Intro to Vector-Borne diseases

What are some examples of flea-borne pathogens and diseases?

Cat scratch disease, flea-borne spotted fever, plague, murine typhus

What are some examples of factors that are driving emergence/reemergence of vector-borne diseases?

Land use changes

Unknown factors

Climate/whether related

Global trade and travel

Vector adaptation

Pathogen factors

Host factors

What is the causative agent of Rocky Mountain Spotted Fever (RMSF)?

Rickettsia rickettsil

What is spotted fever rickettsiosis? (SFR)

Group of diseases caused by closely related Rickettsia species

Which SFR is the most common and most serious SFR in the USA?

Rocky Mountain Spotted Fever

What type of bacterium is R. rickettsil?

Obligate intracellular bacterium

How is R. rickettsii maintained?

Usually maintained in cycle between small mammals (rodents, lagomorphs) and biological vectors (several tick species)

Who are incidental hosts in the transmission cycle of R. rickettsil?

Humans and in most cases dogs

When can dogs be potential reservoir hosts for RMSF?

When the vector is brown dog tick

The American dog tick is commonly associated with transmission of RMSF in what areas of the US?

Middle-eastern US and California

The Rocky Mountain Wood tick is associated with transmission of RMSF in what part of the US?

Western

Which tick is an important vector in Arizona and US-Mexico Border?

Brown Dog Tick

What does it mean when humans are incidental hosts for RMSF?

Not involved in maintenance

What does it mean that humans are dead-end hosts for RMSF?

Do not develop enough rickettsemia and unlikely to transmit R. rickettsil to uninfected ticks

Dogs usually play what role in the maintenance and transmission of RMSF?

Incidental or dead end host, can be reservoir host if brown dog tick

How to prevent RMSF in dogs?

Tick control with approved acaricides

Check and remove ticks from pets asap to prevent transmission —> takes at least 4-6 hours before transmission

No licensed RMSF vaccine for dogs

How do dogs act as sentinels for RMSF in humans?

Dogs are highly susceptible to R. rickettsii and have relatively high exposure to ticks compared to humans

Disease in dogs can serve as sentinel for risk in humans

Dogs and humans may be simultaneously exposed to infected ticks resulting in temporal and spatial clusters of disease

What disease is this image of in humans?

Spotted Fever Rickettsiosis in humans

Spotted Fever Rickettsiosis in humans

Nationally notifiable to PH officials

Flu-like symptoms: acute onset of fever, headache, chills, muscle and joint pain

Invades endothelial cells: vasculitis, rash

Neurological signs, circulatory, and pulmonary complications

Risk of severe disease in immunocompromised

How is RMSF different in Arizona and USA-mexico border?

Transmitted by the brown dog tick

Free roaming dogs spread infected ticks within communities

Warm climate suitable for ticks year round

Incidence very high compared to rest of USA

What is the causative agent of Lyme disease?

Borrelia burgdorferi

What type of agent is Borrelia burgdorferi?

bacterium

What species are important reservoirs for lyme disease?

Rodents

What are humans role in the transmission of lyme disease?

Incidental dead-end hosts

What animals are affected by lyme disease?

dogs, cats, horses

What is the prevalence of lyme disease in the USA?

Major public health concern, accounts for 82% of tick-borne diseases

How is B. burgdorferi transmitted?

Transmitted by Ixodes spp ticks

What is the role of dogs in the transmission of lyme disease?

Incidental dead-end hosts just like humans

What is the role of deer in the transmission of lyme disease?

Source of blood for ticks and tick survival

Deer are not infected with agent and do not infect ticks

How long does it take after tick attachment before transmission of lyme disease occurs?

At least 24 hours

What are the general principles for diagnosis of VBDs?

1. Consider clinical symptoms, season, geographical location, and history of potential exposure

2. Molecular tests detect genetic material of pathogen

3. Serology detects antibodies or antigens to determine exposure to pathogen

4. Microscopy: blood smears or other tissue biopsy smears visualize pathogens in blood or tissues

What are some challenges in the diagnosis of VBDs?

Similar clinical symptoms

Co-infections

Cross reactivity: false positives can occur with related pathogen

Timing of the tests: molecular tests perform better in the acute phase of infection

Discordant results may occur when use different tests

Limitations of serology

What are some examples of nucleic acid amplification testing (NAAT)? and what specimens can be used?

PCR, RT-PCR

Can use various specimens: whole blood, serum, tissues

What does a positive PCR or RT-PCR result mean?

Presence of nucleic acid (DNA)

What does a negative PCR or RT-PCR result mean?

Pathogen not detected in sample

Why might a false negative result occur in a PCR or RT-PCR?

Low pathogen load

What does IFAT stand for?

Indirect immunofluorescence antibody test

What does the IFAT test for?

Presence of IgG and IgM antibodies

Also quantifies antibodies

When should you perform an IFAT test?

During acute and convalescent phase > 4-fold increase in AB titers shows acute infection

Single test: active infection or previous exposure

Can IFAT tests cross react?

Yes, with prior infections or vaccination

What is IFAT testing not ideal for?

Initial stages of infection as it tests for AB and host usually mounts antibody response ~2 weeks after

>4 fold increase in titer between acute and convalescent sera 2-4 weeks apart shows acute infection

How to interpret a negative serology test

No AB detected against the pathogen

Either the animal not exposed to pathogen or is an early infection and AB response has not yet mounted

False negatives may occur

What stain do you use for a blood smear microscopy to test for VBDs?

Giemsa or Wright stain

What does this blood smear micrscopy indicate?

Babesia infection: intra-erythrocytic parasite

What does this blood smear microscopy represent?

Anaplasma: morulae inside neutrophil of dog

What are some characteristics of performing blood-smear microscopy?

Relatively inexpensive

Requires experience person

What is a mosquito-borne arbovirus?

West Nile Virus

What type of virus is west nile virus?

Orthoflavivirus, RNA virus

Arbovirus/arthropod-borne virus transmitted by mosquitoes

What is west nile virus maintained in cycle between?

Wild birds and mosquitoes

What species can the pathogen be present in?

Humans, equines, and avians

How is WNV primarily (99%) transmitted to humans?

By mosquito bite

What are minor/rare transmission routes of WNV to humans?

Contact with cloacal/oral fluids from infected birds

Blood transfusion and organ transplants

Mother-to-child

Lab acquired infections

What are dead-end hosts of WNV?

Humans and horses

Dogs and cats play what role in transmission of WNV?

Can be infected but WNV is not maintained in these species

Can humans transmit WNV to other humans?

Yes, only other humans through unnatural conditions such as a blood transfusion

How to prevent WNV in humans?

Integrate mosquito management

Public education to avoid mosquito bites

Surveillance

What is the surveillance system arbonet?

National surveillance system for arboviruses in USA

Developed in response to emergency of WNV

Electronic: track and report arboviral activity

Monitor arboviruses in humans and non-humans

What is the causative agent of dirofilariasis?

Dirofilaria spp.

What is Dirofilariasis?

Mosquito-borne filarial nematode infection usually associated with carnivores

What factors determine distribution of dirofilariasis?

Vector, climate, domestic or wild carnivore reservoirs

Temperate regions: seasonal transmission

Endemic areas/tropics: year round

Outdoor animals increased risk of infection

Where is dirofilariasis most common in the USA?

Southeastern USA

What is the preferred detection test for dirofilariasis in dogs?

Adult worm antigen detection test

Sensitive and specific

Small fraction of adult-worm infected dogs test negative

Some infected dogs have no microfilaria

What tests will increase chances of diagnosis of dirofilariasis?

Combining microfilaria test and adult antigen test

Routine annual screening in endemic areas

How to prevent dirofilariasis?

Year-round macrocyclic lactone is effective in DOGS

Integrated mosquito control: repellants, environmental control

Infected dogs should be treated

Prevention recommended for cats in endemic areas

Humans: avoid mosquito bites, repellants

What is the causative agent of Chagas disease or american trypanosomiasis?

Trypanosoma cruzi

What is the vector for Chagas disease?

Kissing bugs (triatomine bugs)

What are other transmission routes of Chagas disease?

Food/water contamination linked to outbreaks

Blood transfusion, organ transplants

Canine chagas disease

Becoming health concern in dogs in USA

T. cruzi reported in various wild animals in southern states

Range of clinical symptoms: febrile illness, chronic phase is bad

No cases of canine to human transmission

What does chagas disease have an affinity for?

Cardiac and smooth muscle