. Assoc. Adv. Sci., Pub. 18: 85-88.

Goodman, J. L., D. T. Dennis & D. E. Sonenshine. 2005. Tick-Borne Diseases of Humans. ASM Press, Washington DC.

Klompen, J. S. H., W. C. Black, J. E. Kelrans & J. Oliver 2nd. 1996. Evolution of ticks. Ann. Rev. Entomol. 41: 141-161.

Krantz, G. W. 1978. A Manual of Acarology, 2nd edn. Oregon St. Univ., Corvallis.

Lawrie, C. H., N. Y. Uzcategui, E. A. Gould & P. A. Nuttall. 2004. Ixodid and argasid tick species and West Nile virus. Emerging Infectious

Diseases 10: 653-657.

Mackie, F. P. 1907. The part played by Pediculis corporis in the transmission of relapsing fever. British Med. J. 2: 1706-09.

Matheson, R. 1950. Medical Entomology. Comstock Publ. Co, Inc. 610 p.

Mazzotti, L. 1943. Transmission experiments with Spirochaeta turicata and S. venezuelensis with four species of Ornithodoros.

Amer. J. Hyg. 38: 203-206.

McCall, P. J. 2001. Tick-borne relapsing fever. IN: The Encyclopedia of Arthropod-transmitted Infections of Man and Domesticated

Animals. ed. M. W. Service, Wallingford: CABI, pp 513-516.

McDaniel, B. 1979. How to Know the Mites & Ticks. W. C. Brown, Dubuque, Iowa.

Obenchain, F. D. & R. Galun. 1982. Physiology of Ticks. Pergamon Press, Oxford.

Sauer, J. R. & J. A. Hair. 1986. Morphology, Physiology & Behavioral Ecology of Ticks. Ellis Horwood, Chicester; Wiley, New York.

Schuster, R. & P W. Murphy. (eds.). 1991. The Acari: Reproduction, Development & Life History Strategies. Chapman & Hall, London.

Service, M. 2008. Medical Entomology For Students. Cambridge Univ. Press. 289 p.

Sonnenshine, D. E. 1991. Biology of Ticks, Vol. 1. Oxford Univ. Press, New York & Oxford.

Sonnenshine, D. F. 1993. Biology of Ticks, Vol. 2. Oxford Univ. Press, New York & Oxford.

Weller, B. & G. M. Graham. 1930. Relapsing fever in central Texas. J. Amer. Med. Assoc. 95: 1834-35.