Uganda, a hotspot for neglected

vector borne zoonoses

Joseph M Kungu and Halid.Kirunda

Vector-borne zoonoses

Tremendous success in control of vector borne infections

e.g Trypanasomiasis was scored in the previous decades

(20th century).

This later led to laxity resulting in prioritization of prevention

and control of other infections.

Re-emergence of vector borne zoonoses has occurred, due

to change in global trends (Population growth, uncontroled

movement, climate.

Human host

Zoonotic vector-borne infections are responsible for a

considerable proportion of human deaths (1.4/annum),

with most impact felt in Africa.

They are prominent contributors to emerging diseases,

globally.

Animal hosts

Direct effects of such infections have been underestimated

in animals. The indirect role the animals play in harboring

the pathogens can’t be undermined.

Very few of these conditions are among the diseases

priority for control in developing countries.

Importance of vectors

The ability of vectors to bridge spatial and ecologic gaps

between animals and humans increases opportunities for

emergence. These barriers are not only spatial but behavioral

and ecological e.g yellow fever transmision.

Small adaptations of a pathogen to a vector can have

profound effects on the rate of transmission to hosts.

Importance of vectors

The complexity of vector transmission offers the pathogen

increased opportunities to evolve. In almost no instances is

the arthropod simply a vessel for transmission.

Cont’d

The pathogen replicates in some fashion, which makes it dependent

on an invertebrate host physiology much different from what it will

encounter in its various vertebrate hosts.

As a consequence, epidemic emergence can result from enhanced

transmission independent of increased pathogenicity to humans.

This is especially true of arboviruses that have high potential

mutability.

Role of the environment

Ecosystems provide conducive ground for maintaining

transmission cycles of vectors and pathogens.

They regulate spillover into human and animal populations.

Human activities that alter natural ecosystems also affect

the transmission cycles of vector-borne infectious diseases.

Situation in Uganda

The neglected vector-borne infections of major public

health and socio-economic importance in Uganda are HAT,

schistosomiasis, lymphatic filariasis (LF) and

onchocerciasis.

Others like leshmaniasis, WestNile Virus disease, Dengue,

Crimean Congo, occur but their importance goes

unnoticed.

Situation in Uganda Parasite Disease Agent Affected areas Burden

Protozoa Visceral Leishmaniasis

(Kala-Azar)

Leishmania donovani Pokot County,

Nakapiripirit

district

(NE Uganda)

Unknown;

> 400 cases treated

per year, 70%

from Kenya

Human African

Trypanosomiasis

Trypanosoma

gambiense

NWUganda,predominantly in

Adjumani, Moyo,

Arua & Yumbe

district

In 2004, 354 cases

were reported

T. rhodesiense

SE and E Uganda

In 2005, 154 cases

and 7 deaths were

reported

Viruses RVF, Yellow fever,

Dengue, Crimean Congo,

WestNiile , Sunguru,

Bukakata.

ARBOViruses Uganda

Helminths Lymphatic filariasis

(Elephantiasis)

Wuchereria bancrofti

North of Victoria

Nile and in W

Uganda

54 districts, 14.6million at risk

0.4 – 32.9%

prevalence

Onchocerciasis

(River Blindness)

Onchocerca volvulus

21 districts; highly

endemic in West

Nile region, central

shores of Lake

Albert, Mt Elgon

& foci in SW

Uganda

35 district, > 3.8 million at risk

1.5million affected.

Schistosomiasis

(Bilharziasis)

Schistosoma

haematobium

S. mansoni 38

Districts on

northern shores of

Lake Kyoga districts

73 districts ,Approx. 4 million

cases

16.4 million at risk

Control strategy Intervention Control output Agent targeted

Community education behavioral change All infections

Evironmental

management

To limit the natural

habitats

Vectors

Residual spraying Kill vectors Vectors of filariasis ( pyrethroids,

organophosphates,)

, leishmaniasis (carbamates), malaria

(DDT)

Insecticide treated

nets

Prevent bites Vectors

Traps Depopulate vectors Trypanasomiasis

Vaccination Prevention of infection Yellow fever

Improve sanitation Limit the transmission

cycle

Schistosomiasis

What are challenges encountered?

Complexity of epidemiology and adaptive plasticity of

pathogen and arthropod make the vector-borne diseases

difficult to control, much less to eradicate.

Vaccines are unavailable for all but a few diseases; and

even when they are available, as for yellow fever,

prevention can be difficult to achieve.

Cont’d

Development of resistance of pathogens to treatment e.g

P. falciparum, and treatment for visceral leishmaniasis

remains too expensive and complicated to be widely

practiced where it is most needed.

The constant development of pesticide resistance.

Even when pesticides are efficacious, their effectiveness is

often compromised by human behavior and vector biology,

policies on use e.g DDT.

Changes in climate, land use, and transport have affected

rates of pathogen emergence in ways poorly understood.

Way forward

Research needed in;

The biology and ecology of the vectors and pathogens.

The presence, distribution and abundance of the vectors

and pathogen host populations.

The environmental, climatic, ecological and topographic

conditions of relevance to vector ecology .

Risk assessment to indicate the areas at highest risk of

introduction of a vector that is unlikely to be present.

Conclusion

Vector-borne infections are a result of poverty and have increased poverty levels in developing countries.

Actions to reduce vector-borne diseases will relieve expenses, hence saving for well-being and development of Uganda.

Acknowledgements

Dr. Lutwama, UVRI

Dr. Edrinah Muheki, Wamboka, Moses Adriko of the Vector

Control Division.

Dr.Winyi Kaboyo, MOH

THANK YOU

God bless you in Jesus name

Ecclesiastes 12.12-14