Parasites

Gang of 10

Disease

Parasitic Species

Vector

Disease Specifics (Courtesy of Past Course ParaSites)

1

Ascariasis (roundworm)

Ascaris lumbricoides

http://www.stanford.edu/class/humbio103/ParaSites2006/Ascariasis/index.html

2

Chagas’ Disease (American trypanosomiasis)

Trypanosoma cruzi

Reduviid (“kissing”) bug

http://www.stanford.edu/class/humbio103/ParaSites2006/T_cruzi/index.htm

http://www.stanford.edu/class/humbio103/ParaSites2004/Trypanosomiasis/index.htm

3

Guinea Worm/ Dracunculiasis

Dracunculus medinensis

Copepod

http://www.stanford.edu/class/humbio103/ParaSites2006/Dracunculiasis/Index.htm

http://www.stanford.edu/class/humbio103/ParaSites2005/Dracunculiasis/eradication.htm

Economic Impact:

http://www.stanford.edu/class/humbio103/ParaSites2004/Dracunuliasis/Guinea%20Worm.html

http://www.stanford.edu/class/humbio103/ParaSites2003/Dracunculiasis/Index.html

http://www.stanford.edu/class/humbio103/ParaSites2001/dracunculiasis/DRACUNCULIASIS.html

4

Hookworms

A. duodenale- old word hookworm

N. americanus- new world hookworm

http://www.stanford.edu/class/humbio103/ParaSites2006/Hookworm/index.html

http://www.stanford.edu/class/humbio103/ParaSites2003/Hookworm/hookworm.htm

5

Leishmaniasis

Leishmania tropica or L. major (cutaneous)

L. brasiliensis (mucocutaneous)

L. donovani (cutaneous kala-azar)

Sand fly

http://www.stanford.edu/class/humbio103/ParaSites2006/Leishmaniasis/Index.htm

Vaccine:

http://www.stanford.edu/class/humbio103/ParaSites2006/Leish_vaccine/index.html

6

Lymphatic filariasis

Wuchereria bancrofti, Brugia malayi, B. timori

Anopheles or Mansonia mosquito

http://www.stanford.edu/class/humbio103/ParaSites2004/Filariasis/index.htm

7

River blindness/ Onchocerciasis

Onchocerca volvulus

Black fly

http://www.stanford.edu/class/humbio103/ParaSites2006/Onchocerciasis/index.htm

http://www.stanford.edu/class/humbio103/ParaSites2004/Onchocerciasis/index.htm

8

Schistosomiasis

S. mansoni, S. japonicum, S. haematobioum

Snail

http://www.stanford.edu/class/humbio103/ParaSites2006/Schistosomiasis/index.html

Vaccine:

http://www.stanford.edu/class/humbio103/ParaSites2006/Schisto_vaccine/index.html

9

Sleeping Sickness (African trypanosomiasis)

Trypanosoma brucei gambese (West Africa)

Trypanosoma brucei rhodesiense (East Africa)

Tsetse fly (Glossina)

http://www.stanford.edu/class/humbio103/ParaSites2001/trypanosomiasis/trypano.htm

10

Trichuriasis/ Whipworm

Trichuris trichiura

http://www.stanford.edu/class/humbio103/ParaSites2005/Trichuris/index.htm

Disease Burdens and epidemiological trends, part of the criteria for resource allotment.

(Derived from Remme, et al, Stoever, and class lecture)

Disease

Infected individuals*

Annual Deaths

DALYs lost

Aspects of burden, Ancillary Effects

Epidemiologic Trends

Ascariasis (roundworm)

807 million-as many as 1.3 billion

60,000

10.5 million

Impaired cognitive and physical development, especially in children

Affects more of the world’s population than any other parasitic disease

Chagas’ Disease (American trypanosomiasis)

9.8 million

2.8 million with signs of disease

13,000

586,000

Costs for pacemakers, intestinal surgeries, and supportive care for chronic patients

Successfully eliminated in certain countries through Southern Cone Initiative; similar campaign needed in Central America and Andean countries.

Guinea Worm/ Dracunculiasis

10,000

0

N/A

Physical discomfort/incapacitation and impaired productivity.

On target for elimination from human infection

Hookworms

740 million

65,000

22.1 million

Iron deficiency anemia and protein malnutrition leading to behavioral and developmental deficits

Causes more DALYs lost than any other helminthiasis except lymphatic filariasis

Leishmaniasis (cutaneous, mucocutaneous & visceral)

600,000

51,000

1,810,000

Stigma related to disfigurement (cutaneous, mucocutaneous)

Increasing in number of cases in many areas, complicated by HIV co-infections

Lymphatic filariasis (can lead to elephantitis, lymph drainage disorders)

120 million

(outcome not always elephantitis)

0

4.6 million

Stigma related to disfigurement; economic impact: $1billion lost annually in India

Mectizan® program and Global Programme for the Elimination of Lymphatic Filariasis has successfully controlled transmission in China and several other countries, partly through mass drug administration (MDA)

River blindness/ Onchocerciasis

37 million worldwide

6.5 million of those w/ skin disease

250,000 of those blind

0

951,000

Skin lesions, constant horrible itching,

abandonment of land/entire villages for fear of blindness

Declining disease burden in treated populations

Schistosomiasis (leads to bladder or liver disease)

200 million

~ 280,000 with auxiliary complications

1,713,000

Indirect morbidity/ mortality: growth stunting, nutritional and cognitive impairment

85% of DALYs now focused in Africa, decline elsewhere

Sleeping Sickness (African trypanosomiasis)

300,000

50,000-100,000

1,585,000

Economic factors, abandonment of fertile lands

4x increase in recorded number of new cases since 1990, higher actual incidence

Trichuriasis/ Whipworm infestation

795 million

10,000

1.6 million

Impaired physical and mental development, especially in children.

Periodic deworming has been found effective in improving children’s health and educational achievement.

Video’s detailing some of these diseases further: http://www.who.int/tdr/media/video/b-rolls.htm

why these diseases matter

The outpour of support and funding for major diseases such as HIV/AIDS is well documented and receives substantial media attention. As more scholarship is published, correlations among health care, economic development, and political stability become clear. Disease is known to diminish a country’s economic output, and consequently is closely tied to armed conflict and the breakdown of governance. With the Big Three diseases tuberculosis, HIV/AIDs and malaria garnering the most attention, research, and funding, these parasitic infections can go unnoticed.

This neglect in the face of other huge problems stems in part from the fact that many infected people are clinically sub-symptomatic, making the total scope of the burden of disease hard to precisely quantify. Even asymptomatic infections can impact a child’s growth, cognitive function and contribute to malaise and lethargy (Hotez, et al.). Though hard to see immediately, these factors have a long-term dramatic impact on quality of life and overall diminishment of one’s potential. One specific concomitant disease burden is anemia, especially in pregnant women and fetal development. Iron deficiency anemia results in 12 million DALYs lost annually; it is the most common nutrition deficit worldwide. Stigma also surrounds several of these diseases. Leishmaniasis can result in horrible scarring, and the mucocutaneous form can destroy the sinuses of the face. Elephantitis caused by leishmaniasis results in grossly enlarged extremities or scrotum. 250,000 people with onchocerciasis have been rendered blind. These diseases usually afflict people who are already incredibly poor and resource-limited and further stifle their ability to improve their educational and socioeconomic status.

The multiple complications involved, the malnutrition resulting from intestinal infestation, the anemia and the potential of co-infection with other diseases (urologic shistosomiasis has been demonstrated to increase transmission risk of HIV 3-fold) result in 530,000 deaths annually. In light of this, considerable effort needs to be taken to further implement existing strategies and develop new ones (Stoever and Broder, et al.).


Software: Microsoft Office


Clockwise from top left: woman with lymph edema due to lymph vessel damage from lymphatic filariasis infections; schistosomiasis; severe mucocutaneous leishmaniasis, child’s abdomen enlarged by roundworm infestation. Courtesy of Stoever.)

lack of funding priority

WHO reports indicate that control and elimination targets are falling woefully short. In 2006 it was estimated that control targets for schistosomiasis, lymphatic filariasis and onchocerciasis were only at 10%, 38% and 44%, respectively. In other words, only 62 cents is spent per DALY for the cohort of neglected tropical diseases, compared to $102/DALY for diabetes, $24/DALY for HIV/AIDS, and $6/DALY for malaria. Inexpensive and cost-effective approaches exist for NTDs; the will to organize and allot resources is simply lacking (UFS conference). However, the Gates Foundation’s huge endowment for NTDs signals great promise. Additionally, WHO has elaborated on the need for more funding for these diseases. The graph below demonstrates efforts to allocate research money where it would be most effective or is most needed. Augmented by new support from other sources, this money has allowed stalled research to begin anew and has promoted new drug discovery research (Remme, Feenstra).

Courtesy of Remme et al. Strategic emphases for tropical disease research: a TDR perspective.

The WHO report also categorized the most prevalent parasitic disease based off of epidemiological trends. They are listed as category I, II or III below and some of the research goals for each is summarized here.

Areas of research/goals

(Compiled from Remme, et al. and Hotez, et al.)

Disease Category

(Epidemiological Trend)

Disease Name

Research Goals

I. Re-emerging, uncontrolled: needs novel tools and basic knowledge

Sleeping Sickness

(African trypanosomiasis)

- Drugs

- Diagnostics

- Vector Control

Leishmaniasis

a. cutaneous

b. mucocutaneous

c. visceral (kala-azar)

- Case finding, treatment plans

- Better Drugs

- Better diagnostics

II. Existing control strategy: some not yet proven effective- needs better tools and approaches

Schistosomiasis

- Vaccine Development

Hookworm infestation

- Vaccine Development

- Study of cost effectiveness of de-worming campaigns

Trichuriasis/Whipworm infestation

- Vaccine developments

III. Targeted for elimination: might need better implementation, political will, health infrastructure

Chagas’ Disease

(American Trypanosomiasis)

- New vector control strategies for

reservoirs not living in structure of homes

- Effective treatment for those already infected

Lymphatic filariasis

- Better drug control

River blindness/Onchocerciasis

- Drugs

- Vector elimination

Guinea Worm/Dracunculiasis

- Continued vigilance, nearly eliminated

current approaches: benefits & drawbacks

The three major approaches are

3. Health education: reducing transmission and re-infection by teaching healthy behaviors such as promoting use of latrines/hygienic behavior


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